1. Coexistence between plant species is well known to depend on the outcomes of species interactions within an environmental context. The incorporation of environmental variation into empirical studies of coexistence are rare, however, due to the complex experiments needed to do so and the lack of feasible modelling approaches for determining how environmental factors alter specific coexistence mechanisms.2. In this article, we present a simple modelling framework for assessing how variation in species interactions across environmental gradients impact on niche overlap and fitness differences, two core determinants of coexistence. We use a novel formulation of an annual plant population dynamics model that allows for competitive and facilitative species interactions and for variation in the strength and direction of these interactions across environmental gradients. Using this framework, we examine outcomes of plant-plant interactions between four commonly co-occurring annual plant species from Western Australian woodlands. We then determine how niche overlap and fitness differences between these species vary across three environmental gradients previously identified as important for structuring diversity patterns in this system: soil phosphorus, shade and water.3. We found facilitation to be a widespread phenomenon and that interactions between most species pairs shift between competitive and facilitative across multiple environmental gradients. Environmental conditions also altered the strength, direction and relative variation of both niche overlap and fitness differences in nonlinear and unpredictable ways. Synthesis.We provide a simple framework for incorporating environmental heterogeneity into explorations of coexistence mechanisms. Our findings highlight the importance of the environment in determining the outcome of species interactions and the potential for pairwise coexistence between species. The prevalence of facilitation in our system indicates a need to improve current theoretical frameworks of coexistence to include noncompetitive interactions and ways of translating these effects into explicit predictions of coexistence. Our study also suggests a need for further research into determining which factors result in 1840 | Journal of Ecology BIMLER Et aL.

Alien plant species are known to have a wide range of impacts on recipient communities, from resident species' exclusions to coexistence with resident species. It remains unclear; however, if this variety of impacts is due to different invader strategies, features of recipient communities or both. To test this, we examined multiple plant invasions of a single ecosystem in southwestern Australia. We used extensive community data to calculate pairwise segregation between target alien species and many co-occurring species. We related segregation to species' positions along community trait hierarchies and identified at least two distinct invasion strategies: 'exploiters' which occupy high positions along key trait hierarchies and reduce local native species diversity (particularly in nutrient-enriched situations), and 'coexisters' who occupy intermediate trait positions and have no discernable impact on native diversity. We conclude that trait hierarchies, linked to measures of competition, can provide valuable insights about the processes driving different invasion outcomes.

Community ecology is frequently invoked as complementary to and useful for guiding ecological restoration. While the conceptual literature is devoted to this unification, first‐hand accounts from practitioners and ecologists suggest that integration may be weak in practice. To date, there have been no analyses of how extensively community ecology theory appears in the empirical restoration literature. We address this knowledge gap with the first quantitative assessment of the extent to which community ecology concepts appear in empirical restoration literature by analysing the use of community ecology theories, concepts and conceptually derived tools in the design and interpretation of 1,000+ experimental ecological restoration studies over time (20 years) across all global regions. We also gauge general trends in author demographics, focal ecosystems and taxa targeted by these studies. We found that the incorporation of community ecology into restoration research has increased significantly in recent years. Community assembly and succession theories were the community ecology concepts integrated most often, while the functional traits framework and evolutionary theory have increased in usage recently. Synthesis and applications. Restoration endeavours are increasingly infused with elements of community ecology. Our results highlight the widespread application of deterministic models of community structure in restoration design and the rise of ecosystem service and function‐focused restoration. With this diagnostic summary of these applications, ecologists and restoration practitioners can move forward while directly exploring underdeveloped synergies between theory and practice.