The study evaluates the dynamics of a invasions by the aquatic invasive freshwater macroalga, Nitellopsis obtusa, in lakes across the upper Midwest of the US. Using interannual variability and a latitudinal gradient as a proxy for future climate change we assess the interaction between two global change stressors: climate change and biological invasions. This dataset includes all underlying data and code used for all analyses presented in the article the creation of all data figures. The data includes locations of sampling locations, field data on plant community composition and abundance, and climate data for sampling sites used to quantify annual conditions. All analysis code is written in the R statistical programing languge.

Beaury et al. (2020) attempt to address the scale dependence of evidence for biotic resistance by including environmental covariates that can account for total species richness. However, this approach will incorrectly estimate relationships, driven by the accuracy of the covariates rather than the true relationship between native and non-native species.

Most of the classical theory on species coexistence has been based on species-level competitive trade-offs. However, it is becoming apparent that plant species display high levels of trait plasticity. The implications of this plasticity are almost completely unknown for most coexistence theory. Here, we model a competition-colonization trade-off and incorporate trait plasticity to evaluate its effects on coexistence. Our simulations show that the classic competition-colonization trade-off is highly sensitive to environmental circumstances and coexistence only occurs in narrow ranges of conditions. The inclusion of plasticity, which allows shifts in competitive hierarchies across the landscape, leads to coexistence across a much broader range of competitive and environmental conditions including disturbance levels, the magnitude of competitive differences between species, and landscape spatial patterning. Plasticity also increases the number of species that persist in simulations of multispecies assemblages. Plasticity may generally increase the robustness of coexistence mechanisms and be an important component of scaling coexistence theory to higher diversity communities.

Aim: Biotic homogenization (BH), a reduction in the distinctness of species composition between geographically separated ecological communities in a region, is an important but underappreciated potential consequence of biological invasions. While BH theory has always considered invasions, it has generally been in a relatively narrow context, i.e., that the cosmopolitan nature of invasive species increases BH because of their shared presence across many locations. We sought to evaluate this component of BH as well as broader effects of invasive species on BH through changes in native communities, including overall reductions in species richness or shifts in species composition. Location: Minnesota, USA Time Period: 2002-2014 Major Taxa Studied: Aquatic macrophytes, including both vascular plants and attached macroalgae. Methods: We used surveys of aquatic macrophyte communities from 1,102 shallow lakes in Minnesota, USA (including 248 lakes with repeated surveys) to evaluate relationships between invasion, native species, and BH. Results: We found that the presence of invasive species was associated with BH and that this pattern was reflected in both the total community (i.e., with invasive species included) and in the composition of the native species community alone. We found that invaded lakes were more compositionally similar to each other than uninvaded lakes, but that both groups were becoming more similar over time—despite neither group exhibiting declines in species richness. This pattern was largely driven by shifts in the native community itself, with common species becoming more widespread and rare species becoming rarer. Main Conclusions: Invasive species increase measures of community similarity through their own presence in multiple locations, and also by influencing the composition of native species. These patterns have important implications for conservation and management and suggest that BH should be considered more widely in evaluating the impacts of biological invasions and developing response strategies.

The spread of invasive species is a major component of global ecological change and how and when to manage particular species is a diicult empirical question. Ideally, these decisions should be based on the speciic impacts of invading species including both their efects on native competitors and how they may or may not play similar roles in broader ecosystem functioning. Halophila stipulacea is an invasive seagrass currently spreading through the Caribbean, and as seagrasses are foundation species, the efects of invasion have the potential to be particularly far-reaching. To evaluate the impacts of H. stipulacea we quantiied spread and potential for displacement of native seagrasses as well as the efects of invasion on multiple ecosystem processes, particularly resource support for higher trophic levels and habitat creation. Long-term monitoring suggested that H. stipulacea likely displaces some native seagrasses (Syringodium filiforme and Halodule wrightii), but not others. Halophila stipulacea had lower N and protein levels and higher C:N ratios than native seagrasses, and as such is a poorer quality resource for consumers. We also observed signiicantly lower consumption of H. stipulacea than the native S. filiforme but limited diferences compared to Thalassia testudinum. We found H. stipulacea created a more nutrient limited environment than T. testudinum and there were signiicantly distinct invertebrate assemblages in native- and invasive- dominated seagrass beds, but no diference in species richness or invertebrate biomass. These results suggest that the spread of H. stipulacea would impact a variety of ecological processes, potentially restructuring seagrass ecosystems through both direct impacts on environmental conditions (e.g., nutrient availability) and indirect food web interactions.

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