The effect of temperature, soil nitrogen and gastropods on _Thuja plicata_ growth and reproduction

Humans are changing the environment. For example, nitrogen deposition, rising temperatures, and non-native species are influencing plant communities. These changes have and will continue to affect trees, thus, understanding the response of species to global change will help conservationists plan for the future. Urban areas already experience higher temperatures, elevated CO~2~, greater nitrogen levels, and more non-native species compared to rural areas. The response of trees to urban parks and park edges can therefore be used as a proxy for the net effects of global change on trees. We investigate the growth and reproduction of _Thuja plicata_, a native Pacific Northwest conifer, in both urban and rural forest fragments to understand global change impacts. Data collected from sites include hourly temperature, soil NO~3~^-^, seedling counts, and an increment core. After observing extremely low conifer germination rates across sites, we concluded that factors such as herbivory might be important. Gastropods have been shown to impact communities through consumption of plants at the seedling stage, and to limit seedling survival of a European conifer. The effects of soil moisture, soil nitrogen, and gastropod herbivory on _Thuja plicata_ seedlings was analyzed experimentally to determine the relative effect each might be having on the observed germination rate. Our results suggest that urban forest edges resemble future global change conditions of higher temperature and nitrogen. These global change factors appear to be positively influencing tree growth, suggesting that _Thuja plicata_ will benefit from future conditions. However, low seedling recruitment may be a concern, because it appears that urban and rural forests are currently failing to regenerate on their own. Introduced gastropods could play a role, as they have the ability to reduce seedling biomass significantly. The relative impacts of invasive slug herbivory and other global change factors on native conifer recruitment should be prioritized in future study

Competition and Predation in Simple Food Webs: Intermediately Strong Trade-offs Maximize Coexistence

Competition and predation are fundamental interactions structuring food webs. However, rather than following these neat theoretical categories, mixed interactions are ubiquitous in nature. Of particular importance are omnivorous species, such as intra-guild predators that can both compete with and predate on their prey. Here we examine trade-offs between competitive and predatory capacities by analyzing the entire continuum of food web configurations existing between purely predator-prey and purely competitive interactions of two consumers subsisting on a single resource. Our results show that the range of conditions allowing for coexistence of the consumers is maximized at intermediately strong trade-offs. Even though coexistence under weak trade-offs and under very strong trade-offs is also possible, it occurs under much more restrictive conditions. We explain these findings by an intricate interplay between energy acquisition and interaction strength

Modeling the ecology and evolution of communities: A review of past achievements, current efforts, and future promises

Background: The complexity and dynamical nature of community interactions make modeling a useful tool for understanding how communities develop over time and how they respond to external perturbations. Large community-evolution models (LCEMs) are particularly promising, since they can address both ecological and evolutionary questions, and can give rise to richly structured and diverse model communities. Questions: Which types of models have been used to study community structure and what are their key features and limitations? How do adaptations and/or invasions affect community formation? Which mechanisms promote diverse and table communities? What are the implications of LCEMs for management and conservation? What are the key challenges for future research? Models considered: Static models of community structure, demographic community models, and small and large community- evolution models. Conclusions: LCEMs encompass a variety of modeled traits and interactions, demographic dynamics, and evolutionary dynamics. They are able to reproduce empirical community structures. Already, they have generated new insights, such as the dual role of competition, which limits diversity through competitive exclusion, yet facilitates diversity through speciation. Other critical factors determining eventual community structure are the shape of trade-off functions, inclusion of adaptive foraging, and energy availability. A particularly interesting feature of LCEMs is that these models not only help to contrast outcomes of community formation via species assembly with those of community formation via gradual evolution and speciation, but that they can furthermore unify the underlying invasion processes and evolutionary processes into a single framework

CO2, nitrogen, and diversity differentially affect seed production of prairie plants

