<p> Yellow-cedar is a long-lived conifer of the North Pacific Coastal Temperate Rainforest region that is thought to be undergoing a continued natural range expansion in southeast Alaska. Yellow-cedar is locally rare in northeastern portions of the Alexander Archipelago, and the fairly homogenous climate and forest conditions across the region suggest that yellow-cedar&rsquo;s rarity could be due to its local migrational history rather than constraints on its growth. Yellow-cedar trees in northern range edge locations appear to be healthy, with few dead trees; additionally, yellow-cedar tend to be younger than co-dominant mountain and western hemlock trees, indicating recent establishment in existing forests.</p><p> To explore yellow-cedar&rsquo;s migration in the region, and determine if the range is expanding into unoccupied habitat, I located 11 leading edge yellow-cedar populations near Juneau, Alaska. I used the geographic context of these populations to determine the topographic, climatic, and disturbance factors associated with range edge population establishment. I used those same landscape variables to model suitable habitat for the species at the range edge. Based on habitat modeling, yellow-cedar is currently only occupying 0.8 percent of its potential landscape niche in the Juneau study area. Tree ages indicate that populations are relatively young for the species, indicating recent migration, and that most populations established during the Little Ice Age climate period (1100 &ndash; 1850).</p><p> To determine if yellow-cedar is continuing to colonize unoccupied habitat in the region, I located 29 plots at the edges of yellow-cedar stands to measure regeneration and expansion into existing forest communities. Despite abundant suitable habitat, yellow-cedar stand expansion appears stagnant in recent decades. On average, seedlings only dispersed 4.65 m beyond stand boundaries and few seedlings reached mature heights both inside and outside of existing yellow-cedar stands. Mature, 100 &ndash; 200-year-old trees were often observed abruptly at stand boundaries, indicating that most stand boundaries have not moved in the past ~150 years. When observed, seedlings were most common in high light understory plant communities and moderately wet portions of the soil drainage gradient, consistent with the species&rsquo; autecology in the region.</p><p> Despite an overall lack of regeneration via seed, yellow-cedar is reproducing via asexual layering in high densities across stands. Layering may be one strategy this species employs to slowly infill habitat and/or persist on the landscape until conditions are more favorable for sexual reproduction. This study leads to a picture of yellow-cedar migration as punctuated, and relatively slow, in southeast Alaska. Yellow-cedar&rsquo;s migration history and currently limited spread at the northeastern range edge should be considered when planning for the conservation and management of this high value tree under future climate scenarios.</p>

<p> My study was designed to determine how different thermal defense strategies and the intensity of high temperature challenges might affect demographic and physiological performance of limpets on rocky shores. Found together in the high intertidal zone, <i>Lottia scabra</i> employs a constitutive thermal defense strategy, whereas <i>L. austrodigitalis</i> has an inducible one. I measured loss and growth rates of both species as a function of average daily maximum temperature exposure in the field, and respiration rates for field-collected and lab-acclimated individuals under benign conditions in the lab before and after exposure to one of five peak temperatures (14, 24, 28, 32, or 36 &deg;C) during a 4.5-hour simulated low tide. <i>L. scabra</i> was relatively unaffected by exposure to high temperatures, whereas <i>L. austrodigitalis</i> exhibited significant increases in loss rates from experimental plates, decreases in growth rates, and increases in oxygen consumption, consistent with activation of the heat shock response.</p><p>

