Habitat structure is an important driver of many ecological patterns and processes, but few studies investigate whether habitat structure interacts with other environmental variables to affect community dynamics. The main objective of this study was to disentangle the relative importance of prey availability and shrub architecture on the distribution, abundance, and biodiversity of spiders of northern Utah, USA. We conducted field experiments which focused on: (1) describing the importance of these factors on spider community organization, (2) specifically evaluating whether prey availability mediates the relationship between shrub architecture and spider abundance and biodiversity, and (3) investigating spider and prey responses to manipulations of surrounding vegetation structures. For the first two experiments, big sagebrush shrubs were randomly assigned to six experimental treatments: two levels of prey attractant (shrubs were either baited or not baited) and three levels of foliage density (low, natural/control, or high). The purpose of manipulating both prey availability and shrub architecture was to delineate their significance to spiders. For the last experiment, changes in these factors were investigated at two different levels of spatial context (a single manipulated shrub surrounded by untreated shrubs vs. a manipulated shrub surrounded by a patch of similarly treated shrubs). We found both prey availability and shrub architecture directly influenced patterns of spider abundance and species richness and that spider species diversity and community composition varied in response to shrub architecture alone. Preferences of some spiders for certain shrub types likely reflect differences in foraging strategies or the substrate required to support different types of webs. We also demonstrate that spider response to shrub architecture is the result of multiple processes (i.e., a combination of direct and indirect effects via prey availability) and that surrounding vegetation structures affect spider abundances on shrubs. In addition, prey composition varied among different shrub foliage density treatments, but only when surrounding vegetation structures were also manipulated. More generally, this study suggests that ecological responses to habitat structure are in part mediated by associated variables and the significance of shrub architecture varies depending on the organisms examined and the spatial scale to which they respond most strongly.

A study to determine some ecosystem level effects of an aquatic invertebrate grazer, Hyalella azteca, was performed in aquatic ix microcosms. Impact of the grazer was assessed in three general areas: 1) inorganic nutrient levels of the microcosm water column, 2) productivity and respiration of the biotic community, and 3) plant community composition in the microcosms. The grazing amphipod caused inorganic phosphorus and nitrogen (except ammonia) levels to be elevated in the microcosms. The increase was due, at least partially, to excretion of nutrients into the water by the amphipod. The presence of H. azteca did not significantly alter levels of gross productivity for the whole system nor for the sediment surface. Productivity to respiration ratios were significantly reduced by the grazing amphipod, indicating the amphipod was inhibiting plant biomass accumulation even though gross productivity was not affected. Systems exposed to amphipod grazing had a twenty-five percent lower plant biomass than controls at the termination of the experiment. Gross productivity to plant biomass ratios were significantly higher in grazed systems, indicating a more actively growing plant community was being maintained by the grazer's activities. Plant community composition was significantly altered by the amphipod. Chara biomass was higher in grazed systems, while filamentous algae, blue-green algal colonies and periphyton had significantly higher biomasses in the control systems. The phosphorus distribution within the grazed microcosms was significantly different from that found in the controls. More phosphorus was incorporated into filamentous algae, blue-green algal colonies and the overall plant compartment in the control, while Chara and the water column contained more phosphorus in the grazed microcosms. The amphipod also caused the percent content of phosphorus to be higher in certain plant categories.

