Community Level Impacts Of Microstegium Vimineum On Arthropod Community Structure And Foodweb Dynamics In A Temperate Deciduous Forest

Invasion by non-native primary producers are generally expected to lead to a decline in native species richness, however in some cases, these invasions can actually lead to an increase in diversity and abundance of certain groups of organisms. Arthropods are extremely sensitive to changes in the plant community, particularly herbivores, and the response of these primary consumers can influence predator populations. Microstegium vimineum is an invasive C4 grass that has developed strong populations in the understory of temperate deciduous forests along the east coast of the U.S. This work evaluates the influence that this invader may have on insect and spider abundance and diversity, including changes at the trophic group and functional guild levels. Additionally we evaluate the impacts of both an increase in invasion density and a decrease in native plant diversity on arthropod community structure. In general, we find a significant increase in herbivore abundance, primarily as a result in the increased abundances of concealed chewers, free-living chewers and free-living sap feeders. Free-living sap-feeders also showed an increase in biomass. Spider abundance and diversity also increased in association with invasion by M. vimineum. Both active hunters and sit-and-wait predators showed significant increases in invaded sites. The ratio of adult:immature spiders however had a negative relationship with invasion. These changes in the arthropod community appear to be related to both changes in vegetation structure as well as changes in plant biomass. We found increased abundances in our treatments in which invasion density increased and decreases in the arthropod community in sites where native plants were removed from the system. We also show some support for the idea that carnivores, specifically spiders, may respond more strongly to changes in vegetative complexity, while herbivores, specifically leaf hoppers, may respond more strongly to changes in plant biomass.

There is a clear crisis in the maintenance of global biodiversity worldwide. Climate change and widespread habitat loss, degradation and fragmentation are exerting strong, landscape-scale pressures on biodiversity. Negative impacts of these stressors are seen at all levels of biological organization, but studies at the level of community and food webs are relatively rare. This is in large part due to the large spatial and temporal scales at which food webs operate. Natural microcosms (food webs operating at small spatial scales) have been used to experimentally approach complex theoretical and applied questions in ecology, and have provided many important insights to date. In particular, moss micro-arthropod communities have been used extensively for the study of the effects of habitat fragmentation. Here, we used this ecosystem in a replicated, manipulative experiment to study the combined effects of warming and habitat fragmentation on community and food web structure. In order to do this, we developed tools to estimate diet of Oribatid mites, which were one of the most abundant and diverse taxa in the food web. Stable isotope techniques and analysis of mouthpart morphology allowed us to describe a food web for a moss-microarthropod ecosystem from south eastern Australia. The food web comprised over 100 taxa organized into a suite of feeding guilds: herbivores, fungivores, detritivores, lichenivores and predators. The speciose nature of the system is a strength, and the challenge of dealing with the taxonomy, data storage and food web analysis was met by development of a publicly available taxonomy database/tool, and a food web analysis package. We described temporal variation in a suite of food web attributes across one summer and winter. We found marked differences in food web structure between sampling occasions, with patterns suggestive of temperature- and humidity-driven changes in resource availability. To test the generality of food web structure in our system as compared to other ecosystems, food web attributes were compared to those of a large compilation of food webs from around the world. Comparison revealed similarities in food web structure to other communities across a range of spatial scales and ecosystems. Dissimilarities were also found and discussed. We concluded that the moss-microarthropod system provides an adequate model for achieving a deeper understanding of processes in community ecology. Our experiments assess the assembly of moss-microarthropod communities after an extreme high-temperature event, against a back-drop of altered climate, and in the context of habitat fragmentation. Data provide initial indications that isolated habitats may be more susceptible to negative impacts of warming than less isolated habitats. Variability of responses among replicate landscapes was considerable, with some being relatively resilient. Future understanding of the underpinnings of this resilience could point to management options for resisting rapid environmental change. Our results highlight the value of dispersal in disturbed landscapes and of disturbance-buffered communities in the face of climate change. Given the importance of synergies between disturbances as drivers of biodiversity loss, and considering the paucity of data assessing the combined impacts of climate change and habitat fragmentation on food webs, further research must be carried out in this area. This could build and draw on the model system we have validated for that purpose, enabled by the suite of new tools generated here.

