The Gleasonian view of species distribution suggests species are organised individualistically along environmental gradients owing to species specific variation in physiological tolerance and life history traits. This view implies that species are expected to respond to changes in those environmental gradients individualistically – an idea that is supported by palaeoecological evidence from past ‘climate flickers’. These responses are commonly manifest through changes in a species’ geographical range extent as suitable environmental conditions are tracked. In turn, this will contribute to altered biodiversity at higher organisational scales as community compositions and regional species pools are re-organised. However, there are two substantial problems with this assumption: 1) the current climate change episode differs from past ‘climate flickers’ because the additional impacts of habitat loss and degradation may prevent climate tracking, and, 2) inter-specific interactions are assumed to have no effect on species distribution. Consideration must be afforded to such limitations on species responses if we are to better understand and forecast impacts of environmental change on multiple scales of biodiversity. Although the second issue is well debated in community ecology and alternative hypotheses exist (e.g Clementsian / Eltonian), it is only recently that this has begun to be considered in the context of forecasted responses to environmental change. One way to achieve such consideration is to conduct analyses that encompass multiple species in an attempt to implicitly encapsulate these limitations.
Here I present 2 aspects of my PhD research that follow this approach. I begin with evidence for biotic homogenization of woodland plant communities and explore the potential causes and processes of this pattern. I proceed with an assessment of limitations to climate tracking caused by hydrodynamic dispersal barriers for four rocky shore species with a pelagic larval phase. Both these aspects suggest species are responding individualistically but that these responses are bounded by extrinsic constraints. I conclude with an outline of potential areas for future research that consider the impacts of environmental change in light of such constraints on species richness at multiple scales.