Showing papers by "Michael P. Hassell published in 1996"
TL;DR: Previous work on spatially distributed host-parasitoid interactions is extended to wider questions of community structure, by considering various three-species systems: two parasitoid species attacking a common host species; two host species attacked by a single parasitoids species; or a host-Parasitoids-hyperparasIToid interaction.
102 citations
TL;DR: It is concluded that for general single-species and two-species competition models, the introduction of the spatial dimension in a biologically sensible way has no effect on the overall stability properties.
96 citations
TL;DR: The extent of within-patch dispersal by a tephritid fly and its four major parasitoids was examined over three field seasons and no correlations between movement and insect size were observed.
Abstract: The extent of within-patch dispersal by a tephritid fly and its four major parasitoids was examined over three field seasons. Hosts and parasitoids were marked using acrylic paint and observed as they oviposited into the flowerheads of marsh thistle, Cirsium palustre. The average recapture rate pooled across all species was 22%. The four parasitoids showed consistently greater rates of movement than the host in all three years. In nearly all comparisons, male dispersal was less than female dispersal. There was no evidence that parasitoids moved longer distances after visiting low quality rather than high quality patches. In the one season it was studied, no correlations between movement and insect size were observed. The relevance of these observations to host-parasitoid population dynamics is discussed.
56 citations
TL;DR: It is demonstrated that, paradoxically, a persisting metapopulation may consist of only 'sink' populations (negative average growth rate in the absence of migration) and increasing migration rate generally increases density dependence in persisting meetapopulations.
Abstract: We describe analytical and simulation models of metapopulations consisting of local populations that obey a random walk between a reflecting upper boundary (population 'ceiling') and an absorbing lower boundary (local extinction). We present analytical results for the expected time to local extinction, expected size of local populations, and incidence of density dependence. The latter is defined as the frequency of hitting the ceiling per generation per population. With these models we examine the proposition that a metapopulation consisting of random walk local populations would persist without density dependence. Long-term persistence of a metapopulation is not possible without local populations occasionally becoming large and hence being affected by density dependence. But it is possible to construct examples in which a metapopulation persists for a long time with a low incidence of density dependence, in which cases local populations typically have very short expected lifetimes. We demonstrate that, paradoxically, a persisting metapopulation may consist of only 'sink' populations (negative average growth rate in the absence of migration). Contrary to some previous suggestions, increasing migration rate generally increases density dependence in persisting metapopulations.
56 citations
TL;DR: It is concluded that some communities of hosts and parasitoids may display complex dynamic behavior determined by both local population interactions and the frequency of species invasions, which can depend on the interaction between its dynamics and that of the resident species.
Abstract: We study the population dynamics of a model host-parasitoid community containing two hosts that interact only through a shared generalist parasitoid. Each host is also attacked by a specialist parasitoid, making a community of up to five species of insects. Information from host-parasitoid community ecology is used in deciding how these species interact. By considering both community stability and whether absent species can invade, we predict which communities occur in different regions of parameter space. A crucial determinant of community structure is the relative searching efficiencies of specialists and generalists and the nature of the density-dependent reduction in parasitoid searching efficiency. In some areas of parameter space, there is no dynamically stable end point, and complex cycles occur where the food web structure is constantly changing, species being added through invasion and lost through direct and indirect competitive interactions. We also find that whether a species is able to invade can depend on the interaction between its dynamics and that of the resident species. We conclude that some communities of hosts and parasitoids may display complex dynamic behavior deter- mined by both local population interactions and the frequency of species invasions.
35 citations
TL;DR: It is shown that the existence of a ‘pool’ of dispersing hosts and/or parasitoids can stabilize otherwise unstable population models, i.
Abstract: In host-parasitoid systems occurring in a patchy environment, travelling between breeding sites can result in spatial heterogeneity in the birth and death rates of individuals either because the environment is heterogeneous or because individuals do not distribute evenly in space. A second effect of dispersal is that at any one time, a fraction of the individuals of a population is in transit between breeding sites. While population models have focused on the first effect of dispersal to analyse the consequences of spatial heterogeneity for population dynamics, we develop models to investigate the effects of dispersal per se, i.e. the absence of individuals from breeding sites, on stability in host-parasitoid systems. We show that the existence of a `pool' of dispersing hosts and/or parasitoids can stabilize otherwise unstable population models.
20 citations
TL;DR: Although total biomass per patch was independent of initial egg density, competition between Drosophila larvae leads to the formation of smaller pupae, which resulted in a population that was dominated by suppressed individuals.
Abstract: The role of larval intraspecific competition in laboratory populations ofDrosophila subobscura was investigated. Mortality is density-independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition betweenDrosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate ofD. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the nextDrosophila generation is described.
12 citations