This study examined the effects of seedbed and seedling environment on establishment of early and late seral dominant alpine species. Species studied included late seral dominant forbs (Geum rossii, Artemisia scopulorum, and Polemonium viscosum), early seral dominant forbs (Potentilla diversifolia and Sibbaldia procumbens), a late seral dominant grass (Festuca idahoensis), and early seral dominant grasses (Calamagrostis purpurascens and Deschampsia cespitosa). Germination responses of each species to wet vs. dry cold stratification and light vs. dark conditions were investigated. No statistical differences were observed in the seed germination of early and late seral dominant forbs or early and late seral dominant grasses, but significant differences were observed in the responses of grasses and forbs. Seed germination of forbs was greater under light than dark conditions and following wet cold storage. Effects of fertilization on growth responses and nutrient uptake of G. rossii and D. cespitosawere evaluated in a factorial greenhouse experiment in which seedlings of each species were grown at four levels of nitrogen (N) and phosphorous (P). The late seral dominant forb responded more like a species from a low-nutrient environment exhibiting lower relative growth rates, higher root:shoot ratios, and a smaller response to N than the early seral dominant. A field experiment on the Beartooth Plateau, Montana, examined the soil environment and seedling emergence, growth, and survival of seeded early and late seral dominants on loamy sand soils of a severe disturbance and on peat soils of an undisturbed area during two growing seasons. Effects of fertilizer and mulch were examined on the severely disturbed area. Differences between uncleared turf and turf cleared of vegetation (gap disturbance) were evaluated on the undisturbed area. The gap disturbance had higher levels of N and P and warmer soil than the severe disturbance or vegetated undisturbed area. Soil water potentials were never low enough to result in plant stress. Seedling growth was slow - .005 g to .04 g dry weight the first growing season and .02 g to .20 g the second growing season. Growth was greatest on the gap disturbance and on fertilized plots of the severely disturbed area. Early seral dominants had the largest seedlings and the smallest R/R+S ratios. Mortality was low - odds of .50 were rarely exceeded even after two years. Survival was higher on warm, nutrient rich soils of the gap disturbance. Mulch increased emergence and survival on the severe disturbance. Fertilization increased mortality, probably because an initial pulse of N was followed by a rapid decline. Higher mortality occurred in 1986 than 1985 as 1986 had a shorter growing season and cooler air and soil temperatures early in the growing season.

Tierra del Fuego, at the southernmost tip of South America, is influenced by ozone depletion. The landscape of southern and western Tierra de! Fuego is dominated by peatlands; they are important locally and in the context of global climate change, because they store large quantities of organic carbon. To determine the influence of solar ultraviolet-B radiation (UV-B) on a Tierra de! Fuego peatland, we selectively filtered solar UV-Bin ten pairs of plots. Polyfluorine filters were used to create the Near-Ambient-UV-B Treatment ( 90% solar UV-B), and polyester filters to create the Reduced-UV-B Treatment ( 17% solar UV-B). These filters were first installed in October 1996, and were maintained, September-March, for six years. Following previous plant growth measurements and samples of selected microorganisms under the two UV-B treatments (1996-1999), this dissertation is an account of the more detailed measurements made during the second three-year period of treatments (1999-2001 ). Seasonal sampling of the plant community, microfungi, microfauna, and biogeochemistry of the water and nutrients held by the Sphagnum capitulum was introduced, in an attempt to better understand ecosystem function. Solar UV-B reduced Sphagnum height growth, but this was compensated by more compressed and densely packed Sphagnum capitula. Emergent vascular plants, Nothofagus, Empetrum, and Tetroncium, were more affected than Sphagnum by nearambient UV-B. Solar UV-B altered the Sphagnum-capitulum microenvironment, resulting in: more dissolved organic carbon and phosphorous, higher electrical conductivity, and greater acidity under near-ambient UV-B. Additionally, the populations of testate amoebae and some species of fungi were consistently increased; however, microfungal diversity and rotifer, nematode, and mite populations decreased under near-ambient UV-B. Generally, Sphagnum minimizes the leaching of nutrients by effectively holding water at the capitulum. Solar UV-B altered Sphagnum-capitulum morphology, increased the volume of water held, and made this water more acidic and richer in nutrients. Based on these results, if current trends in ozone depletion were to persist over several decades, a reduction in vascular plant growth, and changes in the trophic relationships of the microorganismal community of the Sphagnum capitulum, would be predicted. These responses have the potential to affect peatland carbon storage and nutrient cycling in Tierra del Fuego.

