Showing papers on "Species richness published in 1985"

Biological determinants of species diversity

Abstract: We consider four categories of biological mechanisms of deter- minants which cause and maintain species diversity: niche relations, habitat diver- sity, mass effects and ecological equivalency. Two of these determinants are origi- nal to this paper: mass effect, the establishment of species in sites where they cannot be self-maintaining; and ecological equivalency, the coexistence of species with effectively identical niche and habitat requirements. The mode of action and ecological implications of each biological determinant are discussed using a schematic method for measuring alpha (community), beta (differentiation), and gamma (regional) diversities. The importance of mass effects and ecological equivalency to species richness is documented with several types of field data from Israel and California, U.S.A. Floristic richness and, in particular, the richness of floristic transitions, are discussed and interpreted by use of the biological determinants of diversity. Contact transitions between distinct floras are rich predominantly because of mass effects. Transitions induced by marked environmental changes are rich because of the combined influences of habitat diversity and mass effects. The rate at which species richness increases with sample area is related to the combined effects of all four biological determinants. This complexity explains the failures of simple species-area models. The relative intensity of each determinant is related to area: niche relations are most important at within-community scales, habitat diversity most important at both within-community and land- scape scales, and ecological equivalency most important at regional scales. We suggest that understanding patterns of species diversity will be enhanced by the partitioning of total species richness into the richness caused by each of the four ecologically distinct determinants of diversity.

Coexistence of plant species with similar niches

Abstract: In the context of a simple mathematical model, we derive several mechanisms whereby plant species can coexist in a community without differing in their trophic niches (their relations with habitats, resources and exploiters). The model is based on the dynamics of species turnover in microsites, and incorporates localized competition, non-uniform seed dispersal and aspects of spatiotemporal environmental heterogeneity. These factors, which are not included in most standard competition models, allow stable coexistence of trophically equivalent species due to: (a) Differences in life-history ‘strategy’. (b) Input of seeds from nearby habitats (spatial Mass Effect). (c) Differences in demographic responses to environmental fluctuations (temporal Mass Effect). (d) Turnover in species composition between different habitat patches.

Patterns of Species Diversity on Coral Reefs

Abstract: The zonation of dominant species and growth forms on coral reefs is one of the most striking patterns found in any natural community (42, 46, 115). Numerous factors may be important in controlling coral distributions and species diversity. These include light, usually correlated with depth; sedimentation; temperature; wave energy; plankton availability; frequency of mortality caused by storms or tidal exposure; and grazing by fish and urchins. Three major studies that correlate variation in physical factors with coral diversity and species composition over depth and horizontal position conclude that the reef environment is extremely heterogeneous and that species composition and diversity are determined not by physical gradients but by microhabitat conditions and complex biotic interactions (19, 88, 89). In spite of the heterogeneity of coral reefs strong evidence suggests that predictable patterns of species diversity exist along a depth gradient. Three separate studies on well-developed reefs have found similar patterns of species diversity in relation to depth. On each reef, diversity (measured by species richness and/or H') was low near the surface and increased to a maximum between 15 and 30 m in depth. (Red Sea 0-30 m (74); Jamaica 0-30 m (58); Jamaica 15-56 m (72); Indian Ocean 0-60 m (108). Below 30 m, diversity decreased gradually at the two sites where deeper surveys were made. Coral reefs have been described recently as being nonequilibrium systems, where competitive exclusion is prevented by frequent disturbances, as pre-

Flow regime, juvenile abundance, and the assemblage structure of stream fishes

Abstract: The assemblage of fishes in a second—order stream in east—central Illinois was compared through seine sampling for two years with distinctly different flow regimes. In both years adult (age >0) fish were most abundant in late spring and early summer while juvenile (age 0) abundance peaked in late summer or autumn. Total density of adult fish differed little between years but large changes in juvenile abundance occurred between years in association with differences in hydrologic regime. High stream discharge had little influence on abundance of juvenile suckers and darters, but some minnow species and all sunfish species exhibited large increases in juvenile abundance during stable to low flow conditions. The largest increase in juvenile abundance occurred among species with prolonged breeding seasons: bluntnose minnow (Pimephales notatus) and striped shiner (Notropis chrysocephalus). Increased juvenile abundance during stable flow conditions resulted in increased species richness in small habitat patches and annual changes in species composition of the community. Models of fish assemblages in small streams need to incorporate ontogenetic changes in the role of stochastic environmental variables in regulating the population size of component species.

