Mutualisms are key determinants of community assembly and composition, but urbanization can alter the dynamics of these interactions and associated effects on ecosystem functions. Legume–rhizobia mutualisms are a model interaction to evaluate the ecological and ecosystem‐level effects of urbanization, particularly urban‐driven eutrophication and nitrogen (N) deposition. Here, we evaluated how urbanization affected the ecology of the mutualism between white clover Trifolium repens and its rhizobial symbiont Rhizobium leguminosarum symbiovar trifolii along an urbanization gradient. We found that the abundance of rhizobium nodules on white clover decreased with urbanization. White clover acquired N from mixed sources of N fixation and uptake from the soil for the majority of the urbanization gradient, but white clover primarily acquired N from the soil rather than N fixation by rhizobia at the urban and rural limits of the gradient. Importantly, we identified soil N as a critical nexus for urban‐driven changes in the white clover–rhizobium mutualism. Taken together, our results demonstrate that urbanization alters the ecological consequences of a legume–rhizobium mutualism, with direct and indirect effects of the urban landscape on an ecologically‐important mutualistic interaction.

Urban environments represent globally replicated, large-scale disturbances to the landscape, providing an ideal opportunity to study parallel evolution in natural populations on a large scale. In recent years, there has been a rapid increase in the number of studies investigating evolutionary responses of a diverse range of taxa across multiple cities. Although parallel evolutionary responses across independent urban environments will depend on the extent to which urban environments converge on similar biotic and abiotic environments, the extent to which cities are environmentally similar has not yet fully been integrated into studies of urban evolution. This chapter begins by asking: Do species display parallel evolutionary responses across independent urban environments? It then briefly reviews a subset of the environmental factors that have driven parallel responses to cities (heat islands, pollution, and habitat fragmentation) and discusses some of the potential causes of non-parallelism. Finally, it ends with practical considerations for the design of future studies aiming to examine parallel evolutionary responses to urbanization. Understanding the shared and unique features of urban environments and identifying parallel species responses to rapid and ongoing urban development will provide important insight into the ubiquity of parallel evolution in nature.

1. A fundamental goal of community ecology is to understand the drivers of community assembly and diversity. Local factors acting on community assembly are typically related to environmental conditions while regional factors are typically related to dispersal. Previous research has not consistently demonstrated | 1679

Resilience of ecosystems to the sudden decline of large‐bodied species is dependent on characteristics of surviving guild members. However, that response may also be mediated by local habitat conditions. Here, we examine the mechanisms behind the observed lack of functional compensation in the algal‐grazing guild by insect grazers following the decline of tadpole grazers in a forested Panamanian stream. We examined: (1) shifts to the individual size distribution of insect grazers between pre‐ and post‐tadpole declines in pool and riffle habitats; (2) tadpole and insect preferences for small‐, medium‐, and large‐sized diatoms; and (3) a causal explanation for why insects did not functionally compensate for tadpole declines. The size distribution of insect grazers following tadpole declines differed between habitats, becoming uniform in pools and more right skewed toward a smaller size class in riffles. In both habitats, tadpoles selectively consumed medium‐sized diatoms but avoided the largest‐sized diatoms. In contrast, grazing insects selectively consumed small‐sized diatoms, but switched to medium‐sized diatoms after tadpole declines. Tadpole declines led to the loss of the strongest interactions between consumers and diatoms. Smaller‐bodied grazing insects could not duplicate these interactions, even with a shift in resource use, providing an explanation for the lack of functional compensation. Furthermore, tadpole declines led to different community structures in each habitat indicating that local habitat conditions mediated the response of surviving guild members. This suggests that the sudden decline of a large‐bodied species does not lead to a singular outcome for the surviving community.

1. Trichoptera is an ecologically and taxonomically diverse order, and caddisfly species are under increasing pressure from anthropogenic threats to larval habitats, rivers, and streams.2. This study evaluated long-term changes in caddisfly communities of the Ogeechee River, a subtropical blackwater river in the south-eastern U.S. Coastal Plain, to understand how changes manifest as a result of ongoing human impacts. Two datasets separated by more than 30 years were used, each representing a 2-year monthly quantitative sampling effort (1981-1983; 2015-2017).3. Community structure of the Ogeechee River caddisflies significantly changed, though not in ways that were predicted. The average sensitivity values of the caddisfly community declined, contrary to the expectation that increasing human impacts on a river ecosystem would promote the survival of more pollution-tolerant taxa. 4. Generic richness increased in the 2010s from the 1980s, perhaps as a result of relaxed competition following declines of large, dominant taxa. The increases in various taxa have resulted in similar overall abundance metrics between time periods, although other studies of Ogeechee River invertebrates indicate that the biomass of the new taxa is far lower than that produced by the assemblages of the 1980s. Functional richness, evenness, and dispersion were higher in the 2010s, but divergence was not.5. This suggests that more nuanced monitoring efforts, focused on the threats to ecological function and the role of caddisflies (and other sensitive freshwater organisms), will be required to evaluate the changes in community structure and determine which taxa are most adversely affected.

