Showing papers on "Species richness published in 1998"

Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity

Abstract: The functioning and stability of terrestrial ecosystems are determined by plant biodiversity and species composition1,2,3,4,5 However, the ecological mechanisms by which plant biodiversity and species composition are regulated and maintained are not well understood These mechanisms need to be identified to ensure successful management for conservation and restoration of diverse natural ecosystems Here we show, by using two independent, but complementary, ecological experiments, that below-ground diversity of arbuscular mycorrhizal fungi (AMF) is a major factor contributing to the maintenance of plant biodiversity and to ecosystem functioning At low AMF diversity, the plant species composition and overall structure of microcosms that simulate European calcareous grassland fluctuate greatly when the AMF taxa that are present are changed Plant biodiversity, nutrient capture and productivity in macrocosms that simulate North American old-fields increase significantly with increasing AMF-species richness These results emphasize the need to protect AMF and to consider these fungi in future management practices in order to maintain diverse ecosystems Our results also show that microbial interactions can drive ecosystem functions such as plant biodiversity, productivity and variability

Benefits of plant diversity to ecosystems: immediate, filter and founder effects

Abstract: 1 It is useful to distinguish between the immediate effects of species richness on ecosystems and those which become apparent on a longer time scale, described here as filter and founder effects. 2 Relationships between plant diversity and ecosystem properties can be explored by classifying component species into three categories – dominants, subordinates and transients. Dominants recur in particular vegetation types, are relatively large, exhibit coarse-grained foraging for resources and, as individual species, make a substantial contribution to the plant biomass. Subordinates also show high fidelity of association with particular vegetation types but they are smaller in stature, forage on a more restricted scale and tend to occupy microhabitats delimited by the architecture and phenology of their associated dominants. Transients comprise a heterogeneous assortment of species of low abundance and persistence; a high proportion are juveniles of species that occur as dominants or subordinates in neighbouring ecosystems. 3 A ‘mass ratio’ theory proposes that immediate controls are in proportion to inputs to primary production, are determined to an overwhelming extent by the traits and functional diversity of the dominant plants and are relatively insensitive to the richness of subordinates and transients. Recent experiments support the mass ratio hypothesis and the conclusion of Huston (1997) that claims of immediate benefits of high species richness to ecosystem functions arise from misinterpretation of data. 4 Attribution of immediate control to dominants does not exclude subordinates and transients from involvement in the determination of ecosystem function and sustainability. Both are suspected to play a crucial, if intermittent, role by influencing the recruitment of dominants. Some subordinates may act as a filter influencing regeneration by dominants following major perturbations. 5 Transients originate from the seed rain and seed banks and provide an index of the pool of potential dominants and subordinates at specific sites. Where the landscape carousel operates against a background of declining diversity in the reservoir of colonizing transients, we may predict that a progressive loss of ecosystem functions will arise from the decline in the precision with which dominants can engage in the re-assembly and relocation of ecosystems.

Identifying Populations for Conservation on the Basis of Genetic Markers

Abstract: To select candidate populations of wild species to be given priority for conservation, genetic criteria gained from the study of molecular markers may be useful. Traditionally, diversity measures such as ex- pected heterozygosity or percentage of polymorphic loci have been considered. For conservation we propose instead that priority should be given to measures of allelic richness. To standardize the results of allelic rich- ness across populations, we used the technique of rarefaction. This technique allows evaluation of the ex- pected number of different alleles among equal-sized samples drawn from several different populations. We also show how the contribution of each population to total diversity can be partitioned into two components. The first is related to the level of diversity of the population and the second to its divergence from the other populations. For conservation purposes the uniqueness of a population-in terms of its allelic composition- may be at least as important as its diversity level. These new descriptors are illustrated by means of isozyme and chloroplast DNA data obtainedfor an endangered tree species, the argan tree of Morocco (Argania spinosa (L.) Skeels). With these analyses the conservation value of the argan tree populations, especially those of two isolates present in the north of the country, can be better appreciated. The methods proposed to identify prior- ity areas for conservation of the genetic resources of the argan tree are compared to those sometimes advo- cated in the case of reserve design, where one of the goals is to maximize species richness.

Ecological Resilience, Biodiversity, and Scale

Abstract: We describe existing models of the relationship between species diversity and ecological function, and propose a conceptual model that relates species richness, ecological resilience, and scale. We suggest that species interact with scale-dependent sets of ecological structures and processes that determine functional opportunities. We propose that ecological resilience is generated by diverse, but overlapping, function within a scale and by apparently redundant species that operate at different scales, thereby reinforcing function across scales. The distribution of functional diversity within and across scales enables regeneration and renewal to occur following ecological disruption over a wide range of scales.

Effects of herbivores on grassland plant diversity.

Abstract: The role of herbivores in controlling plant species richness is a critical issue in the conservation and management of grassland biodiversity. Numerous field experiments in grassland plant communities show that herbivores often, but not always, increase plant diversity. Recent work suggests that the mechanisms of these effects involve alteration of local colonization of species from regional species pools or local extinction of species, and recent syntheses and models suggest that herbivore effects on plant diversity should vary across environmental gradients of soil fertility and precipitation.