Experiments on Disturbance in Old‐Field Plant Communities: Impact on Species Richness and Abundance

Abstract: Changes in species richness and abundance following experimental disturbance were studied in a 7th—yr old field (the “older” field) dominated by Solidago canadensis, and 2nd—yr old field (the “younger” field) dominated by Ambrosia artemisiifolia The two fields were disturbed in late spring 1981 by clipping and removing aboveground plant biomass in experimental plots, which were compared with undisturbed control plots Treatments represented three intensities of disturbance (low, intermediate, and high), as defined by amount of biomass removed and extent of canopy disruption Different patterns of change in richness were observed in each field during the 1981 growing season In the older field the number of species decreased in control plots during the summer In disturbed plots, richness increased with intensity of disturbance, resulting in maximum richness at the highest disturbance intensity during mid— and late summer Several species increased significantly in cover and/or frequency in plots representing intermediate and high intensity of disturbance In the young field, species richness fluctuated in control plots, with peaks in early and late summer In disturbed plots, richness decreased with intensity of disturbance in early summer and increased in midsummer By late summer no difference in richness or species composition was detected between control and clipped plots These patterns of change in richness can be explained by the different effect of treatments on the vegetation structure and by the role of the dominant species in each field In the bi—layered older field, disturbances greatly disrupted the closed canopy of S canadensis, thus providing resource patches (ie, increased light, moisture) for suppressed and invading species In the younger field, the impact of disturbance was only detectable in early and midsummer, and changes in richness were mainly related to the seasonal cycle of the dominant annual A artemisiifolia Results from these experiments provide insights into the mechanisms of species coexistence under natural disturbance regimes comparable to our disturbance treatments They also indicate that the impact of disturbance on species richness depends largely on the nature of the dominants and rates of successional or seasonal change of the community

Diurnal Lepidoptera: sensitive indicators of cultivated and abandoned Grassland

Abstract: (1) In the subalpine region of Central Switzerland (Tavetsch Valley) studies were made of the day-active Lepidoptera faunas in different types of cultivated grassland, in various stages in the development of abandoned grassland and in woodlands (climax vegetation). (2) The results show a close correlation between bufferfly fauna and vegetation type concerning species composition and species richness of Lepidoptera. (3) Species richness of butterflies is highest in early abandoned stages and falls rapidly with the arrival of shrubs and trees. It is also high in traditionally lightly cultivated grassland (unfertilized mown and lightly grazed meadows), but it declines drastically with increasing intensity of cultivation. (4) In general, species richness of butterflies is closely correlated with species richness of vascular plants, but cultivation methods and the short time since abandonment (<5 years) of lightly cultivated grassland have strongly different influences on species richness of Lepidoptera and vascular plants. (5) The results are in contrast to former studies in Central Europe and parallel studies in England. (6) The natural primary habitats of butterflies living in the anthropogenetic types of vegetation investigated and the consequences for nature conservation are discussed.

Species richness in streams of different size from the same drainage basin

Abstract: The species richness of stream benthic invertebrates was studied along a longitudinal profile of the Salmon River, Idaho, during spring, summer, and autumn. Sampling was done using replicate rocks and the analytical approach of Stout and Vandermeer (1975) was used to calculate theoretical number of species present, relative immigration rate, and relative spatial heterogeneity. Species richness varied with stream size, being highest in midorder streams and lower in headwater and high order streams. This downstream shift in species richness conforms to the river continuum concept (Vannote et al. 1980). Possible cause is associated with varying temperature regimes in the different-sized streams as well as other factors. Species richness also varied with season depending on stream size. Low order streams were more individualistic, probably because of a greater influence of local (terrestrial) environmental conditions, but showed a higher richness in summer than in autumn. Larger streams were more similar and ...

Small-scale altitudinal variation in lowland wet tropical forest vegetation.

Abstract: (1) All trees and lianas (>10 cm dbh) on 12.4 ha of primary lowland wet tropical forest at La Selva, Costa Rica, were enumerated. (2) A total of 5530 live stems were encountered, representing 269 species. Palms comprised 25-5% of stems, lianas 2-4%, tree ferns 0-1% and true trees 72-0%. The most abundant species, Pentaclethra macroloba (Mimosaceae), accounted for 13.6% of stems. Species richness ranged from 79 to 107 species per ha. (3) Species composition varies continuously with altitude over a range of 39 m, as shown by a detrended correspondence analysis ordination of data from 0-04-ha subplots. (4) The pool of available species at any altitude is large, and floristic variation between sites at the same altitude is influenced by chance. (5) Seasonally-flooded sites are floristically distinct from sites on higher ground, and show great variation in species composition over short distances. (6) Microtopography and drainage features in a 1.8-ha swamp forest were mapped. There is a dramatic reduction of stem density and species richness with increasingly poor drainage. This lower number of species reflects the exclusion of species intolerant of waterlogged soils.

