An empirical test of the mass effect determinant of species richness

The mass effect determinant of species richness proposed by Shmida & Wilson (1985) was empirically tested at the interface of undisturbed, native vegetation with recovering vegetation on a reclaimed surface mine. The observed decrease in native species richness with distance away from the source area was consistent with the predicted pattern based on Shmida & Wilson's (1985) model.Taxonomic nomenclature follows Hitchcock & Cronquist (1983) except genus Artemisia, which follows Beetle & Johnson (1982).This research was supported by Grant No. DEB81-01827 from the National Science Foundation. Neil West and Charles Romesburg aided in the experimental design and analysis. Patricia Johnson assisted in computer programming.     

Ciliate community associated with aquatic macrophyte roots: effects of nutrient enrichment on the community composition and species richness

The objective of this study was to identify the impact of nutrient enrichment on the diversity of the ciliate community associated with the roots of the aquatic macrophyte Eichhornia crassipes. The experiment was performed in the Garças Lake, located in the Upper Paraná River floodplain, Brazil. We conducted two treatments (fertilized and control) with three replicates each. To increase the initial nutrient concentrations in each mesocosm of the fertilized treatment, we added 1000 μg L⁻¹ of KNO₃ and 200 μg L⁻¹ of KH₂PO₄ during each sampling date. We found a relative high number of ciliate species (85 species) and a predominance of hypotrichs. Among the recorded species, about 25% occurred exclusively in the fertilized treatment. Moreover, detrended correspondence analysis demonstrated that the ciliate community associated with E. crassipes roots changed significantly in response to the nutrient input in such a way that the species composition of the fertilized treatment was remarkably different from that of the control. In contrast to our expectations, species richness in the fertilized treatment was significantly higher than that in the control, refuting our hypothesis that species richness decreases under eutrophic conditions.     

The effect of naturally varying discharge rates on the species richness of lotic midges

Species richness significantly changed both temporally, over a two year period, and spatially, across three sites in a sandy run, in an assemblage of aquatic insects (Chironomidae) inhabiting a fourth order stream in southeastern Ohio, USA. A total of 25 species was encountered, and for a given site and time, richness varied between 0 and 13 species/site with a mean of 3.3. Averaged over two years, the species diversity trend from bank to channel was an increasing number of species with a decreasing variance, indicating a greater stability in species richness in the channel than near the bank. A significant amount of the temporal variability in richness can be explained by variation in the stream discharge rate. Discharge was inversely related to a) species richness and b) the rate of change of species richness, for two sites in the stream center but not for a more protected site near the bank. Abugov's (1982) model of the phasing of disturbances may explain the species richness patterns observed in this study.     

Regional species richness,hydrological characteristics and the local species richness of assemblages of North American stream fishes

1. Local assemblage structure, from a deterministic perspective, is presumably dictated by the regional species pool as well as regulated by local factors. We examined the relationships of the regional species pool and local hydrological characteristics to local species richness of North American freshwater fishes using data sets collected during the National Water Quality Assessment program conducted by the United States Geological Survey. 2. We predicted that local species richness is ultimately constrained by the composition of the regional species pool and further associated with local hydrological factors. Moreover, we predicted that variation in local species richness within major families can be explained by different combinations of hydrological characteristics that represent lineage‐specific responses to the environment. 3. Daily discharge and regional and local species richness data were assembled from 41 stream localities across the United States. Multiple stepwise regressions were conducted to predict local species richness, based on regional species richness, mean discharge and hydrological characteristics quantified by nine variables characterising flow variability. Species richness at each site was calculated for the entire assemblage as well as within the four most species‐rich families in the data set (Catostomidae, Centrarchidae, Cyprinidae and Percidae). 4. Local species richness was best predicted by a combination of regional species richness and discharge magnitude when all species were considered. Regional species richness was a significant explanatory variable of local species richness for three of four families (Catostomidae, Centrarchidae, Cyprinidae), but not for Percidae. Local richness in Centrarchidae and Cyprinidae was positively correlated with temporal flow variability as well as high and low flow duration, respectively, while richness in Catostomidae and Percidae tended to be associated with discharge volume. In addition, local species richness for three of the four major families was positively correlated with species richness of the other families in the assemblage, potentially suggesting the influence of local habitat quality and heterogeneity. 5. Results suggest the importance of the combined influences of the regional species pool and local hydrological characteristics on local richness in freshwater fishes, with variation in richness within each family predicted by different characteristics of flow regimes.     

