American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Maladapted prey subsidize predators and facilitate range expansion”

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Mark C. Urban, Alice Scarpa, Justin M. J. Travis, and Greta Bocedi (Special Feature on Maladaptation)

The evolution of poorly defended prey supplies many benefits to predators

Theoretical research was inspired by the <a href="https://www.journals.uchicago.edu/doi/full/10.1086/681716">authors’ previous research in <i>Am.&nbsp;Nat.</i></a> on how prey species adapt or do not adapt defenses against the predator pictured here, a marbled salamander (<i>Ambystoma opacum</i>).<br />(Credit: Mark Urban)
Theoretical research was inspired by the authors’ previous research in Am. Nat. on how prey species adapt or do not adapt defenses against the predator pictured here, a marbled salamander (Ambystoma opacum).
(Credit: Mark Urban)

Life is good when dinner is quick and easy. But prey usually make dinner difficult for predators by evolving defenses like thorns, shells, camouflage, and poison. Yet prey sometimes evolve to be less defended where predators are rare, like at the edge of a predator’s range. In these situations, prey are likely to become adapted to low-predator conditions, and maladapted to predators. How do these maladapted prey affect the predators that eat them?

Scientists from the University of Connecticut and University of Aberdeen set out to answer this question using a combination of classic analytical theory and supercomputer-sized simulations. By providing a subsidy of easily captured resources, the authors find that maladapted prey can enhance predator abundances, persistence, and geographic range size. Simply put, maladaptation makes dinner easy for predators.

Maladapted prey become even more important when predators are expanding their range, such as during climate change. As predators expand, they encounter less and less defended prey, speeding up the predator’s range expansion. These maladapted prey can even prevent the predator’s extinction during environmental change. These effects can be generalized to any enemy and victim system, ranging from plants and their herbivores to humans and our diseases.

Overall, the work suggests the need to understand not just the adaptive dynamics of predator and prey, but their maladaptive dynamics as well. More generally, we need to work to spend more time considering how both adaptation and maladaptation affect species interactions to get a more complete view of biodiversity patterns, limits to species ranges, and responses to environmental change.


Abstract

Dispersal of prey from predator-free patches frequently supplies a trophic subsidy to predators by providing more prey than are produced locally. Prey arriving from predator-free patches might also have evolved weaker defenses against predators and thus enhance trophic subsidies by providing easily captured prey. Using local models assuming a linear or accelerating tradeoff between defense and population growth rate, we demonstrate that immigration of undefended prey increased predator abundances and decreased defended prey through eco-evolutionary apparent competition. In individual-based models with spatial structure, explicit genetics, and gene flow along an environmental gradient, prey became maladapted to predators at the predator’s range edge, and greater gene flow enhanced this maladaptation. The predator gained a subsidy from these easily captured prey, which enhanced its abundance, facilitated its persistence in marginal habitats, extended its range extent, and enhanced range shifts during environmental changes, such as climate change. Once the predator expanded, prey adapted to it, and the advantage disappeared, resulting in an elastic predator range margin driven by eco-evolutionary dynamics. Overall, the results indicate a need to consider gene flow-induced maladaptation and species interactions as mutual forces that frequently determine ecological and evolutionary dynamics and patterns in nature.