The effects of human-mediated activities on soil quality and functioning have been assessed. Composition and changes in arthropod community structure and laboratory bioassays were performed on urban soils in order to understand the roles of metal contamination on soil organism activities and distribution. Then, comparison of urban, agricultural, industrial and forest soils were performed, monitoring Collembola species and functional traits composition, in order to assess if the impact of urban environment is greater than other kinds of anthropization. Soil organism community was analysed twice a years for evaluating the role of seasonality on anthropic impacted soils. The different kinds of anthropization firstly affected the abiotic properties of the sites. Agricultural and urban soils were the most impacted soils by human activities, which cause changes in vegetation cover, organic matter amounts and accumulation of hazardous elements and compounds. Soils organisms responded to soil abiotic modifications. In particular, in urban environment soil organisms were strongly reduced at high level of metal contamination, whereas organic matter content and climatic conditions played the main role at low-intermediate soil contamination. Collembola community showed a strong reduction in species richness in agricultural soils, with a consequent domination of few tolerant species. Collembola functional trait distribution was mainly affected by the presence and the type of litter and inputs of contaminants. In particular, agricultural environment favoured organisms with traits adapted to soil life surface, whereas forest soils favoured organisms with euedaphic characteristics. Industrial and urban soils showed organisms with both epiedaphic and euedaphic characteristics.

Changes to vegetation architecture within a natural habitat can have profound impacts upon ecological community function, but the relative influence of vegetation architecture itself and potential indirect influences of associated food resources are often difficult to disentangle. I present the results of a three-year study designed to address the community level impacts of changes in big sagebrush (Artemisia tridentata) architecture and associated prey availability upon the ground-dwelling arthropod community. Three experimental sagebrush architecture treatments (low, intermediate, and high foliage density) and two levels of prey insect availability treatment (natural and baited/increased prey availability) were imposed in a sage-steppe ecosystem. The ground-dwelling spider (top predators) and insect (prey) response to all combinations of the six treatments were assessed through abundances in pitfall traps. Chapter 2 demonstrates that changes in a single shrub's architecture did not markedly impact prey arthropod availability on the ground, though an overall increase in arthropod abundance was detected within baited shrubs. This indicates changes to vegetation architecture do not impact prey insect availability for ground-dwelling spiders. Thus, changes in shrub architecture and not the associated prey base directly alter the ground-dwelling spider community. Chapter 3 shows that architectural manipulation of a single sagebrush directly influences the ability of certain ground-dwelling spider guilds to persist beneath the shrub. Data within Chapters 2 and 3 support the conclusion that vegetation architecture directly affects ground-dwelling spider community structure and composition. Finally, Chapter 4 explores how the relative impacts of vegetation architecture and prey availability upon ecological communities can shift depending upon the spatial context in which the manipulations take place, given the differences in mobility of species within the grounddwelling spider and insect prey communities. Within this study, Diurnal and Nocturnal Wanderers responded to manipulations in prey availability at a larger spatial context (patches of 15 shrubs) while more stationary Trappers and Ambushers did not. Through simultaneous manipulation of vegetation architecture (Artemisia tridentata, big sagebrush) and associated insect prey base in different spatial contexts, this dissertation demonstrates that vegetation architecture directly affects ground-dwelling spider community organization at the species and guild levels of diversity. Shifts in spider (predator) functional diversity can ultimately impact arthropod decomposer and herbivore populations, influencing fundamental ecosystem processes such as decomposition and productivity.

