Temporally Auto-Correlated Predator Attacks Structure Ecological Communities

Abstract

For species regulated by a common predator, the P* rule predicts that the prey species that supports the highest mean predator density (P*) excludes the other prey species. This prediction is re-examined in the presence of temporal fluctuations in the vital rates of the interacting species including predator attack rates. When the fluctuations in predator attack rates are temporally uncorrelated, the P* rule still holds even when the other vital rates are temporally auto-correlated. However, when temporal auto-correlations in attack rates are positive but not too strongly, the prey species can coexist due to the emergence of a positive covariance between predator density and prey vulnerability. This coexistence mechanism is similar to the storage effect for species regulated by a common resource. Strongly positive or negative auto-correlations in attack rates generate a negative covariance between predator density and prey vulnerability and a stochastic priority effect can emerge: with non-zero probability either prey species is excluded. These results highlight how temporally auto-correlated species' interaction rates impact the structure and dynamics of ecological communities.

Building modern coexistence theory from the ground up: the role of community assembly

“…For example, alternative stable states are driven by positive frequency dependence, while coexistence is driven by negative frequency dependence (Ke & Letten, 2018; Schreiber et al ., 2019; Mordecai, 2011). Similarly, Schreiber (2021, 2022) discuss the possibility of negative storage effects, which would not contribute to coexistence but rather hamper it. More generally, in a meta-analysis of niche and fitness differences across different ecological communities Buche et al (2022) found that niche differences of coexisting species-pairs differ qualitatively from niche differences of competitively excluded species, independent of whether these were driven by positive or negative frequency dependence.…”

Resolving conceptual issues in Modern Coexistence Theory

“…The temporal storage effect can also be mediated through predation, but only if predation changes concomitantly with the the the environmental parameter. This can happen through temporal autocorrelation in the predator's demographic rates (Schreiber, 2021a), or if predators exhibit behavioral responses to changes in prey density . Prey species can experience a negative temporal storage effect (undermining coexistence) if their predators have type 2 functional responses (Stump, 2017), such that residents can satiate their predators but invader cannot.…”

“…If positive, the coexistence mechanism generally uplifts all species. If negative, the mechanism is generally destabilizing; in models without allee effects, mutualisms, or knock-on extinctions, a negative community-average coexistence mechanism is evidence of priority effects, which are classically presented in a Lotka-Volterra framework (Amarasekare, 2012), but may be mediated through fluctuation-dependent coexistence mechanisms (Chesson, 1988;Schreiber, 2021b;Schreiber, 2021a).…”