Macroecology and experimental evolution are two disparate sub-disciplines with contrasting approaches to the study of biological diversity. First I use macroecology and the Global Invasive Species Database to determine the best predictors of diversity patterns of invasive species around the globe. I show that economic factors account for more of the variance in invasive species richness among countries than typical ecological variables used to explain broad-scale species diversity patterns. I then use a microecological approach in which experimental evolution is performed with the soil bacterium Pseudomonas fluorescens to evaluate the idea that selection in environments varying in productivity will impact the degree of ecological specialization and maintenance of diversity. The results show that although ecological specialization increases with productivity, diversity does not. Both disciplines can be used to inform each other with the aim of explaining the abundance and distribution of species in nature through space and time.

Thermoregulatory indices are based on an estimation of the preferred body temperature range (Tset), but few studies have compared the different methods of measuring Tset or how these methods influence our understanding of the relationship between thermoregulation and physiological performance. For the bearded dragon, Pogona vitticeps, T sets were measured within a thermal gradient and shuttle box. Additionally, performance curves were determined for relative sprint speed and gut passage time. The shuttle box Tset was broader than the Tsets from the thermal gradient. Of the indices examines, only the effectiveness of thermoregulation may remain unaffected by differing methods of measuring Tset. The optimal Tbs for both performances were best described by the 50% Tb distribution. The Tb distributions were negatively skewed, suggesting support for net energy gain being maximized by thermoregulation. This study highlighted the need for more meaningful measures of thermoregulation than those provided only by temperature-dependent performances.

<p> Climate change models predict increased frequency and intensity of extreme thermal events, suggesting that exposure to stressful high temperatures will likely become more common for many organisms. I investigated how frequency of exposure to sublethal temperature stress impacted the relative shell growth and size-specific tissue mass of the California mussel, <i>Mytilus californianus </i>. Mussels were exposed in the lab to 32 &deg;C during simulated low tides 0, 1, 4, or 7 days per week for eight weeks or transplanted into rocky intertidal plots exhibiting a range of thermal conditions in the field for 12 weeks, then challenged with repeated exposures to a more extreme temperature (36, 39, or 42 &deg;C) for 5 sequential days. As predicted by theory, increased frequency of exposure to sublethal heat stress invoked a cost to individuals, expressed as reduced shell growth or size-specific tissue mass, but also resulted in higher survival following subsequent exposure to potentially lethal temperatures. </p><p>

<p> In addition to higher average temperatures, many regions of Earth are also experiencing higher variability. I investigated how prior thermal history and intensity of an acute high temperature challenge affected post-exposure photosynthetic performance of microalgae on rocky shores. I measured community-level net photosynthetic rate (NPR) on experimental plates left in the field for one or seven months before and after exposure to a simulated low tide. After one month, microalgal NPR decreased more after exposure to higher peak temperatures, although the effect was mitigated somewhat by prior exposure to thermal variability. In contrast, after seven months there was no effect of temperature on NPR. There were, however, differences due to shore height and experiment duration, with respect to overall biomass and pre-exposure NPR. Scanning electron microscopy (SEM) suggested that changes in the identity and relative abundances of microalgal taxa associated with increasing aerial exposure during low tides might be responsible.</p><p>

<p> As sea levels rise, management strategies are needed to protect coastal wetlands from increased inundation. Sediment augmentation is a strategy in which a layer of sediment is sprayed across the marsh to raise the marsh's elevation and reduce inundation. This study looks at the short-term impact of sediment augmentation on vegetation and invertebrate communities. Abiotic measurements, invertebrate cores, and plant parameters were analyzed before and after augmentation in a before-after-control-impact (BACI) design. Following augmentation there was a significant decrease in plant cover and invertebrate abundance. The community composition of invertebrates shifted from a dominance of oligochaetes and polychaetes to insects and insect larvae. At six months following augmentation, <i>Salicornia bigelovii</i> began growing throughout the augmentation area, and <i>Spartina foliosa </i> had returned via vegetative spread at the edges of the marsh. Detailing these changes provides information on the ecological impacts of sediment augmentation for this site and inform regional management strategies.</p><p> </p><p>

