Species richness

About: Species richness is a research topic. Over the lifetime, 61672 publications have been published within this topic receiving 2183796 citations.

The intermediate disturbance hypothesis, refugia, and biodiversity in streams

Abstract: The intermediate disturbance hypothesis has been influential in the development of ecological theory and has important practical implications for the maintenance of biodiversity but has received few rigorous tests. WC tested the hypothesis that maximum taxon richness of macroinvertebrates will occur in communities subject to intermediate levels of disturbance at 54 stream sites that differed in the frequency and intensity of flood-related episodes of bed movement. Our results support the intermediate disturbance hypothesis, with both highly mobile and relatively sedentary taxa conforming to the predicted bell-shaped curve. Taxon richness was not related to habitat area (stream width), distance from the headwater, or the diversity of microhabitats (particle size categories) but was significantly and negatively related to the proportion of the substratum made up of small particles. Of all the factors measured, however, bed disturbance was by far the best at accounting for variation in taxonomic richness. We also quantified several kinds of potential refugia for invertebrates and found a positive relationship between richness and a refugia axis that combines amount of dead space with proportion of large substratum particles. The intermediate disturbance hypothesis, whose genesis can be traced back to Hutchinson (1953) and Horn (1975), was proposed by Connell (1978) to account for patterns of diversity in tropical rainforests and coral reefs. It has occupied a central place in the development of ecological theory because all communities are subject to disturbances that exhibit different frequencies and intensities. It also has important practical implications for the maintenance of biodiversity, of which species richness (the number of species present) is the most basic component. The hypothesis is based on the argument that ecological communities seldom reach an equilibrium state, in which the competitively superior species exclude others, because disturbances that kill or damage individuals will continually set back the process of competitive elimination by opening space for colonization by less competitive individuals. For this idea to work, there must be a trade-off between species’ colonizing ability and competitive ability, and the habitat must be patchy and dynamic (Wilson 1994). At one extreme, patches that are frequently and/or intensely disturbed are expected to exhibit low species richness because few species are able to colonize during the brief periods between disturbances or tolerate the high intensities of their impact. At the other end of the scale, patches in which disturbances are infrequent and/or of low

Patterns of plant species richness in relation to different environments: An appraisal

Abstract: We review patterns of plant species richness with respect to variables related to resource availability and vari- ables that have direct physiological impact on plant growth or resource availability. This review suggests that there are a variety of patterns of species richness along environmental gradients reported in the literature. However, part of this diversity may be explained by the different types and lengths of gradients studied, and by the limited analysis applied to the data. To advance in understanding species richness pat- terns along environmental gradients, we emphasise the im- portance of: (1) using variables that are related to the growth of plants (latitudinal and altitudinal gradients have no direct process impact on plant growth); (2) using multivariate gra- dients, not single variables; (3) comparing patterns for dif- ferent life forms; and (4) testing for different shapes in the species richness response (not only linear) and for interaction between variables.

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...

Hydrologically defined niches reveal a basis for species richness in plant communities

Abstract: Species-rich plant communities are prized repositories of biodiversity and a dwindling resource, but how the large numbers of species that characterize such communities are able to coexist is poorly understood. Resource-based competition theory predicts that stable coexistence between species depends on each being a superior competitor in its own niche1. The theoretical problem is that plants all require the same resources and acquire them in a very limited variety of ways, so observed niche overlaps are high2,3 and exclusion of all but the best competitor is the predicted result. This problem, central to community ecology, has elicited a variety of theoretical solutions4,5,6,7, several of which invoke some degree of niche separation in time or space8,9. The signature of niche separation in the field is to be found in community structure, which should indicate (i) smaller than expected niche overlaps on relevant niche axes and (ii) a trade-off between species' resource use on orthogonal axes. Here we provide evidence for the existence of both these conditions in a species-rich plant community.

Designing a Cost‐Effective Invertebrate Survey: A Test of Methods for Rapid Assessment of Biodiversity

Abstract: We investigated three procedures that may lead to rapid and accurate assessment of epigaeic arthropod biodiversity. They are: (1) the identification of taxa whose diversity is correlated with that of others: (2) the identification of times and methods of sampling that produce estimates of diversity representative of more intensive sampling; and (3) the use of morphospecies inventories generated by non-specialists. Ants, beetles, and spiders were sampled from four forest types, in three seasons, using two collecting methods: pitfall trapping and extraction from litter. Specimens were sorted by a non-specialist to morphospecies and by specialist taxonomists to species. Richness (α-diversity) and turnover (β-diversity) were compared for different sampling regimes using morphospecies and species inventories. We found no significant positive correlations between ant, beetle, and spider species richness but there was a strong negative correlation between ant and beetle richness. For beetles alone, richness within the families Carabidae, Scarabaeidae, and Pselaphidae (i.e, avoiding taxonomically problematic families) was significantly correlated with richness within all other families. Assessment of turnover revealed that: (1) the four forest types contained significantly different assemblages of ants and beetles but not spiders and 92) the four forests were less clearly discriminated using species from the three beetle families Carabidae, Scarabaeidae, and Pselaphidae when compared to species from all beetle families pooled. Analyses of single sampling periods and methods revealed that summer and spring pitfall samples were most representative of more intensive sampling. That is: (1) the richness of ants and beetles in these samples was significantly positively correlated with the richness of all other samples and 92) turnover of beetles and ants among the four forests revealed by summer pitfall samples was similar to turnover using all samples. The three beetle surrogate families recorded by pitfall samples in spring, and to a lesser extent summer, showed significant correlations in richness with all other beetle species recorded in the same samples. However, the assessment of turnover was less accurate when only surrogate families were used. The most accurate and cost-effective assessment of turnover was generated by a summer pitfall sample in which data for ants, carabid, and scarab beetles were combined and analyzed as a single data set. Results were largely consistent regardless of whether species or morphospecies were used, which suggests that monitoring and assessment of terrestrial invertebrate biodiversity may be achieved by the careful use of morphospecies. Our results also suggest those invertebrate taxa, sampling methods, and sampling periods that yield the most consistent and reliable assessment of epigaeic invertebrate biodiversity in Australian temperate hardwood forests. However, empirical studies that follow the protocols discussed in this paper are urgently required in different environments. These studies may point the way to more representative monitoring and assessment of terrestrial biodiversity.