Showing papers on "Species richness published in 1992"

Factors influencing levels of genetic diversity in woody plant species

Abstract: The plant allozyme literature was reviewed to: (1) compare genetic diversity in long-lived woody species with species representing other life forms, and (2) to investigate whether the levels and distribution of genetic diversity in woody species are related to life history and ecological characteristics. Data from 322 woody taxa were used to measure genetic diversity within species, and within and among populations of species. Woody species maintain more variation within species and within populations than species with other life forms but have less variation among populations. Woody species with large geographic ranges, outcrossing breeding systems, and wind or animal-ingested seed dispersal have more genetic diversity within species and populations but less variation among populations than woody species with other combinations of traits. Although life history and ecological traits explain a significant proportion (34%) of the variation among species for the genetic parameters measured, a large proportion of the interspecific variation is unexplained. The specific evolutionary history of each species must play an important role in determining the level and distribution of genetic diversity.

Species interactions, local and regional processes, and limits to the richness of ecological communities : a theoretical perspective

Abstract: 1. Are local ecological communities ever saturated with species? That is, do they ever reach a point where species from the regional pool are unable to invade the local habitat because of exclusion by resident species? 2. We review the theoretical evidence for saturation in various community models and find that non-interactive models predict the absence of saturation as expected, but that interactive models do not uniformly predict saturation. 3. Instead, models where coexistence is based on niche space heterogeneity predict saturation, whereas those where coexistence is based upon spatial heterogeneity yield mixed predictions. 4. Thus, theory says that species interactions are a necessary but not sufficient condition for local saturation in ecological time. 5. We then argue that unsaturated (Type I) assemblages are likely to be ubiquitous in nature and that even saturated (Type II) assemblages may not show hard limits to richness over evolutionary time-scales. 6. If local richness is not often saturated, then regional richness is freed from local constraint, and other limits on regional richness (which, in turn, limit local richness) become important, including phylogenetic diversification over evolutionary time-scales. 7. Our speculations inevitably suggest that the principal direction of control for species richness is from regional to local. If correct, then the key to community structure may lie in extrinsic biogeography rather than in intrinsic local processes, making community ecology a more historical science.

The elevational gradient in altitudinal range: an extension of Rapoport's latitudinal rule to altitude.

Abstract: For trees, mammals, birds, reptiles, insects, and amphibians, the species richness on mountaintops is generally less than that of lowland areas. Coincident with this decline in species richness with increasing elevation is an increase in the altitudinal range of species. This pattern is analogous to the relationship between the latitudinal range of species and latitude (Rapoport's latitudinal rule). Both of these Rapoport phenomena, the latitudinal and the new elevational rule discussed here, can be explained as being results of differences in the breadth of climatic conditions organisms experience along the geographical gradients. The influence of latitudinal or altitudinal range size on local species richness is poorly understood, but the tendency for range margins to fall in species-rich, rather than species-poor, areas may mean that species-rich communities contain many species that are maintained only through immigration. The presence of these persistent but locally non-self-maintaining populations may explain the increased number of species found in rich communities as compared to species-poor communities without the need to invoke other differences in local species interactions.

Deep-Sea Species Richness: Regional and Local Diversity Estimates from Quantitative Bottom Samples

Abstract: The deep-sea communities of the continental slope and rise off the eastern coast of the United States have a remarkably high diversity-measured regionally or locally either as species richness or as the evenness of relative abundance among species. In a 1,500-2,500-m depth range off New Jersey and Delaware, 233 30 x 30-cm samples contained 798 species in 171 families and 14 phyla. Addition of stations from sites to the north and south approximately doubled the number of samples and doubled the number of species to 1,597. Species-area curves do not level off within stations or when stations are added together. Moreover, the proportion of species represented by single individuals is high at all scales of sampling, which indicates that much more sampling is needed to adequately represent the species richness either locally or regionally. Diversity changes very little through time at a single site or with distance along a 180-km transect at a depth of 2,100 m. Diversity is maintained by a combination of bioge...