Plant species composition and diversity is often influenced by early life history stages; thus, global change could dramatically affect plant community structure by altering seed production. Unfortunately, plant reproductive responses to global change are rarely studied in field settings, making it difficult to assess this possibility. To address this issue, we quantified the effects of elevated CO2, nitrogen deposition, and declining diversity on inflorescence production and inflorescence mass of 11 perennial grassland species in central Minnesota, USA. We analyzed these data to ask whether (1) global change differentially affects seed production of co-occurring species; (2) seed production responses to global change are similar for species within the same functional group (defined by ecophysiology and growth form); and (3) seed production responses to global change match productivity responses. We found that, on average, allocation to seed production decreased under elevated CO2, although individual species responses were rarely significant due to low power (CO2 treatment df = 2). The effects of nitrogen deposition on seed production were similar within functional groups: C4 grasses tended to increase while C3 grasses tended to decrease allocation to seed production. Responses to nitrogen deposition were negatively correlated to productivity responses, suggesting a trade-off. Allocation to seed production of some species responded to a diversity gradient, but responses were uncorrelated to productivity responses and not similar within functional groups. Presumably, species richness has complex effects on the biotic and abiotic variables that influence seed production. In total, our results suggest that seed production of co-occurring species will be altered by global change, which may affect plant communities in unpredictable ways. Although functional groups could be used to generalize seed production responses to nitrogen deposition in Minnesota prairies, we caution against relying on them for predictive purposes without a mechanistic understanding of how resource availability and biotic interactions affect seed production

CO2, nitrogen, and diversity differentially affect seed production of prairie plants

Plant species composition and diversity is often influenced by early life history stages; thus, global change could dramatically affect plant community structure by altering seed production. Unfortunately, plant reproductive responses to global change are rarely studied in field settings, making it difficult to assess this possibility. To address this issue, we quantified the effects of elevated CO2, nitrogen deposition, and declining diversity on inflorescence production and inflorescence mass of 11 perennial grassland species in central Minnesota, USA. We analyzed these data to ask whether (1) global change differentially affects seed production of co-occurring species; (2) seed production responses to global change are similar for species within the same functional group (defined by ecophysiology and growth form); and (3) seed production responses to global change match productivity responses. We found that, on average, allocation to seed production decreased under elevated CO2, although individual species responses were rarely significant due to low power (CO2 treatment df = 2). The effects of nitrogen deposition on seed production were similar within functional groups: C4 grasses tended to increase while C3 grasses tended to decrease allocation to seed production. Responses to nitrogen deposition were negatively correlated to productivity responses, suggesting a trade-off. Allocation to seed production of some species responded to a diversity gradient, but responses were uncorrelated to productivity responses and not similar within functional groups. Presumably, species richness has complex effects on the biotic and abiotic variables that influence seed production. In total, our results suggest that seed production of co-occurring species will be altered by global change, which may affect plant communities in unpredictable ways. Although functional groups could be used to generalize seed production responses to nitrogen deposition in Minnesota prairies, we caution against relying on them for predictive purposes without a mechanistic understanding of how resource availability and biotic interactions affect seed production

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi-arid annual plant communities

Climate change is predicted to have profound consequences for multispecies coexistence, and thus, patterns of biological diversity. These consequences will be mediated by direct and indirect impacts of environmental change on species’ vital rates and interactions. While the impacts of environmental change on individual species has received much attention to date, the consequences for coexistence mediated by changes in the strength and direction of multispecies interactions are not as well understood. To investigate how coexistence dynamics may be sensitive to environmental change, we conducted a field experiment in a diverse semi-arid annual plant system. We imposed a water manipulation treatment in two sites that vary in aridity and associated rainfall. Focusing on four common annual plant species in these sites, we quantified the fecundity (seed production) of individuals in response to a gradient of intra- and interspecific competitor densities and aridity. We then used these fecundities to parameterize an annual plant population model and examine the influence of aridity and species identity on resultant coexistence dynamics (as a function of stabilizing niche differences and fitness inequalities). While the responses of some vital rates and competitive impacts to watering varied somewhat predictably across sites, coexistence metrics encapsulating changes in these vital rates and interaction strengths did not. Fitness inequalities among our focal species were driven largely by differences in sensitivity to competition, which were almost always much greater than the magnitude of stabilizing niche differences. These findings were surprising given observational evidence suggesting that these species do coexist at local scales in these natural communities. Synthesis. Our study is one of the first to explicitly consider the influence of environmental variation on the individual components of coexistence outcomes. We show that environmental change has the ability to influence coexistence not only through direct pathways (i.e., vital rates), but also indirect pathways (i.e., species interactions). Despite the consistency of many of the responses of these individual components to environmental variation, their combined influence on predictions of both current and future coexistence remains unclear