<p> The structure and functioning of ecosystems across the globe are rapidly changing due to several components of global environmental change (GEC). My dissertation aims to illustrate how regional and local aspects of GEC impact diverse assemblages of species and species interactions. All organisms are embedded in complex networks of species interactions, and future efforts to predict and mitigate the impacts of GEC on ecological communities will be facilitated by such studies that incorporate a suite of species and species interactions. This study advances our understanding of how GEC will impact ecological communities by investigating two questions about GEC: 1) How will shifts in global climate cycles (e.g., El Nino Southern Oscillation), as a consequence of global warming, impact a diverse assemblage of butterflies that exist across a heterogeneous landscape? 2) What are the consequences of woody plant encroachment on complex, specialized interactions between plants, insect herbivores, and natural enemies (e.g., insect parasitoids)? Furthermore, I helped develop a tool to identify characteristics of ecological communities that are essential for promoting the diversity of trophic interactions. While the loss of species diversity is well recognized, interactions among species are vanishing at an astonishing rate, yet we know little about factors that determine the diversity of interactions within a community. Using data from a long-term butterfly monitoring dataset, I was able to demonstrate the utility of large-scale climate indices (e.g., ENSO) for modeling biotic/abiotic relationships for migratory butterfly species. Next, I used encroaching juniper woodlands in the Intermountain West to uncover that population age structure of dominant tress, such as juniper, can affect plant-insect dynamics and have implications for future control efforts in the expanding woodlands. Additionally, reductions of understory plant diversity, as a consequence of juniper expansion, resulted in significantly lower parasitism rates and parasitoid species diversity. Finally, simulated food webs revealed that species diversity and, to a lesser degree, consumer diet breadth, promote the diversity of trophic interactions. As ecosystems across the globe experience changes and the loss of species diversity continues, these findings offer insight into how GEC will impact species and species interactions.</p><p>

<p> As a result of human activities, the level of CO₂ in the Earth&rsquo;s atmosphere has increased by nearly 40% since the industrial revolution. The rate of green house gas emission is accelerating, with current trends exceeding those predicted by &ldquo;worst case&rdquo; global climate change scenarios. The chemistry of the ocean is fundamentally changing as a result of increasing atmospheric CO₂, which dissolves in seawater, making it more acidic, a process referred to as ocean acidification (OA). A rapidly expanding body of science is now being generated to understand the impact of this global environmental change. To date, most studies evaluating OA effects have centered on simplified laboratory analyses that expose single populations to short-term treatments in order to quantify responses of individuals. These designs offer a limited assessment of the degree to which phenotypic plasticity and local adaptation might influence the response of populations to OA. </p><p> To address these questions, I carried out studies on members of Phylum Bryozoa, a species-rich clade of calcified colonial marine invertebrates distributed throughout the global ocean. Bryozoans were selected as a model system for this work because the clade exhibits a broad array of growth and calcification strategies, and because of the relative paucity of data regarding their expected response to future acidification. In addition, bryozoans can be subdivided into genetically identical replicate clones, which can then be assigned to separate treatments, allowing variation across treatments to be uniquely partitioned into the variance components of statistical models. In order to culture bryozoans for comparative experiments, I designed and constructed a new flow-through OA system at the Bodega Marine Laboratory, capable of finely manipulating both the temperature and carbonate chemistry of seawater, allowing for controlled laboratory experiments of long duration. </p><p> In Chapter 1, I performed a comparative 9-month laboratory experiment examining the effects of ocean acidification on the native Californian bryozoan <i> Celleporella cornuta. C. cornuta</i> was sampled from two regions of coastline that experience different oceanographic conditions associated with variation in the intensity of coastal upwelling. Under different CO₂ treatments, the biology of this bryozoan was observed to be remarkably plastic. Colonies raised under high CO₂ grew more quickly, invested less in reproduction, and produced skeletons that were lighter compared to genetically identical clones raised under current atmospheric values. Bryozoans held in high CO₂ conditions reduced their investment in skeletal carbonate, changed the Mg/Ca ratio of skeletal walls and increased the expression of organic coverings that may serve a protective function. Differences between populations in growth, reproductive investment, and the frequency of organic covering production were consistent with adaptive responses to persistent variation in local oceanographic conditions. </p><p> In Chapter 2, I tested whether skeletal mineralogy can vary plastically in some invertebrates using the cosmopolitan bryozoan <i>Membranipora tuberculata</i> as a model. In a 6-month laboratory experiment, I cultured genetic clones of <i>M. tuberculata</i> under a factorial design with varying food availability, temperature, and dissolved CO₂ concentrations. Elevated food availability increased growth in colonies while cold temperatures and high CO₂ induced degeneration of colony zooids. However, colonies were able to maintain equivalent growth efficiencies under cold, high CO₂ conditions, suggesting a compensatory tradeoff whereby colonies increase the degeneration of older zooids under adverse conditions, redirecting this energy to the maintenance of growth. Elevated food and cold temperatures also decreased Mg concentrations in skeletal material, and this skeletal material dissolved less readily under high CO₂ conditions. This suggests that these factors interact synergistically to affect dissolution potential in this and other species. </p><p> Finally, in Chapter 3, I explore stable isotope values for &delta;¹⁸O and &delta;¹³C in the calcium carbonate structures of the bryozoan <i>Membranipora tuberculata</i>. I tested whether this species accurately records both temperature and pH variability during periods of coastal upwelling by analyzing &delta;¹⁸O and &delta;¹³C in colonies grown in the field and in controlled laboratory cultures. Field-grown colonies were out planted next to a Durafet^&reg; pH sensor, which provided a high-resolution record of the temperature and pH conditions these colonies experienced. &delta;¹³C was found to negatively co-vary with pH in both laboratory and field growth, and calculated field temperatures derived from laboratory &delta;¹⁸O temperature calibrations aligned with the records from the pH sensor. &delta;¹⁸O_c values were more depleted under low pH in laboratory trials, which stands in contrast to patterns observed in other taxa. This may indicate that <i>Membranipora</i> utilizes bicarbonate ion (HCO₃^-) in its calcification pathway, and could help explain why many bryozoan species appear to exhibit enhanced growth under high CO₂ conditions. (Abstract shortened by ProQuest.)</p>