The use of Rarefaction Analysis for Estimating Palynological Richness from Quaternary Pollen-Analytical Data

Abstract: Reconstructing temporal changes in diversity from pollen assemblages is potentially important both palaeoecologically and ecologically because community diversity may, in part, result from historical processes. The use of diversity indices such as Shannon's information index or Simpson's index is not appropriate with pollen percentage data because such indices consider both the numbers of different taxa and their relative frequencies or representation. The latter aspect in pollen data is inevitably influenced by inherent differences in pollen production and dispersal. The total number of taxa present in a sample is a robust and useful measure of palynological richness if, and only if, all the pollen counts are standardized to a fixed number of grains. Rarefaction analysis implements such a standardization and provides minimum variance unbiased estimates of the expected number of taxa (t) in a random sample of n individuals taken from a larger collection of N individuals containing T taxa. The underlying m...

Beta diversity on geographic gradients in Britain

Abstract: 1. We measured beta diversity, or turnover in species composition, in each of 15 taxa (including plants, vertebrates and invertebrates), along two common transects: N-S and W-E arrays of 50 x 50km squares across Britain. Comparing taxa, we asked whether high beta diversity is associated with poor powers of dispersal. Within taxa, we asked whether turnover increases consistently with geographic distance. 2. Beta diversity on this scale was found to be low in all groups. Total (transect) species richness increased by only 3-13% per 50 x 50km square, relative to the average value of local (within-square) richness; or by 0-6-6% per square, relative to the maximum value of local richness. Among taxa, beta diversity showed no tendency to be higher in poorer dispersers. 3. In nearly all taxa, beta diversity as defined by Whittaker (1960) increased linearly with distance on the N-S transect. However, this was shown to be largely the effect of gradients in alpha (local, within-square) diversity. Moreover, distance is highly correlated with environmental (climatic) dissimilarity, providing an alternative explanation for distance effects. 4. We conclude that in the British biota, turnover at this scale is more the product of range and habitat restriction than of dispersal limitation; and that turnover is a relatively minor component of regional diversity, because of the predominance of strong gradients in alpha diversity.

Tropical forest biodiversity: distributional patterns and their conservational significance

Abstract: Phytogeographical knowledge of two major patterns important to conservational planning―the distribution of diversity and endemism in tropical forests―are summarized. High diversity forests occur on all three continents and are concentrated in lowland areas with high and evenly distributed rainfall, but with greatest diversity usually occurring in northwest South America forests. Tree and liana species richnessis greatest in upper Amazone and non-tree species richness greatest in the northern andean foothills and southern Central America, suggesting conservational priority for these areas. Endemism is only partly correlated with diversity and is concentrated in isolated patches of unusual habitat, in cloud forsts, in topographically dissected montane areas, and on continental fragment islands, areas which also deserve conservational priority (...)

Species Diversity Gradients: We Know More and Less Than We Thought

Abstract: Patterns in the diversity of species begin to make sense when we reduce them to well-known biological processes and take care to specify the scale of the pattern. Doing this explains why diversity declines away from the tropics (the latitudinal diversity gradient). The extensive tropical regions supply more opportunities for large geographical ranges than any other biome. Allopatric speciation feeds on such large ranges. The large regions of the tropics also probably inhibit extinction. It is a mistake to explain the richness of the tropics by noting that there are more habitats in the tropics. The global scale develops in evolutionary time. On that scale, fine habitat subdivision is a coevolved property of the species in a biome. The more species, the finer they subdivide habitats. So, it is also wrong to imagine that the tropical gradient is nothing more than a species-area curve. The species-area curve is a pattern that exists on a more local scale than the latitudinal gradient, and depends on habitat variability growing as larger areas get included in a sample. We all think that decades ago we should have understood the pattern of diversity and productivity. But the literature isn't even sure what the pattern is. Until recently, theory maintained that higher productivity should sustain more species. Evidence from poorer environments supports that theory. But most empirical evidence, including most experiments, show that diversity declines as productivity rises. Two errors confused us. First, we ecologists always assumed that the theory could not be wrong, so we refused to admit the facts, no matter how often we observed them. Second, we mixed our facts into a wild stew of scales and biomes. Diversity experiments, performed by increasing productivity on a local scale of time and space, tell us nothing about the productivity pattern at large scales. The regional pattern is unimodal. As productivity rises within a region, first diversity rises and then it falls. This pattern exists in mammals, birds, marine vertebrates and invertebrates, and some flora. We do not understand it.