Morphology as a Predictor of Flower Choice by Bumble Bees

Abstract: This paper examines whether the use of 14 plant species as nectar sources by eight species of bumble bees relates systematically to differences in bee morphology. I predicted that a particular bee should have fed from a given plant species if the bee was physically more similar to the other bees visiting that plant species than to bees on any other species. Glossa (=tongue) length, body mass, and wing length all influence a bumble bee's foraging ability and its choice of flowers and were therefore included in the analysis. Morphological differences between bees were associated with use of different plant species; however, the role of bee morphology in flower choice was most evident when preferred plant species bloomed abundantly. The interaction between morphology and flower choice was also influenced by plant species richness, season, the plant species visited, and the species of bee; but was not affected by the time of day that the bee was foraging, overall bee density, or the bee's caste. Bee species with long glossae had access to nectar in a greater variety of flowers than those with short glossae, and they tended to feed from a larger number of plant species. Also, their use of a particular species was less predictable. Discrimination between bees using different plant species depended on joint consideration of several morphological characters: no character alone accurately separated the bees.

Local and Regional Richness of Cynipine Gall Wasps on California Oaks

Abstract: Regional herbivore richness is defined as the total number of herbivore species associated with a host plant in any part of its range. Local richness is the number of species associated with a host population or clump at a single site. These are roughly equivalent to @a and @c diversity. Understanding the mechanisms operating on local richness required a knowledge of the relationship between these two variables, and, specifically, an answer to the question of whether the same processed determine both regional and local richness. When local ecological interactions are weak and herbivore species are widespread, the correlation between richness at these two spatial scales should be strong. If local interactions are strong and herbivore species have restricted ranges due to habitat specialization, then the correlation should be weak. The relationship between local and regional richness was studied in California in the cynipid gall—forming wasps, which are highly specialized on the oak genus, Quercus. Regressions of presence—absence data suggested that geographic range and host taxonomic isolation explain the majority of regional richness variation in this group. Moreover, the very strong correlation between local and regional richness indicated that there is no upper limit to local richness independent of the regional pool. In terms of @a, @b, and @c diversity,@b (between—habitat) diversity does not increase with @b diversity. Instead, there is an unabated increase in @a diversity as @c diversity increases, suggesting that excess niche space is available on host oaks for additional cynipine species, and that limits to similarity of coexisting cynipines have not been reached. This indicates that sufficient information on the causes responsible for local herbivore richness cannot be gained by studying the local host population in isolation. The spatial dynamics of the system are such that measures of the regional pool from which the local assemblage is drawn must also be taken. Finally, cynipine habitat specialization and local interactions are not predictable from regional richness, but may influence local richness on certain oak species independently of regional richness.

Primate communities: their structure and role in tropical ecosystems

Abstract: The structure of primate communities living in a number of undisturbed areas is described and compared. Species richness is highest in tropical rain forests of Africa and South America, where up to 14 different species can share the same habitat. The number of sympatric primates in woodlands and savannas is always much lower. Some striking differences in community structure may be observed between communities living in apparently similar habitats. Three major factors may be held responsible for such discrepancies: history and paleoecology, present spatial heterogeneity of the vegetation, and competition with other taxonomic groups. The role of primates in the functioning of forest ecosystems is discussed. Though their trophic impact may be important, the role they play in seed dispersal appears to be more significant; they contribute greatly to homeostasis, as well as to regeneration, of the rain forests. A number of ecological traits are particularly developed among primates and may have contributed to the rapid evolutionary success of the order. Their predominantly vegetarian diet allows them to build up higher population densities than sympatric carnivorous mammals;their arborealism permits them to make use of all edible plant material available in a tridimensional environment; the opportunistic tendencies of some cebids, cercopithecids, and pongids enable them to take advantage of a variety of habitats and situations; and finally, an extended socialization period and a long life-span, allowing them to develop social traditions, give to many of them a further possibility to adapt quickly to novel situations.