Biodiversity inventories, indicator taxa and effects of habitat modification in tropical forest

Abstract: Despite concern about the effects of tropical forest disturbance and clearance on biodiversity1,2, data on impacts, particularly on invertebrates, remain scarce3,4,5,6,7,8. Here we report a taxonomically diverse inventory on the impacts of tropical forest modification at one locality. We examined a gradient from near-primary, through old-growth secondary and plantation forests to complete clearance, for eight animal groups (birds, butterflies, flying beetles, canopy beetles, canopy ants, leaf-litter ants, termites and soil nematodes) in the Mbalmayo Forest Reserve, south-central Cameroon. Although species richness generally declined with increasing disturbance, no one group serves as a good indicator taxon9,10,11,12 for changes in the species richness of other groups. Species replacement from site to site (turnover) along the gradient also differs between taxonomic groups. The proportion of ‘morphospecies’ that cannot be assigned to named species and the number of ‘scientist-hours’ required to process samples both increase dramatically for smaller-bodied taxa. Data from these eight groups indicate the huge scale of the biological effort required to provide inventories of tropical diversity, and to measure the impacts of tropical forest modification and clearance.

Modulation of Diversity by Grazing and Mowing in Native Tallgrass Prairie

Abstract: Species diversity has declined in ecosystems worldwide as a result of habitat fragmentation, eutrophication, and land-use change. If such decline is to be halted ecological mechanisms that restore or maintain biodiversity are needed. Two long-term field experiments were performed in native grassland to assess the effects of fire, nitrogen addition, and grazing or mowing on plant species diversity. In one experiment, richness declined on burned and fertilized treatments, whereas mowing maintained diversity under these conditions. In the second experiment, loss of species diversity due to frequent burning was reversed by bison, a keystone herbivore in North American grasslands. Thus, mowing or the reestablishment of grazing in anthropogenically stressed grasslands enhanced biodiversity.

Biogeography, biodiversity and fluid dependence of deep-sea cold-seep communities at active and passive margins

Abstract: To date, several cold-seep areas which fuel chemosynthesis-based benthic communities have been explored, mainly by deployment of manned submersibles. They are located in the Atlantic and in the Eastern and Western Pacific oceans and in the Mediterranean Sea, in depths ranging between 400 and 6000 m in different geological contexts in passive and active margins. Our study is based on a review of the existent literature on 24 deep cold seeps. The geographic distribution of seeps, the variations of origin and composition of fluids, and rates of fluid flow are presented as they are important factors which explain the spatial heterogeneity and the biomass of biological communities. Methane-rich fluid of thermogenic and/or biogenic origin is the principal source of energy for high-productive communities; however, production of sulphide by sulphate reduction in the sediment also has a major role. The dominant seep species are large bivalves belonging to the families Vesicomyidae or Mytilidae. Other symbiont-containing species occur belonging to Solemyidae, Thyasiridae, Lucinidae bivalves, Pogonophora worms, Cladorhizidae and Hymedesmiidae sponges. Most of the symbiont-containing cold-seep species are new to science. Different symbiont-containing species rely on sulphide or methane oxidation, or both, via chemoautotrophic endosymbiotic bacteria. A total of 211 species, from which 64 are symbiont-containing species, have been inventoried. Patterns in biodiversity and biogeography are proposed. A large majority of the species are endemic to a seep area and the symbiont-containing species are mainly endemic to the cold-seep ecosystem. A comparison of species found in other deep chemosynthesis-based ecosystems, hydrothermal vents, whale carcass and shipwreck reduced habitats, reveals from the existing data, that only 13 species, of which five are symbiont-containing species occur, at both seeps and hydrothermal vents. The species richness of cold-seep communities decreases with depth. High diversity compared to that on hydrothermal vent sites is found at several seeps. This may be explained by the duration of fluid flow, the sediment substrate which may favour long-term conditions with accumulation of sulphide and the evolution of cold seeps.

Reversal of grazing impact on plant species richness in nutrient-poor vs. nutrient-rich ecosystems

Abstract: To test the hypothesis that the impacts of grazers on plant species richness reverse under contrasting nutrient richness, we analyzed unpublished and published data from lake, stream, marine, grassland, and forest ecosystems. We analyzed data from 30 studies providing 44 comparisons of plant species richness under low vs. high grazing pressure in enriched or nutrient-rich and non-enriched or nutrient-poor ecosystems. All 19 comparisons from non-enriched or nutrient-poor ecosystems exhibited significantly lower species richness under high grazing than under low grazing. In contrast, 14 of 25 comparisons from enriched or nutrient-rich ecosystems showed significantly higher species richness under high grazing than under low grazing. However, nine of these 25 comparisons showed no significant impact of grazers on species richness, while two comparisons showed declines in species richness under high grazing. Based on all the comparisons, plant species richness decreases with high grazing in nutrient-poor ecosystems, while it increases with high grazing in nutrient-rich ecosystems. Although nutrient-rich ecosystems seemed to produce more variable responses to grazers than did nutrient-poor ecosystems, in rare cases high grazing produced a decline in species richness in nutrient-rich environments. We suggest that species richness declines with high grazing in nutrient-poor ecosystems because a limitation of available resources prevents regrowth of species after grazing, which may not be the case in nutrient-rich ecosystems. It is also possible that an increase in species richness under high grazing in nutrient-rich ecosystems may be due to an increase in the dominance of inedible species. Our observation of a grazer reversal of plant species richness under contrasting nutrient richness may have important implications for management of species diversity.

