Species richness

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

Testing a non-equilibrium model of rangeland vegetation dynamics in Mongolia

Abstract: Summary 1. Few studies have tested the applicability of current non-equilibrium models of rangeland vegetation dynamics to a particular ecosystem, or across a range of systems that might be expected to respond differently to grazing. This study assessed the extent to which the non-equilibrium persistent (NEP) model of rangeland vegetation dynamics applies to three distinct Mongolian rangeland ecosystems, the desert-steppe, steppe and mountain-steppe. 2. Standing biomass, vegetation cover and composition, and species richness and diversity were examined along grazing pressure gradients in ecological zones of differing productivity and interannual variability in precipitation. 3. In the desert-steppe, biomass, functional group cover, richness and diversity did not vary along grazing pressure gradients, but all vegetation variables except the cover of weedy annuals and unpalatable forbs varied significantly between years. Vegetation dynamics in this zone largely conformed to the NEP model of rangeland dynamics. 4. In the mountain-steppe, grass and total biomass, total vegetative cover, the cover of grasses, weedy annuals and unpalatable forbs, and richness and diversity varied along grazing pressure gradients. With increasing grazing pressure, grasses decreased and forbs and weedy annuals increased, as the conventional range condition (RC) model predicts. Interannual variation in precipitation influenced total vegetative cover, species and functional group cover, and richness and diversity. 5. In the steppe, forb biomass, grass, forb, unpalatable forb and weedy annual cover, and diversity varied along grazing pressure gradients. Grass biomass and total vegetative cover responded interactively to rainfall and grazing. Forb biomass, grass, forb and weedy annual cover and richness varied between years. Grasses decreased and forbs and weedy annuals increased with increasing grazing pressure, conforming to the RC model. 6. Ecosystem response to rainfall and grazing is complex, and interpretation of the response depends on the specific variables examined. The recent paradigm shift in rangeland science from the RC model to non-equilibrium models has been embraced with such enthusiasm by some that the concept of non-equilibrium rangelands may be as much in danger of being misapplied as equilibrium-based models have been.

Geographical Trends in Numbers of Species

Abstract: Geographic variation in the number of coexisting plant and animal species (species density) often follows repeated patterns; best known is the general increase in species richness from temperate to tropical latitudes. Here we undertake a quantitative analysis of geographic trends in species density for the terrestrial vertebrate faunas of the United States and Australia. Trends in numbers of species of amphibians, reptiles, birds, and mammals are described and are correlated with geographic variation in abiotic environmental measures. Intercontinental comparisons reveal general patterns as well as intriguing and profound differences in vertebrate distributions.

Native Invasions, Homogenization, and the Mismeasure of Integrity of Fish Assemblages

Abstract: Human activities, particularly habitat destruction and species introductions, are resulting in increased homogenization of once unique biogeographic regions. In the southeastern United States, extensive endemism occurs among highland fish species that have specialized ecologies, are adapted to cool, clear, nutrient-poor conditions, and are sediment-intolerant. Highland streams flow into lower elevation systems, which are often inhabited by more widespread, generalist fish species adapted to warmer, more turbid, fine-sediment-rich, and nutrient-rich conditions. Common land use practices, such as deforestation, degrade stream habitats and reduce habitat diversity, which is often correlated with taxonomic and ecological diversity. Habitat homogenization can thus cause assemblage homogenization via loss of native species and addition of nonindigenous species. However, midpoints in the homogenization process may be characterized by constant or even increased species diversity because generalist, sedim...

Disturbance, habitat structure, and the dynamics of a coral-reef fish community

Abstract: Coral reef fishes occupy habitats that are patchy and subject to frequent natural disturbances. Although different types of disturbance are likely to generate different community responses, the relationship between different disturbance agents and their effects on reef fish communities has not been examined experimentally. We studied a set of natural patch reefs, dominated by a diverse array of soft and hard coral cover, at Lizard Island on the Great Barrier Reef (northeastern Australia). The fish assemblages on the reefs were sampled over 4 mo to establish baseline values and then experimentally disturbed. Two types of disturbance were carried out in a factorial combination: pulsed mortality by removing all fish from reefs and pulsed habitat disturbance. Habitat disturbance was applied at two levels: Level 1 consisted only of damaging all live hard corals with a hammer; Level 2 consisted of damaging all live hard corals, and in addition, using a hammer to reduce the height and complexity of the reef matrix. We then monitored the experiment for a further 19 mo, including two recruitment seasons. Unmanipulated control assemblages persisted through time, and despite large changes in total abundance, species composition remained consistent relative to disturbed treatments. Assemblages disturbed by fish removal were resilient, with recolonization from both immigration and larval settlement effectively removing differences between removal treatments and controls 3 mo after manipulation. Habitat disturbance alone generated differences between experimental and control assemblages, which persisted for the duration of the experiment. The more extreme level of habitat disturbance generated more extreme changes in fish assemblages when no pulsed mortality occurred. Habitat disturbance in combination with pulsed mortality generated similar community responses as the habitat disturbance treatment alone. However, fish removal had the effect of eliminating the difference between fish assemblages on reefs subjected to different levels of habitat disturbance. Community response to habitat disturbance was driven by species-specific patterns of reduced abundance of species associated with live coral in combination with increased numbers of those associated with rubble. Declines in the abundance of coral associates on damaged reefs were abrupt, with no recovery observed for the duration of the experiment. In contrast, increases in the abundance of rubble associates were more ephemeral, in that initial high levels of recruitment and immigration were followed by a high rate of loss. Habitat disturbance also generated reefs that typically supported lower fish abundance, fewer species, and increased evenness relative to controls. Our results support a model of patch-reef fish assemblages organized by a combination of deterministic factors (such as habitat structure) and stochastic processes (such as recruitment). These disparate mechanisms operate in concert to generate reasonably consistent patterns of community structure. Habitat structure appears to mediate much of the apparent determinism and is likely to operate both as a reflection of species-specific habitat preferences and by modifying interactions among fish species. Consequently, disturbance plays a substantial role in structuring communities of coral-reef fishes by modifying both spatial and temporal heterogeneity.

Hymenoptera and biodiversity.

Abstract: Hymenoptera: their diversity, and their impact on the diversity of other organisms intraspecific biodiversity in Hymenoptera: implications for conservation and biological control threats to the diversity of solitary bees in a neotropical dry forest in Central America effects of increasing land utilization on species representation and diversity of aculeate wasps and bees in the semi-arid areas of southern Africa comparison of the arboreal ant mosaic in Ghana, Brazil, Papua New Guinea and Australia - its structure and influence on arthropod diversity bees, pollination systems, and plant diversity diversity of native bees and agro-ecosystems parasitic Hymenoptera, biological control and biodiversity parasitoid webs refuges, host population dynamics and the genesis of parasitoid diversity the role and enhancement of parasitic Hymenoptera biodiversity in agro-ecosystems spatial patterns in the description and richness of the Hymenoptera what does tropical society want from the taxonomist? measuring biodiversity for choosing conservation areas Costa Rica: an example for the study of tropical biodiversity.