My research interests focus on resource-consumer interactions examining how species coexist through space and time. This research involves developing appropriate mathematical models and experiments to test hypotheses on species coexistence. Primarily, we use parasitism as the life-history mode to explore the coexistence of multiple species in resource-consumer interactions. A parasite lives so intimately with the host organisms that it is metabolically dependent on its host and parasitic species are known from many of the major taxa - over 50% of all organisms have adopted the parasitic mode of life. Given this ubiquity and diversity, understanding how parasitism influences, structures and affects different species in complex food webs has both applied and fundamental ecological implications.
1. Ecological implications of sharing natural enemies
The processes and mechanisms that underpin coexistence in ecological assemblages can be addressed by examining specific modular based interactions. One module that has attracted recent interest is known as "apparent competition". Theoretically, this interaction arises through the effects of alternative prey in the diet of a generalist natural enemy. As alternative prey are introduced, the abundance of the natural enemy increases and sustain increased levels of attack on both species. Over time, the inferior prey species is expected to be eliminated from the assemblage. Empirically, this interaction is often difficult to test but we have recently demonstrated the effects of a shared parasitoid in a simple laboratory-based moth -parasitoid assemblage (Bonsall & Hassell, 1997).
2. Spatial dynamics of shared enemy interactions
Although shared enemy effects are very common in nature, the dynamics of apparent competition with the exclusion of one prey species appear to be rare. A variety of additional mechanisms have been proposed to counter the ecological effects of apparent competition. These include intraspecific prey density dependence, prey refuges and behavioural responses by the natural enemies. More recently, we have shown how the importance of metapopulation (a population of populations) structure affects the persistence of multispecies host-parasitoid assemblages. Introducing spatial structure (with dispersal) increases the persistence of the shared-enemy module. Moreover, a positive relationship between habitat occupancy and local abundance (one of the most ubiquitous patterns in ecology) can arise very simply as a consequence of the impact of a shared parasitoid on alternative hosts. We have recently started a combined empirical and theoretical programme to explore the spatial aspects of apparent competition.
3. Coexistence of multiple natural enemies.
Currently, we are examining the role of heterogeneity on the coexistence of a multi parasitoid - single host interaction. Through their impact on the population dynamics of their host insects, it is now well known that parasitoids can have a marked influenced on the persistence of species interactions. Within patchy environment, it is known from theoretical and laboratory studies that parasitoids can affect the persistence of single host - single parasitoid interactions. We are extending these theoretical and empirical ideas to examine the role of patchy environments on the persistence of competing parasitoids. Statistical time series techniques are used to reveal the processes regulating the host and parasitoid populations. Age-structured models are being developed and parameterised using information from short-term demographic experiments to show how different ecological mechanisms act concomitantly to promote the persistence of the module in a heterogeneous environment.
4. Impact of diseases on insect population dynamics
We have recently begun to develop a series of models to explore and predict how diseases might impact on the dynamics of their host populations. In particular, we are using age-structured models to explore how multiple pathogens might coexist, how latent and sublethal infections may persist in insect populations and how modified pathogens might persist or outcompete wildtype strains. We are developing stochastic and spatial models to predict the conditions under which coexistence or exclusion might be influenced by demographic and/or spatial transmission processes.
Dr Mike Bonsall provides an insight into the lifestyles of the minibeast. By focussing on the diversity of insects we find in our own gardens, he will look in particular at ‘pest insects’ and how we can use bugs to control bugs.
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