<p> Evolutionary biologists are supremely interested in the events that cause populations to diverge and speciate, and the mechanisms that maintain divergence over time. Here, I investigate the evolutionary history of a boreal bird species complex. Boreal bird species are co-distributed, diverged during the Pleistocene, and generally have patterns of genetic divergence that are consistent with a single &ldquo;boreal&rdquo; clade in northern and eastern North America. The Gray-cheeked Thrush species complex, however, shows a possible species break in eastern North America between the Bicknell&rsquo;s Thrush (<i> Catharus bicknelli</i>) and Gray-cheeked Thrush (<i>Catharus minimus </i>). Using population genetic and genomic analyses of the largest sampling to-date of either species, I find that the eastern break indeed coincides with a species-level divergence, although low levels of admixture in a few individuals and one probable hybrid hint at the possibility of occasional hybridization. Species distribution models (SDMs) of the Last Glacial Maximum revealed that divergence may have been maintained by residence in different late-Pleistocene refugia. However, because speciation occurred mid-Pleistocene, I examined the geographical context of divergence of the Bicknell&rsquo;s Thrush and Gray-cheeked Thrush using multivariate analyses and ecological niche modeling techniques of local-scale habitat data and broad-scale climate and tree species distributions. Local-scale habitat analyses reveal that the thrushes breed at sites with unique tree species composition, physiognomy (forest structure), and ground cover characteristics; furthermore broad-scale analyses reveal that niche divergence, rather than conservatism, was the predominant pattern for these species, suggesting that ecological divergence has played a role in their speciation. This dissertation supports the hypothesis that the Bicknell&rsquo;s Thrush and Gray-cheeked Thrush are distinctive species that breed in divergent local- and broad-scale niches and emphasizes that this species-level divergence seems unique among boreal bird species.</p>

<p> The impacts of a 20,993 L diesel and gasoline spill on the benthic macroinvertebrate (BMI) and diatom communities in Cold Creek and the Santa Ana River (below its confluence with Cold Creek) were assessed by comparing species richness, diversity and compositions between fuel-impacted and reference sites. BMIs and diatoms were sampled four times (13&ndash;26 months after the spill) in sites located upstream from the spill (reference) and in sites located 0.5, 1.3, 2.7 and 3.0 km downstream from the spill (impact). BMI communities up to 2.7 km below the spill and in Cold Creek had (1) lower species richness and diversity for at least 25 months after the spill and (2) dissimilar species compositions for up to 26 months after the spill when compared to the reference site. Diatom communities up to 2.7 km below the spill and in Cold Creek had (1) similar or higher species richness and diversity when compared to the reference site and (2) dissimilar species compositions when compared to the reference site for the entirety of the study. BMI and diatom communities located 3.0 km below the spill and in the Santa Ana River had similar species richness, diversity and compositions when compared to the reference site. These results provide evidence that the fuel spill had an impact on the BMI and diatom communities in Cold Creek and that these communities are still changing.</p>

<p> Like many imperiled fishes, the endangered Pahrump Poolfish (<i> Empetrichthys latos latos</i>) is managed in <i>ex situ</i> refuges. I investigated life history characteristics of females from two such populations at Lake Harriet and Shoshone Stock Pond. Lake Harriet is a relatively large lake with low fish densities located at relatively low elevation and low latitude, while Shoshone Stock is a small pond with high fish densities at a higher elevation and latitude. Females from the Lake Harriet population were larger, and had greater fat content, reproductive allocation, and &lsquo;clutch&rsquo; size than females from the Shoshone Pond population. This divergence, which occurred in three decades, may result in a phenotypic mismatch if the fish are used as a source for restocking their native habitat or stocking new refuges. </p><p> Poolfish conservation may require establishing new populations; however, many sites are inhabited by non-native fish and/or other protected fish species. Thus, managers may wish to consider establishing multi-species refuges that may even already include undesirable species. I established experimental communities that included allopatric and sympatric communities of Poolfish, Amargosa Pupfish (<i>Cyprinodon nevadensis</i>), and invasive Western Mosquitofish (<i>Gambusia affinis</i>). Pupfish persisted in sympatry with both poolfish and mosquitofish, but had higher juvenile production when maintained in allopatry. By contrast, poolfish juvenile production was high in allopatry, but virtually absent in the presence of other species. </p><p> To evaluate the generality of these findings, I established experimental allopatric and sympatric communities of poolfish or pupfish with mosquitofish from two populations that differed in body size: Garrett mosquitofish were approximately twice the mass of Wabuska mosquitofish. Poolfish juveniles had high survival in allopatry, but produced virtually no juveniles when sympatric with either of the two mosquitofish populations. Pupfish juvenile survival was higher in allopatry than sympatric with Garrett mosquitofish, which in turn was higher than sympatric with Wabuska mosquitofish. These results were consistent with the earlier experiment suggesting that poolfish were functionally extirpated but pupfish maintained substantial production in the presence of mosquitofish. These findings suggest that poolfish should be maintained in single species refuges, but that multi-species refuges may protect imperiled pupfish species.</p>