Diurnal rhythm of Viburnum awabuki and Betula luminifera volatiles and electroantennogram response of Batocera horsfieldi

Abstract: SUMMARY (1) A common prediction based on ecological theory is that natural populations of insect predators will be more abundant and effective in diverse plant assemblages. Contrary to expectation, the abundance of the predaceous coccinellid beetle, Coleomegilla maculata (DeGeer), (Coleoptera: Coccinellidae) was higher on corn in monocultures than on corn in two different polycultures. In addition, predation rate by the beetle on egg masses of the European corn borer (Ostrinia nubilalis (Walker)) was higher in monocultures. (2) Important alternative resources for the beetle in these systems were aphids and pollen. Temporal dispersion of pollen and aphids was more even and species richness of the aphids was greater in the polyculture, while overall density of corn pollen and aphids was greater and their spatial distribution more even in the monoculture. (3) The higher density of evenly spaced food rewards in the corn monoculture had the greatest impact on bettle behaviour, resulting in decreased emigration and therefore greater abundance. (4) Plant diversification can have important effects on the density, species richness, and temporal and spatial dispersion of alternative resources of generalist predators. Depending on the particular effects and how a predator responds to them, the predator may be more or less abundant in the diverse system. If diversification results in a greater abundance of food resources, or a more even spatial dispersion of food, then predators can be made more abundant and effective in diversified agroecosystems.

Recolonization by ants of rehabilitated mineral sand mines on North Stradbroke Island, Queensland, with particular reference to seed removal

Abstract: The ant fauna of 12 sand-mined plots representing a range of rehabilitation ages and three undisturbed vegetation controls was surveyed during 1982. Physical and botanical parameters were also measured in each plot. Sixty-four ant species were collected from the 15 study plots, of which 44 had colonized one or more of the mined plots. Ant recolonization proceeded rapidly in plots up to 6 years old and may have been influenced by the passage of time, plant cover, density and diversity variables, the amount of litter and by the paucity of logs. In terms of ant species composition, the mined plots were most different from the undisturbed areas. The older plots exhibited a lower ant species richness and this is believed to have resulted from interspecific competition with the tramp ant, Pheidole megacephala. Ant succession proceeded in a slower fashion in the plots dominated by P megacephala. The influence of ants on seeds applied during broadcast seeding of rehabilitated areas was also investigated. Seed removal by ants was greatest for the arillate seeds of Acacia concurrens but moderate quantities of Allocasuarina spp., Eucalyptus spp. Xanthorrhoea sp. and Banksia spp. were taken also. Seed removal by ants was low in the areas which had recently had topsoil applied except where ants foraged from adjacent rehabilitation areas; here they exerted their influence up to 50 m across the fresh topsoil. Seed removal rates in topsoil adjacent to forest were low. Removal rates in a revegetated area 2.5 years old approached those in forest. This indicates that the previous ant-seed relationship had been partially restored by this time, although the relative contribution of seed harvesters and elaiosome collectors still needs to be assessed.

Immediate effects of Ore on ants in the semi‐arid mallee region of north‐western Victoria

Abstract: The immediate effects of a high intensity wildfire on the ant communities of a heath and a mallee site in semi-arid north-western Victoria are reported. Following fire the number of species trapped on the ground doubled (to ca. 80 each site), total ant abundance decreased by half (due to the demise of previously dominant species), surface activity of reproductive castes increased, and dramatic changes in species relative abundance (including shifts toward greater equitability) occurred. These changes are interpreted in terms of fire-induced simplification of the habitat and release from competition with dominant species. The results appear to illustrate the importance of interspecific competition in structuring foraging activity in mallee ant communities. Observations are also reported on seed-harvesting by ants, including changes in harvester ant abundance, germination from within-nest seed storage, and the first record of Heteroponera removing seeds.

Biological diversification and its causes

Abstract: Three major patterns of diversity are defined and a general hypothesis proposed to explain them. These patterns include (a) macroevolutionary diversity, encompassing temporal changes in species richness within and among clades, (b) global diversity, in which gradients of diversity among communities or biotas vary spatially and temporally, and (c) Phanerozoic diversity, which describes largescale temporal variation in species richness within the entire biosphere. Current explanatory hypotheses for these patterns are generally formulated for systems that are assumed to be in a state of ecological equilibrium, with speciation and extinction rates being diversity-dependent. This paper describes an alternative model of diversification in which speciation and extinction rates are independent of standing diversity. It is postulated that speciation rate is controlled primarily by large-scale changes in lithospheric (geomorphological) complexity. This hypothesis is a deductive consequence of biological data showing that allopatric speciation is the general mode of differentiation, and of geological data showing that tectonic changes within the lithosphere are responsible for the formation of geographic and ecological barriers. This hypothesis makes a number of predictions about patterns of endemism, historical biogeography, and spatial gradients of diversity, and data consistent with these predictions are presented. Other potential regulators of speciation rate (degree of morphogenetic variability within species, behavioral-ecological variability within species, intensity of sexual selection) are discussed and their potential roles in shaping diversity patterns are evaluated. Although they may occasionally be important for explaining some intracladal patterns of diversification, they are insufficient by themselves to account for spatial patterns or long-term changes of diversity within biotas. Extinction rate is postulated to be controlled primarily by spatial and temporal changes in environmental harshness, particularly as the latter is manifested by gradients of temperature and moisture. Considerable neontological and paleontological data suggest that change in harshness is a major factor shaping temporal and spatial patterns of diversity through its effects on extinction rate. Other causal mechanisms of extinction, particularly the tectonic elimination of habitats, may be of importance for specific groups of organisms (e.g., marine shelf communities following continent-continent collisions) at specific localities and times (e.g., near a volcanic eruption) but are not likely to play as important a role as does change in harshness. Together, the two main controls on speciation and extinction define a diversity-independent process of diversification. The biosphere can be viewed as an open thermodynamic system that can be expected to grow in complexity (including diversity) through time as a result of the inflow of matter and energy. This increase in complexity is constrained by external factors (physical changes in the biosphere or