Soil microbes drive the classic plant diversity­ productivity pattern

Ecosystem productivity commonly increases asymptotically with plant species diversity, and determining the mechanisms responsible for this well-known pattern is essential to predict potential changes in ecosystem productivity with ongoing species loss. Previous studies attributed the asymptotic diversity–productivity pattern to plant competition and differential resource use (e.g., niche complementarity). Using an analytical model and a series of experiments, we demonstrate theoretically and empirically that host-specific soil microbes can be major determinants of the diversity–productivity relationship in grasslands. In the presence of soil microbes, plant disease decreased with increasing diversity, and productivity increased nearly 500%, primarily because of the strong effect of density-dependent disease on productivity at low diversity. Correspondingly, disease was higher in plants grown in conspecific-trained soils than heterospecific-trained soils (demonstrating host-specificity), and productivity increased and host-specific disease decreased with increasing community diversity, suggesting that disease was the primary cause of reduced productivity in species-poor treatments. In sterilized, microbe-free soils, the increase in productivity with increasing plant species number was markedly lower than the increase measured in the presence of soil microbes, suggesting that niche complementarity was a weaker determinant of the diversity–productivity relationship. Our results demonstrate that soil microbes play an integral role as determinants of the diversity–productivity relationship

Employing Plant Functional Groups to Advance Seed Dispersal Ecology and Conservation

Seed dispersal enables plants to reach hospitable germination sites and escape natural enemies. Understanding when and how much seed dispersal matters to plant fitness is critical for understanding plant population and community dynamics. At the same time, the complexity of factors that determine if a seed will be successfully dispersed and subsequently develop into a reproductive plant is daunting. Quantifying all factors that may influence seed dispersal effectiveness for any potential seed-vector relationship would require an unrealistically large amount of time, materials and financial resources. On the other hand, being able to make dispersal predictions is critical for predicting whether single species and entire ecosystems will be resilient to global change. Building on current frameworks, we here posit that seed dispersal ecology should adopt plant functional groups as analytical units to reduce this complexity to manageable levels. Functional groups can be used to distinguish, for their constituent species, whether it matters (i) if seeds are dispersed, (ii) into what context they are dispersed and (iii) what vectors disperse them. To avoid overgeneralization, we propose that the utility of these functional groups may be assessed by generating predictions based on the groups and then testing those predictions against species-specific data. We suggest that data collection and analysis can then be guided by robust functional group definitions. Generalizing across similar species in this way could help us to better understand the population and community dynamics of plants and tackle the complexity of seed dispersal as well as its disruption

Local temperature and ecological similarity drive distributional dynamics of tropical mammals worldwide

AimIdentifying the underlying drivers of speciesâ distributional dynamics is critical for predicting change and managing biological diversity. While anthropogenic factors such as climate change can affect species distributions through time, other naturally occurring ecological processes can also have an influence. Theory predicts that interactions between species can influence distributional dynamics, yet empirical evidence remains sparse. A powerful approach is to monitor and model local colonization and extinctionâ the processes that generate change in distributions over timeâ and to identify their abiotic and biotic associations. Intensive cameraâ trap monitoring provides an opportunity to assess the role of temperature and species interactions in the colonization and extinction dynamics of tropical mammals, many of which are species of conservation concern. Using data from a panâ tropical monitoring network, we examined how shortâ term local temperature change and ecological similarity between species (a proxy for the strength of species interactions) influenced the processes that drive distributional shifts.LocationTropical forests worldwide.Time period2007â 2016.Major taxa studiedTerrestrial mammals.MethodsWe used dynamic occupancy models to assess the influence of the abiotic and biotic environment on the distributional dynamics of 42 mammal populations from 36 species on 7 tropical elevation gradients around the world.ResultsOverall, temperature, ecological similarity, or both, were linked to colonization or extinction dynamics in 29 populations. For six species, the effect of temperature depended upon the local mammal community similarity. This result suggests that the way in which temperature influences local colonization and extinction dynamics depends on local mammal community composition.Main conclusionsThese results indicate that varying temperatures influence tropical mammal distributions in surprising ways and suggest that interactions between species mediate distributional dynamics.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149732/1/geb12908.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149732/2/geb12908_am.pd