Showing papers in "Biotropica in 1980"

Gap Partitioning among Tropical Rainforest Trees

Abstract: Published observations on adaptations for seed disperal and seedling establishment are consistent with the hypothesis that rainforest trees partition forest clearings as establishment sites for offspring. Gaps vary importantly in two ways. The size of the opening affects the microclimate of the gap and therefore the conditions for seedling establishment. For any individual tree, the frequency of occurrence of gaps of a particular size range affects the probability that its propagules will reach a gap of suitable size for germination and establishment. In most rainforests large gaps (involving the death of several trees) are probably more rare than small gaps (involving single trees or branches). Interspecific competition for establishment sites has resulted in adaptive compromises in the regeneration strategies of each species. Traits that increase the probability of establishing seedlings in gaps of a particular size range appear to lower establishment in gaps outside this size range. I suggest that the coexistence of many rainforest tree species is at least partially due to their partitioning of canopy gaps by size. Therefore the size-class frequercy distribution of gaps peculiar to a given rainforest is expected to influence the types and diversity of species present. Examination of vegetation data from New and Old World rainforests reveals many patterns consistent with this hypothesis. This framework provides a mechanism for predictive and experimental studies of competitive interactions among rainforest trees. MECHANISMS PROPOSED to account for patterns of species richness within animal communities have relied heavily on resource partitioning (cf. Schoener 1974). Similar hypotheses have been less successful in accounting for plant species diversity. Different plants have similar modes of resource acquisition and share the same few essential resources (light, moistLre, minerals). It is not clear how such uniform resources could be partitioned by physiologically similar species in complex communities (e.g. Richards 1969). Although rainforest species exhibit patterns associated with variation in topography or soil (e.g. Ashton 1964a, Grieg-Smith et al. 1967, Poore 1968, Williams et al. 1969, Austin et a/. 1972, Ashton 1977), species with non-random distributions often show no association with edaphic variation (Schulz 1960, Poore 1968), and overlap along edaphic gradients is high between similar species. It remains difficult to account for high diversity in relatively uniform topographic and edaphic environments. In face of high plant species diversity unexplained by resource partitioning, theorists have invoked stochastic or historical processes to account for modern patterns (e.g. Federov 1966, Van Steenis 1969, Prance 1973, Stebbins 1974, and see Ashton 1969 for a discussion). These hypotheses assume that competitive interaction among plant species is of little importance in the determination of relative abundances of species. Here I suggest that a mechanism for resource partitioning among rainforest trees exists in their differential regeneration in treefall gaps of different sizes and spatial distributions. At a superficial level some of these differences are a well-established part of natural history lore (e.g. Richards 1964, Van Steenis 1958, Budowski 1965) and form the basis of sustained-yield forestry systems (e.g. Taylor 1962, Whitmore 1975). Several papers have emphasized that gaps are an important source of environmental heterogeneity in rainforest (Schulz 1960, Whitmore 1975, 1978, Hartshorn 1978). Nevertheless, it is evident from the literature that gap regeneration strategies have not been considered an important component of competitive interactions among trees. Few studies of rainforest vegetation include attention to the nature and distribution of natural gaps or to differential seedling establishment in them. This paper summarizes data on regeneration patterns of trees within the framework of hypotheses that (1) tree species partition gaps of different spatial distributions and sizes and that (2) partitioning occurs because regeneration strategies keyed to gaps of particular size ranges involve adaptive compromises that restrict the competitive success of the species in gaps of differing sizes. High mortality rates of seeds and seedlings (e.g. Liew and Wong 1973) suggest that selection pressures are likely to be particularly strong on factors affecting dispersal of seeds and establishment of seedlings. Gaps as establishment sites for seedlings are critical resources, and gap partitioning provides an important mechanism through which empirically to examine interspecific competitive interactions among tree species. Rainforest spatial structure and species diversity are reviewed in this light. Experimental tests of the relationships between TROPICAL SUCCESSION 47-55 1980 47 This content downloaded from 157.55.39.159 on Sun, 18 Sep 2016 06:29:01 UTC All use subject to http://about.jstor.org/terms traits described and regeneration success in gaps of different sizes are largely lacking. Support for these hypotheses is therefore based on empirical studies of forest structure and field observations accumulating over the last 50 years of ecological studies of rainforests. This framework is presented in the hope of stimulating the generation of testable hypotheses on competitive interactions among rainforest trees and experimental research on fruit, seed, and seed-

Mycorrhizae influence tropical succession.

Abstract: Most vascular plants depend to some extent on vesicular-arbuscular (V-A) mycorrhizae for mineral uptake, although a few species do not. Some mycotrophic plants cannot grow without mycorrhizae; others grow better without mycorrhizae in fertile soils, but benefit from mycorrhizae in poor soils. Thus, the mycorrhizal fungus content and the fertility of soil influence the occurrence of plant species. Because V-A mycorrhizal fungi depend on mycotrophic plants for carbon, and because they produce few spores which may survive only a short time in the lowland humid tropics, plant community composition in turn affects the mycorrhizal fungus content of soil. This influences the further course of plant succession by affecting which species of plants can subsequently occur in the community. Pool soils may favor alternate stable communities. If mycorrhizal fungi are present, obligately mycotrophic species are the best competitors and should dominate communities. They support an abundance of mycorrhizal fungi, ensuring the continued superiority of obligate mycotrophs. If mycorrhizal fungi are absent, non-mycorrhizal species will comprise the community. Even if mycorrhizal fungi are subsequently introduced, these plants will not support them, favoring persistence of the non-mycorrhizal species. On fertile soils, facultative mycotrophs are most common. They will support infection if mycorrhizal fungi are available when the soils age and fertility declines, paving the way for their replacement by obligate mycotrophs. If mycorrhizal fungi are unavailable, facultatively mycotrophic species will be replaced by non-mycorrhizal plants. Non-mycorrhizal plants may also derive competitive advantage where mycorrhizal fungi are present, from not needing to await infection to start growing. Thus, pioneer species are often non-mycorrhizal. Seral species tend to be facultative mycotrophs, and most lowland tropical forest trees tend to be obligately mycotrophic. Ectomycorrhizal individuals are likely to occur in abundance in nutrient-starved or disturbed habitats, although ectomycorrhizal species are rare in the lowland tropics. Ectomycorrhizal associates may influence tropical succession by lowering populations of V-A mycorrhizal fungi. THIS PAPER SUGGESTS how interactions between vascular plants and mycorrhizal fungi may influence succession. I discuss: 1) how plants depend on mycorrhizae to different degrees for mineral uptake; 2) how different dependence on mycorrhizae might affect the competitive success of plants in soils with different mycorrhizal fungus contents and mineral availabilities, and as a consequence, might influence plant community composition; 3) how plant communities, in turn, may affect mycorrhizal fungus populations; and 4) how further development of a plant community thereby might be influenced. There is evidence for the first three of these interactions; the fourth, consequent successional change, is based on inference. I focus on vesicular-arbuscular (V-A) mycorrhizal associations in the lowland tropics. Ectomycorrhizal associations, rare in the lowland tropics, are discussed as exceptions, because compared to V-A mycorrhizal fungi ectomycorrhizal fungi are more host-specific, disperse better, and some species may not be as dependent on their hosts. PLANTS DIFFER IN THEIR DEPENDENCE ON MYCORRHIZAE Most species of plants are capable of associating with fungi of a single zygomycetous family, the Endogonaceae, to form V-A mycorrhizae (Gerdemanin 1968). By improving mineral nutrition, especially if substrate mineral availability is low or imbalanced, V-A mycorrhizae can increase the growth of host plants (Mosse 1973b), can improve water uptake and resistance to temporary wilting (Safir, Boyer and Gerdemann 1972; Menge et al. 1978), and may improve seedling survival (Baylis 1959; Gerdemann 1965; Kleinschmidt and Gerdemann 1972; Janos 1975a, 1975b, 1977). Mycorrhizae seem to minimize the expense to the host of seeking-out minerals (Harley 1975) even though the hosts supply carbon to V-A mycorrhizal fungi (Ho and Trappe 1973). The external hyphae of mycorrhizae increase mineral uptake, especially uptake of phosphorus which is relatively immobile in soil, probably by providing a large, well-distributed absorbing surface (Mosse 1973b). The advantage of an extensive absorbing surface is diminished in fertile soils (Voigt 1971), however, and continued support of mycorrhizae in fertile soils may decrease host growth (Cooper

Neotropical Forest Dynamics

Abstract: Neotropical forest dynamics are reviewed by focusing on four questions: (1) What is a mature neotropical forest? (2) How long does it take to attain maturity? (3) How important are gaps to species regeneration? and (4) What are the important equilibrium processes in neotropical forest dynamics? The absence of regeneration of dominants has often been used as a distinguishing feature of late secondary forest; however, the abundance of shade-intolerant species in mature forest suggests that local absence of regeneration is an inadequate criterion for distinguishing between late secondary and mature forest. Recent studies estimate forest turnover rates of 75-150 years, indicating tropical forests are much more dynamic than thought previously. The dependence on gaps by almost half of the 320 tree species in a Costa Rican wet forest for successful regeneration illustrates the importance of gaps in tropical forest dynamics. Factors important in determining which species successfully colonize a gap are: time of gap occurrence; proximity and dispersal of seeds; size of gap; substrate conditions; and plant-herbivore interactions.