<p> Given the current mass extinction crisis and continued fragmentation of resources worldwide, the outlook is dire for global biodiversity. Rising global temperature, sea levels, and storm frequency all create environmental conditions that can drive change in species abundance and distribution across a landscape. Those species reliant upon a single type of habitat and resource for survival, termed "specialists", are particularly vulnerable to change due to their inability to utilize a variety of resources well. As a result, specialism is now considered one of the dominant factors determining extinction of species. In this dissertation I explore the effects of disturbance on habitat specialist birds in tidal marshes of the northeastern United States. This ecosystem is important due to the significant ecosystem services it provides to humans, and supports several specialist species including the saltmarsh sparrow (<i>Ammodramus caudacutus</i>). I examine this specialist bird community across scales of space, time, and ecological organization to A) evaluate the impacts of disturbance on tidal marsh communities and B) provide findings and management recommendations for long-term maintenance and conservation of coastal marsh ecosystems, specifically as they pertain to salt-marsh specialist birds. In Chapter 1 I introduce my study system and give background for the current conservation status of tidal marsh birds. In Chapter 2 I generate population trends in the five species particularly specialized to tidal marsh using a database of historical records, and explore potential drivers for population change through local and regional habitat disturbance. In Chapter 3 I expand upon patterns in Chapter 2 ad quantify life history strategy in marsh birds across a gradient of habitat specialization to explore how this metric explains species persistence in tidal marshes. In Chapter 4 I test several theoretical hypotheses from disturbance ecology empirically using traditional and novel community metrics. Finally, in Chapter 5 I respond to research needs identified in Chapter 4 to develop a method for quantification of high-marsh habitat using remote sensing methods. I hope the findings presented here contribute towards understanding of the mechanisms driving biodiversity patterns on our planet and help inform conservation priorities within the changing tidal marsh landscapes.</p>

Past climate change and recent human activity have had major impacts on the distribution of habitats as well as the community and population genetic structure of the species occupying these habitats. In temperate zones, glaciation forced many taxa into southern refugia. In contrast, little is understood about the extent to which tropical taxa and habitats were affected by colder periods. In Southeast Asia, some argue that the tropical forest was replaced by savannah at the Last Glacial Maximum (LGM), whereas others suggest that the forest persisted. Studying population genetic and community structure of forest-dependent species in this region may shed light on which of these scenarios is most likely, as well as provide crucial information on the effects of recent habitat loss. To address these issues, I studied the genetic and community structure of forest-dependent insectivorous bat species in Peninsular Malaysia. Data collected at 22 sites indicated that species richness declined with latitude, consistent with post-glacial expansion of forest. To test this further, I undertook mitochondrial DNA sequencing of a widespread species, Rhinolophus affinis, and found high haplotype diversity, little phylogeographic structure and no demographic growth. These all suggest a long population history in the region with no post-LGM range expansion. Subsequent microsatellite analyses of R. affinis and the congeneric R. lepidus showed that genetic distance followed an isolation-by-distance model, and that allelic diversity was unexpectedly higher in the northern populations. Taken together, my results from the community and genetic analyses disagree with each other. These conflicts are perhaps best explained if observed clines in species richness pre-date the LGM. I conclude that there is little evidence of forest contraction in the LGM. The fact that the highest species diversity was detected in the south, which is experiencing the most forest loss due to human activity, has important conservation consequences.