Edge effect of a pine plantation reduces dry grassland invertebrate species richness

Natural steppes in European agricultural landscapes are characterized by high biotic richness but are subject to fragmentation and associated edge effects. Edge effects on species richness were investigated at an ecotone from a pine plantation to a short-grass steppe in Eastern Austria for eleven invertebrate taxa differentiated into habitat guilds based on known live-history strategies of individual species (grassland species, forest species, generalist species), including Red-Listed and non-threatened grassland species. The large size of the studied grassland site provided an opportunity to test edge effects in the absence of confounding factors and to a gradient length of 208 m into the grassland habitat along a clear-cut border to a pine plantation. All sampling was done by pitfall trapping. Species richness of habitat guilds, but not total richness, was effectively explained by biotic variables reflecting the influence of shading in particular (i.e. soil temperature sums). Total species richness showed a bimodal response pattern, with increases towards the habitat edge and interior grassland habitat. Habitat guilds showed diverging responses to distances from the edge, but no saturation in species richness, with a continuum of edge effects across the entire distance of the grassland samples. Our findings contrast those of previous investigations based on samples taken from smaller patches and across shorter distances from the edge. Methodological and conservation implications are discussed.     

Stochastic relations between species richness and the variability of species composition

Ecological communities change over time and space, and ecologists have long suggested that biodiversity might influence the rate of change. Here we cast new light on this question by demonstrating statistical covariation between species richness and the variability of species abundances and identities within a community (compositional variability). We provide a new analytical framework for several previously published measures of ecosystem functioning and compositional variability. We derive three related variances, each of which measures compositional variability due solely to stochastic sampling processes. Our analyses show that whether relations between species richness and compositional variability are positive, negative or zero, depends on two factors. Not only does the particular variance used affect the relation, but, more importantly, the underlying determinants of species richness can strongly affect the stochastic relations between species richness and compositional variability. This analysis makes clear for the first time how species richness should correlate with important measures of community variability, even in the absence of systematic processes.     

Trends in butterfly species richness in response to the peninsular effect in South Korea

Aim The Korean peninsula is elongated in shape and is connected to the Asian continent on the north. The peninsular effect – a decline in species density or richness as a function of distance from the mainland base (towards the distal tip) of a peninsula – was evaluated for plants and animals in different peninsulas. The aims of the present study were to describe the pattern of butterfly species diversity and to determine what factors may be responsible for this pattern along the Korean peninsula. The distribution pattern of butterfly species in South Korea before and after the Korean War was also investigated. Location South Korea (34–38° N, 126–129° E). Methods Forty‐three quadrats, each 1/2° latitude by 1/2° longitude, and three data sets – butterfly distribution data from 1938 to 1950, butterfly distribution data from 1976 to 1999, and the combined data – were analysed. The influence of four variables – latitude, longitude, area and maximum altitude – on each quadrat was investigated using multiple regression analysis. Results and conclusion The analyses revealed a marked peninsular effect: there was a significant positive correlation between butterfly species richness and latitude. Additionally, habitat diversity, expressed as maximum altitude, was significantly correlated with butterfly species richness. I conclude that both the geographical orientation and habitat diversity contribute to butterfly species diversity across South Korea. Comparison of ranges between the older and recent data sets suggests that geographical distributions of several species are dramatically reduced in size. These species may be used for future conservation activities in South Korea.     