Gorongosa: a history of an African landscape, 1921-2014, focuses on changes in the Gorongosa ecosystem, in central Mozambique, southeastern Africa. Environmental changes result from natural, non-human causes and from the activities of humans. I describe four socioecological events: African and Portuguese interactions, Gorongosa National Park, the effects of Mozambique’s civil war, and the Park's restoration in the aftermath of the civil war. Prior to European partition of Africa in 1884-85, Mozambique did not exist as clearly a demarcated territory as it is now. Today, the sense of Mozambicanhood bears traces of Portuguese colonial era experience. The demarcation of Mozambique’s boundaries and the reshaping of the colony until 1975 was a painful process that both the Africans and Portuguese colonialists endured; these physical and social separations from the rest of southern Africa represented the first human-induced changes in southern Africa. The endeavors to reshape Mozambique did not end with political boundaries. Painful processes, including the reshaping of Gorongosa National Park in the Gorongosa ecosystem, continued after border demarcations. Countless Mozambican and Portuguese lives were lost in the long trajectory within the colony as the Africans and the Europeans all developed a sense of unity in diversity while reshaping their attitude of and about Mozambique. After independence in 1975, internal transformations and wars continued reshaping Mozambique and Mozambicans, as different nationalists sought to maintain their colonial experience. These dynamics marked the environmental history of the Mozambican and Portuguese peoples and are often reflected in the prevalence of high sympathy, which the two peoples share toward one another. Gorongosa: a history of an African landscape, 1921-2014, critically celebrates these collective achievements.

The framework of a stream ecosystem simulation model is described. Using this framework and data from two different geographical areas, a cold desert stream and a generalized mountain stream, exploratory sensitivity analysis was performed on the model. This was accomplished by qualitatively comparing outputs of a series of simulations in which a different level of a driving variable was used in each simulation. Based on these results, recommendations are made for improving the structure of the model.

Biscayne National Park is located off the southeast coast of Florida and attracts approximately half a million visitors annually. Managers of Biscayne National Park are proposing a new General Management Plan (GMP) in order to update the recreational and commercial use of resources in the park. A Fishery Management Plan (FMP) is also being drafted simultaneously in conjunction with the Florida Fish and Wildlife Conservation Commission in order to address concerns associated with management of fish stocks within the park. The proposed plan alternatives of the GMP and the recommendations of the FMP were developed in response to the negative impacts on the park's marine ecosystem due to exponential population growth of the adjacent Miami metropolitan area. Problems associated with decreasing water quality, habitat degradation, and species exploitation contribute to the diminishing integrity of resources in the park and surrounding area. Currently commercial and recreational fishing are allowed in most of Biscayne National Park. The National Park Service's proposed alternatives are highly complex in order to make an attempt at appeasing stakeholder interests. In addition the recommendations of the FMP join the GMP alternatives in omitting marine reserves, a management practice that is widely thought by the scientific community to be an important step in marine resource rehabilitation. At present, there is a noticeable absence of scientific information and lack of participation of scientists in management decisions. Biscayne National Park would ultimately benefit by incorporating marine reserves into the park, and adjusting them based on scientific studies conducted by an appointed Scientific Advisory Board. Partnerships with state, federal, and international agencies could promote the idea of being a part of a marine reserve network for optimal resource protection in the Caribbean. An increase in revenue from a permit system and entrance fees would also promote enforcement and protection of park resources. Simple but strong regulation in the park could also help alleviate enforcement problems. In addition education of park resource users should be expanded inside and outside the park.