Urbanization drastically alters landscapes in ways that can threaten local biodiversity. Although species loss has been well documented in urban habitats, why some species persist and not others, and how species interactions change remain poorly understood, especially for species with specialized niche requirements. Here, we test the hypothesis that urbanization disrupts specialized plant-herbivore interactions, and these effects vary according to the characteristics of both cities and the features of the organisms themselves. To test this hypothesis, we surveyed milkweed specialist herbivore communities in the early and late growing season of the common milkweed (Asclepias syriaca) across six cities that varied in size by two orders of magnitude. Four results are most important to answering our research questions: (1) the abundance of herbivore species was higher in urban than in rural habitats, whereas leaf herbivory was higher in rural than in urban habitats, and these effects varied between seasons and among cities; (2) the higher species diversity and abundance are likely due to a few species being more associated with rural habitats and other species more common in urban habitats, and thus, urbanization alters insect community composition; (3) the species with the lowest dispersal abilities, Rhyssomatus lineaticollis and Liriomyza asclepiadis, were those that were most strongly affected by urbanization, with R. lineaticollis less abundant and L. asclepiadis more abundant in urban areas; and (4) urbanization influenced plant-herbivore interactions by reducing herbivory, but it did not alter species interactions among herbivorous insects. Biodiversity loss, particularly declines of habitat and host specialists, in urban areas remains a critical concern for conservation. Our results indicate that at least some specialist herbivores are more abundant in urban areas than in rural areas and that species interactions remain intact. Lindsay S. Miles and David Murray-Stoker contributed equally to the work reported here.

Mutualisms are key determinants of community assembly and composition, but urbanization can alter the dynamics of these interactions and associated effects on ecosystem functions. Legume-rhizobia mutualisms are a model interaction to evaluate the ecological and ecosystem-level effects of urbanization, particularly urban-driven eutrophication and nitrogen (N) deposition. Here, we evaluated how urbanization affected the ecology of the mutualism between white clover (Trifolium repens) and its rhizobial symbiont (Rhizobium leguminosarum symbiovar trifolii) along an urbanization gradient. We found that the abundance of rhizobium nodules on white clover decreased with urbanization. White clover acquired N from mixed sources of N fixation and uptake from the soil for the majority of the urbanization gradient, but white clover primarily acquired N from the soil rather than N fixation by rhizobia at the urban and rural limits of the gradient. Importantly, we identified soil N as a critical nexus for urban-driven changes in the white clover-rhizobium mutualism. Taken together, our results demonstrate that urbanization alters the ecological consequences of a legume-rhizobium mutualism, with direct and indirect effects of the urban landscape on an ecologically-important mutualistic interaction.

13Swan and Brown (2017) recently addressed the effects of restoration on stream 14 communities under the meta-community framework. Using a combination of headwater and 15 mainstem streams, Swan and Brown (2017) evaluated how position within a stream network 16 affected the outcome of restoration on invertebrate communities. Ostensibly, their hypotheses 17 were partially supported as restoration had stronger effects in headwater streams: invertebrate 18 taxonomic richness was increased and temporal variability decreased in restored reaches; 19 however, these results were not consistent upon closer scrutiny for both the original paper (Swan 20 and Brown 2017) and the later erratum (Swan and Brown 2018). Here, I provide a secondary 21 analysis of the data, with hypotheses and interpretations in the context of stream, 22 metacommunity, and restoration ecology. I did not find any effects of restoration on local 23 diversity, spatial dissimilarity, or temporal variability, let alone differential effects of restoration 24 between headwaters and mainstems; these results are contrary Swan and Brown (2017, 2018), 25 who reported that restoration increased taxonomic richness, increased spatial dissimilarity, and 26 decreased temporal variability in restored headwater streams. I demonstrate further that the 27 statistical tests conducted by Swan and Brown (2017, 2018) were invalid and, therefore, 28 recommend the use of the results presented here. More broadly, I suggest that river and stream 29 restoration will likely have greater success if a regional approach is taken to designing and 30 implementing restoration projects. 31Keywords: biodiversity, community ecology, freshwater ecology, metacommunity theory, open 32 science, restoration ecology 33In a recent study, Swan and Brown (2017) evaluated how restoration affected community 35 diversity in streams through the use of metacommunity theory. Under this framework, local 36