Estimating the richness of species with variable mobility

The vast majority of species are animals that, unlike most plants and fungi, are variably and often highly mobile. While species' mobility affects species' probabilities of being sampled, effects of movement on the estimation of species richness have yet to be systematically investigated. Information-rich abundance-based estimators may be able to address variably mobile species but the accuracy of these estimators has also yet to be investigated. Here, we address both issues by variably sampling simulated landscapes with up to 250 species and evaluating the performance of ten non-parametric estimators and one species accumulation curve. Our results show that some abundance-based estimators are as accurate as better known and tested incidence-based estimators. Increased movement heterogeneity between the species reduced estimator performance by reducing the sample coverage, which systematically determined which estimator was most accurate. Based on these findings, we present the first decision framework for choosing the most accurate of many available abundance-based species-richness estimators. These decisions, based on data coverage, can significantly improve investigators' ability to estimate faunal species richness.     

Relative influence of regional species richness vs local climate on local species richness in China's forests

Disentangling the relative effects of local and regional processes on local species richness (LSR) is critical for understanding the mechanisms underlying large‐scale biodiversity patterns. In this study we used 1098 forest plots from 41 mountains across China, together with regional flora data, to examine the relative influence of local climate vs regional species richness (RSR) on LSR patterns. Both RSR and LSR for woody species and all species combined decreased with increasing latitude, while richness of herbaceous species exhibited a hump‐shaped pattern. The major climatic orrelates of species richness differed across spatial scales. At the regional scale, winter coldness was the best predictor of RSR patterns for both woody and herbaceous species. At the local scale, however, productivity‐related climatic indices were the best predictors of LSR patterns. Local climate and RSR together explained 48, 54 and 23% of the variation in LSR, for overall, woody and herbaceous species, respectively. Both local climate and RSR independently influenced LSR in addition to their joint effects, suggesting that LSR patterns were shaped by local and regional processes together. Local climate and RSR affected LSR of woody species mainly through their joint effects, while there were few shared effects of climate and RSR on the LSR of herbaceous species. Our findings suggest that while geographic RSR patterns are mainly determined by winter coldness, the ecological processes driven by productivity may be critical to the filtering of regional flora into local communities. We also demonstrate that biogeographic region is not a good surrogate for regional richness, at least for our dataset. Consequently, whether biogeographic region can effectively reflect regional effects needs further examination.     

Explaining species richness from continents to communities: the time-for-speciation effect in emydid turtles

Speciation is the process that ultimately generates species richness. However, the time required for speciation to build up diversity in a region is rarely considered as an explanation for patterns of species richness. We explored this "time-for-speciation effect" on patterns of species richness in emydid turtles. Emydids show a striking pattern of high species richness in eastern North America (especially the southeast) and low diversity in other regions. At the continental scale, species richness is positively correlated with the amount of time emydids have been present and speciating in each region, with eastern North America being the ancestral region. Within eastern North America, higher regional species richness in the southeast is associated with smaller geographic range sizes and not greater local species richness in southern communities. We suggest that these patterns of geographic range size variation and local and regional species richness in eastern North America are caused by glaciation, allopatric speciation, and the time-for-speciation effect. We propose that allopatric speciation can simultaneously decrease geographic range size and increase regional diversity without increasing local diversity and that geographic range size can determine the relationship between alpha, beta, and gamma diversity. The time-for-speciation effect may act through a variety of processes at different spatial scales to determine diverse patterns of species richness.     

Removing the confounding effect of habitat specialization reveals the stabilizing contribution of diversity to species variability

Earlier studies have found that diversity, S, stabilizes the relative variability of combined biomass or abundance of species making up a community. However, the effect of S on variability of constituent species has been elusive. We hypothesize that the proportion of specialists increases with S and, because specialists are more variable, this shift in composition will mask the stabilizing effect of S on populations of species making up a community. The test uses data on variability and ecological specialization of species in 49 natural rock pool invertebrate communities. Initial analyses produced inconclusive results similar to earlier studies. However, when variability owing to species' specialization was factored out, S reduced species' abundance variability, although not in all communities. Our study explains why the stabilizing effect of diversity on populations has not been found earlier.     