Distribution and Medical Ecology of the Blow Flies (Diptera: Calliphoridae) of Peru

Abstract: The altitudinal distribution and medical ecology of 26 species of blow flies along an Andean transect in central Peru are given, based on ca. 25,000 flies collected in 1979, 1980, and 1981. Five species are reported for the first time from Peru: Hemilucilia hermanlenti Mello, Phaenicia eximia (Wiedemann), Phaenicia ochricornis (Wiedemann), Phaenicia sericata (Meigen), and Sarconesia versicolor Bigot. In the wet season, when flies are most abundant, and on the eastern slope of the Andes, species richness was greatest at 1,800 m at eusynanthropic and hemisynanthropic sites, and at 200 m at asynanthropic sites. Although the western slope had fewer species, richness was maximum near the same altitude. In general, species diversity was greater near human habitats than in the wild. Ten species showed an upward shift of 300 to 600 m in their range in the wet season, with few species invading another biotic zone. The synanthropic indices of 13 species at 200, 1,000, 2,500, and 4,000 m in wet and dry seasons are given. Three of five species showed increased synanthropy with elevation and two of eight species increased synanthropy in the dry season. The bait preferences of 20 species, the propensity of 14 species to enter homes, and the diurnal activity curves of 9 species are presented. Based on this study, the medically most important blow flies in Peru are Cochliomyia macellaria (F.), P. eximia, Phaenicia ibis (Shannon), Sarconesia magellanica (LeGuillou), Sarconesia chlorogaster (Wiedemann), and Compsomyiops spp., with a combined range from tropic to alpine zones. The ecological niches of 26 species are defined according to altitude, synanthropy, food preferences, endophily/exophily, and diurnal flight patterns.

Past rates of change, species richness, and a model of vegetational inertia in the grand canyon, arizona

Abstract: Two measures of vegetational change in the Grand Canyon illustrate that the greatest changes of the last 20,000 yr occurred between 14,000 and 6000 yr B.P. with peak values between 12,000 and 8000 yr B.P. for species flux, and peak values between 10,000 and 6000 B.P. for change relative to the modern communities. Changes in dominant species show that Wisconsin species departed from some elevational zones before the arrival of Holocene species, suggesting lowered species richness in the interim. This inference was supported by low species numbers recorded in packrat middens between 12,000 and 9000 yr B.P. In addition, Holocene species invaded within their modern elevational limits, suggesting that the controlling climatic changes had already occurred well before the invasion. These observations may explain the discrepancies between southwestern paleovegetation records and estimates of the timing of global changes in paleotemperatures. The observed patterns are incorporated into a model of "vegetational ine...

Do predaceous stoneflies and siltation affect the structure of stream insect communities colonizing enclosures

Abstract: Experiments in Colorado and New York streams assessed the effects of predaceous stoneflies on benthic invertebrate community establishment in enclosures providing uncolonized habitat. Aspects of prey community structure measured were density, species richness, relative species abundance, and body size. Unexpected inorganic sediment deposition allowed evaluation of direct effects on Colorado stream benthos and indirect effects on predation. Predaceous perlids and perlodids consistently reduced the density and, therefore, rate of prey community establishment in enclosures. Although New York perlids disproportionately reduced densities of some prey species, Colorado stoneflies caused nonsignificant declines in individual prey species densities, the composite effect of which was a significant whole-community response. Predators did not affect prey species richness nor change the taxonomic composition (species additions or deletions) of communities colonizing enclosures. However, the relative abundance of prey...

