My dissertation encompasses three studies of social behavior. Two explore the reproductive conflicts that occur between cooperating individuals. I examine conflict at two levels: within colonies of the social wasp, Eustenogaster fraterna, and within chimeric multicellular organisms formed by the social amoeba, Dictyostelium discoideum. The third project investigates the occurrence of sexual reproduction in a natural population of D. discoideum. Eustenogaster fraterna belongs to the basal eusocial family of stenogastrine wasps. Colonies are small averaging only 2.7 adult females but only one mated female. I examined the reproductive and genetic structure of 18 colonies by genotyping all within-colony individuals and assessing the ovarian development of females. My results show that 85% of females were potential reproducers. Adult females were not related as full sisters. Some brood could not be assigned to any of the adult females, suggesting that subordinate females could inherit the nest and replace the dominant female. D. discoideum live as free-living, single cells, but when starved they aggregate to form a multicellular fruiting body. Genetically distinct clones of D. discoideum co-aggregate to form genetic chimeras. 20% of cells form the stalk of the fruiting body and die, while others become reproductive spores. One clone can exploit the other by contributing less than its proportional share to the sterile stalk. I investigated whether cheating is a strategy dependent on the relative proportion of the clones aggregating. In a chimera, a rare clone could benefit by avoiding forming the stalk because it is less related to the reproductive part. My results do not support the frequency-dependence strategy. I investigated the occurrence of sexual reproduction in a natural population of D. discoideum, using the approach of estimating linkage disequilibrium in the population at one site. My results show that recombination does occur and is due to sexual reproduction not to parasexuality. In sum, conflicts within societies can be mitigated. E. fraterna workers gain insurance advantages by obtaining indirect genetic benefits or inheritance of work force. D. discoideum clones gain cheating advantages either when rare or common in the aggregation. Recombination yields novel genotypes; this might increase the complexity of interactions between co-aggregating clones.

<p> In this study, I focus on the loss of species diversity&mdash;and therefore morphological diversity&mdash;within the Cimolodonta (Multituberculata) during the Cretaceous-Paleogene (K-Pg) extinction, followed by their recovery in the Puercan (earliest Paleogene). Teeth make up the majority of the cimolodontan fossil record, allowing inferences of dietary ecology, body size estimates, and phylogenetic proximity. I analyzed morphological disparity within the restricted phylogenetic framework of the Cimolodonta. I addressed 3 questions: 1) Did the conditions of the K-Pg extinction select for or against cimolodontan dental morphologies, if it was selective at all? 2) Do levels of cimolodontan morphological similarity return to pre-extinction levels in the Puercan? 3) Do the Puercan Cimolodonta recover morphology lost during the extinction, or do the Cimolodonta morphologically diverge from the pre-extinction morphospace? I used Euclidian inter-taxon distance measures derived from dental character data to perform a principal coordinates analysis (PCO), generating a multidimensional representation of morphological similarity. To assess the selectivity versus non-selectivity of cimolodontan extinction across the K-Pg boundary, I analyzed the axes of the morphospace for morphological character gradients. I tested for extinction selectivity to determine the probability of generating the survivor-specie morphospace by chance. These results indicate significant (P = 0.0006) selection affecting cimolodontan survival across the K-Pg extinction. Overall morphospace occupation changed significantly (P &lt; 0.015) in the Puercan as well. I attribute this change in morphospace occupation to the diversification of the Taeniolabididae and incomplete recovery of Late Cretaceous morphospace by the Puercan Cimolodonta. Vacancies in the Puercan cimolodontan morphospace may be a result of changes in available dietary resources, or competitive exclusion. The Taeniolabididae occupy a morphospace region distant from the remainder of the Puercan Cimolodonta, supporting independent studies suggesting they were an immigrant taxon rather than a product of rapid phenotypic divergence. My results indicate selection taking place over the K-Pg extinction for small body size within the Cimolodonta. I also find evidence of partial reoccupation of Late Cretaceous cimolodontan morphospace in the Puercan, indicating ecological niche recovery.</p>

<p> Green roofs are an emerging technology promoted primarily for stormwater management but little has been published about their potential for biodiversity performance. This is the first study to explore the potential for creating prairie-like, non-succulent, native plant communities on unirrigated extensive green roofs in the southeastern United States. Ten experimental green roof platforms were used to: 1) identify native species and methods of establishment appropriate for green roof applications in the southeastern United States; 2) examine the effects of introducing natural soil into a commercially available green roof soil media mixture on the survival and establishment of native prairie species; and 3) examine the composition of early successional green roof plant communities. Eleven planted species were successfully established and 46 colonizing species were identified. It was found that the addition of native prairie soil did not significantly affect survival, overall cover, or biodiversity in terms of species richness and evenness.</p>