No description available.

No description available.

<p> Stream temperature (ST) is a primary determinant of individual stream species distributions and community composition. Moreover, thermal modifications associated with urbanization, agriculture, reservoirs, and climate change can significantly alter stream ecosystem structure and function. Despite its importance, we lack ST measurements for the vast majority of USA streams. To effectively manage these important systems, we need to understand how STs vary geographically, what the natural (reference) thermal condition of altered streams was, and how STs will respond to climate change. Empirical ST models, if calibrated with physically meaningful predictors, could provide this information. My dissertation objectives were to: (1) develop empirical models that predict reference- and nonreference-condition STs for the conterminous USA, (2) assess how well modeled STs represent measured STs for predicting stream biotic communities, and (3) predict potential climate-related alterations to STs. For objective 1, I used random forest modeling with environmental data from several thousand US Geological Survey sites to model geographic variation in nonreference mean summer, mean winter, and mean annual STs. I used these models to identify thresholds of watershed alteration below which there were negligible effects on ST. With these reference-condition sites, I then built ST models to predict summer, winter, and annual STs that should occur in the absence of human-related alteration (r² = 0.87, 0.89, 0.95, respectively). To meet objective 2, I compared how well modeled and measured ST predicted stream benthic invertebrate composition across 92 streams. I also compared predicted and measured STs for estimating taxon-specific thermal optima. Modeled and measured STs performed equally well in both predicting invertebrate composition and estimating taxon-specific thermal optima (r² between observation and model-derived optima = 0.97). For objective 3, I first showed that predicted and measured ST responded similarly to historical variation in air temperatures. I then used downscaled climate projections to predict that summer, winter, and annual STs will warm by 1.6 &deg;C - 1.7 &deg;C on average by 2099. Finally, I used additional modeling to identify initial stream and watershed conditions (i.e., low heat loss rates and small base-flow index) most strongly associated with ST vulnerability to climate change.</p>

<p> Climate change is a global process that will impact local places in heterogeneous and unpredictable manners. This dissertation considers whose knowledge and observations could contribute to conservation and climate adaptation planning, how perceptions influence social-ecological feedbacks, and how science could be more relevant to decision-makers and local residents. In Chapter 2, I report on interviews (n=36) conducted with ranchers and recreation-based business owners in Colorado to understand their self-perceptions of resilience and vulnerability. I find that ranchers perceive more exposure and sensitivity to climate change and they also demonstrate more adaptive capacity than recreation businesses. In Chapter 3, I convey results from interviews (n=83) completed with various long-term residents of the region surrounding Denali National Park and Preserve. I find that people who have more direct and ongoing experience with natural resources (subsistence users, bus drivers, business owners) have a greater number and more diverse observations of change than Park employees or scientists. In Chapter 4, I describe results from interviews (n=26) with community-defined Gunnison Sage-grouse experts. I find that formal and observational experts had very different explanations of the decline of Gunnison Sage-grouse and disagreed about potential conservation strategies. In Chapter 5, I describe multi-method surveys (41) conducted with ranchers in the Gunnison Basin to understand their perceptions of the potential listing of the Gunnison Sage-grouse under the Endangered Species Act, and their planned responses. I find that ranchers tend to have negative perceptions of the listing and that they plan to take actions, including sales of land and water and decreased participation in conservation efforts, which may result in harm to the Gunnison Sage-grouse. In Chapter 6, I review stakeholder-generated climate change needs assessments (63) to assess the suggestions made to make science more relevant to decision-making. Their suggestions include: interdisciplinary approaches, place-based focus, increased data-sharing and collaboration, and user-driven research. This dissertation demonstrates the importance of understanding perceptions for effective conservation and adaptation, identifies the existence of proactive adaptation strategies, highlights the value of local knowledge in specific situations, and reveals how failure to engage local people may lead to inequitable outcomes.</p>