Anthropic disturbances reduce ecosystem functionality by disrupting interactions between aboveground and belowground communities. Interactions between plants and belowground biota (i.e., soil fauna) shape ecosystem functions, diversity, and structure aboveground. In disturbance scenarios, some plant community attributes might influence the response of secondary consumers and decomposers (i.e., soil fauna) to new conditions. Both resource provision (i.e., litter), habitat availability, and trophic interactions can be affected by disturbance (i.e., management). The type and intensity of the disturbance regulate the community response aboveground, but response patterns for soil fauna are still unclear. A challenge for sustainable forest management is predicting belowground changes based on aboveground structural conditions and traits. Understanding the relationship between disturbance, plant traits, and soil fauna dynamics is relevant for predicting functional changes at the ecosystem level. Yet, the relative importance of those factors for soil fauna community structure in disturbance scenarios is uncertain. This dissertation explores this research gap in a woodland system by focusing on two disturbance types: 1) a gradient of strip-harvest intensity and 2) multiple nutrient enrichment. In woodlands, firewood harvest and fertilization are standard silvicultural practices with unknown consequences for soil biodiversity and function. First, I characterized the quantitative relationship between a gradient of harvest intensity and the microarthropod community response. For this, I analyzed the interplay of plant community structure, litterfall provision, and microarthropod community structure (Chapter 2). Second, I analyzed the impact of nutrient enrichment on soil fauna using the addition of three macronutrients: nitrogen (N), phosphorus (P), and potassium (K). This is the first time a multiple nutrient addition experiment, including K, was implemented in a temperate woody community. Using this experiment, I quantified the short-term impacts of multiple nutrient enrichment on microarthropod community structure (Chapter 3) and their functional role (Chapter 4). Overall, the results collectively suggest that intermediate levels of disturbance intensity and N addition do not represent ecological risks for microarthropod communities and their functional role in the short term. In this work, I discuss and contrast the relative importance of resource provision, resource quality, and plant community structure for microarthropods in woodlands under management. Considering these three aboveground elements can help design sustainable practices that allow soil health conservation and belowground ecosystem service provision.

Steep climatic gradients may select for clinal adaptation in plant functional traits with implications for species interactions and response to future climate change. Although local adaptation and plasticity in plant functional traits have been documented for many species, less is known about population level variation in plasticity and whether such variation is driven by adaptation to environmental variation. Whether clinal adaptation in plants cascades up to influence arthropod community structure and patterns of diversity is virtually unknown. We examined clinal variation in Artemisia californica traits and performance - and plastic responses to environmental change - in a common garden of plants sourced from populations spanning a 700 km gradient characterized (from south to north) by a fourfold increase in precipitation and a 61% decrease in interannual precipitation variation. Plants cloned from five populations along this gradient were grown for 3 years in treatments of high and low precipitation. We collected whole arthropod communities from common garden plants to test whether geographic patterns of intraspecific variation in A. californica lead to parallel patterns of variation in arthropod community structure. We found that genetically based physiological, herbivore defense, and phenological traits and plant performance in A. californica varied among source populations with most traits varying clinally in concordance with the steep latitudinal gradient in the abiotic environment and environmental variability. Overall, precipitation variability at population source sites was the best predictor of variation in plasticity among populations. Additionally, we found genetic variation in arthropod community structure, with density, evenness, and diversity increasing clinally with latitude. Overall, we show that patterns of intraspecific variation in arthropod communities correspond to patterns of variation in plant functional traits for this species. These striking, clinal patterns in plant traits and plasticity are indicative of adaptation to both the mean and variability of environmental conditions. Such clinal adaptation in plants is likely a primary factor influencing arthropod community structure and diversity at the landscape level. Our findings demonstrate that contemporary patterns of adaptation to environmental clines will mediate future plant responses to projected climate change, with implications for the maintenance of biodiversity at higher trophic levels.

Edge effects resulting from forest fragmentation are likely to alter the distributions and interactions of resident species. I evaluated changes in species composition, species turnover, and relative abundance of ground arthropods across replicated transects extending from regenerating clearcuts into old-growth Douglas-fir forests. Arthropods were collected from 3-August to 14-September in 1997 and 23-May 1998 to 31-July 1998 using pitfall traps. Pitfall traps were positioned at 75 m (in the clearcut), -25, 0 (forest edge), 50, 100 and 200 m into the forest in 1997. In 1998, traps were repositioned at 25, 0, 25, 50,lOO, and 200 m into the forest. Changes in species composition and relative abundance were compared using non-metric multidimensional scaling ordination. Two-hundred, five species representing 24,178 individuals were collected. Edge effects on species composition and relative abundance were apparent up to 100 m into old-growth forests. Species were characterized as edge-phobic (interior forest associates), edge-philic, edge-insensitive or as edge-input (clearcut associates). The majority of species were characterized as either edge-phobic or edge-input species. Seasonal patterns in activity are also reported. To further address the impacts of edges on community structure, changes in species abundance of predator taxa across the edge-forest gradient were compared to four models of resource partitioning. Observed patterns of species abundance did not differ across the edge-forest gradients and were consistent with a model of random assortment (or non-equilibrium) where an individual predator species utilizes resources independently of other predators. This pattern was consistent whether species abundance was expressed as numerical abundance or biomass. This study suggests that edge effects resulting from forest fragmentation alter species composition and may negatively affect interior forest species. Furthermore, although species composition changes across forest edges, this study suggests that resource partitioning by a trophic group such as predators remains unaffected by forest edges.