Elevational correlates of speciation and intraspecific geographic variation in plumage in Andean forest birds

Abstract: -Intraspecific variation in plumage was used to test the null hypotheses that geographic variation in 280 species of elevationally restricted Andean forest birds is independent of elevation and is not a function of patchy geographic distribution. Both null hypotheses were rejected. At most taxonomic levels, geographic variation in plumage was correlated positively with both the mean of its elevational distribution and the size of its geographic range. Vertical amplitude of elevational distribution was not a significant predictor of geographic variation in plumage in most taxa. Independent of these elevational correlates, patchily distributed species showed significantly more geographic variation than continuously distributed species. These results show that geographic variation and presumably ongoing speciation phenomena are greater at higher elevations. The decreased species richness at high elevations may be attributable to a higher rate of extinction from catastrophic disturbance as well as to ecological factors that limit sympatry in newly formed species. Received 6 August 1984, accepted 26 December 1984. IN this paper I examine the relationship between elevational distribution and possible speciation phenomena in Andean forest birds. Two initial observations are pertinent. First, on an elevational gradient in Peru, Terborgh (1977) found a negative correlation between elevation and bird species richness, canopy structure, and number of plant strata. Second, geographic barriers to dispersal and gene flow increase with elevation. Catastrophic vicariant events (e.g. glaciation, landslides, vulcanism, forest fragmentation by climatic events) are more prevalent in the physiographically complex Andean highlands than in the adjacent foothills and

Biogeographic patterns and Plio-Pleistocene extinction of Bivalvia in the Mediterranean and southern North Sea

Abstract: An evaluation of the history of polysyringian species (filibranchs and eulamellibranchs) reveals that the huge early Pliocene bivalve fauna of the Mediterranean Basin (MB) and North Sea Basin (NSB) suffered heavy extinction during late Pliocene and early Pleistocene time. This is evidenced by low survivorship of early Pliocene species in the Recent and by a decline in species richness of the two basins from 323 known early Pliocene species to 198 living species. Several kinds of evidence indicate that cooling rather than the areal effect of eustatic sea-level lowering was the primary cause of the excessive extinction: (1) heavy Plio-Pleistocene extinction of mollusks was not global but concentrated around the margins of the northern Atlantic—an ocean fringed by polar ice caps; (2) taxa of tropical affinities were most severely affected; (3) heavy extinction occurred in the MB in areas not marked by facies change; (4) in the MB the onset of extinctions coincided with the onset elsewhere, but because of tectonic activity, water depths in the MB were not under tight eustatic control; (5) 14 species present in both the MB and NSB during early Pliocene time are now restricted to waters south of the NSB; and (6) the majority of species common to the two basins during the early Pliocene (eurythermal species) have survived to the present. Molluscan data support palynological evidence that the climate in the MB was warmer and less seasonal in early Pliocene time than today, when latitudinal temperature gradients are steeper. Molluscan evidence indicates that the North Sea is exceptional in being less seasonal (though cooler) today than in early Pliocene time, and we attribute this anomaly to the local effects of the Gulf Stream, which was strengthened in mid-Pliocene time by the uplift of the Isthmus of Panama. The heavy extinction in the MB and NSB about 3.2–3.0 ma ago approximately coincided with the earliest deposition of glacial tills in Iceland and with isotopic shifts in the tests of planktonic foraminifers preserved in deep-sea cores. Additional heavy extinction probably coincided with a pulse of severe cooling in late Pliocene time, 2.5–2.4 ma ago. Heavy extinction of mollusks in the MB and NSB continued into the early Pleistocene but not into the middle and late Pleistocene, apparently because by this time it was primarily only eurythermal species that survived. Today the molluscan faunas of the MB and NSB are unusually eurythermal; few species are restricted to a single biogeographic province.

Two-year study of male orchid bee (hymenoptera: Apidae: Euglossini) attraction to chemical baits in lowland south-eastern Perú

Abstract: Chemical baits corresponding to natural orchid fragrance chemicals were used to attract and sample male orchid bees in terra firme and flood plain forest sites on the Tambo-pata Reserve in south-eastern Peru. The study was conducted monthly for two years. A total of 38 species of bees was collected at these chemical baits, and although most species were collected from both habitats, 11 species were significantly more common in one habitat than the other. There was considerable variation in the number and types of chemicals to which each of the orchid bee species was attracted.Two cycles of seasonal abundance occurred annually in the number of orchid bee individuals and species collected at the chemical baits. A major peak occurred a month following onset of the wet season, and a minor peak occurred during the dry season. Species body size was related to seasonal activity, but additional factors such as flowering phenology and nest parasites were also probably involved.The number of orchid bee species found on the Tambopata Reserve was similar to the number found in forest sites of eastern and central Brazil, Costa Rica, and Panama. This homogeneity in species richness is in marked contrast to other insect groups such as Odonata, Lepi-doptera, Asilidae (Diptera), Tabanidae (Diptera), and Cicindelidae (Coleoptera), for which the species numbers recorded on the Tambopata Reserve are the highest for any similar sized area in the world.