<p> The low-lying topographic nature of salt marshes makes plants in these communities particularly vulnerable to increased salinity and inundation exposure associated with sea level rise. Both increased salinity and inundation have been cited as major causes of reduced plant performance and survival in marsh and areas fringing marsh. In addition to limitations imposed by physical stress, interspecific interactions have also been shown to mediate the performance and survival of salt marsh and salt marsh fringing species. The Stress Gradient Hypothesis (SGH) postulates that species interactions shift from competitive to facilitative as stress levels increase and predicts that (a) the frequency and intensity of facilitative interactions increase as conditions become more stressful for plants and (b) the strength of competitive interactions increases as abiotic stress levels diminish. The SGH has been rigorously tested to examine how both the frequency and intensity of species interactions change under varying physical stress levels. Studies conducted in salt marsh systems have shown facilitation to be as strong of a driving force as competition in influencing plant performance and survival and have shown that while competition appears to be the pervasive force in the less physically stressful terrestrial zones fringing salt marshes, facilitation influences the performance and survival of species in harsher marsh areas. Under conditions of sea level rise, it remains unclear if the nature of interspecific interactions would shift as stress levels change. This research endeavors to examine the interplay between abiotic stresses and biotic interactions under conditions of increased salinity and inundation exposure. </p><p> The first study presented here investigated the effects of increased inundation and soil salinity associated with sea level rise on four salt marsh fringing species, and assesses how competition and facilitation impact survival of salt marsh fringing plant survival under these changing conditions. All plant species experienced reduced growth and photosynthetic inhibition below their current distributional positions, both in the presence and absence of neighboring above ground vegetation. The findings also signal a potential shift in the nature of interspecific interactions from competition to facilitation to neutral as plants begin to experience increased salt and inundation exposure. </p><p> The second study aimed to disentangle the effects of increased soil salinity and increased soil moisture on four salt marsh fringing species, and to examine the effects of plant neighbors. The results showed that fringe plants exposed to increased inundation experienced a two-fold reduction in performance and survival over 750 g pure salt addition, suggesting that inundation may be a more important limiting factor than salinity with rising sea levels. Landward transplants at the forest-fringe margin exposed to lower soil salinity and decreased inundation exhibited a three-fold increase in performance and survival when compared to controls. Neighbor manipulation studies, which consisted of trimming neighboring vegetation to ground level, again suggested that interspecific interactions in salt marsh fringing species may shift from competitive to facilitative with climate-induced sea level rise. Overall, our findings suggest that salt marsh fringing species may not be able to tolerate changing conditions associated with sea level rise and their survival may hinge on their ability to migrate towards higher elevations. </p><p> The final experiment tested the Stress Gradient Hypothesis and investigated the relative importance of facilitation and competition in a salt marsh system under varying stress levels. This study also ascertained whether salt or inundation exposure is the primary influence on salt marsh plant performance and survival. As in previous studies, our findings suggest that many salt marsh plants don't require, but merely tolerate harsher abiotic conditions. The results showed that plants at higher elevations were depressed by strong competitive pressure from neighboring fringe species while plants at lower elevations benefited from the presence of neighbors. Collectively, the results of these studies indicate that species interactions are an integral driver of plant distribution in salt marsh communities. Furthermore, our findings indicate that changing stress levels may not always result in a shift in the nature of interspecific interactions. These studies have endeavored to show that the interplay between competition and facilitation interacts with physical processes to determine the growth and performance of both fringe and marsh plant species. The paucity of studies examining the roles of species interactions and changing abiotic stress levels on multiple salt marsh and salt marsh fringing species warrants the need for additional research. The responses of salt marsh and salt marsh fringing species to sea level rise can not only serve as very valuable and sensitive indictors of climate change, but will also aid in predicting the future location of the marsh-fringe-forest ecotone, which is predicted to shift inland as sea levels continue to rise.</p>

<p> The hollow curve species abundance distribution describes the pattern of large numbers of rare species and a small number of common species in a community. The species abundance distribution is one of the most ubiquitous patterns in nature and many models have been proposed to explain the mechanisms that generate this pattern. While there have been numerous comparisons of species abundance distribution models, most of these comparisons only use a small subset of available models, focus on a single ecosystem or taxonomic group, and fail to use the most appropriate statistical methods. This makes it difficult to draw general conclusions about which, if any, models provide the best empirical fit to species abundance distributions. I compiled data from the literature to significantly expand the available data for underrepresented taxonomic groups, and combined this with other macroecological datasets to perform comprehensive model comparisons for the species abundance distribution. A multiple model comparison showed that most available models for the species abundance distribution fit the data equivalently well across a diverse array of ecosystems and taxonomic groups. In addition, a targeted comparison of the species abundance distribution predicted by a major ecological theory, the unified neutral theory of biodiversity (neutral theory), against a non-neutral model of species abundance, demonstrates that it is difficult to distinguish between these two classes of theory based on patterns in the species abundance distribution. In concert, these studies call into question the potential for using the species abundance distribution to infer the processes operating in ecological systems.</p>