Statistical methods for estimating species richness of woody regeneration in primary and secondary rain forests of northeastern Costa Rica

Abstract: The study of plant communities requires a basic understanding of the abundance, distribution, and number of species present Yet, in obtaining this information, scientists can rarely sample the entire community or area of interest In practice, data from numerous small sub-samples provide a basis for extrapolating to a larger area, Such extrapolating must take into account the well-supported observation that estimates of local species richness depend strongly on the number of individuals and the area sampled (Gleason, 1922; Preston, 1948) Although researchers must rely heavily on extrapolations for many kinds of ecological studies, relatively little attention has been focused on improving the accuracy, applicability, and accessibility of species-richness estimators in vegetation studies, particularly in higly diverse tropical ecosystems If robuts and accurate statistical estimators of species richness that are reasonably insensitive to sample size can be found, they can serve to provide a quantitative basis for identifying conservation priorities, for comparative biogeographic or regional studies, and for assessing long-term changes in species richness Bunge and Fitzpatrick (1993) and Colwell and Coddington (1994) provided a broad overview of statistical approaches for estimating species richness form samples Here, we evaluated the performance of several of these methods in estimating species richness of young woody regeneration in six tropical forest sites We compared the performance of various estimation techniques within individual sites as well as across a range of sites differing in successional status and in woody species abundance and spatial distribution We focused specifically on two size classes of wood regeneration: 1) established seedlings 1m in height, but

Experimental Tests of the Dependence of Arthropod Diversity on Plant Diversity

Abstract: Because a diversity of resources should support a di- versity of consumers, most models predict that increasing plant di- 1998) have found that increasing plant diversity increases versity increases animal diversity. We report results of a direct ex- arthropod herbivore diversity. However, these studies are perimental test of the dependence of animal diversity on plant confounded by changes in plant community composition diversity. We sampled arthropods in a well-replicated grassland ex- that correlate with changes in plant diversity. The rela- periment in which plant species richness and plant functional rich- tionship between plant diversity and herbivore diversity ness were directly manipulated. In simple regressions, both the may be nonlinear because herbivore loads are often lower number of species planted (log2 transformed) and the number of in polycultures due to differences in the ability of herbi- functional groups planted significantly increased arthropod species richness but not arthropod abundance. However, the number of vores to locate host plants in mixed stands, suitability of species planted was the only significant predictor of arthropod smaller patches of host plants, and/or differences in the species richness when both predictor variables were included in effects of parasites and predators (reviewed in Andow ANOVAs or a MANOVA. Although highly significant, arthropod 1991). species richness regressions had low R 2

Why More Productive Sites Have More Species: An Experimental Test of Theory Using Tree‐Hole Communities

Abstract: One of the most common explanations for an increase in species richness with productivity is what we have dubbed the "More Individuals Hypothesis." According to this hypothesis, more productive sites can support higher total abundances and, since species richness is an increasing function of total abundance, so will it be of productivity. This hypothesis assumes that communities are limited by productivity. We tested the More Individuals Hypothesis using the detritivorous aquatic insect communities of tree holes. When tree holes with varying levels of productivity (debris amount) were allowed to be colonized (through oviposition), more productive tree holes did have more species but not more individuals. Neither was total energy use strictly proportional to productivity. Only in communities forced to disassemble through productivity reductions were the predictions of the More Individuals Hypothesis satisfied. Ovipositing adults may prefer productive tree holes not because they contain more resources but because they are anticipated to be less likely to dry out. In tree holes, and more generally, the More Individuals Hypothesis is an insufficient explanation for increases in species richness with productivity because it neither accounts for the different processes of local colonization and extinction nor allows body size to correlate with extinction risk.

Community Assembly Rules, Morphological Dispersion, and the Coexistence of Plant Species

Abstract: In order to find and define any assembly rules for communities, we must first investigate the patterns among species assemblages. We used a series of null models to test for patterns in wetland plant composition at the level of species, functional guilds, and traits. At the species level, we found significant checkerboard and nestedness patterns. Three functional guilds had some tendency to contribute a constant percentage to species richness, but after Bonferroni correction there was no significant pattern. Coexisting plant species showed no consistent overall pattern of morphological dispersion. However, when we considered each of 11 traits in turn, we found that 4 traits were overdispersed and 3 were underdispersed. Thus there are morphological assembly rules that constrain wetland plant community composition. These results reconcile contrasting views of community assembly. Communities can be simultaneously structured by a tension between two forces: abiotic external forces that constrain certain traits within limits and biotic internal forces that tend to keep coexisting species from being too similar. Because our sites vary along a fertility/disturbance gradient, we also investigated how trait dispersion varies in space. Trait dispersion increases with soil fertility; soil phosphorus explains about 36% of the variance in mean nearest neighbor distance. Species richness tends to decline with mean nearest neighbor distance, which contrasts with the general pattern for animal assemblages.