On the meaning and measurement of nestedness of species assemblages.

Abstract: Nestedness of species assemblages occurs when thebiotas of sites with lower numbers of species tend to be subsets of the biotas at richer sites. We develop new quantitative and statistical techniques for measuring, testing, and comparing nestedness, and apply these methods to data from the literature. Significantly nonrandom nestedness was present in all 27 assemblages examined, and tended to be stronger in systems dominated by extinction, such as landbridge islands. Sets of assemblages that were very strongly nested were more likely to have greater species richness on one or a few large sites than on several smaller sites of equivalent total area — that is, to fall toward the “single large” side of the “Single Large Or Several Small” (SLOSS) continuum. Our analysis indicates that nestedness, when quantified as a single number for a presence-absence matrix, measures community-wide differences in incidence (the frequency of occurrence or “distribution” of species). Factors that lead to consistent differences among species in immigration or extinction rates cause strong patterns of nestedness of species assemblages. Nestedness is negatively related to beta diversity: nestedness is low when beta diversity is high, and vice versa. Conservation managers will thus seek to minimize nestedness and the development of nested structure in systems of nature reserves.

Comparison of Tropical Tree Plantations with Secondary Forests of Similar Age

Abstract: The structure and dynamics of small plantations of pine (Pinus caribaea; 4 and 18.5 yr old in 1980) and mahogany (Swietenia macrophylla; 17 and 49 yr old in 1980) were compared with those of paired secondary forest stands of similar age and growing adjacent to each other under similar edaphic and climatic conditions. The study was conducted in the Luquillo Experimental Forest between 1980 and 1984. Comparisons included a variety of demographic, production, and nutrient cycling characteristics of stands. Although the small unmanaged plantations had a lower number of species in understory than paired secondary forests, the understory of the older plantations developed high species richness, including many of native tree species. After 17 yr, native tree species invaded the overstory of plantations. After 50 years the species richness in the understory of a mahogany plantation approached that of its paired secondary forest. Plantation un- derstories had important ecological roles, including high nutrient accumulation. Understory plant tissue, particularly leaf litter, had higher nutrient concentration in pine plantations than in paired secondary forests. Understory biomass in plantations accumulated a higher proportion of the total nutrient inventory in the stand than did the understory in paired secondary forests. Plantations had higher aboveground biomass and net aboveground bio- mass production than paired secondary forests. Higher root densities and biomass were found in secondary forests as were greater depth of root penetration, higher nutrient con- centration in roots, and more microsites where roots grow, than paired plantations. These characteristics may improve the capacity of secondary forests relative to that of paired plantations to rapidly recapture nutrients that become available by mineralization and that could otherwise be lost through hydrological or gaseous pathways. Both forest types accumulated nutrients and mass, but secondary forests recirculated nutrients much faster than the plantations, which tended to store the nutrients. Plantations had higher leaf fall and total litterfall, had litterfall with lower nutrient concentrations, accumulated more nutrients in litter, decomposed more litter on an annual basis, exhibited more variation in the spatial distribution of litter mass, and had more month-to-month variation in litter storage than paired secondary forests. Litter of the secondary forests, on the other hand, had a faster nutrient turnover than plantation litter, though plantations retranslocated more nutrients before leaf fall than did secondary forests. Nutrient retranslocation increased with plantation age. Plantations, particularly pine plantations, produced more litter mass per unit nutrient return than did paired secondary forests. Total nutrient storage in soil gave the best correlation with nutrient use efficiency estimated as element: mass ratios in various compartments. Nutrient use efficiency ranked differently among forest pairs, depending upon which nutrient and ecosystem parameters were being compared. Because of high retranslocation of nutrients, and in spite of greater nutrient "need" to produce higher biomass, plantations had nutrient demands on soil similar to paired secondary forests. Among the ecosystem parameters measured, nutrients in leaf fall correlated best with differences in soil nutrients across stands. Nutrient concentrations in understory species appeared to be a sensitive indicator of whole-stand nutrient use efficiency. Some of the observations of the study could be attributed to intrinsic differences between small un- managed plantations and secondary forests, but many could be explained by species dif- ferences (i.e., timing of leaf fall), age of plantation (i.e., accumulation of biomass or species), or the relative importance of angiosperms and gymnosperms (i.e., nutritional quality of litter). The study challenges the conventional dogma with respect to differences between plantations and native successional ecosystems and underscores the dangers of generalizing about all tropical tree plantations or all natural tropical forests, or even extrapolating from one sector of the ecosystem to another.

