The effects of colonization, extinction and competition on co-existence in metacommunities.
ABSTRACT 1. The co-existence of competitors in heterogeneous landscapes depends on the processes of colonization, extinction and spatial scale. In this study, we explore the metapopulation dynamics of competitive interactions. 2. Rather than simply evaluating the outcome of interspecific competition in the traditional manner, we focus on both the local population dynamic effects and the regional metapopulation processes affecting species co-existence. 3. We develop a theoretical model of regional co-existence to generate a set of predictions on the patterns of colonization necessary for co-existence and the regional processes that can lead to competitive exclusion. We empirically test these predictions using metacommunity microcosms of the interaction between two bruchid beetles (Callosobruchus chinensis, Callosobruchus maculatus). 4. Using well-replicated time series of the interaction between the bruchids and statistical methods of model fitting, we show how the qualitative and quantitative pattern of interspecific competition between the bruchid beetles is shaped by the structure of the metacommunity. 5. In unlimited dispersal metacommunities, the global exclusion of the inferior competitor is shown to be influenced more by the processes associated with extinction rather than low colonization ability. In restricted dispersal metacommunities, we show how the co-existence of competitors in a spatially heterogeneous habitat (patches connected through limited dispersal) is affected by Allee effects and life-history [colonization (dispersal) - competition] trade-offs.
- American Naturalist - AMER NATURALIST. 01/1995; 145(4).
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ABSTRACT: 1The hypothesis that multiple infections might disrupt or alter the density-dependent processes regulating a host–pathogen interaction is explored using time series from a well-known laboratory insect–pathogen model system.2We compare the population dynamics of the same host (Plodia interpunctella) infected with a single (granulovirus) or multiple (granulovirus and nucleopolyhedrovirus) pathogens and show how the dynamical fluctuations are altered by the presence of this second pathogen.3Using a maximum likelihood-based approach, we explore the density-dependent mechanisms underpinning the host–pathogen interaction. These regulatory processes differ between single and multiple infections. In singly infected systems, the density-dependent mechanisms of regulation operate through birth rate while in doubly infected systems, density dependence is mediated through death rate.4Further, these deterministic dynamics are modulated by the effects of demographic stochasticity. This stochastic process, the overall sum of individual probabilities of births, deaths and infection influence the changes in population size. In the Plodia–granulovirus system, nonlinear density-dependent births coupled with demographic noise is the necessary prerequisite for the observed dynamics. In the multiple infection system, noise acts together with disease transmission and mortality to affect the population dynamics.5We discuss the implication of these differing regulatory processes in the different-sized species assemblages in the presence of noise for understanding the ecologies of host–pathogen interactions.Journal of Animal Ecology 08/2005; 74(5):937 - 945. · 4.84 Impact Factor
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ABSTRACT: A method is described for the minimization of a function of n variables, which depends on the comparison of function values at the ( n + 1) vertices of a general simplex, followed by the replacement of the vertex with the highest value by another point. The simplex adapts itself to the local landscape, and contracts on to the final minimum. The method is shown to be effective and computationally compact. A procedure is given for the estimation of the Hessian matrix in the neighbourhood of the minimum, needed in statistical estimation problems.01/1965;