Species Coexistence: Ecological and Evolutionary Perspectives

Abstract: Introduction: conceptual threads Origination: the basis of coexistence Origination and evolution of communities Patterns of species richness: temporal dimension Patterns of species richness: spatial dimension The niche, resources and species assembly Niche apportionment and relative abundances of coexisting species Competition, co-operation and coexistence Agent-mediated coexistence: predation and disturbance Patchiness, heterogeneity and stochasticity Traits and coexistence Stability and conservation of coexisting species Concluding remarks

Biodiversity and ecosystem functioning: A mechanistic model

Abstract: Recent experiments have provided some evidence that loss of biodiversity may impair the functioning and sustainability of ecosystems. However, we still lack adequate theories and models to provide robust generalizations, predictions, and interpretations for such results. Here I present a mechanistic model of a spatially structured ecosystem in which plants compete for a limiting soil nutrient. This model shows that plant species richness does not necessarily enhance ecosystem processes, but it identifies two types of factors that could generate such an effect: (i) complementarity among species in the space they occupy below ground and (ii) positive correlation between mean resource-use intensity and diversity. In both cases, the model predicts that plant biomass, primary productivity, and nutrient retention all increase with diversity, similar to results reported in recent field experiments. These two factors, however, have different implications for the understanding of the relationship between biodiversity and ecosystem functioning. The model also shows that the effect of species richness on productivity or other ecosystem processes is masked by the effects of physical environmental parameters on these processes. Therefore, comparisons among sites cannot reveal it, unless abiotic conditions are very tightly controlled. Identifying and separating out the mechanisms behind ecosystem responses to biodiversity should become the focus of future experiments.

Plant species richness in riparian wetlands—a test of biodiversity theory

Abstract: In this study, flood frequency, productivity, and spatial heterogeneity were correlated with plant species richness (SR) among wetlands on a coastal island in southeast Alaska. Studies of 16 sites in or near the Kadashan River basin demonstrated nonlinear, unimodal relations between flood frequency and SR, productivity and SR, and linear re- lations between SR and the spatial variation of flood frequencies (SVFF) within a site. SVFF is caused by microtopographic variation in elevation. A nonlinear regression model relating SR to flood frequency and SVFF explained much of the variation in SR between wetland communities. Sites with intermediate flood frequencies and high SVFF were spe- cies-rich, while sites frequently, rarely, or permanently flooded and with low SVFF were species-poor. The data suggest that small-scale spatial variation can dramatically alter the impact of disturbances. The data also support Michael Huston's dynamic-equilibrium model of species diversity, which predicts the effects of productivity and disturbance on diversity patterns. Species- rich sites had low to intermediate levels of productivity and intermediate flood frequencies, and species-poor sites had very low or high flood frequencies and low productivity, sup- porting the model's predictions. The model was tested at contrasting spatial scales (1000 m2 and 1 M2). At the 1000-M2 scale, Huston's model predicted 78% of the variation in SR. At the microplot scale, relationships between SR and flood frequency were weaker, and the dynamic-equilibrium model predicted only 36% of the variation in SR.

Estimating species richness: the importance of heterogeneity in species detectability

Abstract: Estimating species richness (i.e., the actual number of species present in a given area) is a basic objective of many field studies carried out in community ecology and is also of crucial concern when dealing with the conservation and management of biodiversity. In most studies, the total number of species recorded in an area at a given time is taken as a measure of species richness. Here we use a capture–recapture approach to species richness estimation with North American Breeding Bird Survey (BBS) data in order to estimate species detectability and thus gain insight about its importance. In particular, competing models making different assumptions about species detectability are available. We carried out analyses on all survey routes of four states, Arizona, Maryland, North Dakota, and Wisconsin, in two years, 1970 and 1990. These states were chosen to provide contrasting habitats, bird species composition, and survey quality. We investigated the effect of state, year, and observer ability on the propo...

Species richness in a successional grassland: effects of nitrogen enrichment and plant litter

Abstract: We conducted a field experiment in a successional grassland to investigate the short-term effects of nitrogen enrichment and plant litter on plant species richness and on the establishment of a native grass (Andropogon gerardi) that was experimentally introduced to the study site as seed. Additions of nitrogen fertilizer to experimental plots over two growing seasons increased plant production as indicated by increases in both living plant biomass and litter biomass. Increased productivity reduced species richness by effectively preventing the seedling establishment of the subordinate forb species and reduced the recruitment of Andropogon gerardi by inhibiting both germination and survival. Litter removals carried out at each of two levels of nitrogen enrichment (no nitrogen, nitrogen added) showed that litter significantly reduced species richness by the same amount in fertilized and unfertilized plots, suggesting that living biomass and litter were purely additive, rather than interactive in their effects. In contrast, the results of litter additions suggested that the declines in richness associated with fertilization could largely be due to the suppressive effects of increased litter biomass alone. As a whole, the results indicate that litter and living biomass are largely substitutable in their inhibitory effects on species richness in highly productive successional grasslands due to their independent and equivalent capacities to attenuate light to very low levels. This study highlights the combined roles of competition and plant litter in influencing the diversity of grasslands through effects on seedling establishment.