Diverse and contrasting effects of habitat fragmentation.

Abstract: Different components of an ecosystem can respond in very different ways to habitat fragmentation. An archipelago of patches, representing different levels of fragmentation, was arrayed within a successional field and studied over a period of 6 years. Ecosystem processes (soil mineralization and plant succession) did not vary with the degree of subdivision, nor did most measures of plant and animal community diversity. However, fragmentation affected vertebrate population dynamics and distributional patterns as well as the population persistence of clonal plant species. The results highlight the dangers of relying on broad community measures in lieu of detailed population analyses in studies of fragmented habitats.

Influence of Selective Logging on Bird Species Diversity in a Guianan Rain Forest

Abstract: The composition and structure of the bird com- munity were investigated in French Guiana (northeastern Amazonia) I year and 10 years after selective logging and compared with bird community composition and structure in undisturbed primary forest A point-count method was used in which 937 0.25-ha sample quadrats were censused for 20 minutes each. Whereas logging removed little more than 3 trees/ha, 38% of the forest undergrowth was destroyed and a higher proportion of the canopy was opened or dam- aged. An overall 27-33% decrease of species richness, fre- quency, and abundance occurred after logging with a less marked decline of diversity and evenness indices, a substan- tial increase in the proportion of dominant species, and a 45% difference in species composition, weighed by fre- quency, between logged and undisturbed forest communi- ties. Forty-two percent of the species from the primary forest decreased sharply or disappeared after logging and only 34% increased or remained unchanged. Microhabitat selection was the main correlate of sensitivity to disturbance. Most affected by logging were species associated with the under- story of tall mature stands especially terrestrial species, members of mixed flocks, and solitary sallying insectivores, all of which decreased by 70% to over 90%. Most birds as- sociated with canopy, small gaps, and vine tangles declined by only 10-30%. Small frugivores and species associated with clearings or edges increased. Among other factors, phys-

Influence of Tributary Spatial Position on the Structure of Warmwater Fish Communities

Abstract: We found a significant and positive relationship between fish species richness and four measures of stream size (drainage area, stream order, link magnitude, and downstream link) in three Illinois ...

Plant and Soil Controls on Mycorrhizal Fungal Communities

Abstract: A field experiment was conducted to examine the relative importance of soil factors and plant species on communities of vesicular-arbuscular mycorrhizal (VAM) fungi. Populations of VAM fungal spores were studies in 4-yr-old monocultures of five successional grass species grown in gradient of soil mixtures ranging from pure subsurface sand to pure sandy loam topsoil. A total of 19 species of VAM fungi were found across all treatments. Of the 12 most abundant VAM fungal species, 6 species had a significant dependence on both soil mixture and host species, while 2 were dependent only on soil and 2 only on host. To our knowledge, these are the first results indicating that even closely related hosts (five grasses) may cause divergence in VAM fungal communities on initially identical soils. Cluster analysis of the similarity of fungal communities by host plant species showed that fungal communities in the two late successional grasses to be most similar to one another and least similar to the fungal communities in the early successional grass species. Cluster analysis of the similarity of fungal communities by soil mixture showed the fungal communities in the sandy end of the soil gradient diverged predictably from the fungal communities in the black soil end of the gradient. These results support the hypothesis that soil factors and plant species may be of equal importance in regulating the species composition of VAM fungal communities.

