Positive interactions within and between populations decrease the likelihood of evolutionary rescue

Abstract

Positive interactions, including intraspecies cooperation and interspecies mutualisms, play crucial roles in shaping the structure and function of many ecosystems, ranging from plant communities to the human microbiome. While the evolutionary forces that form and maintain positive interactions have been investigated extensively, the influence of positive interactions on the ability of species to adapt to new environments is still poorly understood. Here, we use numerical simulations and theoretical analyses to study how positive interactions impact the likelihood that populations survive after an environment deteriorates, such that survival in the new environment requires quick adaptation via the rise of new mutants—a scenario known as evolutionary rescue. We find that the probability of evolutionary rescue in populations engaged in positive interactions is reduced significantly. In cooperating populations, this reduction is largely due to the fact that survival may require at least a minimal number of individuals, meaning that adapted mutants must arise and spread before the population declines below this threshold. In mutualistic populations, the rescue probability is decreased further due to two additional effects—the need for both mutualistic partners to adapt to the new environment, and competition between the two species. Finally, we show that the presence of cheaters reduces the likelihood of evolutionary rescue even further, making it extremely unlikely. These results indicate that while positive interactions may be beneficial in stable environments, they can hinder adaptation to changing environments and thereby elevate the risk of population collapse. Furthermore, these results may hint at the selective pressures that drove co-dependent unicellular species to form more adaptable organisms able to differentiate into multiple phenotypes, including multicellular life.

Change in prey genotype frequency rescues predator from extinction

“…Only few studies on ER have incorporated species interactions and community dynamics and it is currently unclear which conditions influence the probability of ER. For example, studies on mutualistic interactions [16] have shown a decrease in the probability of ER while studies focusing on antagonistic interactions [14,15,17] found a decrease or increase in the probability of ER. An important determinant for ER in communities is how many species are threatened by extinction and their interactions within the community.…”

“…Theoretical studies have started to integrate the effect of multispecies interaction into research on ER [11][12][13][14][15][16]. There are however only few studies exploring ER in communities with multiple species [17,18] and the conditions under which populations can be rescued through evolutionary change in communities are still poorly explored [19].…”

“…As populations interact with other populations, it is, however, possible that changes in species interactions and indirect ecological and evolutionary processes affect the demography of a population [9,10] and thus the probability of rescue. Theoretical studies have started to integrate the effect of multispecies interaction into research on ER [11–16]. There are however only few studies exploring ER in communities with multiple species [17,18] and the conditions under which populations can be rescued through evolutionary change in communities are still poorly explored [19].…”

Exclusion of the fittest predicts microbial community diversity in fluctuating environments

“…cross-feeding), for example, might increase alpha and gamma diversities, because such interactions enable species to coexist [72]. This could result in an increase in beta diversity because the extinction of one species increases its partner species' extinction probability [73,74].…”

Change in prey genotype frequency rescues predator from extinction

“…As species interact with other species, it is, however, possible that changes in their interactions and indirect ecological and evolutionary processes affect the demography of a population [9][10][11] and thus the probability of rescue. Theoretical studies have started to integrate the effect of multi-species interaction into research on ER [12][13][14][15][16][17]. There are, however, only few studies exploring ER in communities with multiple species [18,19], and the conditions under which species can be rescued through evolutionary change in communities are still poorly explored [20].…”