Estimating species richness using the jackknife procedure

An exact expression is given for the jackknife estimate of the number of species in a community and for the variance of this number when quadrat sampling procedures are used. The jackknife estimate is a function of the number of species that occur in one and only one quadrat. The variance of the number of species can be constructed, as can approximate two-sided confidence intervals. The behavior of the jackknife estimate, as affected by quadrat size, sample size and sampling area, is investigated by simulation.     

How enrichment,ecosystem size,and their effects on species richness co‐determine the stability of microcosm communities

Nutrient enrichment, ecosystem size, and richness each may directly affect the stability of both populations and communities. Alternatively, nutrient enrichment and ecosystem size each may directly affect richness, which in turn may affect stability. No previous studies, however, have tested empirically how these three factors interact and co‐determine stability. We manipulated nutrient input and ecosystem size in replicate microcosms containing a diverse bacterial flora, and a range of green algae and heterotrophic protozoa, and used these manipulations and the resulting variation in species richness to measure their combined effects on temporal stability of both populations and communities. Results showed that nutrient enrichment and ecosystem size controlled protist richness, and their effects on stability could be mediated by richness. In addition, both community‐level and population‐level stability increased with protist richness. Furthermore, mean species evenness and mean species richness was negatively related. Effects of statistical averaging, overyielding, and component population stability were identified as possible mechanisms involved explaini ng the stabilizing effects of richness on community stability. Their relative strength in influencing stability, however, is likely to change as mean evenness decreased with increasing richness. This decrease in evenness would tend to weaken the strength of the statistic averaging effect, but increase the strength of the other two mechanisms due to relatively lower population variability (component population stability) and higher mean biovolumes of dominant protists (overyielding).     

The effect of the taxon and geographic range size of host eucalypt species on the species richness of gall-forming insects

Abstract This field study was designed to test whether the taxonomic group and geographic range size of a host plant species, usually found to influence insect species richness in other parts of the world, affected the number of gall species on Australian eucalypts. We assessed the local and regional species richness of gall-forming insects on five pairs of closely related eucalypt species. One pair belonged to the subgenus Corymbia, one to Monocalyptus, and three to different sections of Symphyomyrtus. Each eucalypt pair comprised a large and a small geographic range species. Species pairs were from coastal or inland regions of eastern Australia. The total number of gall species on eucalypt species with large geographic ranges was greater than on eucalypt species with small ranges, but only after the strong effect of eucalypt taxonomic grouping was taken into account. There was no relationship between the geographic range size of eucalypt species and the size of local assemblages of gall species, but the variation in insect species composition between local sites was higher on eucalypt species with large ranges than on those with small ranges. Thus the effect of host plant range size on insect species richness was due to greater differentiation between more widespread locations, rather than to greater local species richness. This study confirms the role of the geographic range size of a host plant in the determination of insect species richness and provides evidence for the importance of the taxon of a host plant.     

The effect of energy and seasonality on avian species richness and community composition

We analyzed geographic patterns of richness in both the breeding and winter season in relation to a remotely sensed index of seasonal production (normalized difference vegetation index [NDVI]) and to measures of habitat heterogeneity at four different spatial resolutions. The relationship between avian richness and NDVI was consistent between seasons, suggesting that the way in which available energy is converted to bird species is similar at these ecologically distinct times of year. The number and proportion of migrant species in breeding communities also increased predictably with the degree of seasonality. The NDVI was a much better predictor of seasonal richness at finer spatial scales, whereas habitat heterogeneity best predicted richness at coarser spatial resolutions. While we find strong support for a positive relationship between available energy and species richness, seasonal NDVI explained at most 61% of the variation in richness. Seasonal NDVI and habitat heterogeneity together explain up to 69% of the variation in richness.