Plant species coexistence - the role of historical, evolutionary and ecological factors

Abstract: None of seven existing theories seeking to explain the coexistence of plant species, could singly explain the pattern of species richness found e.g. in calcicolous grasslands. A more general explanation of species coexistence utilizes an idealized concept, the null community, defined as an undisturbed community within stable zonal vegetation including the whole pool of potential species. The number of potential species will then be dependent mainly on evolutionary factors (speciation, species traits). The majority of «real» communities have a smaller species pool for historical reasons―migration has not taken place (...)

Predicting crustacean zooplankton species richness

Abstract: Data from 66 North American lakes were collected to construct a model for predicting the number of crustacean zooplankton species expected in a lake. The chosen lakes have a range from 4 m* to 80 x lo9 m2 surface area, range from ultra-oligotrophic to hypereutrophic, and have zooplankton species lists based on several years of observation. The number of crustacean zooplankton species in a lake is significantly correlated with lake size, average rate of photosynthesis (parabolic function), and the number of lakes within 20 km. A multiple linear regression model, using these three independent variables, explains -75% of the variation in log species richness. Prediction of species richness was not enhanced by knowledge of lake depth, salinity, elevation, latitude, longitude, or distance to the nearest lake. The North American species-area curve is statistically different from and steeper than the corresponding European curve.

Invertebrates as determinants and indicators of soil quality

Abstract: Invertebrates are an integral part of soils and are important in determining the suitability of soils for the sustainable production of healthy crops or trees. We discuss the importance of the soil invertebrate fauna in relation to terrestrial habitats and global biodiversity as we understand it. We describe the role of the main invertebrate groups in soils, including earthworms, termites, springtails, and nematodes, and how they determine soil quality. Practical problems in dealing with the invertebrate fauna include sampling, taxonomy and availability of biological information on species. Various measures are available that use invertebrates to assess soil quality, each with its advantages and disadvantages. They include abundance, biomass, density, species richness, trophic/guild structure, food web structure, keystone species and ecosystem engineers. We propose the three most useful and practical of these as suitable to be combined with other biological (microbial) and non-biological (hydrological, physical, chemical) criteria into a single index of soil quality that might be used on a regional, if not international basis.

Drought and biodiversity in grasslands

Abstract: The local species richness of four different grassland fields fell an average of 37% during a 1988 drought that decreased above-ground living plant mass by an average of 47% Despite the return to more normal plant mass and precipitation during the next two years, there was no significant recovery in species richness in the 46 permanent plots, suggesting that local species richness became recruitment limited The drought led to the loss of annual species independent of their abundance For perennial grasses, perennial forbs, legumes and woody species, the probability of a species being lost from a plot was significantly negatively correlated with its predrought abundance These results demonstrate that environmentally extreme conditions can limit species richness by causing the local extinction of rare species Because droughts of this intensity occur about every 50 years in the prairie, periodic drought may have limited prairie diversity Moreover, if the accumulation of greenhouse gases leads to a more variable or extreme climate, it could cause increased rates of species extinctions

Quantification of Loss and Change in Floridian Reef Coral Populations

Abstract: Six coral reef locations between Miami and Key West were marked with stainless steel stakes and rephotographed periodically between 1984 and 1991. The monitored areas included two photostations in the Looe Key National Marine Sanctuary, two photostations in the Key Largo National Marine Sanctuary, and two photostations in the Biscayne National Park. Stations were monitored for species number, percent cover, and species diversity of the scleractinian and hydrozoan stony corals. Monitoring began in 1984 for photostations in the National Marine Sanctuaries and in 1989 for stations in the National Park. All six areas lost coral species between the initial survey year and 1991. Survey areas lost between one and four species; these losses constituted between 13% and 29% of their species richness. Five of the six areas lost live coral cover. Based upon photographs taken repeatedly at these locations, net losses ranged between 7.3% and 43.9%. In the one station showing an increase in coral cover, the increase was only for the canopy branches of Acropora palmata ; understory branches of this same species lost surface area at the same rate as canopy branches gained area. For most of the common species, there was a reduction in the total number of living colonies in the community, and a diminution in the number of large, mature colonies. Throughout the study period, there was no recruitment to any of the photostations by any of the massive frame building coral species. Mortality of this magnitude is often associated with hurricane damage, but in this survey the losses occurred during a period without catastrophic storms. Sources of mortality identifiable in the photographs include (1) black band disease and (2) “bleaching” other potential sources of mortality are also considered. We conclude, for our survey areas, that loss rates of this magnitude cannot be sustained for protracted periods if the coral community is to persist in a configuration resembling historical coral reef community structure in the Florida Keys.