Bird abundance and diversity along an urban-rural gradient : A comparative study between two cities on different continents

Abstract: We compared the avifauna in two cities, Quebec (Canada) and Rennes (France), in order to define general responses of wildlife in an urban ecosystem. These cities have a similar urban structure that permits investigation along an urbanization gradient from downtown to rural residential areas. However, they are in opposite temperate climate and imbedded in a forested and an agricultural landscape, respectively. Plots ranging from 10 to 20 ha were surveyed in winter and spring by recording all birds seen or heard. Most plots could be located along a gradient according to proportions of vegetated open space. Both the Shannon-Wiener and Simpson indices of diversity indicated a pattern of increasing diversity from most to least urbanized areas in spring. Winter species diversity and richness was low in Quebec compared to Rennes, reflecting the much harsher winter conditions in Quebec. Breeding densities of House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris) were quite similar in Quebec and Rennes, as were densities of European Blackbirds (Turdus merula) and its ecological equivalent in Quebec, the American Robin (Turdus migratorius). The type of surrounding landscape can not explain the variation of species numbers within the city. If we examine the urban environment as a new ecological system rather than a degraded environment, we can regroup birds in two major species groups: the omnivorous species adapted to the urban environment and its particular food resources such as garbage and the species that find, in the urban environment, resources which they normally exploit in their usual habitat.

Experimental tests of effects of plant productivity and diversity on grassland arthropod diversity

Abstract: Because the quantity, quality, and heterogeneity of resources should affect the diversity of consumers, plant productivity, plant composition, and plant diversity may influence the diversity of trophic levels higher up the food chain (''bottom-up'' control of diversity). Increasing plant productivity may increase herbivore diversity by: increasing the abundance of rare resources (''resource rarity hypothesis''), increasing herbivore abun- dance and local persistence (''consumer rarity hypothesis'') or increasing intraspecific den- sity dependence (''density dependence hypothesis''). Increasing plant diversity may increase the diversity of herbivores because herbivores specialized on these new plant species can persist locally. Increasing the diversity of herbivores could likewise increase the diversity of predators and parasites, although parasite and predator diversity may also respond directly to changes in vegetation. Here I use data from a well-replicated grassland experiment at Cedar Creek, Minnesota, to analyze the responses of arthropod diversity to independent manipulations of (1) plant productivity and (2) plant diversity and composition. Long-term nitrogen addition (''historical treatment'') decreased plant diversity and favored C 3 grasses. Short-term nitrogen addition (''modern treatment'') increased plant productivity without appreciably changing plant diversity or plant composition. Arthropods were sampled using both sweep nets and vacuum samplers. Total arthropod species richness and abundance, as well as species richness and abun- dance of every trophic group (detritivores, herbivores, parasites, and predators), were sig- nificantly greater in plots with higher levels of modern fertilization and greater plant pro- ductivity. Path analysis supported the consumer rarity hypothesis, because modern fertil- ization increased herbivore species richness only indirectly by increasing herbivore abun- dance. Surprisingly, higher levels of historical fertilization that lowered plant species richness (but did not change plant productivity) significantly increased total arthropod species richness, did not affect detritivore or herbivore species richness, and significantly increased parasite and predator species richness. Direct and indirect effects of historical fertilization on the species richness of trophic groups were separated statistically using block regression chain modeling. Herbivore species richness was decreased through the direct pathway, but this was offset through indirect effects so that there was no overall response to historical fertilization. In plots with low plant diversity, similar numbers of herbivore species supported a greater diversity of parasites and predators. These results suggest that the diversity and composition of plants control the diversity of consumers not only directly by determining available resources, but also indirectly by influencing the interactions between herbivores and their parasites and predators.

