The effect of environmental fluctuations – Could climate change promote species’ invasion success?

The global climate change is presumed to increase the amount of fluctuations in the environmental conditions. This could increase the amount of species invasion into new areas if fluctuations affect the ecological and evolutionary processes that make species successful as invaders, and native communities and their environments more susceptible to invasions1. Disturbed environments are assumed to be more prone to invasions and the fluctuations in invasive species’ home range could pre-adapt them to tolerate similar conditions elsewhere. Under fluctuating conditions, natural selection could potentially favor traits like generalism, which is profitable in adaptation to wide range of conditions2. These attributes could lead to better competitive ability of the invader against the native species, especially if the native species are mal-adapted to tolerate fluctuating conditions. Moreover, the distant relatedness between the invasive species and its native competitors is hypothesized to reduce their competition for the same resources and so increase the success of the invader3. We tested these theories of how fast environmental fluctuations and relatedness of species could affect the invasion success, with our aim to find effects that would be generalizable over the species. In this study, the invasion success meant the ability of the invader population to competitively displace the population of its competitor species. Bacterial species that had evolved in stable or fluctuating temperature were competed against the dominant bacterial invader Serratia marcescens, which had also evolved in stable or fluctuating temperature and the invasions were initiated in environments with similarly stable or fluctuating temperature. In addition, the competitor species were differently related to the invader. The results indicated strong species-specific effects on invasion success, which could be due to the more intense competition detected between closely related species. For most of the species, the rapid temperature fluctuations during invasion made invasions more successful. Unexpectedly, the evolution in the fluctuating environment did not significantly enhance the success of S. marcescens. Instead, our study showed that under fast fluctuations, natural selection could select for generalist genotypes, which invade better also in suboptimal environments. We found the superiority of S. marcescens also when its competitor species had mal-adapted to tolerate thermal fluctuations, but this result was strongly affected by one species. Overall, our results indicate that in the future, the traits of the invader, the attributes of its native competitors and the environmental conditions during invasion need to be considered together when predicting the success of the invasive species under fluctuating conditions. 1. Saarinen K., Lindstrom L. & Ketola T. 2017. BioRxiv 186254. 2. Lee C.E. & Gelembiuk G.W. 2008. Evol. Appl. 1: 427–448. 3. Darwin C. 1859. Murray, London.peerReviewe