<p> Across the Arctic, taller woody shrubs, particularly willow (<i> Salix</i> spp.), birch (<i>Betula</i> spp.), and alder (<i> Alnus</i> spp.), have been expanding rapidly onto tundra. Changes in vegetation structure can alter the physical habitat structure, thermal environment, and food available to arthropods, which play an important role in the structure and functioning of Arctic ecosystems. Not only do they provide key ecosystem services such as pollination and nutrient cycling, they are an essential food source for migratory birds. In this study I examined the relationships between the abundance, diversity, and community composition of arthropods and the height and cover of several shrub species across a tundra-shrub gradient in northwestern Alaska. To characterize nestling diet of common passerines that occupy this gradient, I used next-generation sequencing of fecal matter. Willow cover was strongly and consistently associated with abundance and biomass of arthropods and significant shifts in arthropod community composition and diversity. Key nestling prey items were positively associated with both willow and ericaceous shrubs. Diet composition varied significantly among bird species and spatially within species, however, I found that temporal variability in prey abundance did not have a strong relationship to the probability of consumption. I predict that the wide temporal window of prey availability and high diet diversity may protect these birds against negative impacts from climate-driven shifts in prey phenology and abundance. Taken together, my results suggest that shrub expansion could result in a significant shift in Arctic food-web structure and an increase in food availability for insectivores, although future ecosystem change in the Arctic is likely to be heterogenous as shrub types are expanding at different rates and in different places across the Arctic.</p><p>

<p> Coastal systems are facing many challenges including climate change, sea-level rise, storm surge, and erosion, all of which contribute to land loss. In Louisiana, this has led to the development of a coastal Master Plan supported by habitat suitability index (HSI) models to predict wildlife responses under various management scenarios. However, these models were not originally intended for this purpose and their functionality at large spatial scales is unclear. My goal was to use maximum entropy modeling, using the software MaxEnt, to predict how various bird distributions might change with coastal restoration and management. During 2015-2017, I recorded the locations of brown pelican, gadwall, green-winged teal, mottled duck, and roseate spoonbill across southern Louisiana, measuring salinity, water depth, and vegetation when the species were detected. Using environmental projections from the Coastal Protection and Restoration Authority, I predicted the probability of occurrence for each target species for current conditions and projected the distributions into the future at 25 and 50 years using sea-level rise and coastal change scenarios. Predictive models for each species under current conditions show good agreement with field observations. Future models generally show reductions in areas of potentially high habitat use, with a few notable exceptions in brown pelicans and roseate spoonbills. Both modeling approaches had advantages and disadvantages; neither were superior in predicting wildlife habitat. I recommend increasing the resolution and quality of environmental data to improve estimates of suitable habitat, habitat use, and restoration outcomes for wildlife. </p><p>

<p> Imperilment in North American freshwater fishes is primarily due to habitat alteration, deterioration, and fragmentation. In response to the aquatic biodiversity crisis, there has been a call for action by the Center for Biological Diversity, with a petition for the federal listing of 404 aquatic species in the southeastern U.S. This thesis focuses on a petitioned species, the Caddo Madtom, <i> Noturus taylori.</i> The chapters in this thesis address the genetic variation, habitat limitations, and status of the Arkansas endemic. In summation, <i> N. taylori</i> was found to have a high level of genetic variation for an endemic madtom, and is relatively abundant throughout its distribution range. Additionally, <i>N. taylori</i> was found to exhibit variable habitat association within and among the drainages it inhabits. These data will provide an updated status for federal and state agencies for <i> N. taylori,</i> which will be informative for listing and conservation management decisions for the species.</p><p>