Alien and native species in Central European urban floras: a quantitative comparison

Abstract: The paper provides quantitative information on the occurrence of alien species in Central European cities and analyses factors determining the richness of alien and native floras in this habitat type. Data for 54 cities (25 Polish, 24 German, 4 Czech and 1 Austrian) were gathered, and the representation of archaeophytes (i.e. aliens introduced before 1500 ad), neophytes (introduced after that date) and native species was expressed. In an average city there were 87.4 archaeophytes (15.2% of the city flora) and 172.4 neophytes (25.2%) giving a total of 259.7 for alien species (40.3%). The number of native species averaged 386.5. The numbers of species in each category of immigration status increased significantly with city size. For neophytes, the species-area relationship showed a higher slope (0.49) on log–log axes than for both archaeophytes (0.16) and native species (0.30). Not only the number, but also the relative contribution of neophytes to the total flora, increased with city size, indicating that neophytes are the group which are most closely associated with human activity. On the other hand, archaeophytes were better represented in smaller cities, as they were confined to rural environment. A step-wise multiple regression was used to test for environmental variables acting as significant predictors, and explained between 40 and 65% of variation in the species numbers for particular categories of immigration status, providing the best fit for neophytes. City size was the best predictor for each characteristic, except of the proportion of total aliens, where the percentage of explained variability was low (8.2%), with latitude being the only significant predictor. Temperature was another highly significant predictor for the number of archaeophytes and total aliens, reflecting the origin of aliens in warmer areas. There was an effect of region on some flora characteristics. Polish cities had significantly higher proportion of archaeophytes and of total aliens than German cities. It is concluded that the occurrence of native and alien species in urban floras follows rather different pattern.

Complementarity and the use of indicator groups for reserve selection in Uganda

Abstract: A major obstacle to conserving tropical biodiversity is the lack of information as to where efforts should be concentrated. One potential solution is to focus on readily assessed indicator groups, whose distribution predicts the overall importance of the biodiversity of candidate areas1,2. Here we test this idea, using the most extensive data set on patterns of diversity assembled so far for any part of the tropics. As in studies of temperate regions2,3,4,5,6,7,8, we found little spatial congruence in the species richness of woody plants, large moths, butterflies, birds and small mammals across 50 Ugandan forests. Despite this lack of congruence, sets of priority forests selected using data on single taxa only often captured species richness in other groups with the same efficiency as using information on all taxa at once. This is because efficient conservation networks incorporate not only species-rich sites, but also those whose biotas best complement those of other areas9,10,11. In Uganda, different taxa exhibit similar biogeography, so priority forests for one taxon collectively represent the important forest types for other taxa as well. Our results highlight the need, when evaluating potential indicators for reserve selection, to consider cross-taxon congruence in complementarity as well as species richness.

Taxonomic distinctness and environmental assessment

Abstract: The objectives of this paper are to test the performance of the taxonomic distinctness index, δ+, in a number of environmental impact scenarios, to examine its relationship with functional diversity and to examine the influence of habitat type and diversity on the index. The index was applied to data on free-living marine nematodes from the coasts of Britain and Chile. The taxonomic distinctness of nematodes from environmentally degraded locations was generally reduced in comparison with that of more pristine locations, often significantly so. Some habitat types may have naturally lower values of taxonomic distinctness than others. However, unless the habitats are degraded in some way the δ+ values do not generally fall below the lower 95% confidence limit of the simulated distribution under a null hypothesis that the assemblages behave as if they are a random selection from the regional species pool. This ameliorates the problem encountered with species richness measures of biodiversity, which are much more strongly affected by habitat type and complexity, thus making comparisons difficult between data sets from different habitats or where habitat type is uncontrolled. Taxonomic distinctness in marine nematodes is shown to be related to trophic diversity: a reduction in trophic diversity will lead to a reduction in taxonomic distinctness, although not necessarily to a reduction in species richness. Trophic composition itself is clearly affected by pollution, but is also strongly responsive to the major influence of habitat type. These features of the taxonomic distinctness index, coupled with its lack of dependence on sampling effort or differences in taxonomic rigour between workers and a statistical framework for the assessment of the significance of departure from expectation, suggest that it may prove to be a biologically and ecologically relevant measure of biodiversity. This paper demonstrates that the taxonomic distinctness index has a number of theoretical and logistical advantages over measures of species richness for the purposes of environmental assessment.

Beetle species responses to tropical forest fragmentation

Abstract: The effects of forest fragmentation on beetle species composition were investigated in an experimentally fragmented tropical forest landscape in Central Amazonia. Leaf-litter beetles were sampled at seven distances from the forest edge (0–420 m) along forest edge-to-interior transects in two 100-ha forest fragments and two continuous forest edges, and at an identical series of distances along two deep continuous forest transects. Additional samples were taken at the centers of two 10-ha forest fragments and two 1-ha fragments. This sampling regime allowed discrimination between edge and fragment area effects. Beetle species composition changed significantly and independently with both decreasing distance from forest edge and decreasing fragment area. Edge effects on species composition were mediated by six important environmental variables: air temperature, canopy height, percent ground cover of twigs, litter biomass, litter moisture content, and an air temperature × distance from edge interaction effect, due to the different temperature profiles of edges with differing edge vegetation density. Population densities of 15 of the 32 most abundant beetle species tested (47%) were significantly affected by forest fragmentation. Species responses were classified empirically into four major categories: (A) edge sensitive, area insensitive; (B) area sensitive, edge insensitive; (C) edge and area sensitive; and (D) edge and area insensitive. Within these categories, trends in density were either positive (deep-forest species), or negative (disturbed-area species), with species showing the full spectrum of responses to fragmentation. The vast majority of species were adversely affected. Estimated species loss rates from forest fragments were: 49.8% of common species from 1-ha fragments, 29.8% from 10-ha fragments, and 13.8% from 100-ha fragments. Declining density was a significant precursor of species loss from forest fragments, but other species that did not show significant population density responses to fragmentation were also absent from some fragments, presumably by chance. The probability of species loss from forest fragments was not correlated with body size or trophic group for the 32 common species, although for the entire beetle assemblage (993 species) proportions of species in different trophic groups changed significantly with fragmentation. Rarity and population variability (in undisturbed forest) were significant predictors of susceptibility to fragmentation. Surprisingly, though, common species were significantly more likely to become locally extinct in small fragments than rarer species. This lends empirical support to models of multispecies coexistence under disturbance that suggest competitively dominant but poorly dispersing species are the first to become extinct due to habitat destruction. Thus, rarer species are predicted to be better dispersers and better at persisting.