Leaf-Cutting Ant Herbivory in Successional and Agricultural Tropical Ecosystems

Abstract: Herbivory by Atta cephalotes was measured in four plant communities of different complexity in Costa Rica. The four communities were a monoculture of cassava {Manihot esculenta) and three diverse assemblages, each 1.5 yr old: (1) successional vegetation, unmodified by the in- vestigators; (2) imitation of succession, a community of investigator-introduced species designed to mimic the unmodified succession; and (3) enriched succession, a successional vegetation that the investigators had augmented by propagule inputs. Each ant colony had access to all four community types simultaneously. The average herbivory rate (daily cutting of leaf per square metre of ground, all treatments combined) was ~ 150 mg (or 38 cm2). In communities with greater leaf area index, structural complexity, and species richness, A. ceph? alotes cut lower portions of total leaf area. Before harvest of the cassava monoculture, the herbivory rate of A. cephalotes was 87.9 cm2m~2d_1 in the monoculture, 21.4 in the imitation, 14.7 in the succession, and 6.8 in the enriched succession community. These amounts represented 0.3% of total leaf area in the monoculture and a mean of 0.03% of total leaf area in the three complex ecosystems. Cassava, which occurred in three of the four communities, was attacked most heavily (per unit leaf area) in the imitation successional community, least heavily in the enriched succession, and at inter- mediate intensity in the monoculture. In response to loss of their preferred forage (cassava) through harvesting by humans, the ants cut more leaf tissue in the three species-rich communities, especially the imitation. As cassava resprouted in the monoculture, A. cephalotes' rate of attack on the three diverse treatments reurned to preharvest levels. Atta cephalotes cut only 17 of 332 available plant species. They cut proportionally more woody than herbaceous species, more introduced species than natural colonizers, and species with below- average water contents. Plant relative abundance alone did not determine host plant selection, but most of the attacked species were cut in proportion to their total leaf area.

The predatory Chironomidae of an iron-rich stream: feeding ecology and food web structure

Abstract: . 1. Three species of Tanypodinae (Chironomidae) were found in an acid and iron-rich stream in southern England. Maximum abundance was achieved in summer and they were sparse at other times. Individuals were aggregated on the stream bed and were overrepresented in accumulations of leaf litter. 2. The diets of all three species consisted of a mixture of prey (prominently detritivorous chironomid larvae) and detritus. More detritus and fewer prey were taken in winter than in summer. 3. When comparing large tanypod species with small and, intraspecifically, late instars with early, the proportion of guts containing prey increased with increasing body size. 4. Stonefly larvae were more prominent in the diet of Zavrelimyia barbatipes (Kieffer) in summer than in winter but for the other two species the reverse was true. A bigger proportion of Trissopelopia longimana (Staeger) guts contained prey in early summer than in August whereas more Macropelopia goetghebueri (Kieffer) guts contained prey in August. This was apparently a consequence of seasonal differences in the distribution of body size among the populations of these two species. 5. The stream contains two further common predators, Plectrocnemia conspersa (Curtis) and Sialis fuliginosa Pict. These are important predators of tanypod larvae but might also compete with them since they severely deplete populations of prey taken in common. 6. Analysis of the food-web in Broadstone Stream reveals remarkably high values of connectance (C and Cmax) and of species richness times connectance (SCmax). Such characteristics are theoretically associated with fragile and dynamically unstable food webs, and may be found in ‘constant’ environments. There is also an apparently unusual prevalence of omnivory in the community.

Catastrophe, Extinction, and Species Diversity: A Rocky Intertidal Example

Abstract: Geographically widespread episodes of catastrophic mortality affect local species diversity. Sea ice has been a frequent catastrophic mortality agent on rocky shores in New England during the historical past. Empirical demographic data and the historical record of winters with sea ice were used in a population projection model of intertidal barnacles. Projections indicate that animals that live exclusively in the zone affected by ice would have become extinct under the conditions of sea ice disturbance that have existed in New England during the past 300 yr. This may explain the absence from New England of abundant, large, long—lived species with delayed reproduction that are restricted to the mid to low intertidal zone. Such species are common elsewhere in the world on shores unaffected by ice. Given the cyclic nature of the postglacial climate, global patterns of species richness may be influenced by climatically induced extinction pressures of this kind. See full-text article at JSTOR

Growth Rates and Population Structure of Moraceae Trees in Sarawak, East Malaysia