The ecology of two intermittent streams in Victoria, Australia.: III. Temporal changes in faunal composition

Abstract: SUMMARY 1. Temporal changes in species richness, total abundance, and numbers of individuals in seven functional feeding groups were compared between pools and riffles at four sites on two intermittent streams in Victoria sampled during a drought year followed by a wetter year. 2. Species richness increased steadily over time, peaking in the riffles just before flow ceased. Maximum species richness occurred in the pools shortly after flow stopped, implying emigration from the drying riffles. There were two peaks in total numbers, first in autumn when flow commenced and again in late summer as flow diminished. Generalist feeders (collector-gatherers and collector-scrapers) were usually abundant throughout the year. Scraper densities rose in late spring-early summer in conjunction with enhanced periphyton growth, whereas predator numbers steadily increased during the year, peaking in all habitats just before they dried. 3. Several floods in spring significantly reduced species richness and total numbers of individuals but recovery to pre-flood levels was generally complete within 2 weeks. Although floods had little effect upon succession, as indicated by trajectories in ordination space, the dry period interrupted otherwise cyclical sequences, consistently resulting in arch-shaped trajectories. Faunal change appeared to be allogenic, driven by the seasonal cycle of environmental phases. 4. A group of early colonists or ‘pioneer’ species was replaced after several weeks by heterogeneous groups of ‘mid-successional’ taxa responsible for differences in faunal composition between riffles and pools. When flow diminished, these groups were replaced by ‘summer’ species, apparently capable of tolerating deteriorating environmental conditions, and potentially intensifying biotic interactions. 5. We suggest that the cyclical temporal changes in assemblage composition observed in this study represent ‘seasonal periodicity’, whereas recovery after unpredictable disturbances such as floods that temporarily disrupt the cycle fits the definition of ‘succession’. Succession rate is a measure of resilience, recovering to the cyclical trajectory that would exist in the absence of disturbance. ‘Lag effects’ brought about by reduced recruitment during the drought were not evident until the following year, emphasizing the significance of historical events and the need for long-term studies to describe the ecology of intermittent streams adequately.

Fire Frequency and Community Heterogeneity in Tallgrass Prairie Vegetation

Abstract: Pattern in plant communities is a function of many biotic and abiotic factors and these factors operate on different species at different spatial scales (Pielou 1960, Greig-Smith 1979, Legendre and Fortin 1989). One product of the nonrandom distribution of species at different spatial scales is community heterogeneity. In this paper, spatial heterogeneity is the mean degree of dissimilarity in species composition from one point to another in a community (Inouye et al. 1987, Collins 1990). Heterogeneity differs from pattern analysis in that the latter is a measure of the degree of spatial autocorrelation, or distance decay in the case of gradients, in a community (Palmer 1988, Legendre and Fortin 1989).

Recovery of temperate-stream fish communities from disturbance: A review of case studies and synthesis of theory

Abstract: To evaluate the relative effect of autecologic factors, site-specific factors, disturbance characteristics, and community structure on the recovery of temperate-stream fish communities, we reviewed case histories for 49 sites and recorded data on 411 recovery end points. Most data were derived from studies of low-gradient third- or fourth-order temperate streams located in forested or agricultural watersheds. Species composition, species richness, and total density all recovered within one year for over 70% of systems studied. Lotic fish communities were not resilient to press disturbances (e.g., mining, logging, channelization) in the absence of mitigation efforts (recovery time >5 to >52 yr) and in these cases recovery was limited by habitat quality. Following pulse disturbances, autecological factors, site-specific factors, and disturbance-specific factors all affected rates of recovery. Centrarchids and minnows were most resilient to disturbance, while salmonid populations were least resilient of all families considered. Species within rock-substrate/nest-spawning guilds required significantly longer time periods to either recolonize or reestablish predisturbance population densities than did species within other reproductive guilds. Recovery was enhanced by the presence of refugia but was delayed by barriers to migration, especially when source populations for recolonization were relatively distant. Median population recovery times for systems in which disturbances occurred during or immediately prior to spawning were significantly less than median recovery times for systems in which disturbances occurred immediately after spawning. There was little evidence for the influence of biotic interactions on recovery rates.

