Heterogeneity in patch quality buffers metapopulations from pathogen impacts Daniel J. 1 Becker and Richard J. 1,2 Hall 1Odum School of Ecology, University of Georgia 2Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia Background Modeling approach Simulation results Many wildlife persist as metapopulations on a network of ephemerally occupied habitat connected by dispersal. For metapopulations in decline (c < xL), metapopulation persistence always requires some degree of resource improvement (extinction in black at low f and q). A common conservation practice for rescuing declining metapopulations is to increase habitat patch quality through provisioning of food resources. Along a gradient of increasing patch quality (q) and the fraction of high-quality patches (f), resource improvement first promotes disease-free metapopulation persistence (white), followed by pathogen invasion to an endemic (light blue) or pandemic equilibrium in which all occupied patches are infected (dark blue). Yet provisioning can also harm wildlife by facilitating the local transmission and spatial spread of pathogens such as Mycoplasma gallisepticum in house finches. Under moderate local resource improvement (q = 2), occupancy is maximized for mixtures of low- and high-quality patches, and pathogen invasion only occurs when the majority of patches are provisioned. A pressing need exists to understand how the effects of local resource improvement influence landscape-level infection dynamics and metapopulation persistence. House finch © A. Davis Study objectives Our primary objective is to ask under which conditions resource improvement can reduce or improve patch occupancy in the presence of a virulent pathogen. Here we develop a simple metapopulation model to determine how equilibrium occupancy and pathogen prevalence are related to two parameters describing resource improvement across a landscape: Yet with strong local provisioning (q = 4), the pathogen not only invades at a lower fraction of improved habitat, but also can establish and infect all occupied patches. (a) We use differential equations to model patch transitions between three types: unoccupied (black), occupied by the host but not the pathogen (white), and occupied by host and pathogen (infected, blue). (b) We consider two patch types: unmanaged (low quality, square) and improved by resource provisioning (high quality, circle). The parameter q is defined as the ratio of the persistence times of high- versus low-quality patches. (c) The metapopulation is configured by defining the fraction of patches at which resource improvement occurs (f). (d) A snapshot of metapopulation structure and (e) a time series of total patch occupancy and pathogen prevalence. 1. The increase in patch quality due to provisioning (q) 2. The fraction of patches improved by management (f) Daniel Becker PhD Candidate Email: [email protected] Although improving habitat patch quality is necessary to prevent the extinction of declining metapopulations, making resource conditions “too good” has consequences for the invasion and spatial persistence of virulent pathogens. Our finding of maximized occupancy at mixtures of low- and high-quality habitat patches suggests that resource-poor patches may act as “sinks” for pathogens, as infected low-quality patches undergo rapid local disease-induced extinction. By varying these parameters, we derive the following: 1. Conditions for metapopulation persistence 2. Thresholds for pathogen invasion and persistence 3. Equilibrium occupancy and infection prevalence Conclusions (e) ) Therefore, heterogeneity in habitat patch quality may be an under-recognized mechanism for buffering metapopulations from pathogen impacts. Acknowledgements: We thank Sonia Altizer and members of the Altizer and Ezenwa Labs at the University of Georgia for helpful comments and insight. Funding was provided by the National Science Foundation, the Odum School of Ecology, and the ARCS Foundation.
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