The "old-growth controversy" in the Pacific Northwest recognized thinning as the primary silvicultural practice for land managers to produce wildlife habitat while continuing to produce timber. For the foreseeable future, forest stands will be harvested to produce forest gaps and a patchwork of trees of different ages. In order to evaluate the effect of thinning on biodiversity, nine 15-year-old harvests of this type (age=70 years) were paired with adjacent old-growth and even-aged, unthinned "pole" stands. Since soil is the crucible of terrestrial biodiversity, it is critical to contrast the effects upon the forest floor of this future practice with current management. Soil and litter fauna were monitored along 250 meter transects (pitfall and Berlese sampling at ten-meter intervals) to meet the following objectives: 1) to determine biological diversity on public lands, per federal mandate, and use diversity as a management tool; 2) compare levels of biodiversity between three management strategies; 3) determine best methods to assay arthropod diversity; and 4) identify structural and environmental determinants of arthropod diversity and abundance. The study's hypotheses were: 1) old-growth forests will have greater arthropod diversity than thinned stands; 2) thinned stands will have greater arthropod diversity than unthinned stands; and 3) species found within old-growth stands, but not within unthinned pole stands, will also be found in thinned stands. This study contrasted nine Western Hemlock/Douglas-fir sites each with contrasting old-growth, thinned and unthinned pole management stands. Sites were equally blocked in Southern Oregon, the Coast Range, and the Cascade Mountains. No segment of the arthropod fauna. (i.e., pitfall-trapped epigeic macroarthropods, Berlese-extracted litter-dwelling meso- and microarthropods, or soil-dwelling microarthropods) exhibited a management (treatment) effect throughout the entire region. When the regional blocking was removed, within-region analysis generally revealed that old-growth was most distinct. Old-growth stands had the highest abundance of individuals, but were comprised of the fewest species. Thinned stands were characterized by the highest species richness. Within-region analysis revealed an interaction of management effects and specific locale effects; locale effects dominated for soil microarthropods and epigeic macroarthropods, while management options dominated for litter arthropods. Within the Southern Oregon region, I attempted to correlate arthropod community structure (canonical correspondence analysis (CCA) of within-stand samples) with a suite of soil chemical and microbiological descriptors. Full analysis of twelve variables within one exemplary stand revealed several potential trends (negative: dissolved organic carbon, soil moisture, distance from the beginning of the transect; positive: total CO2 field respiration, mineralizable nitrogen, water-induced respiration, substrate-induced respiration). Relatively shallow slopes and very low r-value coefficients of correlation characterized all statistical tests. Few of the trends apparent at one site were paralleled at more than one other site; at all sites potential correlates had very low r-values. No community revealed separate clouds in CCA analysis, indicating distinct "micro-communities" of arthropods inhabiting distinct micro-habitats. Lack of distinctive species assemblages and lack of correlation with microhabitat variables indicated that arthropods respond on different temporal and/or spatial scales then the microbial-oriented variables, and that each taxon is responding in an individual manner.

This open access book describes the serious threat of invasive species to native ecosystems. Invasive species have caused and will continue to cause enormous ecological and economic damage with ever increasing world trade. This multi-disciplinary book, written by over 100 national experts, presents the latest research on a wide range of natural science and social science fields that explore the ecology, impacts, and practical tools for management of invasive species. It covers species of all taxonomic groups from insects and pathogens, to plants, vertebrates, and aquatic organisms that impact a diversity of habitats in forests, rangelands and grasslands of the United States. It is well-illustrated, provides summaries of the most important invasive species and issues impacting all regions of the country, and includes a comprehensive primary reference list for each topic. This scientific synthesis provides the cultural, economic, scientific and social context for addressing environmental challenges posed by invasive species and will be a valuable resource for scholars, policy makers, natural resource managers and practitioners.