Tropical succession: manifold routes to maturity

Abstract: Several characteristics of successional species and communities typical of the lowland, humid tropics are compared with those of drier and colder tropical environments. Suggested trends of successional species characteristics along a gradient from benevolent to harsh tropical environments include: fewer but more specialized taxa; more striking ecological equivalence between biogeographic regions; increased vegetative reproduction; less palatable leaves; denser wood; and decreased importance of chlorophyllous stems. Hypothesized trends of the communities along this same gradient include: slower regrowth; increased resilience (drier sites only); fewer seral stages; and patchier distribution of leaf area. As tropical soils are degraded through misuse, there is a tendency for ruderal vegetation from drier (or colder) environments to invade degraded landscapes in wetter (or warmer) areas. Regrowth and resilience of high-elevation tropical forests are so slow that these communities may never reestablish after clearing. TROPICAL SUCCESSIONAL ECOSYSTEMS conjure up an image of dense tangles of luxurious, impenetrable regrowth: the "jungles" of popular fiction. However, there are many more combinations of rainfall and temperature regimes in the tropics than in temperate zones. Just as this environmental heterogeneity leads to a broad array of mature ecosystems, it also produces a tremendous variety of successional communi-

Movement Patterns of Jaguar

Abstract: Jaguar on two small ranches in southwestern Brazil had a density of about one animal per 25 sq km. Females ranged over at least 25-38 sq km and males over twice that much terrain. The ranges of females overlapped, and the range of a resident male included the ranges of several females. Jaguar and puma ranges also overlapped, but each species favored parts not much used by the other. Day-and-night radio tracking revealed precise travel and activity patterns of two female jaguar. The social system of jaguar is in most respects similar to that of other large solitary cats such as puma, leopard, and tiger. As PART OF A WILDLIFE STUDY in the Pantanal region of Mato Grosso, Brazil, we collected information on jaguar (Parnthera onca). Data were gathered intermittently between April 1977 and September 1978 on the Acurizal and Bela Vista ranches (17?45'S, 57?37'W) at the western edge of the Pantanal, a vast swampy plain near the Bolivian border. During 1977 we assessed the impact of jaguar predation on a prey population (Schaller and Vasconcelos 1978) and deduced movement patterns from spoor; during 1978 we radio-tracked two jaguars. Ranch hands on Acurizal shot two of the study animals, and this action prematurely terminated our research there. Because jaguar literature is based mainly on anecdotal accounts by hunters and naturalists (see Guggisberg 1975), our preliminary findings contribute a more substantial understanding of the species and provide data for comparison with information available on other large, solitary cats (Hornocker 1969, Muckenhirn and Eisenberg 1973, McDougal 1977). STUDY SITE The Acurizal ranch, 137 sq km in size, consists of a strip of land, 24 km long and 5-10 km wide, between the Paraguay River and the crest of the Serra de Amolar which at its northernmost point ceases abruptly at the shore of Lake Gaiba. Two broad valleys, named here the First and Second valleys, cut into the range (fig. 1). Three kilometers north of Acurizal, across Lake Gaiba, is Bela Vista, an island of about 90 sq km, its size varying somewhat with the water

A rainforest chronicle: a 30-year record of change in structure and composition at El Verde, Puerto Rico.

Abstract: Measurements over approximately a 30-year period in a Dacryodes-Sloanea forest indicate two distinctive phases in stand development. Secondary species were common in the early stand (1940's), and rapid accumulations of biomass and basal area were measured. Many new species entered the stand, and the number of stems increased. In contrast, the stand of the 1970's approached steady-state for biomass and basal area accumulations, and, relative to earlier measurements, fewer stems and fewer species were recorded in the plot. This apparent dichotomy can be correlated to the periodic disturbance caused by tropical storms. The last severe hurricane to strike Puerto Rico occurred in 1932, 11 years prior to the establishment of the El Verde plot. It is postulated that the early measurements reflect the rapid recovery of the stand following this hurricane, with both invading secondary species and residual primary species present in the stand. Subsequent perturbations (i.e.,, cutting and another storm) were insufficient to disrupt the unmistakable trend toward a mature forest and the stand quickly approached steady-state conditions.

Flowering and fruiting periodicity in a premontane rain forest in Pacific Colombia.

Abstract: The timing and levels of flowering and fruiting were studied in a premontane rain forest in western Colombia. Flower production is less seasonal than fruit production, and periods of peak fruiting do not always closely follow the periods of higher flowering activity. Fruit production is more equitably distributed through the year than in seasonal tropical environments, but there are two small fruiting peaks that center on the wetter portions of the year. Proportionally fewer canopy species than understory species produce bird-dispersed fruits, and almost all understory trees produce this type of fruit. Species of Miconia fruit sequentially through the year, but the total number of individuals in fruit varies seasonally. This variation is apparently offset by an increase in fruiting activity of other trees as there is no marked seasonal depression in the availability of fruit for birds.

Seed stocks in Ghanaian forest soils.

Abstract: Topsoil samples were collected from two 1 m2 quadrats in six mature forest sites, each representative of a Ghanaian forest type, and regularly watered to promote seed germination. Each sample was subdivided; half the subsamples were exposed to full sunshine, while the other half were shaded until germination ceased and then transferred to full sun. A total of 2028 seedlings belonging to 90 species (of which only 10 species occur in mature forest) were recorded in the sunlit boxes. Only 120 seedlings, of 25 species, germinated in the shade, but a further 41 species were recorded when the shaded boxes were subsequently exposed to sunshine. We conclude that most seedlings germinated from seeds whose dormancy is broken by exposure. WHEN MATURE TROPICAL FOREST is cut and cleared, it is quickly replaced by fast-growing herbs, climbers, and woody plants of species quite different from those present in the original forest. Various opinions have been advanced as to how this happens. One possible explanation is that the seeds from which these colonizing pioneers grow lie dormant in the soil from the time of one gap phase to the next. If this were true, seed longevities of up to several hundred years would be implied. Alternatively, dispersal agents might be responsible for a more-or-less continuous rain onto the forest floor of seed from pioneer species growing in gaps or secondary forest elsewhere. Two possible fates may be envisaged for seeds of pioneer species dispersed onto the floor of intact forest: they might germinate, but the resulting seedlings quickly succumb, or they might lie dormant until the forest is disturbed and the canopy removed. Four main aspects of the problem thus require investigation. Firstly, the size and composition of the pioneer seed stock in soils under mature forest; secondly the distribution and intensity of pioneer seed rain; thirdly the length of viability of pioneer seed; and finally the environmental requirements for germination. Several workers have investigated soil seed stocks by removing samples of topsoil from apparently undisturbed forest, watering the samples under exposed conditions, and assessing the seedlings which come up in them. Symington (1933), one of the first to undertake such experiments, reported that Malaysian forest soils contain abundant dormant pioneer seed, but Whitmore (1978) points out that Symington failed to protect his samples from possible contamination by seed which could have reached them from nearby secondary forest species during the course of the experiment. Other workers have avoided this problem: Liew (1973) and Guevara and GomezPompa (1972) protected their seed boxes from contamination by placing them in greenhouses, while Keay (1960) noted that the species of seedlings recorded in his boxes were not present in the area where the experiments were performed. With respect to the characteristics of the seed rain, Richards (1952: 383) has pointed out that most pioneer species fruit more or less continuously, and that their propagules are provided with efficient dispersal mechanisms. Gomez-Pompa et al. (1976) recently discovered, in an investigation in Mexico, that three of the four commonest seed species to be found in the guts of birds were pioneer species recovered from the soil in nearby primary forest. Although a heavy, widespread rain of poineer seed thus seems probable, direct measurements have not been published. Neither are data available on longevity of dormant seed. So far as the requirements for germination are concerned, all the authors mentioned above concur that seed dormancy is widespread among pioneer species. Ng (1978) states, however, that 'dormancy is not particularly characteristic of pioneer species in the humid tropics,' but by dormancy he implies only mechanical dormancy or the need for after-ripening. Most experiments have, in fact, failed to distinguish between the various possible causes of dormancy. V6azques-Yanes (1976) concludes from an extensive series of experiments, both in the laboratory and the field, that a light requirement is universal for the lPresent address: Department of Botany, The University, Aberdeen AB9 2UD, Scotland, U.K. 256 BIOTROPICA 12(4): 256-263 1980 This content downloaded from 157.55.39.157 on Fri, 08 Jul 2016 05:20:45 UTC All use subject to http://about.jstor.org/terms germination of pioneer species in the Mexican tropical forest where he worked, but he does not seem to have considered temperature as a possible factor.

