As a result of non-native species introductions, novel plant communities are forming across an increasingly large portion of the earth’s land surface. Novel plant communities differ in composition from historical communities, and thus there is a growing need to understand how they function. We still have a relatively poor understanding of the degree to which environmental variation influences the outcomes of species interactions in novel communities and if these dynamics differ for native and non-native species. Improving our understanding of the mechanisms behind interaction-mediated changes in community diversity is an important step in being able to predict the effects of global change on the formation and persistence of novel plant communities. In this talk, I discuss the results from a field experiment testing how local-scale environmental gradients impact the outcomes of complex species interactions occurring among native and non-native species in the annual plant-dominated York Gum woodlands of southwest Western Australia. Specifically, our study examines the extent to which outcomes of direct and higher-order species interactions differ along gradients in canopy cover and soil phosphorus, as well as by species attributes and the species and functional composition of their neighbourhoods.
Results/Conclusions
We found that the fitness of focal species was strongly impacted by both local environmental factors and competition. Specifically, the effects of overhead canopy cover and the details of focal plant’s competitive neighbourhoods (abundance, composition, and functional diversity) had stronger effects on fitness outcomes than elevated soil phosphorus resulting from anthropogenic eutrophication. We also found that the relative importance of abiotic and biotic aspects of local environments varied among native and non-native species, with native species having more consistent responses to changes in their environment than tested exotics. Our results highlight that species interactions in diverse plant communities are the net result of a variety of complex species interactions. We found strong evidence that under some common abiotic environmental conditions dense local neighbourhoods significantly facilitate many native plant species in this system, highlighting the need to look beyond competitive dynamics in novel communities. When taking large-scale patterns of species occurrences into account from observational studies, our experimental findings underscore that novel plant community dynamics may be influenced to large degree by complex interactions occurring over small spatial and temporal scales.