Connectivity is a major contributor to the overall dynamics of marine populations. However, it still remains challenging to describe connectivity on ecologically meaningful scales of time and space. This is a major impediment to evaluating the impacts of marine protected area with respect to fisheries management objectives. This dissertation brings together a wide array of spatial and connectivity information in the Gulf of Mexico (GOM) with the goal of 1) understanding the spatial distribution of fish populations and source-sink dynamics and 2) evaluating whether this information can be integrated, through a modeling framework, to identify closed areas that could be beneficial to fisheries management in the Gulf of Mexico. First, a generalized additive modelling (GAM) approach is used to describe the distribution of a large number of species groups (i.e. functional groups) across the Gulf of Mexico (GOM) using a large fisheries independent data set (SEAMAP) and climate scale (decades) oceanographic conditions. Next a numerical Lagrangian particle transport model was developed that incorporates two major connectivity processes; site specific larval production and oceanographic transport for an entire large marine ecosystem and over multiple years. The two components are then combined to develop larval dispersal patterns for the entire GOM and identify areas operating as larval sources and sinks. Last, this information is integrated into an end-to-end ecosystem model to evaluate effectiveness of closing source and sink areas for the management of reef fish fisheries. Closed area managemeny simlautions for reef fish indicated closing reef fish source areas, as opposed to sinks, in the GOM is most efficient method of increasing total biomass and yield. However, the impacts across individual functional groups were site specific. Ultimately, these simulations demonstrate the inclusion of connectivity information could improve fishery management objectives in an ecosystem context.

Experts and organizations involved in freshwater resources management have emphasized the importance of long-term urban resource planning and management that considers the tight coupling which exists between human - nature - technology systems. The resistance of contemporary urban growth efforts to consider resource carrying capacities and ecosystem requirements has led to costly unintended consequences including the deterioration of natural capital and their associated ecosystem services, and the degradation of water resource flows. As these problems continue to worsen, resource experts have called for the development of a new water resource management paradigm inclusive of various sustainability criteria. Historically water-rich Florida has demonstrated increased resource strain over the past four decades, in spite of the creation of some of the nation's most comprehensive water resource and growth management legislation. The Southwest Florida Water Management District was originally created to manage regional flooding in 1961 and has undergone a tremendous expansion in statutorily mandated resource responsibilities over the past 40 years. This case study utilized semi-structured surveys of current and former agency employees to examine the agency's expansion into integrated water resource management amidst rapid regional urbanization.

A large part of the environmental restoration required by the Comprehensive Everglades Restoration Plan calls for more water-storage on lands south of Lake Okeechobee in order to restore the natural water flows of the Everglades watershed. The Everglades Agricultural Area (EAA) can be used for increased water storage in order to relieve coastal estuaries of excess water in the rainy season. This water storage can deliver additional ecosystem services of soil retention and reduced CO2 emissions that could compensate farmers for the cost of water storage by increasing long term farm profitability. The goals of this study were 1) to quantify the environmental and economic trade-offs of different water storage scenarios using water-tolerant sugarcane cultivars, and 2) to quantify the amount of water storage possible in the EAA under different water storage scenarios. A mathematical model was developed to calculate soil depth, soil subsidence, depth to the water table, sugarcane production, farm return, water storage and carbon loss for three different sugarcane cultivars with different water-tolerances. A GIS tool is also developed to estimate the amount of water storage possible in the EAA. The study found that even though water-tolerant sugarcane cultivars experience higher yields and net returns than non-water-tolerant cultivars the water storage costs with these water tolerant cultivars was greater. Raising water tables on farm lands did have the environmental benefits of reduced soil subsidence, extended farm life and increased years of water storage. However total CO2 emissions rise from 14 to 136%. Results of the GIS analysis revealed that water storage capacity for a DWT of 61 cm is 1,404,562 ac-ft, 1,417,400 ac-ft for DWT 45 cm and 1,474,692 ac-ft for DWT 20 cm. The GIS analysis was also able to identify flow ways that could possibly carry water south from Lake Okeechobee and ultimately to the WCAs south of the EAA. These results show that raising water tables in the EAA to deliver the ecosystem service of expanded water storage is overall more costly, but yearly costs are very low. Therefore water storage on farmlands is an affordable interim method of water storage.