<p> The white shrimp <i>Litopenaeus setiferus</i> is harvested throughout its range in the western Atlantic Ocean and is particularly important in supporting a commercial fishery in the northern Gulf of Mexico (nGoM) concentrated in Texas and Louisiana. Mortality rates of young (juvenile) white shrimp in estuarine nursery areas may have a large effect on the adult population. Understanding the temporal and spatial variation in mortality rates and other population parameters (i.e., density, growth rate, and secondary production) is important for the management of white shrimp in determining how estuaries function as nursery areas and can also be useful in identifying coastal habitats that best support white shrimp populations. My objective was to examine and describe the population dynamics, with a focus on mortality, of juvenile white shrimp populations in Sabine Lake, an estuary of the nGoM. I estimated density, growth, mortality, and secondary production in three areas along the estuarine salinity gradient. Most of these metrics were generally higher in areas of high salinity and total secondary production was relatively high in all three areas. Approximately half of the potential fish predators collected in my study area had preyed upon juvenile penaeid shrimps based on an examination of fish gut contents. Given their abundance within estuaries of the nGoM, these fish predators may have a large impact on populations of juvenile white shrimp. Mortality rates of juvenile white shrimp estimated with mark-recapture and length-frequency data were relatively similar to each other and within the range of the few values previously reported. Two commonly used age-based mortality estimators originally developed for fishes provided reasonably unbiased mortality rates for juvenile penaeid shrimps, although both estimators provided relatively high biased estimates at the lowest mortality rates considered. </p>

<p> Animals that live in groups face a dual challenge of effectively exploiting their environment while at the same time maintaining cohesion with other group members. Maintaining cohesion requires group members to come to consensus about when and where to move, despite the fact that they may not always agree. In this thesis, I investigate how individuals in groups make movement decisions, and how these individual decisions scale up to group-level properties. Using a laboratory experiment with golden shiners (<i>Notemigonus crysoleucas </i>), I first investigate the interaction network over which information spreads, finding that decisions are better predicted by whom individuals can see rather than whom they are close to, with potential consequences for the global spread of information (Chapter 2). I then investigate collective movement behavior in the wild using high-resolution GPS data from members of a troop of olive baboons (<i>Papio anubis</i>). I first show that baboons are consistent in the spatial positions they occupy within the group, and that the observed patterns may be understood based on a very simple mechanism by which individuals maintain cohesion with different numbers of their neighbors (Chapter 3). By quantifying how group members move relative to one another, I then show that baboon movement decisions are consistent with a shared decision-making process, rather than despotic leadership by dominant individuals, and that the patterns of decision-making are consistent with simple models of collective motion (Chapter 4). Finally, by incorporating a fine-scale, three-dimensional reconstruction of the habitat through which the baboons move, I show that habitat structure, in addition to social factors, also exerts an important influence on individual movement decisions, resulting in changes in the emergent structure and movement of the group (Chapter 5). Taken together, these results highlight that by combining high-resolution animal tracking, remote sensing, and analytical methods, we can begin to extend our understanding of collective animal movement from laboratory studies to complex animal societies living in the wild.</p>