Phylogeny and classification of neotropical fishes

Abstract: This chapter describes the species richness and phylogenetic relationships among the Neotropical freshwater fish, emphasizing the main diagnostic characteristics of each group. Both themes are effervescent, involving studies and discussions that require constant updates. They also face a high rate of descriptions of new species and new relationship hypotheses. In this chapter, we provide a picture of the knowledge available through early 2018, and we suggest that readers use it to search for updated information.

Water-energy dynamics, climate, and prediction of woody plant species richness: an interim general model

Abstract: Predictable geographic patterns in the distribution of species richness, especially the latitudinal gradient, are intriguing because they suggest that if we knew what the controlling factors were we could predict species richness where empirical data is lacking (e.g. tropics). Based on analyses of the macro-scale distribution of woody plant species richness in Southern Africa, one controlling factor appears to be climate-based water-energy dynamics. Using the regression models of climate's relationship to species richness in Southern Africa, I was able to describe an Interim General Model (IGM) and to predict first-order macro-scale geographic variations in woody plant species richness for the continent of Africa, as well as elsewhere in the world—exemplified using South America, the United States and China. In all cases, the geographic pattern of variation in species richness is in accord with geographic variations in vegetation (visual comparison with vegetation maps) and net primary productivity. What validation was possible (Africa and U.S.A.) suggests that the IGM provides ‘reasonable’ estimates for actual woody plant species richness where species richness is in relative equilibrium with climate. Areas of over- or under-prediction support the contention of earlier workers that edaphic, topographic, historical, and dispersal factors need to be considered in a more complete explanation for spatio-temporal variations in species richness. In addition to providing a means for systematically estimating woody plant species richness where present-day empirical data is lacking, the Interim General Model may prove useful for modelling the effects of climate change (past/future) on species richness (and, by association, the vegetation).

Bioindication using trap-nesting bees and wasps and their natural enemies: community structure and interactions

Abstract: 1. Results from four field studies show that communities of trap-nesting bees and wasps and their natural enemies are promising bioindicators for ecological change or habitat quality. These small and easy-to-handle communities can be analysed with respect to (i) species richness and related parameters, and (ii) ecological functions or interactions. The communities comprise Hymenoptera (Apidae, Sphecidae, Eumenidae, Pompilidae) and natural enemies belonging to many insect taxa. Traps consisted of 150–200, 15–20-cm long, reed internodes, put into tins or plastic tubes of 13–15 cm diameter; wooden posts with 2–10 of such reed-filled tins were exposed in the target habitat. 2. Species richness and abundance of bees (but not wasps) were closely related to plant species richness of the habitat, a measure of the bees’ food resource. However, availability of nest sites of above-ground nesting species was equally important: meadows with old trees supported greater populations than meadows without trees. A threefold increase in exposed traps resulted in a twofold increase in species. 3. The sensitivity of this bioindicator system profits from the fact that evaluations rely not only on presence/absence data, descriptive population attributes or diversity indices, but also on interactions or ecological functions. Monitoring ecological responses or multitrophic interactions, and their relationship to species diversity, is rarely done but much needed. Ecological functions include (i) the percentage mortality of trap-nesting bees and wasps due to parasitoids and predators, which was correlated with the species richness of these natural enemies; (ii) seed set of allogamous plants due to successful pollination by trap-nesting bees; and (iii) biological control by the predacious wasps. 4. With increasing isolation of fragmented habitats (when traps were exposed in a cleared agricultural landscape), both species richness of natural enemies and percentage mortality (parasitism and predation) declined significantly. In a comparison of habitat types (grasslands and field margins), species richness of the trap-nest community correlated with plant diversity, but percentage mortality, due to parasitism and predation, with field age only. The threshold distance to the nearest habitat was 106–530 m for a 10–50% decrease in mean mortality, and the mortality increased greatly in habitats that were older than 5 years. Accordingly, these studies emphasize the significance of a continuum of old habitat patches for the augmentation of natural enemies. 5. Exposure of standardized traps is an experimental approach with a small, interacting and reproducing community that can be easily characterized by simple parameters. Taxonomy and biology are well known, and quick evaluations can be done using the close correlation between the number of occupied traps and species richness. Species richness of trap-nesting bees and wasps was closely correlated with that sampled by sweep nets. Further criteria of indicator taxa that apply to this system are discussed in the text.

