Testing large‐scale hypotheses using surveys: the effects of land use on the habitats, invertebrates and birds of Himalayan rivers

Abstract

Summary1. Piecemeal changes in land use might have cumulative eects on regional biodiversity. However, this hypothesis is dicult to test experimentally at the scales involved, so alternative approaches are required. Here, we illustrate some of the strengths and weaknesses of surveys for evaluating the eects of land use on rivers and river birds over a large area of the Himalayan mountains. 2. We surveyed 180 streams and their catchments in north-west India and Nepal in 1994±96. We then used analysis of covariance (ANCOVA), multiple linear regression and multiple logistic regression to assess how stream habitat structure, stream chemistry, aquatic invertebrate abundance and the occurrence of river birds were aected by land use after accounting for altitudinal pattern. 3. Streams draining terraced catchments diered signi®cantly in habitat structure from other streams. They had more physical modi®cations, wider channels, fewer cascades, ®ner substrata and simpler riparian vegetation with fewer trees. We detected no clear eects of land use on stream chemistry, but terracing was accompanied by signi®cantly increased abundances of benthic dipterans, ephemeropterans and total aquatic invertebrates. 4. River bird occurrence was best explained by altitude, and secondarily by habitat structure. Some of the habitat features in¯uenced by terracing signi®cantly aected birds both positively (grey wagtail Motacilla cinerea) and negatively (little forktail Enicurus scouleri, river chat Chaimarrornis leucocephalus, brown dipper Cinclus pallasii, plumbeous redstart Rhyacornis fuliginosus). However, only in the grey wagtail did the presence of terracing per se aect occurrence unequivocally; eects on other species were either small or confounded by altitude. 5. We cannot refute the hypothesis that catchment land use aects Himalayan river ecology, but our data on the regional consequences for river birds were equivocal. We suggest that large-scale surveys, although providing one of the few pragmatic methods of assessing large anthropogenic eects on ecosystems, will need careful design to factor out potential confounds if they are to be used to test hypotheses robustly. They should also be supported where possible with process studies, intervention studies and model applications to independent data.

Generalized linear and generalized additive models in studies of species distributions: setting the scene

“…Examples include the use of regression analyses to predict the distribution of tree and shrub species (Austin et al, 1983(Austin et al, , 1990Lenihan, 1993;Franklin, 1998;Guisan et al, 1999), of herbaceous species (Guisan et al, 1998;Guisan and Theurillat, 2000), of aquatic plant species (Lehmann, 1998), of terrestrial animal species (Pereira and Itami, 1991;Augustin et al, 1996;Manel et al, 1999;Guisan and Hofer, 2001;Jaberg and Guisan, 2001;Zimmermann and Breitenmoser, 2002), of birds (Manel et al, 1999(Manel et al, , 2000, of aquatic animal species (invertebrates; Manel et al, 2000), of plant communities (Zimmermann and Kienast, 1999), or of structural vegetation types (Brown, 1994;Frescino et al, 2001). At a higher level of complexity, these approaches have also been used to investigate the distribution of plant (Currie and Paquin, 1987;Margules et al, 1987;Pausas, 1994;Heikkinen, 1996;Wohlgemuth, 1998) and animal diversity (Owen, 1989;Currie, 1991;Fraser, 1998).…”

Habitat preferences of breeding Water RailRallus aquaticus

“…We aim to explain the distribution and abundance of Water Rail by investigating potential food availability and habitat characteristics at the site level. The survey, undertaken on a regional scale, is typical of the type of ecological research required to examine large-scale hypotheses while contributing profitably to environmental management (Ormerod et al 1999, Manel et al 2000.…”

Exploring the links between natural resource use and biophysical status in the waterways of the North Rupununi, Guyana

“…Modified versions of the RHS have been used in a number of countries to assess river systems and to assess the relationship of land use change amongst habitats, invertebrates and birds (e.g. Manel et al, 2000). RHSs were taken of all water bodies identified by the Makushi as being important for fisheries.…”