Regulation of "momentary" diversity by dominant species in exceptionally rich ant communities of the

Abstract: I report observations on exceptionally diverse ant communities in the seasonally arid tropics of northern Australia that indicate that interference competition from dominant species regulates the number of ant species foraging at rich food sources in a manner analogous to humped diversity models applicable to communities of plants and sessile marine invertebrates. I adopt two novel approaches to the study of humped diversity patterns. First, I look at the effect of temporal changes in the foraging abundance of dominant species, presumably linked to temporal changes in climatic favorability, on "momentary" diversity within a community. Second, I relate diversity directly to the abundance of dominant species rather than to some environmental variable that is assumed to control their abundance. Iridomyrmex spp. and Oeco- phylla smaragdina were dominant ants at the forest and savanna sites studied: they occurred at a large proportion (35%-85%) of tuna baits, they dominated and monopolized most (>80%) of the baits at which they occurred, they had the highest mean abundance scores at baits, and they were far more abundant at baits than expected from their representation in pitfall catches. The total abundance of nondominant ants, species richness, and species diversity at baits all exhibited humped relationships with the combined abundance of Iridomyrmex and Oecophylla, which indicates that dominant species suppressed the foraging abundances and diversity of other species under climatically favorable conditions. There were important site differences in the expression of this humped pattern: the abundance of dominant species was never low in the savanna, and here only the descending part of the hump was expressed. This study appears to be the first time that any humped diversity pattern caused by competitive exclusion has been documented in terrestrial animal communities. Several models of the control of diversity in communities of plants and sessile intertidal organisms feature a humped relationship between local species richness and gradients of resource availability (Grime 1973, 1979), productivity (Tilman 1982), or disturbance (Connell 1978; Huston 1979; Wilson and Keddy 1988), with the latter including herbivory (Lubchenco 1978) and predation (Paine 1974; Con- nell 1975; McCauley and Briand 1979). A common theme is that diversity initially increases with environmental favorability but then decreases as conditions al- low highly competitive species to become so dominant that they exclude other species. These humped diversity models have so far considered only spatial variation in diversity. However, in mobile animals the opportunity exists for dominant species to exert a temporal influence on species diversity. That is, in any given

Community structure of a species-rich temperate forest, Ogawa Forest Reserve, central Japan

Abstract: Species assembly and niche differentiation were studied, and future species composition was predicted by simple Markov models, in an old-growth deciduous forest at the Ogawa Forest Reserve in central Japan. The dominant species in our 6ha study site are Quercus serrata, Fagus japonica, and F. crenata.

The Janzen-Connell model for tropical tree diversity: population implications and the importance of spatial scale.