Self and cross pollination of Encyclia cordigera (Orchidaceae) in Santa Rosa National Park, Costa Rica

Abstract: The epiphytic deciduous forest orchid Encyclia cordigera was manually self-pollinated, out-crossed against one other parent, and out-crossed against a maximum number of other parents in Santa Rosa National Park, Costa Rica. There was no difference in the percent inflorescences that set fruit between selfed and single-parent out-crossed plants, and on the inflorescences that set fruit there was no difference in the percent flowers that bore fruit (85 to 92% for 119 and 82 flowers). However, only 5 percent of the multiple-fathered inflorescences failed to set some fruit, and 97 percent of the flowers set fruit; these values are significantly different from those for the selfed plants and flowers. The overall percent of inflorescences that bore fruit and the percent flowers that bore fruit was very much greater on the hand-pollinated plants than on the unmanipulated ones growing only a few meters away. This finding may indicate that fruit set by E. cordigera is pollinator limited, but other interpretations are given. Is Encyclia cordigera (ORCHIDACEAE) SELF-INCOMPATIBLE and does the number of fathers for a plant's fruit crop influence the size of that fruit crop? E. cordigera is a common epiphytic orchid in the deciduous forest lowlands of Guanacaste Province, Costa Rica. It is especially common in Crescentia alata trees in the flat plateaus in the center of Santa Rosa National Park (SRNP), where this study was conducted. Large numbers of these orchids flower from late February to late March (mid-dry season). E. cordigera flowers are produced 1-13 per inflorescence, and those on one inflorescence open during a period of about one week. If not pollinated or relieved of pollinia, the flowers last at least 10 days. Once pollinated, the white portions of the petals turn yellow and the ovary begins to swell. In nature, mediumto large-sized black female carpenter bees (Xylocopa spp.) enter the flowers in search of nectar and receive the viscidium on the frons or top of the head; the bright yellow pollinia are then later stripped off on the stigma of another flower. The three petals of the flower and the column are colored white and lavender, and shaped such that they are very similar to the flower of Gliricidia sepium, a common legume tree that is heavily visited by these 72 BIOTROPICA 12(1): 72-74 1980 same bees for nectar at the time E. cordigera is in bloom. MATERIALS AND METHODS All orchids were relieved of their pollinaria by sticking the pointed end of a ball-point pen cap or clip into the flower and then withdrawing it with an upward motion. The sticky viscidium readily adhered to the plastic surface. The cap over the four pollinia was knocked off, and in the case of self-pollinated flowers, the pollinia were then placed on the sticky stigma. In outcrossed flowers, the pollinia were carried to another plant and placed on the stigma of a flower that had already been relieved of its pollinaria by the experimenter. Only inflorescences with intact and unpollinated open flowers were used, and all flowers on a test inflorescence were pollinated. Occasionally during transfer one of the four pollinia would fall off, but usually all four pollinia were placed in contact with the stigma. Outcrossed inflorescences were of two types. "Single father" inflorescences had all their flowers pollinated by pollinia brought from a single other parent (and usually the other parent received the pollinia from the plant that received its pollinia). This content downloaded from 207.46.13.127 on Fri, 14 Oct 2016 04:07:12 UTC All use subject to http://about.jstor.org/terms "Multiple father" inflorescences had each flower on the inflorescence pollinated by pollinia from a different pollen donor: if there were n flowers on the plant, that plant's clutch had n fathers. Within 24 hours after pollination, the stigmatic surface of a pollinated E. cordigera flower swells to engulf the pollinia and is no longer sticky, so that we have assumed that none of the flowers were subsequently pollinated by bees after the experiment. Flowers of E. cordigera do not self-pollinate if the pollinia are not physically moved to the stigma by an outside

Seasonal and annual variation of insect abundance in the Nairobi National Park, Kenya.

Abstract: A Malaise trap erected at the interface of grassland and forest in the Nairobi National Park was used to monitor insect abundance during a five-year period. Annual rainfall patterns during the study were extremely variable and included periods of major drought. Increases in insect density that followed the rains were largely due to an increase in the number of individuals per species, but the number of species also increased as much as threefold. The timing of peak seasonal abundance of phytophagous insects (grasshoppers and leafhoppers) and parasitic Hymenoptera was variable from year to year, thus suggesting dependence on environmental variables such as rainfall or host density. By contrast, several insect groups less dependent upon plants showed distinct seasonal meaks of abundance that were quite consistent each year. One annual peak of abundance was observed among Chrysopidae, Psocidae, Tabanidae, and Sarcophagidae. Two peaks were recorded for Asilidae and Satyridae. SEASONALITY IS A CONSPICUOUS FEATURE in the life history of many organisms in temperate zones, but information for tropical organisms remains sketchy. In the tropics, temperature changes are slight, and seasonal changes in rainfall exert the most dramatic effect on the environment. Rainfall patterns, however, can vary greatly from year to year, and for some organisms low rainfall is not likely to present as severe an obstacle as winter in a temperate zone. Thus, for some tropical species development appears to be aseasonal (e.g., Owen and Chanter 1972, Ehrlich and Gilbert 1973, Leuthold and Leuthold 1975) or to continue over a prolonged period (MacArthur 1972). Yet, many other tropical species are highly seasonal, perhaps as a response to close packing of competitors (MacArthur 1972) and to the selection of seasons that are best suited for active development. Distinct seasonal cycles have been observed in tropical plants (Janzen 1967, Burger 1974), fish (Kirschbaum 1975), birds (Snow and Snow 1964), rodents (Field 1975), some large mammals (Leuthold and Leuthold 1975), and several groups of insects from the Neotropics (Fairchild 1942, Galindo et al. 1956, Ricklefs' 1975) and Africa (Owen and Chanter 1970, Owen 1972, Duviard and Pollet 1973, Bigger 1976, Leston 1977). This-report examines the temporal distribution of insects sampled with a Malaise trap in the Nairobi National Park, Kenya, during a five-year period from August 1972 to July 1977. Marked seasonality was observed among several insect taxa, and the overall abundance of insects fluctuated greatly, especially in response to several periods of severe drought. METHODS STUDY AREA.-The trap was erected in grassland 2 m from a forest edge (fig. 1) in the western portion of Nairobi National Park (1?21'S, elevation 1800 m) within 2 km of the Langata gate. According to the Holdridge classification system (Holdridge et at. 1971) the forest would be considered a tropical premontane dry forest. It is dominated by Brachylaena hutchinsii and Croton megalocarpus while the grassland, which is derived from forest, is characterized by Themeda triandra: and Pennisetum clandestinum (Verdcourt 1962, Lind and Morrison 1974). Characteristically, the region has two rainy seasons (fi. 2): the long rains from mid-March to the end of May bring about 450 mm of rainfall and the short rains from mid-October to mid-December yield around 250 mm. Precipitation at other times brings the annual total to 900 mm (50-year average). Mean monthly temperature (fig. 2) ranges from 17?C during July and August to 20?C in March. Monthly rainfall data used in figure 3 were based on records of the East African Meteorological Department for Wilson Airport, a station located 4 km from the study

Nutrient scavenging of rainfall by the canopy of an Amazonian rain forest.