Altitudinal gradients in tropical forest composition, structure, and diversity in the Sierra de Manantlán

Abstract: 1 Data on the composition, structure and diversity of plant communities were gathered along a 1000-m altitudinal transect from tropical seasonal dry forest to cloud forest on calcareous Cerro Grande in Jalisco, Mexico. 2 A total of 470 species, 292 genera and 103 families of vascular plants occurred in 43 samples of 0.1 ha, stratified at 100-m elevational intervals between 1500 and 2500 m a.s.1. There were 97 tree species, 76 shrubs, 70 vines, 181 terrestrial herbs, 39 epiphytes, 3 hemiparasites, 3 succulent rosette shrubs and 1 saprophyte. 3 Forest composition varied continuously with altitude, based on the Shipley & Keddy (1987) test, ordination via reciprocal averaging, and elevational trends in the Sorenson similarities of samples at adjacent altitudes. supporting the individualistic hypothesis of plant community organization. 4 Understorey herbs, shrubs and vines showed the greatest decline in species number with increasing altitude. This pattern is hypothesized to result from the more open, more frequently disturbed, and more completely deciduous canopies at lower, drier elevations. The proportion of evergreen woody plants was greater at higher altitudes, reflecting less seasonal aridity and greater soil leaching. The proportion of endozoochorous species increased with altitude, while the proportion of pterochorous and ectozoochorous species decreased, reflecting trends in the hypothesized efficacy of these mechanisms of seed dispersal. 5 Total basal area of woody plants > 2.5 cm d.b.h. and basal area per tree both increased roughly fourfold between 1500 and 2500 m. 6 Species richness decreased sharply with altitude, due mainly to decreases in terrestrial herbs, and (to a lesser extent) shrubs and vines. The average number of species per 0.1 ha declined from 134 at 1500 m to 43 at 2500 m. The numbers of species, genera and families per sample declined linearly with elevation. Species composition of samples within an altitudinal band showed greater horizontal turnover (β diversity) at lower elevations, showing that low-elevation forests are not only locally more diverse, but spatially more patchy. Community composition varies roughly six times as rapidly with elevation as with the same distance horizontally. 7 A cascading series of effects of elevation on soil fertility, anti-herbivore defences, and the level of density-dependent mortality may account for the observed drop in diversity with elevation, and would be consistent with lower β diversity and greater basal area at higher elevations.

Biodiversity Assessment and Conservation Strategies

Abstract: The efficient representation of all species in conservation planning is problematic. Often, species distribution is assessed by dividing the land into a grid; complementary sets of grids, in which each taxon is represented at least once, are then sought. To determine if this approach provides useful surrogate information, species and higher taxon data for South African plants and animals were analyzed. Complementary species sets did not coincide and overlapped little with higher taxon sets. Survey extent and taxonomic knowledge did not affect this overlap. Thus, the assumptions of surrogacy, on which so much conservation planning is based, are not supported.

The role of complementarity and competition in ecosystem responses to variation in plant diversity

Abstract: To investigate how plant diversity affects ecosystem-level processes such as primary production and nutrient cycling, I established an experimental plant diversity gradient in serpentine grassland using four functional groups of plants: early season annual forbs (E), late season annual forbs (L), perennial bunchgrasses (P), and nitrogen fixers (N). These groups differ in growth form, phenology, and other traits relevant to nutrient cycling (e.g., rooting depth, litter C:N ratio). Two or three species of each type were planted in single-group treatments, and in two-, three-, and four-way combinations, giving a range of richness from zero to nine species. I tested the hypothesis that, because of complementary resource use, increasing functional group diversity will lead to higher net primary production. At the scale of this experiment (α-diversity and yearly production), more diverse treatments were not necessarily the most productive. Live plant biomass varied more within than among levels of diversity. In most two-, three-, and four-way mixtures of functional groups, overall productivity did not differ significantly from the average of the yields of component one-group treatments. This pattern apparently resulted from competition: early season annuals and late season annuals reduced the biomass of perennial bunchgrasses (the most productive group in monoculture) below levels expected from monoculture yields. Relative Yield Totals (RYT) indicated complementary resource use in the EL and LP two-way and ELPN four-way mixtures. In the EL mixture, complementarity appeared to result from temporal rather than spatial partitioning of resources. Because of shifts in root:shoot ratio in mixtures, however, only the LP treatment had consistently significant RYT >1 when assessing total (roots plus shoots) productivity and nitrogen yield. These results show that (1) composition (the identity of the species present) can be at least as important as richness (the number of species present) in effects on ecosystem processes; (2) competition during critical parts of the growing season may prevent absolute increases in net primary production with increasing diversity, despite complementary resource use at other times of the year; and (3) shifts in belowground allocation in species mixtures can have significant effects on estimates of productivity and resource use as species diversity changes.