Abstract: The maintenance of high diversity in tropical forests has long intrigued biologists. While explanations for tropical tree species richness are nearly as varied as the forests, much recent theory and empirical work have focused on what Clark and Clark (1984) termed the Janzen-Connell model. Independently derived by Janzen (1970) and Connell (1971), the model proposes that distanceand density-responsive seed and seedling enemies play a major role in maintaining species in the community by providing a \"spacing\" mechanism that disallows new recruitment inthe vicinity of existing conspecific adults. Distance-responsive enemies center their attacks around the adult tree, killing an ever-greater proportion of seeds and seedlings with increasing proximity to the adult. Densityresponsive nemies disproportionately attack high-density patches of seeds and seedlings, killing an ever-greater proportion with increasing density. Since the greatest densities of dispersed seeds tend to be found beneath and near fruiting adults, both classes of enemies are expected to concentrate their attacks in the vicinity of parent rees. Consequently, the model hypothesizes that mortality near parents is virtually complete, recruitment is limited to areas at some distance from conspecifics, and adults are more evenly spaced than expected from the pattern of seedfall. The open space in the vicinity of adults, then, is available for colonization by other species, competitive xclusion is less likely, and a large number of species can coexist in the community. Although elegantly simple on the surface, the model does not lend itself to an equally simple empirical test. The Janzen-Connell model actually presents a complex set of hypotheses, assumptions, and predictions that have led to a diversity of approaches to its evaluation (see Clark and Clark 1984). Effort has not been equally expended, however. The focus has primarily been on the existence and operation of the hypothesized spacing mechanism and on the ability of such spacing to maintain high diversity (Caswell 1978; Hubbell 1979, 1980; Augspurger 1983; Clark and Clark 1984; Connell et al. 1984; Becker et al. 1985; Howe et al. 1985; Hubbell and Foster 1986, 1987; Schupp 1988; Schupp and Frost 1989). In contrast, the population-level implications of the model have received little mpirical attention. Inherent in the model is the notion that the depredations of distanceand density-responsive enemies help regulate populations at relatively low densities (Caswell 1978; Hubbell and Foster 1986, 1987; DeAngelis and Waterhouse 1987). With few adults in a population, much of the habitat is far from the existing adults

Rarefaction Analysis of Morphological and Taxonomic Diversity

Abstract: Our assessment of morphological diversity is influenced by morphological extremes and therefore depends on sample size (taxonomic richness). Rarefaction predicts the morphological diversity that would probably be observed in a sample of reduced size, thereby allowing both compensation for differences in sample size that may be strictly preservational, and analysis of diversity structure, that is, the relationship between morphological and taxonomic diversity. Middle and Late Cambrian trilobites exhibit a diversity structure characterized by many variations on a few morphological themes. In contrast, Middle and Late Ordovician trilobites occupy a larger range of morphospace per unit of species richness. Diversity structure in the Devonian is similar to that in the Middle and Late Ordovician, but the magnitude of morphological diversity is lower in the Devonian, as many fewer species are observed. For blastoids, different aspects of morphological diversity (range of morphospace occupied, number of character states possessed, and number of different regions in morphospace occupied) exhibit different relationships to taxonomic richness. In all cases Permian blastoids are characterized by a diversity structure in which morphological diversity per unit of taxonomic richness is greater than for Devonian blastoids. Changes in mor- phological diversity in fissiculate blastoids appear to reflect evolution of continuous variation in thecal morphology more than changes in the number of character states. Saunders and Swan's data on Namurian ammonoids illustrate some significant differences in diversity structure among strati- graphic levels, but many apparent differences in morphological diversity are consistent with the possibility that they reflect the sampling of different numbers of species from the same underlying diversity structure. Rarefaction curves are also presented for idealized increases and decreases in diversity, and these are compared to some of the observed changes in trilobites, blastoids, and ammonoids.

Species richness and seed dispersal to secondary woods in southern Poland.

Abstract: Twenty-seven secondary woods, 32-51 years old, occurring on a limestone hill near Krakow, Poland, were investigated. Twenty-five woods were Scot's pine woods; twelve of them were planted. They differ in area, shape and isolation from the primary woods. 195 species of vascular plants were found in the secondary woods, including fifty-nine small shrub and herb woodland species (out of the seventy woodland species growing in the nearby primary woodlands). Only thirteen woodland species occuffed in more than a half of the secondary woods. Statistical analysis included ten independent variables (area, age, shape, distance to primary woodlands, cover of tree and shrub layer, and others) and two dummy variables. The results of a stepwise multiple regression analysis show that the number of all species depends only on area. The number of woodland species is significantly dependent on distance from the source of diaspores, area, shape, age and type of soil. The number of conifer woodland species is independent of wood age, which affects the number of broadleaf woodland species. A close relationship was found between the type of dispersal of woodland species and their distribution in secondary woods. Hovering and flying anemochores and endozoochores are the best colonizers, the worst are heavy anemochores, myrmecochores and barochores. The slow rate of the secondary succession in the study woods is due to poor colonizing ability of many woodland species as well as to the effect of the xeric conditions on the establishment and growth of seedlings.