Abstract: To understand the relationship between the dynamics of tropical rain forests and the population processes of individual species, data are needed on the rates at which trees grow, die, and establish. Data on the family Moraceae have been extracted from long-term forestry studies in Sarawak, on the northwest coast of Borneo, an area at the center of species richness of Old World tropical forests. These data can also be combined with forest maps and logging studies to investigate the importance of competition and disturbance in controlling tree growth. Tree populations of Moraceae species had mean annual diameter increments of between 0.4 and 3 mm/yr. Growth rates increased two to six times in the 1 st and 2nd yr following (selective) logging, but began to decline somewhat in the 3 rd and 4th yr. Growth rate variation among trees in a population was considerable, with most trees showing little or no growth, and a few, high growth rates. Saplings of Artocarpus species increased in diameter at the same mean rate as adult trees. Annual mortality rates were low in primary forest, typically <3%, and indicated stable populations. In logged forest, annual mortality of Artocarpus species was considerably higher, between 5 and 8% for trees and still higher for saplings. Adults and saplings ofFicus, a pioneer species, had much higher annual mortality rates than individuals of Artocarpus. Growth rates of Moraceae trees in primary forest were positively correlated with the growth of the nearest conspecific trees, the mean growth rates of the three nearest neighbors of any species, and the mean distance to the nearest neighbors, but were not correlated with the diameter ofthe tree itself and the mean diameter ofthe three nearest neighbors. Analysis of patches of three trees of any species in primary forest revealed that there were no detectable differences among patches in either tree size or growth rate. Tree growth rates of small patches in logged forest were negatively correlated with distance to the nearest forest opening. Even the significant relationships between tree growth rate and immediate neighborhood explained only a relatively small portion of the total variation in growth rate. The remaining variation may be due to variation in plant genotype and local environment.

Total species count in a Costa Rican tropical rain forest

Abstract: There are several studies which support the contention that some tropical rain forests (trf) have more plant species on small areas of up to a few hectares than any other kind of vegetation on earth (Parsons & Cameron 1974, Whitmore 1984a). Next richest, but far poorer, are Mediterranean heaths in South Africa (fynbos) and Australia (Figure 1) which have about the same total number of species as there are tree species >10 cm diameter at breast height (dbh) in trf. In fact, statements about species richness in trf are based almost entirely on counts of tree species over a given minimum dbh, usually 10 cm. The range per hectare is from about 20 to a maximum count of 223 at Mulu, Sarawak (Proctor et al. 1983, Whitmore 1984b). Here we report a count of 233 vascular plant species on just 100 m2 of a lowland trf in Costa Rica. This is equivalent to about one-sixth of the total flora of the British Isles on half the area of a singles tennis court (97.8 m2). There were also 32 bryophytes, all epiphytic; non-vascular plant species have not been included in previous counts in trf. The count was made by destructive sampling of a 10 X 10 m plot in lowland trf on a broad ridge-top 2 km west of the Rio Puerto Viejo near Horquetas (840 05' W, 100 22' N), about 6 km SSE of Finca La Selva, in the Atlantic lowlands of Costa Rica, at an elevation of about 100 m. The forest reaches 50 m tall. Pentaclethra macroloba (Willd.) Kuntze is the commonest big tree (as in the well-known La Selva forests) but it is not the tallest. Mean annual rainfall at La Selva is about 4000 mm with a relatively dry season January to April (Frankie et al. 1974 give fuller details). The total numbers of species and individuals in different synusiae (life form classes) are shown in Table 1 (voucher specimens are held at Oxford). Most remarkable is the very large number of species, 132 or 57% of all vascular

Birds of restocked conifer plantations in wales

Abstract: (1) Five minute counts at 326 points in sixty-two conifer plots, restocked 2-11 years previously, contained 3258 records of thirty-one species of songbird in the breeding season. Density and species richness greatly exceeded previous findings on newly afforested ground. (2) Significant associations between the occurrences of individual bird species and habitat factors were shown. (3) The habitat was simplified to two principal component axes, which were attributed to succession of the conifer habitat and a conifer-broadleaf gradient. (4) The mean position of each species on the two axes was as expected. Outliers were species of open ground or those more often found in broadleaf woodland. (5) Overall bird densities increased with succession and declined along the gradient from pure conifer to much broadleaf admixed with the crop. Species richness did not vary significantly along these axes. (6) A relationship between species richness and plot area was due to larger plots holding greater numbers of birds. Only one species occurred disproportionately infrequently on smaller plots. (7) Areas adjoining thicket-stage conifer crops older than those studied held lower bird densities than centres of the plots.