Abstract: Fluxes of nutrient elements entering the forest canopy by rainfall are compared with fluxes to the forest floor by throughfall, for two tropical rain forest types growing on soils of low nutrient content in southern Venezuela. In contrast with other forests, total yearly rainfall fluxes of calcium, sulfur, and phosphorus were greater than corresponding throughfall fluxes. For other elements, rainfall fluxes were occasionally greater than throughfall fluxes. We hypothesize that these nutrients are intercepted in the canopy by algae and lichens growing on leaf surfaces, resulting in nutrient conservation in this nutrient-limited ecosystem. THE RAIN FOREST WHICH COVERS much of the central and eastern portion of the Amazon Basin grows on soils low in essential nutrient elements (Sioli 1975, Klinge and Ohle 1964). Despite the low nutrient content of the soils, the forests appear large and vigorous. The question of how the forests survive in the nutrient-poor environment has interested ecologists for many years, and it has been hypothesized (Richards 1952) that nutrient-conserving mechanisms evolved in these ecosystems which have enabled these forests to survive and grow in this nutrient-poor environment. In order to study the structure and function of the Amazon rain forest, including nutrient-conserving mechanisms, an ecological project has been established near San Carlos de Rio Negro, Venezuela, lat. 20N, 67?W (Medina et al. 1977). The area is within the northern part of the drainage basin of the Amazon River. Some of the initial results of the project have shown that there is virtually no nutrient input to the ecosystem from the mineral soil and subsoil (Klinge et al. 1977, Stark and Jordan 1978, Stark and Spratt 1977). This finding means that atmospheric input must be a major source of nutrients for the central Amazon forests. In this paper we report that nutrients are filtered out of the rainwater as the water passes through the forest canopy, and we hypothesize that this interception is an important nutrient-conserving mechanism for the Amazonian

Plant Reproductive Characteristics during Secondary Succession in Neotropical Lowland Forest Ecosystems

Abstract: During secondary succession in tropical America, reproductive characteristics of the constituent plants change as species constitution changes in the direction of 'climax' or equilibrium. Self-compatibility is more prevalent in early stages, while outcrossing is more the rule in later stages as dicliny, dioecism, and self-incompatibility beome more frequent. Observations indicate that plants of increasingly large stature and seral position are more widely spaced, and tend to have larger brightly colored flowers and larger pollinators. Associated understory plants come to have small unicolorous flowers and small pollinators as light availability decreases. Plants of early stages have primarily small, many-seeded dehiscent fruits, while plants with large, few-seeded fleshy fruits come to dominate equilibrium forests, particularly in wet forest. Canopy emergent trees, epiphytes, and lianas of mature forest are exceptional in employing wind-dispersal. Many of these changes correlate well with the thesis that pioneer plants are more highly r-selected, while plants of more mature forest tend to be K-selected. ALTHOUGH THE STUDY OF SECONDARY SUCCESSION in temperate latitudes signalled the onset of ecological endeavor (Cowles 1899, Clements 1916), only in recent years has the study of succession in the tropics made significant advances. The study of reproductive characteristics of plants in seral sequences has lagged even further behind. Our studies and those of others (Bawa 1974, Vasquez-Yanes 1974a, McKey 1975, Ruiz Zapata and Kalin Arroyo 1978) allow some preliminary conclusions and hypotheses on the nature of reproductive characteristics of plants in different seral stages. In this paper we consider the various portions of reproductive biology as a sequence of topics, i.e. floral biology, seed biology, and breeding systems. We then contrast findings from lowland wet and dry forest habitats, and finally integrate our findings and hypotheses with

Demography of an undergrowth palm in littoral Cameroon.

Abstract: This study of Podococcus barteri in Cameroon, equatorial West Africa, shows that the longevity of this small palm is in the range of 63-74 years. Seasonality is more pronounced in flowering than in leaf production. Adults produce one leaf per year, each lasting about five years in the crown. Proliferation by stolons begins many years before flowering. The leafy stolons may grow two-eight or more years before establishing the ramets. Inflorescence development, flowering, and seed maturation take about 1.4 years. Only 0.08 percent of the ovules become mature seeds. A stage projection matrix gives the annual population growth rate as 1.2 percent. The growth index X is more sensitive to changes in mortality of juveniles and young adults than of seeds-seedlings, mature-old adults, or stolons. Mortality at several stages of sexual reproduction and the size advantage of ramets account for the greater importance of cloning to population dynamics, although the relative energetics have not been assessed. IN LOWLAND WET FORESTS, the occasional disruption of the deep-shade and sunfleck environment by falling trees results in luxuriant growth of many species. Tree-fall gaps have been considered the main organizing feature of population and community dynamics (Aubreville 1938, Jones 1956, Whitmore 1975, Hartshorn 1978). The pattern of spatial and size distributions of many species reflects the focus of their establishment and/or maturation in gaps, but other species do not conform (e.g., Richards and Williamson 1975). The comparatively sparse plant cover of the long-enduring, abysmal gloom of the floor of mature forest has been largely ignored even in vegetation studies, and the growth and reproductive behavior of this flora is virtually unknown despite its accessibility. Palms are a particularly abundant part of this lower stratum, and convenient to study as their geometric simplicity much facilitates observation and analysis of their behavior. Even for relatively longlived species, demographic projections can be made from short-term observations (Hnatiuk 1977, Van Valen 1975 based largely on Bannister 1970). In contrast to the diversity of small palms in Malayan and American forests (Whitmore 1973, Moore 1973a), there are only two species in mature forest undergrowth in Africa. Podococcus barteri is occasionally common in the littoral region of Cameroon, growing in clusters often of 10-4 or 10-3 ha, with stem densities up to seven per m2. The habit, distribution, growth, and reproduction of Podococcus will be described here, with the purpose of assessing seasonality, the time scales relevant to individual life history, the stability of the population (of plant modules, not genets), and its sensitivity to disturbance of existing growth, reproduction, and mortality schedules. Demographic treatment of long-lived woody plants lags far behind that of herbs (Harper 1977), and is of particular interest for Podococcus as a species of the mature phase of lowland forest, and one which both clones and produces seed.

Floral Ecology and Hummingbird Pollination of Combretum farinosum in Costa Rica

Abstract: The pollination biology of Combretum farinosum, a hummingbird-pollinated, outcrossing liana of the dry forest in Costa Rica, was investigated in order to determine the evolutionary interactions between nectar rewards and pollinator foraging behavior. Plants generally produced many flowers, arranged in dense inflorescences which were highly synchronized in development, and with large nectar output per flower. Inflorescences change color from green on the first day, to greenorange (day 2), orange (day 3), and red (days 4 and 5). Only green, first-day inflorescences secrete nectar, and these were visited preferentially by all hummingbirds. Red inflorescences contained little nectar, were rarely visited (2% of all visits), and probably serve as "flags" to attract pollinators. The hummingbirds Chlorostilbon canivetii and Archilochus colubris foraged as transients, moving primarily between plants, while Amazilia saucerottei and A. rutila foraged as tenants at single plants and periodically defended small sections of large plants. The visitation rate per inflorescence increased with effective plant size (= number of nectar-producing inflorescences) for tenants, but not transients. Mean seed set per inflorescence decreased with effective plant size, but seed production per plant increased. Seed set was not limited by hummingbird visitation rate per se, as expected seed set per inflorescence (calculated from visitation rate and the number of flowers probed per visit) increased with plant size. Despite the higher visitation rate of tenants to large plants, seed set per infloresconce did not increase due to the low outcrossing potential of tenants as compared to transients, and the occasional removal of transients by territorial tenants. I suggest that the large nectar production of Combretum has evolved to satiate potentially territorial species and reduce the advantages of patch defense-increasing the number of outcrossing visits per plant. This pollinator-satiation strategy is an evolutionarv parallel of that found in seed-dispersal systems; in both cases foraging behavior is altered through resource abundance. PLANT REPRODUCTIVE CHARACTERISTICS result fronm selection operating on life history and breeding system in the context of maximizing reproductive success. The evolutionary advantages of sex (Maynard Smith 1971, 1978; Williams 1975) have effected an astonishing diversity of floral characters "designed" to manipulate the pattern and process of pollen movement. With the exception of autogamy, all forms of sexual reproduction in angiosperms require the intraspecific movement of pollen to a receptive stigma via some external agent. When animal vectors perform this transfer a reward is required, except in cases of dupery in which plants trap pollinators (Proctor and Yeo 1973) or induce pseudocopulation (Kullenberg 1961). The strategies and tactics utilized by plants in the evolutionary development of their floral attractiveness to pollinators are largely functions of the pollinators' nutritional and energetic demands (Heinrich and Raven 1972, Baker and Baker 1975). The level of reward offered can markedly affect pollinator movement patterns and, as a result, plant reproductive success (Willson and Rathcke 1974, Frankie et al. 1976, Carpenter 1976). Thus, plants will evolutionarily manipulate the spatial distribution, quantity, and quality of reward to optimize pollinator movement (Janzen 1977). This can be achieved by varying floral distribution on an individual and by regulating reward level through variations in the 1) numbers of flowers/plant, 2 ) nectar volume/flower, 3) nectar composition, and 4) the rate and duration of nectar flow. The extent to which resource abundance and distribution affect reproductive success is highly dependent on breeding system, with self-incompatible species most affected by sedentary pollin-