<p> The main goal of this study was to determine the thermal ecology of the small tree lizard <i>Urosaurus ornatus</i> in a Chihuahuan Desert landscape. The study site was located at Indio Mountains Research Station (IMRS), Hudspeth County, Texas. We obtained body temperature (Tb) data on 385 lizards collected from April 2007 to June 2014 during the active period using a cloacal thermometer. Additionally, we recorded air temperature (Ta) and substrate temperature (Ts) of lizard microhabitats at the time of capture, and the operative temperature of lizard models left in the sun and shade from May to September 2014. My results showed that the mean Tb for all adult lizards was 33.6 &plusmn; 2.8&deg;C, with a range of 24.0 to 40.2&deg;C. This average Tb was similar but lower than those found in other populations in Southwestern United States. The results indicated that <i>U. ornatus </i> at IMRS displays mostly a thigmothermic behavior. Thermoregulatory behavior of these individuals showed that <i>U. ornatus</i> is a thermoconformer on IMRS. There was no statistical difference in mean Tb between males and females or between non-gravid females. However, there was a significant difference between lizards found in the sun and lizards found in the shade. It is expected that rising global temperatures will influence this region and therefore will have an impact on the population of <i>U. ornatus </i> too; possibly affecting aspects such as time for feeding, reproducing, and of course thermoregulating. Thus, it is important for us to understand the thermoregulatory needs of ectothermic organisms as they are dependent on the direct environmental temperatures for survival, especially since many recognize that rapid global warming has already been activated by human misuse of natural resources.</p>

<p> Seabirds are ecosystem engineers with two major impacts on island ecosystems: they bring large quantities of marine nutrients to the terrestrial environment in the form of guano, carcasses, feathers, eggs, and spilled food, and they disturb the soil surface. Burrowing seabirds can denude the soil surface of all seedlings and leaf litter, plowing them under and loosening the soil. However, seabirds are colonial, and burrows are not even spaced over the surface of an island, producing spatial variability within a single island that might reveal how seabird activities control island ecosystem function. </p><p> In this dissertation I review seabird island ecology in general, focusing on how introduced predators have reduced seabird populations, interrupting seabird activities and altering island ecology. I then describe three studies designed to quantify the effects of seabirds on soil and plant properties within individual islands and compare these patterns across islands varying in seabird density, especially where seabirds have declined because of invasive rats (<i>Rattus</i> spp.). </p><p> I used geostatistics to quantify the spatial variance in seabird burrows and various soil and plant properties (including soil and leaf N) within six islands of low, intermediate, and high burrow density. I found that burrow density was not a good predictor at within-island scales, and though the variance of some soil properties (pH, soil &delta;¹⁵N, and soil compaction) peaked on intermediate islands as expected, variables reflecting the soil N cycle (net ammonification and net nitrification potential, NH₄⁺ and NO₃^-) continued to increase in variability on very high-density seabird islands. Ecosystem properties clearly responded to seabirds at different spatial scales, possibly because seabirds deposit guano at different spatial scales than they dig. </p><p> Using data within three rat-invaded and three rat-free islands, I used structural equation models to examine seabird influences on N cycling. I found some mechanisms that were constant across islands, such seabird-related decreases in soil water and pH, but other mechanisms differed between invaded and uninvaded islands, suggesting that rats manifest an alternative state for island N cycles, which may or may not be reversible. </p><p> Finally, I investigated whether plants can use ammonia (NH₃ gas) volatilized from seabird islands, measuring NH₃ concentrations across 10 islands and within a single island where I also experimentally manipulated plant N demand. Both rat-invaded and rat-free islands produced meaningful concentrations of NH₃ gas, and multiple plant species including <i> Melicytus ramiflorus</i> and <i>Coprosma macrocarpa</i> used it for up to 20% and 30% (respectively) of their total leaf N. Plant N demand modified NH₃ uptake, suggesting that plants located not on seabird colonies, but downwind, may benefit the most from this gaseous N source. </p><p> I suggest that future studies attempt to estimate thresholds of burrow density at which seabird-controlled ecosystem properties can recover from rat invasion.</p>

