Evolution in response to an abiotic stress shapes species coexistence

Abstract

Adaptation to novel environments have been documented at the population, phenotype and genotype level. However, the ecological consequences of this process are often ignored. For example, recent evolutionary history in different environments is expected to lead to increased growth rates and competitive abilities. These traits have been identified as key ingredients underlying species coexistence, which suggests that adaptation to new environments may shape species coexistence patterns. However, this hypothesis remains untested. To tackle this issue, we performed experimental evolution of two herbivorous spider mite species (Tetranychus urticae and T. evansi) feeding on tomato plants grown under high or low cadmium concentrations. We combined phenotypic analyses with structural stability theory to show that both the cadmium environment and evolution in it changed the coexistence patterns of the two species by increasing niche differences. In fact, the presence of cadmium reduced interspecific competition and led to facilitation between the two herbivores, entailing stable coexistence independently of the previous evolutionary history. Evolution in the cadmium environment also reduced interspecific competition in the ancestral environment, producing stable coexistence. These results show that evolution in a new environment, even in absence of interspecific competitors, affects long-term species coexistence. Importantly, it highlights that biotic interactions (within or between populations) should be accounted for when describing adaptation to novel environments.