Species richness

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

Biogeographic Evolution of Madagascar's Microendemic Biota

Abstract: The endemic species richness on Madagascar, relative to landmass area, is unparalleled in the world. Many organisms on the island have restricted geographical ranges. A comprehensive hypothesis explaining the evolution of this microendemism has yet to be developed. Using an analysis of watersheds in the context of Quaternary climatic shifts, we provide a new mechanistic model to explain the process of explosive speciation on the island. River catchments with sources at relatively low elevations were zones of isolation and hence led to the speciation of locally endemic taxa, whereas those at higher elevations were zones of retreat and dispersion and hence contain proportionately lower levels of microendemism. These results provide a framework for biogeographic and phylogeographic studies, as well as a basis for prioritizing conservation actions of the remaining natural forest habitats on the island.

Ecological limits and diversification rate: alternative paradigms to explain the variation in species richness among clades and regions.

Abstract: Diversification rate is one of the most important metrics in macroecological and macroevolutionary studies. Here I demonstrate that diversification analyses can be misleading when researchers assume that diversity increases unbounded through time, as is typical in molecular phylogenetic studies. If clade diversity is regulated by ecological factors, then species richness may be independent of clade age and it may not be possible to infer the rate at which diversity arose. This has substantial consequences for the interpretation of many studies that have contrasted rates of diversification among clades and regions. Often, it is possible to estimate the total diversification experienced by a clade but not diversification rate itself. I show that the evidence for ecological limits on diversity in higher taxa is widespread. Finally, I explore the implications of ecological limits for a variety of ecological and evolutionary questions that involve inferences about speciation and extinction rates from phylogenetic data.

Importance of spatial scale to habitat use by breeding birds in riparian forests: a hierarchical analysis

Abstract: Patterns of habitat use by breeding birds were studied in cottonwood riparian forests along 100 km of the South Fork of the Snake River in southeastern Idaho, United States, from 1991 to 1994. A hierarchical approach was used to examine habitat use at three spatial scales: microhabitat (local vegetation characteristics), macrohabitat (cottonwood forest patch characteristics), and landscape (composition and patterning of surrounding [matrix] vegetation types and land uses). This paper addresses a series of predictions about species’ distributions that incorporate the different spatial scales. Bird distribution and abundance and vegetation data were collected on 57 cottonwood forest patches ranging in size from 0.40 ha to 205 ha. The surrounding landscape changed from a valley surrounded by mountains, on the upstream end of the study area, to a narrow canyon adjacent to natural upland vegetation in the middle section, and to a wide, open floodplain dominated by agriculture on the downstream end. The best predictors of high species richness (r2 = 0.71) were natural and heterogeneous landscapes, large cottonwood patches, close proximity to other cottonwood patches, and microhabitats with relatively open canopies. Distribution and frequency of occurrence were evaluated for 32 species of small land birds. The most frequent significant predictor of species occurrence was the landscape component: increases in upland natural vegetation with decreases in agriculture. Both interior and edge specialists were found in arid land, cottonwood riparian forests that are linear in nature, with large amounts of edge. Nest predators, brood parasites, and exotic species responded positively to human-altered landscapes. Landscape patterns were the primary influence on distribution and occurrence of most bird species, whereas macrohabitat and microhabitat were of secondary importance. Thus, surrounding landscape (matrix) features should be a primary consideration for selecting riparian reserve areas.

Host specificity of Lepidoptera in tropical and temperate forests

Abstract: For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15 degrees S to 55 degrees N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater beta diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.

Impacts of alien plant invasions on species richness in Mediterranean-type ecosystems: a meta-analysis

Abstract: Besides a general consensus regarding the negative impact of invasive alien species in the literature, only recently has the decline of native species attributable to biological invasions begun to be quantifi ed in many parts of the world. The cause-effect relationship between the establishment and proliferation of alien species and the extinction of native species is, however, seldom demonstrated. We conducted a meta-analysis of studies in Mediterranean-type ecosystems (MTEs) to examine: (1) whether invasion of alien plant species indeed causes a reduction in the number of native plant species at different spatial and temporal scales; (2) which growth forms, habitat types and areas are most affected by invasions; and (3) which taxa are most responsible for native species richness declines. Our results confi rm a signifi cant decline in native species richness attributable to alien invasions. Studies conducted at small scales or sampled over long periods reveal stronger impacts of alien invasion than those at large spatial scales and over short periods. Alien species from regions with similar climates have much stronger impacts, with the native species richness in South Africa and Australia declining signifi cantly more post-invasion than for European sites. Australian Acacia species in South Africa accounted for the most signifi cant declines in native species richness. Among the different growth forms of alien plants, annual herbs, trees and creepers had the greatest impact, whereas graminoids generally caused insignifi cant changes to the native community. Native species richness of shrublands, old fi elds and dune vegetation showed signifi cant declines, in contrast to insignifi cant declines for forest habitats.