Climate change is projected to cause significant shifts in precipitation patterns across the Amazon basin. This dissertation is designed to address key uncertainties surrounding our ability to predict the fate of the Amazon rainforest in a drier climate. The second chapter is an assessment of the ability of four leading dynamic vegetation models—CLM3.5, ED2, IBIS and JULES—to replicate observation from two long-term ecosystem-scale drought experiments in the eastern Brazilian Amazon. This analysis revealed that these four models can reliably predict plant and ecosystem carbon fluxes under the present climate, but still require substantial development for predicting the consequences of severe drought. These four models were not parameterized to mechanistically represent soil water-stress or the competitive differences in plant hydraulics that exist between tree species. Therefore, chapter three is a field-based study designed to quantify the range of variation in two plant hydraulic traits—xylem-P50 and turgor loss point (TLP)—that exists in mature tropical trees. The field measurements were made on four genera common to both experimental study sites. Each genus was categorized a prior into one of four plant functional types: early- versus late-successional that were each subdivided into drought-tolerant versus intolerant. Xylem-P50 and TLP occurred at water potentials that were 0.7 to 1.1 MPa and 0.75 MPa higher, respectively, in the drought-intolerant genera compared to the tolerant genera. In comparison, the early- versus late-successional genera showed no significant differences in xylem-P50 and TLP, thereby revealing two orthogonal axes of competition: one along a successional gradient and the other along a soil moisture gradient. The results from chapter three were then used to parameterize and test a new mechanistic water-stress formulation in the Ecosystem Demography (ED2) model, which became the basis of chapter four. With the new water-stress formulation, ED2 successfully replicates the observed reductions in total aboveground biomass in the drought experiments. It also more realistically captures the compositional and structural shifts that occur as a result of severe droughts. This dissertation makes an important contribution that advances the science of tropical forest drought ecology and enhances our ability to make reliable predictions about the fate of tropical forests in a future drier climate. / Biology, Organismic and Evolutionary

Predicting diversity is a central theme of ecology. In this thesis, two aspects of diversity were explored, number of vegetation types and species richness. In the first chapter, I examined the relationship between number of vegetation types and standing crop in wetlands. Fifteen individually homogeneous wetland sites which represented a broad standing crop gradient were sampled in eastern Canada. There appears to be an inverse relationship between number of vegetation types and standing crop. In chapter 2, I investigated the relationship between species richness and standing crop at two levels of organization: the among vegetation types level and the within vegetation type level. The results indicated that the model of species richness proposed by Grime had predictive power at a coarse-grained level of organization, among vegetation types, but did not survive the transition to a finer-grained level of organization, the within vegetation type level. Therefore, the higher level processes which structure species richness patterns among vegetation types are not the same processes that determine richness patterns within a vegetation type. Numerous forces, abiotic or biotic, can maintain or alter vegetation states and species richness at different levels of organization. In the third chapter, I tested whether these "assembly forces" had the potential to duplicate the patterns observed in chapters 1 and 2 in a large microcosm experiment. Chapter 4 investigated the effects of a disturbance involving the complete removal of above ground vegetation in five wetlands of varying standing crop found on the Ottawa River. The results indicated that the wetland standing crop gradient and the diversity patterns observed along this gradient were likely the result of an underlying natural disturbance gradient. In chapter 5, I considered the results from chapters 1 to 4 with regards to the conservation value, potential threats, and proper management techniques for wetlands, particularly for low standing crop wetlands. In addition to the fifteen wetlands surveyed in chapter 1, additional low standing crop wetland sites from the Georgian Bay area in Ontario and the Tusket River Valley in Nova Scotia were surveyed. The results revealed that low standing crop wetlands had many more nationally rare species than did high standing crop wetlands, in addition to the higher species richness and higher number of vegetation types discussed above. The results of the microcosm experiment revealed that low standing crop wetlands may be severely threatened by eutrophication and by an invasive Eurasian weed, Lythrum salicaria. In each of the five wetland sites examined in the field experiment, L. salicaria exhibited dramatic increases in abundance over the three year observation period. Further, the disturbance treatment at each site did not slow the invasion of L. salicaria, but instead increased the rate of invasion in at least one site. I conclude that low standing crop wetlands, despite their high conservation value, are severely threatened and must be protected from the effects of eutrophication and invasion by Lythrum salicaria. (Abstract shortened by UMI.)