Geographic variation in life-history and reproductive traits is frequently assumed to reflect localized, genetically based adaptation to the environment. In this study, I examine variation in the reproductive characters of house wrens breeding at two elevations in Colorado during the 1985-1987 breeding seasons. Egg and nestling transplant experiments were performed in an attempt to discover the relative contributions of environmental and genetic factors to the observed variation between sites. / Wrens breeding at low (1100 m) and high (3000 m) elevations differ in a number of reproductive characters. Wrens breeding at the high-elevation site initiated egg laying later in the season, produced larger clutches containing bigger eggs, and incubated them longer than did wrens breeding at the low-elevation site. Nestling periods were also longer at high elevation. Reproductive success (number of chicks fledged/eggs laid) was 0.5 young higher at the high site. Chicks hatched from high-site eggs were larger than were low-site chicks. This size difference was maintained throughout the nestling period. / Patterns of within-population variation in traits differed between elevations. At the low site, fitness-related traits, such as clutch size and reproductive output, were strongly influenced by date of initiation. Reproductive success was greatest for early, above-modal-sized clutches. At the high site, hatching failures associated with above-modal-sized clutches significantly reduced reproductive output. There, modal-sized clutches initiated late in the season produced the most young. / In experiments in which eggs were transplanted between sites, incubation times shifted toward those of the foster population. Although nest environment influenced incubation period, transplanted eggs rarely hatched in synchrony with eggs originating in the foster nest. In nestling-transplant experiments, chicks reared at the high-elevation site showed greater weight gain and tarsus growth than did their sibs reared at the low elevation, but, genetically unrelated chicks reared together did not differ significantly in growth. Observed differences between natural populations in embryo and nestling development are, partly, attributable to the direct effect of environmental differences. / Source: Dissertation Abstracts International, Volume: 54-07, Section: B, page: 3444. / Major Professor: Frances Crews James. / Thesis (Ph.D.)--The Florida State University, 1993.

Intraspecific variation in plumage was used to test the null hypotheses that geographic variation of 280 species of elevationally-restricted Andean forest birds is independent of elevation and is not a function of patchy geographic distribution. Both null hypotheses were rejected. / At most taxonomic levels, geographic variation in plumage is positively correlated with both the mean of its elevational distribution and the size of its geographic range. Vertical amplitude of elevational distribution is not a significant predictor of geographic variation in plumage. Independently of these elevational correlates, patchily distributed species show significantly more geographic variation than continuously distributed species. / These results show that geographic variation and presumably on-going speciation phenomena are greater at higher elevations. The decreased species richness at high elevations may be attributable to a higher rate of extinction from catastrophic disturbance as well as to ecological factors that limit sympatry in newly-formed species. / Source: Dissertation Abstracts International, Volume: 44-11, Section: B, page: 3275. / Thesis (Ph.D.)--The Florida State University, 1983.

The ecological consequences of storage allocation was studied in the euryhaline topminnow Poecilia latipinna, the sailfin molly. In the first study, fish raised in the laboratories at different temperatures had the highest triacylglycerol levels in the liver and viscera. Liver and testis size were greater in fish from the cold rearing. These effects of juvenile history on tissue size were permanent. In the second study, phenotypic plasticity of tissue biomass and storage level was measured in fish reared under different environmental conditions. Liver-viscera mass was larger, but testis mass smaller in fish reared at 23$\sp\circ$C, and the opposite pattern occurred for fish reared at 29$\sp\circ$C. Triacylglycerol level and content were affected by a population by temperature interaction. Finally, whether differences in resource allocation produce differences in fitness was tested by coupling manipulations of resource allocation in the sailfin molly to field measurements of its fitness. In experiment 1, with a longer photoperiod, fish from the high food level grew the most, and larger fish grew less than smaller fish. Fish from the high food level had the highest storage level, fish from the low food level the least, and untreated fish had an intermediate level. Gonad mass was greatest for fish on the high food level. Food level and size class interacted to affect survivorship in the freshwater pond. Storage level decreased over the winter, and differences caused by the food treatment persisted. In experiment 2, with a shorter photoperiod, fish from the high food level grew the most, and the larger fish grew the least, but there was also an interaction between food level and size class. Fish on the high food level had a greater storage level than the low food level and untreated fish, which had the same storage levels. Fish on the high food level had / greater liver-viscera and soma masses than the low food level and the untreated fish. The acute mortality in the freshwater pond was not related to storage. Storage levels declined in all fish in the saltwater pond over the winter, but the storage differences caused by the food treatment persisted. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6031. / Major Professor: Joseph Travis. / Thesis (Ph.D.)--The Florida State University, 1993.

