Habitat Simplification Research Articles

Why should the habitat-level approach underpin holistic river survey and management?

1. The UK's new River Habitat Survey (RHS) is founded upon the assumption that species depend upon habitats and that higher habitat heterogeneity supports higher biodiversity in river channels, riparian zones and floodplains. 2. The paper reviews the evidence for this assumption. Physical habitats—of substrate and velocity conditions—are created by predictable physical forces acting within the river ‘continuum’, modified by colonization and metabolism of biota. Numerous studies have shown that habitats have distinct biotic assemblages. 3. River management has, in the past, generally simplified habitat structure but, in order to mitigate the worst effects and restore damaged rivers, it is necessary to have a sound understanding of this term as it applies to all components of the river system (channel, riparian zone and floodplain). 4. RHS has a nested approach to river channel habitats and at one level, ‘functional habitats’, the link between river processes and river biodiversity has been demonstrated. ‘The functional habitats’ concept is now used in river management for mitigation of engineering channel works and restoration of drought-damaged rivers. 5. Similar nested approaches still need to be developed in the riparian zone and river-influenced floodplain. Sustainable river management needs to come to terms with the dynamic nature of river habitat change as well as to quantify the economic benefits which habitats provide. © 1998 John Wiley & Sons, Ltd.

Effects of Sampling Area and Subsampling Procedure on Comparisons of Taxa Richness among Streams

the biotic integrity of communities. In all cases, we make the implicit and sometimes brash assumption that we can really measure the number of taxa in a community. Although measuring taxa richness might appear straightforward, accurate measurement has been extraordinarily difficult; and despite years of effort, no universally accepted methods for its measurement have emerged. The essential problem is that we can never completely census a taxonomic assemblage or entire community; we rely instead on estimates that describe some portion of the real taxa richness of an assemblage. The problem of knowing what percent of the taxa present have been collected is exacerbated when investigators fail to explicitly define their universe of interest (i.e., the spatial bounds of the community or communities in question). Comparisons of taxa richness among studies that used different sampling and subsampling methods are especially difficult and should be viewed skeptically. The difficulty of obtaining accurate measurements of richness is due to the collector's curve

Impact of commercial forest management on geophilous carabid beetles (Coleoptera: Carabidae) in tall, wet Eucalyptus obliqua forest in southern Tasmania

Abstract The impact of silvicultural practices (clearfelling, slash burning and sowing) on carabid beetle communities in tall wet Eucalyptus obliqua forests in southern Tasmania was examined using traplines of pitfalls in a chronosequence of regenerating coupes. Total species richness (n= 18) was modest compared to other temperate forests and was not systematically changed by forest management, although it was considerably lower in 20 year old regrowth than in younger regrowth or old‐growth controls, possibly due to habitat simplification. The Shannon‐Weiner Index was at a minimum in intermediate aged regeneration. TWINSPAN analysis assisted recognition of beetle communities typical of broad stages in the forest succession, with a major dichotomy between most old‐growth sites plus young sites and intermediate plus advanced regeneration sites. Vector fitting of environmental variables in an ordination of the sites by non‐metric multidimensional scaling revealed a significant influence for the age of regeneration and litter depth, but not bare ground percentage or soil pH. Survival of carabids in the habitat mosaic created by commercial forestry activity is likely to depend on both reinvasion from edges and survival of individuals in the fire‐protected refuges that exist within the coupes. Pioneer species were winged, small in size, and non‐endemic whereas the opposite was true of the fauna in the older sites. Carabids in eucalypt forests have good potential as indicators but their seasonality in occurrence demands that sampling be extended over most of the year.

A pest is a pest is a pest? The dilemma of neotropical leaf-cutting ants: Keystone taxa of natural ecosystems

Leaf-cutting ants of the generaAcromyrmex andAtta are considered the principal polyphagous pests of the Neotropics Although some members of these genera are of economic importance, have a broad geographic distribution, and are extremely good colonizers, others are endemic and closely interact with native ecosystems. Control is generally practiced against any colony, irrespective of its taxonomic status. Indiscriminate control coupled with habitat destruction threatens endemic species with extinction, and, through habitat simplification, favors other pest species. As nests ofAtta are large, having several square meters of nest surface, the endemic taxa can be easily used as environmental indicators for natural ecosystems Likewise, the pest species can be used to detect environmental disturbance As these ants are keystone species and easily identified by nonspecialists, efforts should be made to integrate these into viable conservation programs