How (co)evolution alters predator responses to increased mortality: extinction thresholds and hydra effects

Abstract

Citation: Cortez, M. H., and M. Yamamichi. 2019. How (co)evolution alters predator responses to increased mortality: extinction thresholds and hydra effects. Ecology 100(10):Abstract. Population responses to environmental change depend on both the ecological interactions between species and the evolutionary responses of all species. In this study, we explore how evolution in prey, predators, or both species affect the responses of predator populations to a sustained increase in mortality. We use an eco-evolutionary predator-prey model to explore how evolution alters the predator extinction threshold (defined as the minimum mortality rate that prevents population growth at low predator densities) and predator hydra effects (increased predator abundance in response to increased mortality). Our analysis identifies how evolutionary responses of prey and predators individually affect the predator extinction threshold and hydra effects, and how those effects are altered by interactions between the evolutionary responses. Based on our theoretical results, we predict that it is common in natural systems for evolutionary responses in one or both species to allow predators to persist at higher mortality rates than would be possible in the absence of evolution (i.e., evolution increases the predator mortality extinction threshold). We also predict that evolution-driven hydra effects occur in a minority of natural systems, but are not rare. We revisited published eco-evolutionary models and found that evolution causes hydra effects and increases the predator extinction threshold in many studies, but those effects have been overlooked. We discuss the implications of these results for species conservation, predicting population responses to environmental change, and the possibility of evolutionary rescue.Notes: The terms J ij denote entries of the Jacobian in Eq. 3. All conditions assume the sign structure in Eq. 3. Coevolution conditions result in synergistic effects of prey and predator evolution, provided the conditions for only prey evolution and the conditions for only predator evolution are satisfied.

Uniting Community Ecology and Evolutionary Rescue Theory: Community-Wide Rescue Leads to a Rapid Loss of Rare Species

“…In this case, not just a single pathogenic bacterium faces a changed environment, but a complex community consisting of many thousands of species (Arumugam et al, 2011;Cho and Blaser, 2012), must adapt to avoid extinction. Whilst many models exist that study how a population of a single species, or a community composed of two species, adapts to environmental change (Hoffmann and Sgrò, 2011;Martin et al, 2013;Northfield and Ives, 2013;Osmond and De Mazancourt, 2013;Cortez and Yamamichi, 2019), fewer models exist that describe the response of an entire community composed of multiple species to an altered environment, although there are some examples (De Mazancourt et al, 2008;Bell, 2017;Lasky, 2019). Furthermore, empirical results, describing community wide adaptation, such as those presented by Bell and Gonzalez (2011), Low-Décarie et al (2015), Bell et al (2019), and Roodgar et al (2019), are clearly calling for such models.…”

Change in prey genotype frequency rescues predator from extinction

“…Mismatches between responses of, for example, consumer and their resources can lead to the extinction of species that are not directly affected or to a lesser amount by the environmental change, when their resource declines [41–43]. Incorporating evolutionary responses in one or more species could impact the probability of survival of a threatened population [44], either through the mechanism of IER as studied here, through effects on coevolution [12,44,45] or changes in selection and demographic changes [46].…”

Change in prey genotype frequency rescues predator from extinction

“…Mismatches between responses of for example consumer and their resources can lead to the extinction of species that are not directly affected or to a lesser amount by the environmental change, when their resource declines [41–43]. Incorporating evolutionary responses in one or more species could impact the probability survival of a threatened population [44], either through the mechanism of IER as studied her, through effects on coevolution [11,44,45] or changes in selection and demographic changes [46].…”