Metapopulations with habitat modification

Abstract

Significance Beavers build dams, which dramatically alter the local landscape and ecological community. Bacteria modify the chemistry of their environment, changing its suitability for other microbes. Viral infections induce adaptive immunity, blunting future infection by similar strains. These apparently dissimilar situations share common features: An organism causes lasting changes to the environment that affect other species—even after the beavers emigrate, the bacterial colony collapses, or the infection is cleared. To understand the dynamics of these systems, we extend a metapopulation model (in which local populations inhabit patches connected by dispersal) to incorporate “patch memory,” modeling environmental modification. This model can produce complex dynamics and illuminates mechanisms that promote diversity in the meta-ecosystem and affect its robustness to changing environmental conditions. Across the tree of life, organisms modify their local environment, rendering it more or less hospitable for other species. Despite the ubiquity of these processes, simple models that can be used to develop intuitions about the consequences of widespread habitat modification are lacking. Here, we extend the classic Levins metapopulation model to a setting where each of n species can colonize patches connected by dispersal, and when patches are vacated via local extinction, they retain a “memory” of the previous occupant—modeling habitat modification. While this model can exhibit a wide range of dynamics, we draw several overarching conclusions about the effects of modification and memory. In particular, we find that any number of species may potentially coexist, provided that each is at a disadvantage when colonizing patches vacated by a conspecific. This notion is made precise through a quantitative stability condition, which provides a way to unify and formalize existing conceptual models. We also show that when patch memory facilitates coexistence, it generically induces a positive relationship between diversity and robustness (tolerance of disturbance). Our simple model provides a portable, tractable framework for studying systems where species modify and react to a shared landscape.