Life History and Growth Relationships of Cichla ocellaris, a Predatory South American Cichlid

Abstract: This paper examines the life history and growth relationships of Cichla ocellaris, a predatory South American cichlid. Data from extensive field studies in Gatun Lake, Panama, where C. ocellaris was introduced, present a complete life history for this species from pair formation through parental care of the young. These data are relevant to fish management and culture efforts, since C. ocellaris is one of the few New World cichlid species which is exploited commercially. New interpretations of the evolution of parental care patterns in cichlids, and the possible significance of latitudinal differences in parental care patterns among guarders, are included. Creel surveys allow comparison of length/weight ratios from native habitats in Brazil and Venezuela, non-native lacustrine habitats in Panama' and Hawaii, and non-native riverine habitats in Panama. These results indicate that the potential for short-term harvest of cichlid production is higher in lake habitats, but for long-term continuous harvest, it is greater in rivers. Este trabajo trata sobre los estudios de los diferentes estadios de desarrollo y relaciones de crecimiento de Cichla ocellaris, un ciclido dulceacuicola suramericano introducido en el Lago Gatuin, Panama. Los estudios desarrollados incluyen desde el periodo de apareamiento hasta el desarrollo del adulto. El trabajo hace enfasis en: apareamiento, desove, cuidado paternal y mecanismos de defensa de los juveniles (coloracion y comportamiento). Se discute adem'as la evolucion del cuidado parental en neces. Los datos provenientes de las pesquerias no permitieron hacer comparaciones de las relaciones de talla/peso para diferentes habitats: nativos (Brazil y Venezuela); no nativos lacustrinos (Panam'a y Hawaii); no nativos fluviales (Panama'). Los resultados mostraron una alta produccion en periodos cortos para los lagos. Sin embargo, los rios mostraron una alta produccion en periodos largos. Esta conclusion permitira dirigir mejor los esfuerzos que se haran para manejar y cultivar esta especie de alto valor comercial. THE CICHLIDAE, a family of secondary fishes (i.e., capable of tolerating seawater for at least a brief period of time), are largely indigenous to Central America, South America, and Africa. Their preferred habitat is lentic (slow-moving) waters, and of the approximately 1000 species in the family (Goldstein 1973), the vast majority are associated with lakes. For instance, in the Great Lakes of East Africa there are nearly 400 species, almost all endemic (Fryer and Iles 1972). A parallel New World example, although of much more recent origin (Myers 1966), is found in the Great Lakes of Nicaragua and their associated drainage basins which contain approximately 75 percent of the almost 100 Central American species, mostly of the genus Cichiasoma. In addition to the many lake forms there are also riverine cichlids, but these are generally considered more primitive, closer to the original stock from which the entire group has evolved (Regan 1906). A recognition of the preeminence of cichlids in lentic rather than lotic (fast-moving) aquatic environments is fundamental to an understanding of this family's ecology. Several characteristics may have enabled cichlids to exploit lentic habitats. Their fully enclosed (physoclistous) air bladder, in which the secretion of gases can maintain a constant bladder volume with depth, allows them to frequent relatively deep waters in lakes; for example, in Lake Tanganyika, cichlids dominate the deepest fish fauna in the littoral regions between 100-120 meters (Lowe-McConnell 1975). In addition, cichlids have fins and associated musculature ideally suited for accurate and finely controlled movements, including the ability to fan water. Fanning enables cichlids to rear young in oxygen-depleted lakes by providing a steady flow of water over the developing eggs, thus allowing them to be independent of river flow for spawning. Finally, well-developed oral incubation of young provides protection against egg and larval predators. The body form of cichlids bears a striking resemblance to such North American centrachids as the bluegill, crappies, sunfish, and bass species. Morphologically, the major distinctions between the two families are, first, that cichlids usually have an incompete lateral line on at least one side of their body, whereas centrarchids have complete lateral lines; second, cichlids have a single nostril at each side of the head, while centrarchids have a pair on each side, typical of percoid fishes. The ecological significance of these two morphological differences is unknown. While both Cichlidae and Centrarchidae are members of the same suborder Percoidei (with 144 BIOTROPICA 12(2): 144-157 1980 This content downloaded from 157.55.39.223 on Wed, 24 Aug 2016 04:14:03 UTC All use subject to http://about.jstor.org/terms about 60 families), parallel evolution in aquatic habitats may be more responsible for their similar morphology than any close taxonomic relationship. Cichlids derive their notoriety from two sources. First, as brightly colored fishes which adapt well and breed in aquarium tanks (i.e., lentic habitats), they are highly favored pets. Some delights of the fish fancier are the Jack Dempsey (Cichlasoma biocellatum), the discus (Symphysodon sp. ), the Oscar (Astronotus ocellatus), and the graceful angelfish (Pterophyllum sp.), all of South America. Second, one genus of African cichlid, still called by its common name "tilapia," has achieved a worldwide distribution because of its commercial importance. This species, formerly Tilapia mossambica, is now placed with all related mouthbrooders of this group in the genus Sarotherdon (see Trewavas 1973). Many species in this genus can be cultured easily in rearing ponds on a diet of relatively inexpensive food. Sarotherdon esculentus feeds on phytoplankton with fine gillrakers and a mucous secretion to trap the algae (Greenwood 1953). There is a considerable literature on the rearing of tilapia (Thys van de Audenaerde 1968), and the fish has been highly touted as a potential solution for the world protein shortage, although its development as an important food resource has not yet lived up to expectations. In Africa, a great number of cichlid species are commercially exploited on a large scale. For instance, in Lake Victoria the yearly catch of cichlids for consumption has been estimated at greater than 30,000 metric tons (Fryer and Iles 1972:387). In contrast, relatively few of the New World's approximately 200 species of cichlids find their way to markets in large numbers. The probable reasons for this disparity are 1), the dearth of large lakes in the New World; 2), the presence in Africa of European nationals who were able to adapt their expertise in marine fisheries management to African lakes; and 3), differences in local availability of alternative food resources. In addition, in the New World most of the aboriginal peoples have been exterminated or displaced by Europeans, over the past four centuries, and recent anthropological evidence (R. Cooke, pers. comm.) suggests that the former Indian populations relied considerably more on fishes as a regular part of their diet. Undoubtedly, all of these natural and historical factors have played a part in this striking difference between Old and New World exploitation of cichlids as food sources. One notable exception to this above generalization is the South American predatory cichlid Cichla ocellaris, whose fine taste and abundance in native habitats have made it an important commercial species. In Manaus, Brazil, this species is brought into local markets for sale by the thousands, and commands one of the highest prices. According to Meschkat's (1960) estimate, C. ocellaris is the most frequent cichlid sold commercially in Manaus, with a ranking of 17 among all freshwater fishes in total yearly catch. In addition, C. ocellaris is an excellent sport fish, and for this reason has been introduced to various water bodies throughout its native range and in other countries, including Hawaii (Devick 1969), Puerto Rico (Erdman 1972), and Panama. In Panama its presence has had measurable and dramatic effects on the local fish fauna (Zaret and Paine 1973). Cichla has also been successfully reared in Brazil in artificial ponds (Sawaya and Braga 1946, Braga 1952, Fontenele 1950), although these culturing activities appear to have lapsed. There are four species of the genus, all native to South America. These include: C. ocellaris and C. temensis, which are sympatric throughout the Amazon and Orinoco basin (Eigenmann and Allen 1942, Fowler 1954); C. intermedia, which so far has been ~~~~~~~~~~~~~~* v

Variation in leaf size with respect to climate in Costa Rica.

