Patterns, causes and consequences of rarity in plant populations
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Density dependence and spatial scaling in insect-plant interactions
Density dependence -- the process by which a species' abundance affects its population growth rate -- has been a central concern of population ecologists for many years. Much of my research has been devoted to a mechanistic analysis of how density-dependence occurs in the interactions between plants and the insects (pollinators and herbivores) that feed upon them. My work relies mainly on field experiments in which I manipulate various aspects of a plant's local abundance: the number of individuals in a patch, their spacing, their size, and/or their competitive environment. Both mathematical models and field results to date show that sparsely-populated plants can face sharp declines in the quantity and quality of pollinator visits, causing potentially serious reproductive problems at low density. Herbivore responses to plant abundance have proved much less consistent, and the differences between them remain an interesting topic for future work. To resolve the confusion may require a fundamental rethinking of the role of scale in density dependence, as different herbivores may respond to density on very different scales.
Conservation biology: population and community viability in a changing biota
Much of my current and planned research relates in some way to the conservation of biological populations and communities. Work underway in my group as part of the ALARM consortium is investigating the decline of European pollinator communities and of the pollination services they provide. As part of the UKPopNet research consortium, we will be examining the network of nature reserves in the Yorkshire and Humberside area (and in Britain) to test the adequacy of cover. I am particularly interested in trying to develop techniques that incorporate population viability in reserve selection algorithms. Other recent work has concerned the autocorrelation of extinction risk. Populations close together in space are more likely than average to share the same fate, with profound implications for global extinction risk and optimal conservation strategies. Other recent work has demonstrated that the spatial patterns in populations can be used to infer past and future extinction risk.