<p> The Gulf of Mexico is home to a large proportion of the wintering population of the threatened piping plover, but little is known about the bird&rsquo;s ecology in this region. In Louisiana, the majority of wintering piping plovers are found on the state&rsquo;s rapidly eroding barrier islands. Between August 2013 and May 2014, we conducted shorebird surveys to assess the abundance and habitat use patterns of piping plovers on a barrier island refuge in south central Louisiana. Seventy-five percent of piping plovers observed were foraging, mostly (92%) in the intertidal zone; 20% were roosting in more diverse microhabitats. To characterize the prey base for piping plovers on the islands, we collected core samples in the intertidal zone of two islands on the refuge. The invertebrate community was dominated by haustoriid amphipods, which comprised 87.5% of individuals collected. Bivalves and polychaetes accounted for 9.3%, and 2.7%, respectively. We used generalized linear models to evaluate the effects of environmental predictors on amphipod abundance and odds of bivalve and polychaete presence at the sample site scale, and also on piping plover densities at the transect scale. Moisture had a positive effect on amphipod abundance and polychaete presence. Seasonal patterns and between-island differences were observed in all three taxa, but these effects differed between main beach habitat and the gulf- and bay-sides of prominent sand spits. Amphipod densities and piping plover densities were correlated on Trinity Island and during spring 2014, but prey abundance did not differ between sample sites where piping plovers were foraging versus random sites. Uncertainty in the degree to which piping plover distributions in Louisiana are driven by prey abundance is of concern because the extensive beach nourishment programs being implemented to stave off coastal land loss may have potentially substantial impacts to benthic invertebrates and their predators.</p>

<p> Although knowledge of peatland CH₄ and CO₂ exchange in temperate mountain ecosystems is available, information about carbon (C) exchange in peatlands of the Andean mountains is limited and these ecosystems may behave differently given the particular characteristics of the Andean tropics. These ecosystems are highly productive and under pressure by grazing. Our first objective was to measure baseline carbon dioxide (CO₂) and methane (CH₄) flux in an undisturbed peatland in Cayambe-Coca National Park. Our second objective was to quantify CO₂ and CH₄ fluxes in an intensively cattle grazed peatland near Antisana Ecological Reserve. CO₂ and CH₄ effluxes were measured using a static chamber method. The mean NEE values for the undisturbed and disturbed site were -0.69 &plusmn; 0.08 and -1.25 &plusmn; 0.13 g CO₂ m^-2 hr^-1 respectively. A significant correlation between microtopography and CO₂ and CH₄ flux was found in the undisturbed site, with higher NEE, GPP, ER and CH₄ values in hummocks than in lawns. Microtopography doesn&rsquo;t seem to be a controller of CO₂ efflux in the grazed site, although the NEE and GPP rates are higher than those found in the undisturbed site, and show a linear relationship with vegetation cover. CH₄ emissions in the undisturbed site were low (8.1 &plusmn; 1.17 mg CH₄ m^-2 d^-1). However, CH₄ emissions at the grazed site were very high (132.25 &plusmn; 34.22 mg CH₄ m^-2 d^-1), which might be attributed to the high physical impact and inputs from cattle. In summary, it appears that cattle grazing may be capable of large changes to C exchange and greenhouse gas fluxes in Andean peatlands. </p>

<p> Tree species are expected to respond to recent and future changes in climate and other environmental factors such as pollution. In this dissertation I studied environmental controls on the growth and distributions of forest tree species in mountains of the northeastern United States, focusing particularly on spruce-fir forests. To determine if mountains could provide climate change refugia for tree species, I collected <i>in situ</i> microclimate measurements to quantify elevational shifts in suitable temperature regimes over time. To determine how species elevation distributions have changed since the 1960s, I resampled historical vegetation plots on Whiteface Mountain, New York. I also surveyed current species distributions along elevation gradients on 11 additional mountains in New York, Vermont, New Hampshire, and Maine to determine if smaller size classes were found at higher elevations than larger size classes of the same species (suggesting an ongoing upslope migration). Finally, I collected tree cores on these mountains to determine how climate change and acid rain affect tree growth. I found that the temperature regimes in the northeastern U.S. have already moved upslope hundreds of meters since the 1960s and are expected to continue shifting upslope suggesting that mountains in the northeastern U.S. may not represent climate change refugia for spruce-fir forest species. Elevational distributions of spruce-fir and lower elevation northern hardwood trees did not show evidence of a synchronous upslope shift in elevation as expected from recent climate change. Instead, species showed varied (individualistic) shifts with elevation that may be partly driven by other factors such as land-use history. Tree growth was found to be increasing, primarily due to reductions in precipitation acidity and only partially due to climate warming. Thus, elevational distributions of tree species appear to lag recent climate change although tree growth rates respond to environmental change more immediately. This dissertation provides some of the first evidence suggesting that reductions in acid rain have had direct, measurable impacts on the growth of a terrestrial organism. Managers should continue to monitor tree species growth and distributions especially at range margins as they respond to multiple environmental drivers of change.</p>