Abstract: Leaf-size variation with respect to climate was studied at 38 sample sites in Costa Rica. The variation in leaf size was analyzed by plotting the sample sites on Holdridge's (1967) life zone chart and comparing the percentage of species having large leaves (greater than 20.25 sq cm in area) in the different life zones. Three foliar belts could be identified in the tropical basal and altitudinal belts. Although the percentage of species having large leaves is significantly different between the foliar belts, the variation in leaf size is not continuous along environmental gradients either within or between foliar belts. The variation in leaf size within each foliar belt recognized suggests that other environmental parameters also have an important influence on leaf size. Extreme care must be exercised in the estimation of paleoclimate by angiosperm paleobotanists because of the potential variation in leaf size within a single foliar belt and the recognition that this variation does not follow climatic gradients. A CORRELATION BETWEEN LEAF SIZE distribution and climate in individual plant communities was first postulated by Raunkiaer (1934). He emphasized the effect of precipitation on leaf area. As precipitation decreased, the average leaf area in a flora also decreased. The percentage of species having large leaves should be greatest in the tropical lowlands with a net decrease in leaf area being noted when moving into drier environments. Temperature, the second major climatic variable recognized by ecologists (e.g., Holdridge 1967, Holdridge et al. 1971), was not emphasized in relation to leaf size because Raunkiaer (1934) felt that region-specific effects attributable to temperature either did not occur or could not be recognized. When analyzing the distribution of species having large leaves from around the world, Dilcher (1973) pointed out that plants do not respond to single climatic variables but to the total environment. For this reason, Dilcher attempted to correlate leaf-size distribution with both temperature and pre-

The seasonal cycle and nests of Epicharis zonata, a bee whose cells are below the wet-season water table (Hymenoptera, Anthophoridae).

Abstract: A nest aggregation of Epicharis zonata in coastal French Guiana was periodically examined from October 1976 to August 1977. There is only one generation per year; adults emerge and nest during the dry season. Waterproof cells constructed in level, sandy soil were well beneath the water table during the west season. Prepupae passed at least nine months within the cells.

Foraging by Bucket-Brigade in Leaf-Cutter Ants

Abstract: Atta cephalotes foragers transfer leaf fragments to "carrier" ants at junctions of new branch trails and the established trail. A more pronounced specialization into "harvesters" and "carriers" is exhibited by A. sexdens rubropilosa in which smaller ants harvesting in the tops of tall trees drop material to the ground where larger workers collect it. COLUMNSOF LEAF-CUTTER ANTS (Myrmeciinae: Attini), carrying leaf and flower fragments along trails to the nest, are a common sight in the neotropics. Workers cut fragments from a variety of trees, shrubs, and crop plants, and culture a fungus on them, the specialized hyphae of which serve as their sole food source (Weber 1966, Hubbell and Rockwood 1980). As in many other eusocial insects, including bees, termites, and especially ants, a trail pheromone helps to guide the workers between nest and food source (Wilson 1971, Moser and Blum 1963). W e describe here a novel two-stage relay process in foraging leaf-cutter ants, involving a transfer of material from one ant to another. This relay process, serves to increase the speed of new food-source utilization, and to increase the efficiency of exploitation of established food sources. Foraging efficiency is a significant problem for leaf-cutters which must often travel long distances, sometimes over 100 meters, to harvest leaves of tree species best able to support fungus growth (Cherrett 1968, Hubbell and Rockwood 1980). RELAY COOPERATION DURING NEW TRAIL FORMATION We studied the foraging of Atta cephalotes L. in a tropical dry forest in Santa Rosa National Park, Guanacaste Province, Costa Rica (lat. 10' 50", long. 85' 37"). Trails from the nest lead to particular trees or shrubs or to small, oval, ground-foraging areas where ants forage solitarily. The ants may later establish a trail leading to a particularly acceptable plant within the oval. The discoverer ant lays a pheromone trail connecting the new source to the main trail, and within an hour a branch is established. Laden A. cephalotes normally carry their loads all the way into the nest: The first ants to visit a new source, however, carry their loads only as far as the main trail, where they drop them, or antennate other ants and transfer their load to them. These "carriers" then carry the fragments to the nest. To learn more about branch trail formation and about the transfer of information regarding the locations of new, high-quality food sources to other workers, we performed experiments in October and November 1975. In these experiments, bread crumbs or leaves of Bursera ~imaruba, a preferred tree species, were placed in an oval ground-foraging area 1 meter from an established trail. Figure 1 shows that in one such experiment a trail to the bread crumbs (black circle) developed as a branch off the main trail (heavy line), and figure 1A traces the tortuous paths of the first two crumb-bearing ants back to the main trail. Both touched their gasters repeatedly to the ground, a behavior which indicates pheromone deposition (Moser and Blum 1963). Typically such individual trails gradually consolidate as more ants visit the food and lay pheromone Figure 1B shows the paths of three ants returning to the main trail 40 minutes after discwering the bread. The trail has become narrow and points directly to the nest (not shown in the figure). A decline in the percentage of ants dropping or transferring their loads upon reaching the main trail was always found to accompany trail consolidation. Table 1 shows how, in another experiment, this petcentage declined over a 50-minute period subsequent to the discovery of bread. In this experiment, 12 percent of the drops and transfers occurred along the way between the bread and the main trail, 83 percent occurred along the first meter of the main trail, 5 percent occurred along the second meter of the main trail, and none in the last two meters to the nest. This typical localization of dropping or transferFIGURE 1. A. Paths back to the main trail (heavy line) of the first two ants to discover the new food source (black circle). The x's mark the sites where the ants dropped or transferred their loads. B. Paths of three recruits 40 minutes after discovery of the food. These ants continued straight to the nest (to the right) with their loads. ring the bread led us to hypothesize that some abruptly encountered feature of the main trail, such as familiar landmarks, trail pheromone, or heavy ant traffic, stimulates these behaviors. As the new branch trail becomes more like the main trail, dropping and transferring is less often stimulated. Although main trails sometimes appear as distinct grooves worn in the ground, this characteristic was not a distinguishing feature in the experimental site, so we began exploring the other possibilities. W e determined in another experiment in M:iy 1976 that sudden encountering of trail pheromone by itself could produce dropping or transferring behavior. Two 46 x 61 cm cardboard rectangles were nailed to the ground for 30 hours, the "control cardboard" at a site where ants were not foraging, and the "trail cardboard" on an active trail, the long axis parallel to the trail. Ants marked the trail cardboard. The next evening each cardboard was laid between a pile of bread crumbs in an oval ground-foraging area and a main trail one meter away. Care was taken that the two sites where the cardboards were laid were equivForaging in Leaf-Cutter Ants 211 alent in terms of ground cover, slope, and traffic of the main trail; at neither site had the ants previously been exposed to bread. Each cardboard was oriented wlth its long axis parallel to the main trail, so that the pheromone trail on the trail cardboard lay perpendicular to the most direct path from crumbs to main trail. TABLE 1. Percentage o f ants dropping or transferring loads i n each o f five 10-minlcte periods after discovery o f the food.

Robbing of exotic plants by introduced carpenter and honey bees in Hawaii, with comparative notes.

