Ecological and genetic effects of introduced species on their native competitors

TL;DR

This study models how varying competition intensity affects native species persistence amid invasive species introductions, revealing a non-linear relationship where intermediate competition levels are most detrimental, with ecological and genetic factors interacting.

Contribution

It introduces two stochastic models to analyze the combined ecological and genetic impacts of invasive species, highlighting the complex, non-linear effects of competition on native species survival.

Findings

Native species persistence is lowest at intermediate competition levels.

Higher competition speeds native species exclusion despite requiring more introductions for invasion.

Ecological and genetic effects interact synergistically, affecting invasion outcomes.

Abstract

Species introductions to new habitats can cause a decline in the population size of competing native species and consequently also in their genetic diversity. We are interested in why these adverse effects are weak in some cases whereas in others the native species declines to the point of extinction. While the introduction rate and the growth rate of the introduced species in the new environment clearly have a positive relationship with invasion success and impact, the influence of competition is poorly understood. Here, we investigate how the intensity of interspecific competition influences the persistence time of a native species in the face of repeated and ongoing introductions of the nonnative species. We analyze two stochastic models: a model for the population dynamics of both species and a model that additionally includes the population genetics of the native species at a locus involved in its adaptation to a changing environment. Counterintuitively, both models predict that the persistence time of the native species is lowest for an intermediate intensity of competition. This phenomenon results from the opposing effects of competition at different stages of the invasion process: With increasing competition intensity more introduction events are needed until a new species can establish, but increasing competition also speeds up the exclusion of the native species by an established nonnative competitor. By comparing the ecological and the eco-genetic model, we detect and quantify a synergistic feedback between ecological and genetic effects.