<p> Glacier runoff (i.e., meltwater and rainwater discharged at the glacier terminus) provides about half of the freshwater discharge into coastal margins of the Gulf of Alaska, where contemporary glacier melting rates are among the highest in the world. Roughly 410 billion metric tons of glacier runoff enter the Gulf of Alaska each year. With freshwater discharge volumes of that magnitude, I hypothesized that glacier runoff has both direct and indirect effects on the receiving coastal marine ecosystems that support rich food webs, abundant and diverse marine communities, commercial fisheries and tourism industries. To examine the influence of glacier runoff on coastal marine ecosystems, I focused on three questions: 1) How does the marine food web respond to physical and biological gradients induced by glacier runoff? 2) What is the contribution of riverine organic matter (OM) and ancient carbon resources in glacier runoff to marine food webs from plankton to seabirds? and 3) How does the influence of glaciers on coastal marine ecosystems differ at small to large spatial and temporal scales? I measured physical, chemical and biological indices within four fjord systems along the eastern Gulf of Alaska coast. In chapter one I used geostatistics as well as parametric and non-parametric models to demonstrate a strong influence of glacier runoff on ocean conditions and coastal food webs across all the fjord systems. In chapter two I used isotopes (&delta;²H, &delta;¹³C, &delta;¹⁵N, and &delta;¹⁴C) to trace riverine OM and ancient carbon resources into the marine food web. This work included the development of a novel multi-trophic level 3-isotope Bayesian mixing model to estimate the proportion of allochthonous resources in animal tissues. Mean estimates from 14 species groups spanning copepods to seabirds ranged from 12&ndash;45 % riverine OM source assimilation in coastal fjords, but ancient carbon use by marine food webs was low. In the third chapter I synthesized information on the scale-dependent influence of glaciers on lower-trophic level productivity, predator-prey interactions and ways that humans may be affected by anticipated changes in glacier coverage. This contemporary understanding of glacier influence on coastal ecosystems aligns with paleoenvironmental evidence suggesting that over geological time scales glaciers have and will continue to shape marine ecosystems in the Gulf of Alaska.</p>

<p> In the last several decades, ecological stoichiometry has emerged as a promising framework for predicting how shifts in the relative availability of N and P influence biological processes from cellular to ecosystem scales. However, explicit tests of ecological stoichiometry theory from ecosystem scale experiments remain rare. In this dissertation, I present the results of a three year experiment where five detritus-based headwater streams were continuously fertilized with N and P at different concentrations, creating a range of molar N:P ratios (from 2:1 to 128:1), for two years following one year of pre-nutrient enrichment monitoring. </p><p> Nutrient enrichment of the five detritus-based streams resulted in significant shifts in the N and P content of leaf detritus, which is the primary food resource for the invertebrate communities. Patterns of invertebrate productivity among the five streams were closely related to the N:P ratio of leaf detritus, providing strong evidence of food web P-limitation. In addition to effects on overall productivity, nutrient enrichment resulted in shifts in the taxonomic composition of the resident invertebrate community, which were largely driven by increased biomass of a few common detritivores. Nutrient enrichment also had significant effects on organic matter flows within the detrital food webs, as flows of all detrital resources to consumers increased following nutrient enrichment. Increased organic matter flows were necessary to support higher rates of invertebrate production following enrichment and were significantly related to the N:P ratio of leaf detritus, which accounted for ~2/3 of total organic matter flows. Furthermore, invertebrates consumed a greater proportion of the total mass of leaf litter lost from these systems annually following enrichment, a pattern that was once again driven by the N:P ratio of leaf litter. </p><p> The results of this study provide compelling support for ecological stoichiometry as a framework for predicting consequences of altered N and P dynamics. Our ability to predict how ecosystems respond to shifting N and P availability remains an important challenge in contemporary ecological research given the globally pervasive nature of anthropogenic impacts on biogeochemical N and P cycles.</p>

<p> Stabilized water levels of the upper St. Lawrence River have reduced plant diversity and allowed competitively dominant taxa such as <i>Typha </i> x <i>glauca</i> and <i>Typha angustifolia </i> to displace productive sedge meadow habitat. This research studied the effects of two wetland enhancement techniques using habitat heterogeneity and manipulating hydrology. Dredge spoils from pothole excavations in <i> Typha</i> marshes were reconfigured to create habitat mounds. These habitat mounds created from an exposed seed bank had less <i>Typha</i> spp. and were more diverse than the surrounding remnant <i>Typha</i> marshes. Sedge meadow vegetation did not successfully colonize these habitat mounds. Water levels at two wetlands were raised above the water levels of the upper St. Lawrence River. Raising water levels increased floating leaf aquatic vegetation but did not decrease <i>Typha</i> spp. Alternative enhancement methods may be necessary to control <i>Typha</i> spp. while restoring sedge meadows.</p>

