The fate of individual species depends on their ability to establish and persist when at low densities, just as the diversity of ecological communities depends on the establishment and persistence of low-density, ‘invader’ species. Theory predicts that abiotic conditions and the competitive make-up of the resident community generate a fitness surface that limits the phenotypes of species that can establish, creating an intricate dependency of diversity on interactions between abiotic conditions, invader traits and resident traits. We use an invasion experiment to ask how leaf traits of 20 plant species (invaders) alter their absolute fitness in experimental fragments hosting over 70 resident species by testing two hypotheses: (i) differences in traits between introduced and resident species determine survival of the introduced species; and (ii) survival of the introduced species depends on traits matching underlying abiotic conditions. In our analyses, we tested whether transplant survival depended on transplant traits, the distance of those traits from mean traits of the resident community, and variation in resident community traits, all within the context of abiotic conditions.
Results/Conclusions
We found that an interaction between invader traits and abiotic conditions determined survival, as did interactions between functional diversity of residents and abiotic conditions. Optimal invader traits depended on the abiotic environment, with higher soil nutrients increasing survival of high SLA species. Although differences in mean trait values between invaders and the resident community had no effect on the fitness of invader species, variation in resident traits lowered invader fitness and had especially strong effects in low resource environments. Unlike other abiotic conditions, fragment size had consistent effects irrespective of invader identity, decreasing survival in larger fragments. Our results show that abiotic and biotic factors interact in complex ways to determine the likelihood and identity of invaders, creating fitness landscapes that structure local diversity and the functional identities of new species.