Understanding the impact of third-party species on pairwise coexistence

Abstract

The persistence of virtually every single species depends on both the presence of other species and the heterogeneous environmental conditions. Because in natural settings many of these conditions are unknown, research has been centered on finding the fraction of possible conditions (probability) leading to species coexistence. The focus has been on the coexistence probability of two species in isolation or that of an entire multispecies system. However, it is unclear how a system can affect differently the coexistence expectation of each of its constituent pairs. Here, we derive long-term (using analytical calculations) and short-term (using simulations and experimental data) system-level indicators of the effect of multispecies systems on pairwise coexistence under unknown environmental conditions. We demonstrate that the fraction of conditions incompatible with the possible coexistence of a pair of species in isolation tends to become vanishingly small within systems of increasing numbers of species. Yet, the fraction of conditions allowing pairwise coexistence in isolation remains approximately the center of the probability distribution of pairwise coexistence across all possible systems. While the likelihood of short-term survival is always greater than or equal to that of long-term survival, we found in general stronger (resp. weaker) short-term buffering effects within systems than in isolation under negative (resp. positive) long-term effects. We show that both long-term and short-term effects of a system are not equally distributed across all of its possible pairs, but these differences can be mapped and anticipated under environmental uncertainty.Author SummaryIt is debated whether the frequency at which two species coexist in isolation or within a single environmental context is representative of their coexistence expectation within larger systems and across different environmental conditions. Here, using analytical calculations, simulations, and experimental data, we show how multispecies systems can provide the opportunity of pairwise coexistence regardless of whether a pair of species cannot coexist in isolation across different environmental conditions. However, we show that this opportunity is not homogeneously granted across all pairs within the same system. We provide a framework to understand and map the long-term and short-term effects that a system has on the coexistence of each of its constituent pairs. Our work can have useful applications in bio-restoration and bio-medicine subject to unknown environmental conditions.

Higher Order Dynamics in the Replicator Equation Produce a Limit Cycle in Rock-Paper-Scissors

“…This simplifying assumption is violated by the intrinsic existence of high-order interactions (HOI's), for which there is growing evidence [8][9][10][11][12][13][14][15][16][17][18]. A higher-order interaction occurs when three or more species act together as a subgroup to shape community behaviour [2,[8][9][10][11][12][19][20][21]. In the case of random interactions in ecological communities, the occurrence of HOIs can alter the established relationship between diversity and stability [10], leading to new evolutionary trajectories.…”