An improved understanding of how behavior influences the genetic structure of populations would offer insight into the inextricable link between ecological processes and evolutionary patterns. This dissertation aims to demonstrate the need to consider behavior alongside genetics by examining the population genetic structure of two species of highly migratory cetacean across multiple scales and presenting an exploration of some potential lines of enquiry into the behavioral mechanisms underlying the patterns of genetic population structure observed. The first empirical chapter presents a population genetic analysis conducted on a data set of new and existing samples of Bryde’s whale (Balaenoptera edeni spp.) collected from the Western and Central Indo-Pacific and the Northwest Pacific Ocean. Levels of evolutionary divergence between two subspecies (B. e. brydei and B. e. edeni) and the degree of population structure present within each subspecies were explored. The subsequent three empirical chapters represent a series of population- and individual-level genetic analyses on a data set of more than 4,000 individual humpback whales (Megaptera novaengliae) sampled from across the South Atlantic and Western and Northern Indian Oceans over two decades. Patterns of genetic population structure and connectivity between breeding populations are examined across the region, and are complemented by an assessment of genetic structure on shared feeding areas for these populations in the Southern Ocean. Collectively, these studies demonstrate that a hierarchy of behavioral processes operating at different spatial scales is likely influencing patterns of genetic population structure in highly migratory baleen whales. Notably, for humpback whales, the widely assumed model of maternal fidelity to feeding areas and natal philopatry to breeding areas was found not to be applicable at all spatial scales. From an applied perspective, the complex population patterns observed are not currently accounted for in current management designation and recommendations for applying these findings to the management and protection of these species are presented. As these empirical studies highlight the importance of behavior as a potential mechanism for shaping the genetic structure of species, the final chapter offers a research prospectus describing how behavioral and genetic data may be integrated using new individual-based modeling techniques to integrate data and information from the fields of behavioral ecology and population genetics.

Thesis (Ph. D.)--University of Oklahoma, 1970. / Includes bibliographical references (leaves 75-79).

Thesis (B.A.)--Haverford College, Dept. of Philosophy, 2002. / Includes bibliographical references.

<p>Natural enemies are ubiquitous in nature. In many communities, natural enemies have a major effect on the diversity of their prey. Their effects are very diverse: they can promote or undermine the ability of their prey to coexist through a variety of mechanisms. As such, an important step in understanding how diversity is maintained will be to understand how different forms of predator behavior affect prey coexistence. In this dissertation, I study how two major types of predators affect plant coexistence in two different communities. </p><p> First, I study natural enemies in tropical forests, using both theory and empirical work. In tropical forests, most natural enemies are thought have a narrow host range, and be distance-responsive (i.e., mainly harm seeds and seedlings that are near adults of their main host). Previous theoretical work has shown that specialized natural enemies can maintain diversity of their prey, whether or not they are distance-responsive. However, it is unknown whether specialist natural enemies are more or less able to promote prey coexistence if they are distance-responsive. Using theoretical models, I show that distance-responsive predators are less able to maintain diversity. Additionally, I show that habitat partitioning does not interfere with the ability of distance-responsive predators to maintain diversity, even if it causes seedling survival to be highest near conspecific adults. </p><p> From an empirical aspect, I studied the host range of seed-associated fungi. Soil-borne microbes, such as fungi, are thought to play an important role in maintaining diversity in tropical forests. However, the microbial community itself is often treated as a black box, and little is known about which microbes are causing major effects, or how specialized seed-microbe associations are. Here I use experimental inoculations to examine the host range and effect of a guild of seed-associated fungi that are thought to be mainly pathogens. I show that fungal species are differentially able to colonize different seed species, and have species-specific effects on seed germination. I show that in many cases, plant phylogeny, and to a lesser extent fungus phylogeny, are good predictors of colonization. </p><p> Finally, I study how an optimally foraging granivore can promote (or undermine) coexistence amongst annual plants, using theory. Optimal foraging theory is one of the major theories for how predators behave; despite this, little is known about whether an optimally foraging predator could promote coexistence amongst a diverse community of prey. Previous models have shown than two species can coexist due to optimal foraging, but did not test whether multiple prey can coexist, nor if the effect is altered by environmental variation. Here, I show that if the predators specialize on different prey at different times, the predators can allow multiple prey species to coexist. In this case, environmental variation has little effect on the ability of predators to maintain diversity. If the predators are generalists, they cannot maintain diversity. Additionally, I show that generalist predators will create a negative storage effect, undermining coexistence. </p>