<p> While environmental controllers of decomposition have been extensively studied, organic matter quality and biotic controllers of decomposition, such as detritivore preference and manipulation of detritus, are largely understudied. In the studies described in this dissertation, a range of biotic controllers of detrital dynamics in aquatic ecosystems are presented. Crayfish, as model shredders, produce a diverse pool of fine particulate organic matter (FPOM) through fragmentation of coarse particulate organic matter (CPOM) and fecal production in the laboratory. Crayfish process maple leaves at a greater rate than oak leaves, and produced a greater amount of FPOM from maple compared to oak. Crayfish-generated FPOM had lower C:N ratios and increased bacterial abundances compared to original CPOM. Further, hydropsychid caddisfly and simuliid blackfly larvae confer greater growth efficiency when reared on crayfish-generated FPOM compared to mechanically ground FPOM in the laboratory, indicating that crayfish increase bioavailability of FPOM. No differences in growth or metamorphosis of simuliid larvae were observed when larvae were lab-reared on crayfish-generated FPOM from CPOM of different tree species (<i>i.e.</i>, sugar maple, sycamore, or white oak) or different stream conditioning times (<i>i.e. </i>, 30 or 150 d). This suggests that crayfish processing reduces organic matter origin effects on bioavailability. Changes in macrophyte abundance in a tropical wetland due to competition and ecosystem management can affect litter availability and litter quality. In two field-based, replacement series experiments with floating-mat macrophytes (<i>Eichhornia crassipes</i> and <i>Neptunia oleracea</i>), no interspecific competition was detected. However, <i>E. crassipes</i> dominated experimental enclosure biomass through attrition. Decomposition rates were faster for <i>E. crassipes</i> litter compared to <i>N. oleracea</i> litter within enclosures, but no differences in decomposition rates were detected by floating-mat species composition. Both synergistic and antagonistic diversity effects were observed on decomposition dynamics in an experiment varying litter richness from one to five species. Additionally, cattail (<i>Typha domingensis </i>) eradication efforts lead to changes in the decomposition landscape within the wetland, as <i>E. crassipes</i> colonizes managed areas, and decomposition rates were slower for litter of <i>T. domingensis</i> compared to <i>E. crassipes</i>. The compounding effects of litter species, detritivore interactions, and anthropogenic impacts on organic matter dynamics illustrate that it is critical to consider ecosystem function in ecosystem management. </p>

<p> I investigated the determinants of distributional patterns in the mussel <i> Mytilus californianus</i> in the Strait of Juan de Fuca in Washington State. A three pronged approach including evolutionary, geomorphological, and population ecology research methods elucidated processes determining the density and distribution of the species as well as forces impacting its future trajectory. Primary conclusions include: 1. Changes in aerial temperatures in Washington State in the near future are unlikely to dramatically influence the abundance and distribution of <i>Mytilus californianus.</i> 2. The interaction of sea level rise with the geomorphological features of rocky coasts has the potential to dramatically change the distribution and abundance of shallow water depth restricted species like <i>Mytilus californianus.</i> 3. Distributional patterns of <i> Mytilus californianus</i> occurring at multiple spatial scales are a result of the integration of population vital rates as determined by environmental gradients, and variation in vital rates are sometimes scale dependent (growth and recruitment rates) and sometimes not (survival rates). 4. Mussel populations were most sensitive to variation in growth rates, least sensitive to variation in recruitment rates, and intermediately sensitive to variation in survival. 5. <i>Mytilus californianus</i> density is unlikely to be primarily controlled by variation in growth rate or recruitment rate.</p>

<p> This project assesses the elevation of several vegetation zones of the Los Cerritos Wetlands in Southern California to determine the possible effects of sea level rise on the salt marsh vegetation, the foundation of coastal salt marsh ecology. Steamshovel Sough in the Los Cerritos Wetland contains ideal habitat for the project. This coastal salt marsh is unique in that it abuts artificial elevation gradients of urban development on all sides. The confined nature of the wetland restricts its ability to adjust to future sea levels, a process known as coastal squeeze, which calls the sustainability of this scarce ecosystem into question. In-situ surveying of indicator species Parrish's Glasswort and Pacific Cordgrass (<i>Arthrocnemum subterminale </i> and <i>Spartina foliosa</i>) revealed the habitat elevations above sea level. Modelling various sea level rise scenarios using the habitat ranges determined through in-site surveying reveal expected future habitat zones. Los Cerritos Wetland has a notable susceptibility to sea level rise because of topographic convolutions created by local urban development. One and two foot sea level rise scenarios project substantial zone shifts resulting in pronounced winners and losers. The results here highlight the delicacy of the marsh and its intimate relationship to sea level, and hold a powerful utility to restoration project managers seeking to create a salt marsh that reflects the natural distribution of various habitats and which possesses longevity in the face of the changing environment.</p>