Abstract: In Hawaii, a carpenter bee (Xylocopa sonorina) and the honey bee (Apis mellifera) use floral perforations to obtain nectar. With its maxillae, X. sonorina perforates corollas and calyces of introduced plant species; in corollas of different lengths and diameters, the perforations made are significantly different in length. Through these perforations, X. sonorina imbibes nectar without pollinating the flowers. Old and New World Xylocopa spp. perforate the flowers of at least 22 families. Apis mellifera obtains nectar through perforations made by X. sonorina. Elsewhere in the world, A. mellifera uses previously made perforations in flowers to obtain nectar from at least 10 plant families. These bees are "robbers" of some plants in that they take floral provisions in ways that are unlikely to effect pollination. THIS STUDY WAS MADE primarily to examine diversity of flower-perforation and flower-robbing behavior in an exotic carpenter bee Xylocopa (Neoxylocopa) sonzorina (Smith) (Anthophoridae) toward plants in Hawaii. Also included are notes regarding nectar robbing by honey bees (Apis mellifera L. (Apidae) ) in Hawaii, a literature survey of flower perforation by Xylocopa spp. and A. mellifera, and the use of pre-made perforations by A. mellifera elsewhere in the world (appendices 1 and 2). The introduced plants that were studied are Asystasia gangetica (L.) T. Anders. (Acanthaceae), Thevetia peruviana (Pers.) K. Schum. forma aurantiaca (Apocynaceae), Hibiscus rosa-sinensis L. (Malvaceae), Plumbago capensis Thunb. (Plumbaginaceae), and Stachytarpheta sp. (Verbenaceae). Williams (1927) and Nishida (1967) reported floral perforation of other plants by X. sonorina in Hawaii, and Schremmer (1972) described in detail how X. sonorina perforates flowers. Apis mellifera was introduced to Hawaii around 1857; X. sonorina, about 1874, when it was characterized as a new species by Smith (1874) who erroneously transcribed Sunda Islands instead of Sandwich Islands (Lieftinck 1956). Flowers such as those listed above have evolved tubular corollas to restrict insect and avian visitors to those which are likely to cause pollination while collecting nectar, pollen, or both. However, certain animals, e.g., bees, birds, and some Lepidoptera (Pammel 1888, Muller 1895, Swynnerton 1916, Parthasarathy Iyenger 1923, Porch 1924, 1929; and see references in Barrows 1976), which would otherwise be excluded from such flowers, obtain floral provisions by using floral perforations. This mechanism has been called flower perforation, mutilation, robbery, thievery, raiding, or burglary, depending on the author. "Floral robber" (and its synonyms), "primary robber," and "secondary robber" are confusing literature terms. Depending on the investigator, these words have been used to imply that an animal may or may not pollinate a particular flower through the use of perforations in flowers that it or another animal has made; or an animal may acquire floral provisions through natural floral orifices which presumably did not evolve for pollinator use. In this study, a floral robber is considered to be an animal which obtains floral provisions in such a way that it is unlikely to pollinate a particular flower. Robbery may or may not involve floral perforation by a robber (Haeseler 1975, Barrows 1976) since the perforation may already exist. Appendices 1 and 2 summarize plant relationships with Xylocopa and other animals from the standpoint of floral perforation, not robbing, since many investigators did not report whether or not a particular animal pollinated a flower when it used perforations. However, many animals listed in the appendices are probable robbers. At different times, individual animals may pollinate or rob particular flowers (Meidell 1944, Macior 1966, Koeman-Kwak 1973). Moreover, an animal species might be a pollinator of one plant species and a robber of another. For example, Xylocopa virginica L. pollinates Passiflora (Frankie and Vinson 1977), but it perforates and probably only robs other plants such as Lonicera japonica Thunb. (pers. obs.). Therefore, a primary robber is an animal that perforates a flower species, obtains floral provisions, but does not pollinate the flower; a secondary robber is an animal that uses a previously made perforation, obtains floral provisions, but does not pollinate the flower (I.ken 1962). An animal presumably can be both a primary and secondary robber of a plant, although this BIOTROPICA 12(1): 23-29 1980 23 This content downloaded from 157.55.39.209 on Sat, 14 May 2016 04:43:19 UTC All use subject to http://about.jstor.org/terms has not been conclusively demonstrated. Some plant species may have decreased seed production due to robbery (Ogle 1869, Kerner 1873, Delpino in Pammel 1888, and Meeuse 1961), but Heinrich and Raven (1972) suggest that robbers may increase pollination of some flowers because they cause functional pollinators to make more visits. It is usually nectar that is taken through perforations, but the andrenid bee Perdita hurdi Timberlake obtains pollen through perforations which it makes in unopened flowers, nectar being collected through natural floral orifices from normally open flowers (Hurd and Linsley 1963). MATERIALS AND METHODS Floral perforation was observed to occur on Oahu, Hawaii, primarily on the campus of the University of Hawaii, Manoa, during the hours of 0700 to 1900 from late November to early December 1976. All the A. mellifera and X. sonorina observed were females. Flower samples from tall bushes (T. peruviana and H. rosa-sinensis) were taken from their sides about 1 to 2 m above the ground. Asystasia gangetica and P. capensis flowers were collected mainly from upper inflorescences. Tongues of recently killed bees were artificially extended and measured from bases to stipes to distal ends of glossae. The abbreviation M is used to indicate median; X, mean; N, sample size. For convenience, some methods are described in the Results and Discussion. To facilitate statistical analysis, smaller samples were sometimes selected from larger ones with use of a random number table. RESULTS AND DISCUSSION Tongues of 10 A. mellifera were from 5 to 6 mm long (X = 5.8, M 6), and tongues of seven X. sonorina were all 10 mm long, being significantly longer than those of A. mellifera (p < 0.001, MannWhitney U-test). Thus A. mellifera may not be able to reach nectar through perforations made by X. sonorina. Xylocopa sonorina perforated flowers of various colors and shapes. Corolla length and diameter and the length of the perforations varied significantly among samples of 20 randomly selected flowers of Thevetia peruviana forma aurantiaca, Asystasia gangetica, Hibiscus rosa-sinensis, and Plumbago capensis (in both tests: x256.27, d. f. 3, p 0.001, median test). Flowers of T. peruviana (fig. 1) were pentamerous, actinomorphic, pinkish-orange, and had corollas from 51 to 63 mm long (X =572 M_= 56.0) and from 16 to 33 mm in diameter (X M = 25.5, N= 50); those of A. gangetica (fig. 24 Barrows 2) were pentamerous, zygomorphic, light yellow to white or lavender, and had corollas from 28 to 36 mm long (X 30.9, M= 30) and from 28 to 37mm in diameter (X_-33.1,M 23.5,N= 20); those of H. rosa-sinensis (fig. 3) were pentamerous, actinomorphic, with bright pink petals, yellow staFIGURE 1. Longitudinal view of a flower of Thevetia peruviana forma aurantiaca with part of its calyx and corolla removed to show the interior. A-anther; C-calyx; P-petal; PR-perforation made by Xylocopa sonorina; Sstigma. Bar = 1 cm.

Leaf Decomposition Rates in Costa Rican Lowland Tropical Rainforest Streams

Abstract: Whole leaves of five species of riparian plants and five species of upland plants were placed in a tropical stream in a wet, lowland, Costa Rican forest. Leaves of the five riparian species disappeared faster than did the leaves of the upland species. Whole leaves of four species of riparian plants were placed in three streams and on the forest floor. Two species, Ficus glabrata and Trema micrantha, decomposed within 32 days; Ardisia sp. and Pithecelobium longifolium did not decompose over that period. For the two species that decomposed, decomposition occurred at a slower rate on the forest floor than in a stream 50 m from the forest floor site. Leaves of one species, F. glabrata, decomposed faster in water in the wet than in the dry season. Decomposition rates were similar for leaves of F. glabrata and T. micrantha placed in three streams during the wet season. Results differ markedly from previously published results for tropical streams. Differences in the dynamics of allochthonous leaf nutrient inputs into heterotrophic mid-latitude and tropical streams are discussed. BECAUSE STREAMS AND RIVERS running through forested watersheds receive very little sunlight, nutrients from primary production of aquatic origin contribute little toward the accumulation of basic nutrients by which the biogeochemical cycle operates. Nutrient inputs come primarily from ground water, tributaries, precipitation runoffs, or from terrestrial insects and plants parts, especially leaves, falling into the water (Boling et al. 1975, Fittkau 1969, Cummins 1974). In addition to serving as nutrient input sources, leaves serve as substrata for aquatic invertebrates. Consequently, considerable literature has developed concerning the role leaves play in heterotrophic mid-latitude streams (Peterson and Cummins 1974, Reice 1974, Davis and Winterbourn 1977, Kaushik and Hynes 1971, Cummins et al. 1973, Iverson 1973). In tropical areas where soil nutrients are very low (Janzen 1974), essential elements from soil and rain are concentrated by both terrestrial and streamside emergent plants (Howard-Williams and Junk 1977). In lowland tropical areas studied, leaves have the highest content of total elements of all plant parts (Klinge and Rodrigues 1968, Stark 1971a, b). It is probable that plant tissue, especially leaves, provide heterotrophic streams with a source of essential element unattainable to any major degree by runoff. As such, the roles that any plant parts play in tropical rainforest streams may be accentuated, in particular, in tropical environments low in soil nutrients. Not only do all plants concentrate essential elements from nutrient-poor soils, but some defensive compounds produced by secondary plant metabolic pathways are found at higher levels within leaves from plants grown on nutrient-poor soils (Janzen 1974, Davies et al. 1964, McKey et al. 1978) than in plants on "good" soils. Defensive compounds, in general, may be allelopathic to decay organisms or may be more difficult to break down by those organisms than other nutrient-rich compounds in the plant

Dry-Season Overlap in Activity Patterns, Habitat Use, and Prey Selection by Sympatric African Insectivorous Bats

