Commentary: Scale-dependence of spatial patterns of insect distribution and abundance

Abstract

news and update ISSN 1948-6596 commentary Scale-dependence of spatial patterns of insect distribution and abundance The most recent issue of Ecography (February 2010) contained eight papers devoted to patterns in the distributions and abundance of insects, and to the dependence of these patterns on spatial scale. It has been known for some time that our perception of patterns of biodiversity, and the relative importance of the factors that determine these patterns, vary with the spatial scale consid- ered (Whittaker et al. 2001). However, as Hortal et al. (2010) point out in their introduction to the Ecography special issue, most previous analyses have focused on species richness patterns, not on the distributions of individual species. Further- more, in these previous studies, as in conservation and ecology research more generally (Clark and May 2002), there has been strong bias towards vertebrate animals and plants: in a meta-analysis of 394 studies of species richness patterns across different spatial scales (Field et al. 2009), only 68 focused on insects. The growing number of macro-ecology studies that do focus on insects is probably a reflection of increasing knowledge about the distributions of these species. In rela- tion to the number of species they represent, in- sects are still massively under-sampled (Newbold 2010), but there are now nearly 15 million geo- referenced distribution records for insects in the Global Biodiversity Information Facility database (http://www.gbif.org), spread across all conti- nents except Antarctica. Covering a wide range of taxa, geographical regions and methodologies, these papers together make an important contribution to our under- standing of patterns of insect biodiversity at dif- ferent spatial scales. Scale-dependence in the drivers of biodiver- sity patterns The different studies in this special issue consid- ered patterns of insect distribution and abun- dance at a wide range of scales. This is reflected in the different factors identified as important in ex- plaining observed patterns and in the different methods used for analysis. Several of the studies considered very broad (country-level or continental) scales, suc- cessfully using species distribution models with climate variables to explain distribution patterns (Lobo et al. 2010, Kriticos and Leriche 2010, War- ren et al. 2010, Soberon 2010). At finer scales, other factors emerge as more important. In agri- cultural fields in the UK, arthropods showed pat- terns of co-occurrence that suggest an effect of biotic interactions (Bell et al. 2010). At small scales, micro-climate and topography are also im- portant. In a national park in Hawaii, the extent of an Argentine ant (Linepithema humile) invasion was modelled better using microclimate data than landscape-level climate variables (Hartley et al. 2010), and a metapopulation model for the silver- spotted skipper butterfly (Hesperia comma) in Britain suggested that as the global climate warms, the ability to inhabit more northerly- facing aspects with warmer micro-climates is al- lowing faster rates of range expansion (Wilson et al. 2010). Although it has been suggested several times that multi-scale models with different sets of drivers would help to better understand diver- sity patterns (e.g. Mackey and Lindenmayer 2001) and to make better predictions of species’ re- sponses to environmental change (Randin et al. 2009), this approach remains relatively rare in practice (but see e.g. Anderson et al. 2007). The marked variation with scale in the relative impor- tance of different explanatory variables, and the decline in the importance of landscape-level cli- mate variables at the finer resolutions, lends weight to the argument for including factors such as biotic interactions, habitat, and microclimate into models in a multi-scale framework. Several of the studies explicitly tested the effect of spatial scale on the conclusions drawn from biogeographical analyses (Cabeza et al. 2010, frontiers of biogeography 2.2, 2010 — © 2010 the authors; journal compilation © 2010 The International Biogeography Society