Indirect effects occur when the interaction between two species is influenced by a third species. Recent empirical and theoretical evidence suggests that indirect effects have important influences on population regulation and community structure. Most studies of indirect effects have examined chains or networks of predation or competition. Indirect effects can also involve other types of interactions, yet their role in structuring communities is rarely considered. One such interaction, biological habitat modification, is ubiquitous in marine habitats, especially through the alteration of sediments or the creation of hard substrates. In soft-bottom habitats, the shells of dead molluscs are important for shelter or attachment of many organisms, and mollusc predators should have strong indirect effects on the community by regulating the availability of these substrates. Because shells are produced by living organisms, their abundance and quality will also be influenced by the dynamics of the mollusc population and by processes that destroy or alter the shells. / I examined the indirect effects of the horse conch (Pleuroploca gigantea), a predatory gastropod, on a suite of fish and invertebrates that use bivalve shells (the pen shell Atrina rigida) as shelters and/or nest sites in St. Joseph Bay, Florida. Exclusion experiments indicated that horse conchs are a major source of Atrina mortality. Experimental additions of new shelters caused an increase in abundance and reproductive activity in three species of fish (two blennies and a clingfish). Increased rates of shell availability caused an increase in reproductive output for both individuals and the local population of Chasmodes saburrae, the Florida blenny, probably because new shells provide a greater surface area for eggs compared to older shells. I used a simulation model, based on measurements of natural variation in Atrina population and shell resource dynamics, to compare the relative effects of horse conch predation and other factors on Chasmodes. Although pen shell density had the strongest effect, horse conch abundance also strongly influenced blenny reproduction. Thus, both the field experiments and the model predict that, by regulating the availability of new shells, the horse conch has a positive indirect effect on reproduction in Chasmodes. / Source: Dissertation Abstracts International, Volume: 57-04, Section: B, page: 2296. / Major Professor: William Herrnkind. / Thesis (Ph.D.)--The Florida State University, 1996.

Using descriptive and experimental approaches, I determined the relative importance of ecological processes acting within a tropical tadpole species assemblage. Fifty-three aquatic sites were sampled to establish natural patterns of species occurrence. Transplants were performed to see if differences in habitat can explain observed distribution patterns. By exposing different tadpole species combinations to the same predators, I could determine the intensity of predation rates on these tadpole species. The effect of interspecific interactions and how those interactions might vary with variation in breeding phenology were tested in pairwise rearings of tadpole species varying the time of encounter of one species with respect to the other. / Twenty-five tadpole species were encountered in 4 distinct habitat types (terra firme, peccary wallows, stream-side, and stream sites). Although each species uses sites with certain abiotic attributes, I could not detect any large-scale species assemblages that co-occur in habitats with similar characteristics. Occurrence patterns of tadpole species concorded with the results from transplants for only one tadpole species indicating that abiotic factors cannot account for much of the observed patterns. Predators reduced tadpole survival in 3 out of 4 different experimental prey-species combinations. Aeshnid naiads killed the most tadpoles, followed by Libellulid naiads. Predators preferred P. tomopterna, the less abundant species, over O. taurinus. / Variation in timing of introduction and the stock of eggs of O. taurinus affected the performance of both of the other species, but in different ways. This result indicates that breeding phenology can affect both the type and intensity of interspecific interactions. / Experimental manipulations and occurrence patterns of predators in natural sites suggest that predation is the major force acting on populations of tadpoles. Competition will probably be important only in the absence of predators. Larval anuran species assemblages seem to be are subjected to the same ecological pressures in tropical systems as they are in temperate ones. / Source: Dissertation Abstracts International, Volume: 51-09, Section: B, page: 4156. / Major Professor: Joseph Travis. / Thesis (Ph.D.)--The Florida State University, 1990.