Abstract: We used mist nets, ultrasonic sensors, light tags, and analysis of feces to examine habitat use, activity patterns, and prey selection of some insectivorous bats during the dry season at the Sengwa Wild Life Research Area (18?10'S; 28013'E) between 7 and 28 June 1977. The results show broad overlap in all parameters investigated for the 13 species present in the area during the dry season. During the wet season, some species of insectivorous bats relied more on beetles than on moths as food, or vice versa. The lack of food partitioning, particularly in the dry season, appears to conflict with theories of niches and competitive exclusion, but it is in accord with predictions based on optimum foraging strategy. We conclude that most insectivorous bats are opportunistic feeders, a strategy which results in a mosaic of specialized and generalized diets and which is compatible with their energetic demands. We report the first record of Tadarida chapini from Zimbabwe (Rhodesia). FOOD AND ROOSTS are two potentially limiting resources which may be partitioned by sympatric species of bats (Tamsitt 1967, Fenton 1970, McNab 1971, Humphrey 1975). Partitioning of food resources can involve habitat (Handley 1967) and/or time (Kunz 1973) and/or types of food (Black 1972, 1974). A variety of studies has shown that bats can be either very selective in their feeding (Buchler 1976a), or generalized in their diets reflecting local abundances of insects (Belwood and Fenton 1976, Anthony and Kunz 1977). Bradbury and Vehrencamp (1976) found broad overlap in prey size between five species of Neotropical emballonurids which showed flexible feeding behavior, and Kunz (1974) reported that Myotis velifer adjusted its foraging patterns to meet local conditions. A reflection of the flexibility in foraging behavior is provided by Fenton and Morris' (1976) experiments which demonstrated that some insectivorous bats were opportunistic, rapidly responding to concentrations of insects. Similar responses to concentrations of food occur for other bats as well (Fleming et al. 1977, Gould 1978). Our purpose here is to report some observations we made of activity patterns, habitat use, and prey selection by some sympatric African insectivorous bats, and to interpret these results in the context of resource partitioning (e.g., Schoener 1974) and optimal foraging strategy (e.g., Pyke et al. 1977). The field data for this study were gathered during the dry season in an African deciduous forest; they are compared to previously published wet-season data from the same locality (Fenton 1975, Fenton et al. 1977). We made our observations in the vicinity of the Hostes Nicolle Institute of Wild Life Research (18?10'S; 28013'E, ca. 820 m above sea level) in the Sengwa Wild Life Research Area, ca. 110 km west of Gokwe, Zimbabwe. Most of our work was done at the same sites used by Fenton (1975) and Fenton et al. (1977), and included miombo and mopane woodland, riparian forest, pans with and without water, and some locations along the Sengwa and Lutope Rivers (for details of vegetation and physiography see Cumming 1975). Several different types of habitats can be identified in the study area based on the composition of plant communities, but most of the area is open woodland, whether miombo or mopane (fig. 1). However, woodlands along the rivers may have higher densities of trees than woodlands away from the rivers, and the Sengwa River is bordered by open, grassy floodplain (fig. 1). While during the wet season some bats were more commonly captured in a specific habitat (Fenton 1975), during the dry season this distinction was much less clear. Furthermore, captures in one habitat or another do not necessarily reflect the use of these habitats by insectivorous bats (see below). MATERIALS AND METHODS We captured bats in 9 or 12 m, 351 mm mesh mist nets or in a Tuttle trap (Tuttle 1974) set at various locations near the Institute. Bats were removed from the nets or trap, sorted by sex and species, and then either released (sometimes after tagging) or held overnight in cloth bags to permit collection of feces. Bats held for collection of feces were those which had fed prior to capture (determined by palpation of the BIOTROPICA 12(2): 81-9

A natural ecosystem analog approach to the design of a successional crop system for tropical forest environments.

Abstract: A crop system analogous to a natural successional plant system in a tropical forest environment is described. Field-experiment results and comparisons between the successional crop system and crop systems described by other investigators suggest that the successional crop system has agronomic potential. This potential is related to characteristics of the crop system which reduce weed competition and the energy required to manage the crop system. There is evidence to support a hypothesis that agricultural viability of a particular crop system is directly related to the degree of similarity of that crop system to a natural plant system in the same environment. TROPICALAGRICULTURAL RESEACH has been characterized by a search for high-yielding varieties of crops. The new varieties often require irrigation, fertilizer, and additional labor (Paddock 1970). Farmers have been reluctant to accept some of the new varieties because they require the use of these expensive subsidies. Another reason for the slowerthan-expected acceptance of these varieties may be that the farmers' management unit is the farm rather than the crop species. The use of a new variety often requires changes in farm management the farmer may not be willing or able to make. This situation suggests that agronomic research should be applied to a management unit larger than the crop species. The crop system is a management unit currently receiving considerable attention in "multiple

The phenology of the dryland forest of Mauna Kea, Hawaii, and the impact of recent environmental perturbations.

Abstract: The forest of Mauna Kea, Hawaii, was studied from 1973 through 1975 in order to define composition and phenology patterns of the two dominant tree species, and to determine the influence of man and feral mammals upon the ecosystem. There was a significant change in tree species composition across a 150 m elevational gradient; soil characteristics, drainage conditions, past disturbances by man, and browsing pressure by feral mammals are suggested as possible reasons. Although species composition varied with elevation, the tree density did not change. The phenological patterns of Sophora chrysophylla were found more closely tied to the weather pattern than were those of Myoporum sandwicense. Methods of pollination and seed dispersal were different between Sophora and Myoporum, and the spread of the latter is thought to be related to increased seed dispersal by recently introduced avian species, in conjunction with the limitation of Sophora reproduction due to browsing pressure by feral sheep. Because of the changes that are affecting the ecological organization of this community, the forest and its associated fauna need to be carefully examined in terms of present management policies. ONE OF THE LAST REMAINING NATIVE DRYFOREST ECOSYSTEMS in Hawaii is composed of 12,000 hectares of high mountain savanna on the southwestern slope of Mauna Kea. Sophora chrysophylla (Leguminosae) and Myoporum sandwicense (Myoporaceae) are the most abundant trees, with scattered stands of Euphorbia olowaluana (Euphorbiaceae), Santalum ellipticum (Santalaceae), Dubautia arborea (Compositae), and two small plantings of introduced pine, eucalyptus, and cedar. Shrub and ground-cover species are considered elsewhere. No one has described the phenology of this forest although Hartt and Neal (1940) gave a species account of the vegetation on the eastern slope of Mauna Kea. This ecosystem has been greatly influenced by the activities of man and introduced animals for the last 100 years (Warner 1960). Until the 1950's Parker Ranch grazed horses and cut Sophora for fence posts. Since the 1820's herds of feral sheep have roamed these volcanic slopes eliminating much of the Sophora reproduction by destroying the younger trees (Giffin 1976). Because of these perturbations, information was desperately needed on the present condition of the forest. This study was undertaken from April 1973 through August 1975 to compare forest composition and reproductive strategies of the two primary tree species (Sophora and Myoporum) in an effort to understand ecological interactions and influences on the forest as it exists today. METHODS Study sites were selected on the southwestern slope of Mauna Kea at elevations of 1980, 2130, and 2290 m along the jeep road from Kilohana to Puu Laau (fig. 1). The 1980 and 2130 m sites were open to grazing by feral sheep, while the 2290 m study site was fenced on all sides. Five contiguous 30 x 30 m releves, arranged in the shape of a T, were arbitrarily established near the center of each study site. All trees taller than 2 m (the height when Sophora and Myoporum first flower) were numbered, tagged, and, with the aid of a grid system, recorded on a map. Circumference at breast height (CBH) measured 1.4 m above the ground, was determined with a tape measure, and total tree height was measured with a clinometer. Canopy density, flowering, and fruiting were measured monthly (see Lamoureux 1973, Frankie et al. 1974). Canopy density was determined by standing under each tree and recording the percentage of open sky observed. Flowering and fruiting were measured by estimating the number of available terminal branches on each tree, and recording the percentage of those that possessed fully opened flowers or mature ripe fruit. To offset the phenomenon of trees in one area being in heavy flower while 500 m away others lacked blossoms, every month I systematically walked across each study area outside the releve's, measuring the nearest tree each 30 m until 50 trees had been considered. These data were then added to those obtained from the releves. With the density of trees and intensity of flowering known, it was possible to extrapolate the yearly lPresent address: Department of Zoology and C.P.S.U., University of California, Davis, California 95616, U.S.A. 282 BIOTROPICA 12(4): 282-291 1980 This content downloaded from 207.46.13.127 on Fri, 14 Oct 2016 04:07:05 UTC All use subject to http://about.jstor.org/terms Mauna Kea Game Management Area