Showing papers by "Stephen E. Williams published in 2006"

Novel methods improve prediction of species' distributions from occurrence data

Abstract: Prediction of species' distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species' distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species' occurrence data. Presence-only data were effective for modelling species' distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.

Habitat history improves prediction of biodiversity in rainforest fauna.

Abstract: Patterns of biological diversity should be interpreted in light of both contemporary and historical influences; however, to date, most attempts to explain diversity patterns have largely ignored history or have been unable to quantify the influence of historical processes. The historical effects on patterns of diversity have been hypothesized to be most important for taxonomic groups with poor dispersal abilities. We quantified the relative stability of rainforests over the late Quaternary period by modeling rainforest expansion and contraction in 21 biogeographic subregions in northeast Australia across four time periods. We demonstrate that historical habitat stability can be as important, and in endemic low-dispersal taxa even more important, than current habitat area in explaining spatial patterns of species richness. In contrast, patterns of endemic species richness for taxa with high dispersal capacity are best predicted by using current environmental parameters. We also show that contemporary patterns of species turnover across the region are best explained by historical patterns of habitat connectivity. These results clearly demonstrate that spatially explicit analyses of the historical processes of persistence and colonization are both effective and necessary for understanding observed patterns of biodiversity.

Detecting climate change induced range shifts: where and how should we be looking?

Abstract: Global climate warming is expected to cause systematic shifts in the distribution of species and consequently increase extinction risk. Conservation managers must be able to detect, measure and accurately predict range shifts in order to mitigate impacts on biodiversity. However, important responses to climate change may go unnoticed or be dismissed if we fail to collect sufficient baseline data and apply the most sensitive analytical tests. Here we use randomizations of a contemporary data set on rainforest birds of north-eastern Australia to quantify the sensitivity of three measures for assessing range shifts along altitudinal gradients. We find that smaller range shifts are detectable by analysing change in the mean altitude of presence records rather than upper or lower range boundaries. For a moderate survey effort of 96 surveys, measurements of change in the mean altitude of 34 species have the capacity to provide strong inference for a mean altitudinal range shift as small as 40 m across the species assemblage. We also show that range shifts measured at range boundaries can be potentially misleading when differences in sampling effort between contemporary and historical data sets are not taken into account.

Niche breadth and geographical range: ecological compensation for geographical rarity in rainforest frogs.

Abstract: We investigated the relationship between diet specialization and geographical range in Cophixalus, a genus of microhylid frogs from the Wet Tropics of northern Queensland, Australia. The geographical ranges of these species vary from a few square kilometres in species restricted to a single mountain top to the entire region for the widespread species. Although macroecological theory predicts that species with broad niches should have the largest geographical ranges, we found the opposite: geographically rare species were diet generalists and widespread species were diet specialists. We argue that this pattern is a product of extinction filtering, whereby geographically rare and therefore extinction-prone species are more likely to persist if they are diet generalists.

Vertebrates of the Wet Tropics rainforests of Australia: species distributions and biodiversity

Abstract: One of the most basic elements of ecology and conservation biology is knowing what species occur in what places. As conceptually simple as this may sound, it is an incredibly difficult and complex undertaking, although probably the single most important fact underpinning all of ecology. It is impossible to make informed decisions about conservation management without some knowledge on the general geographic distributions of species. The aim of this report is to provide readers with my best estimate of the distribution of as many species of rainforest vertebrates as possible at this time within the Wet Tropics bioregion. Understanding biodiversity necessitates understanding the factors that determine the distribution of each constituent species. Approximately 350 species of vertebrates occur in the rainforests of the Wet Tropics bioregion, however, only about 153 species have their core distributions in the rainforest. In this report, I present distribution maps for the 177 species of Wet Tropics vertebrates where there was sufficient data to produce a useful map (the vast majority of true rainforest species), and twelve species richness maps based on overlaid distribution maps (Appendix B). The distribution maps represent a combination of bioclimatic modeling, habitat preferences, biogeographic distributions and expert knowledge. Also included is a comprehensive species list of all vertebrates in the Wet Tropics bioregion (Appendix A), with information on the conservation status, range size (of the mapped species), habitat specialisation and summaries of species richness by taxa both in spatially continuous maps and in tabulated form. The CD-ROM enclosed in the back cover (Appendix C) provides a PDF version of this report, which is embedded with hyperlinks to enable easy viewing of any species maps from the Index to Maps and those mapped species listed in Appendix A.

Climate change as a threat to the biodiversity of tropical rainforests in Australia

Abstract: [Extract] Forest destruction is thought to be the greatest threat to biodiversity in the tropics, particularly in the Amazon and tropical Asia (W. F. Laurance 1999). Climate change is sometimes discounted as a threat to tropical biotas and has been less studied in the tropics than in temperate, boreal, and arctic ecosystems. However, climate change has already produced significant and measurable impacts on almost all ecosystems around the globe and has altered species distributions, the timing of biological behaviors, assemblage composition, ecological interactions, and community dynamics (L. Hughes 2000; Walther et al. 2002; Parmesan and Yohe 2003; Root et al. 2003, 2005; Pounds et al. 2006). Recent analyses based on bioclimatic-distribution modeling suggested that climate change is potentially a greater threat to global biodiversity, including that in many tropical ecosystems, than is habitat destruction (Thomas et al. 2004).

Predicting and detecting impacts of climate change on montane rainforest birds in the Australian Wet Tropics

Abstract: Global climates are changing rapidly, and biological responses are becoming increasingly apparent. Some models indicate that models will largely consist of latitudinal and altitudinal shifts in the potential distributions of species, while others suggest that the complete disappearance of critical climate types and dependent species.