Ovenbirds (Seiurus aurocapillus) and Swainson's Warblers (Limnothlypis swainsonii) wintering in Jamaica exhibited divergent foraging behaviors, with Ovenbirds picking prey from the leaf litter surface and Swainson's Warblers flicking leaves aside to search for prey concealed beneath the leaf litter. The two species consumed significantly different prey: Ovenbirds feeding primarily on ants, and Swainson's Warblers most frequently consuming beetles and spiders, but also consuming roaches and small geckos. The differences in foraging strategies help explain the species' different habitat use patterns. Because of the ubiquity of ants, Ovenbirds are habitat generalists whereas Swainson's Warblers are dependent on habitats that have a well-developed canopy, leaf litter layer, and an abundant leaf litter fauna Ovenbird body condition declined seasonally, concurrent with seasonal declines in prey biomass. Rectrix regrowth rates and overwinter change in body mass were significantly correlated with ant biomass on Ovenbird territories. In habitats and years in which prey biomass decreased to <2.5 mg/0.25 m 2, Ovenbirds were not able to maintain body mass. The results confirm the hypothesis that dry season desiccation significantly decreases arthropod populations and the severity of the dry season strongly affects habitat quality for Ovenbirds Swainson's Warblers appear to be more tolerant of dry season leaf litter desiccation than Ovenbirds, as habitats with a deep leaf litter layer provided refugia for invertebrates. Correspondingly, Swainson's Warbler showed no seasonal decline in dry forests where they were relatively common. These results underscore the need for conservation of dry forests for the geographically restricted Swainson's Warblers Ovenbirds defended spatiotemporal territories, such that home ranges of neighboring birds overlapped, but individuals were not in the same place at the same time. Home range size was not significantly correlated with prey biomass. However, I experimentally decreased ant biomass on portions of the home ranges of four individuals. These birds showed a significant increase in home range size and movement rates. Control birds showed no change in either variable. These results strongly suggest that Ovenbirds constantly monitor food resources and adjust home range size accordingly and that food abundance limits winter habitat carrying capacity / acase@tulane.edu

Landscapes are created and transformed by human beings as they engage in a dialogue with their biotic and abiotic environment. The Q'eqchi'---the fourth largest group of the Maya language family with speakers numbering over 700,000---are the primary transformers of the lowland forested landscapes of northern Alta Verapaz. However, families actively involved in this transformation are new arrivals to the area and hail from a botanical environment wholly different from the lowland tropical forests of their new home. This dissertation is based on 17 months of ethnographic and ethnobotanical research in two Q'eqchi' communities---one in the highlands, the other in the lowlands---and unravels the cultural process of behavioral and linguistic adaptation to an unfamiliar botanical environment Using the Mesoamerican aldea as the unit of analysis, the methods of this controlled comparison are both qualitative and quantitative. Participant observation and a long-term, personal commitment to the communities and the Q'eqchi' language provided an intimate understanding of ethnobotany as applied to the cultural domains of house construction, home gardens, agriculture, harvesting of forest resources, local and regional markets, and plant related lexical patterns. Community surveys, home garden inventories, and a plant trail experiment provided a large, quantitative data set that helped determine patterns in the cultural matrix. Basic descriptive statistics, multilinear regression, multi-dimensional scaling, cluster analysis, agreement matrices, and consensus analysis were all employed to help determine the patterns of cultural adaptation within the two communities The cultural data show that, although the lowlands are indeed largely unfamiliar to the migrants, distant and recent histories have played a role in preadapting the Q'eqchi' to the lowlands. Through these historical and contemporary channels, knowledge of plants and other characteristics of the lowland forests have reached the highlands, essentially helping to homogenize plant knowledge and behavior across any artificial altitudinal categories. Nevertheless, the lowlands are drastically new and the needs and stressors of the new ecological and cultural environment seem to elicit numerous instances of behavioral and lexical modification The 'worldy' Q'eqchi'---an ethnographic enigma when compared to other Mayan groups---have been stigmatized in the conservation and anthropological literature as the 'invaders' of a 'pristine' ecological haven in northern Guatemala. Until this community and the Guatemalan government understand and address the pressing problems in the highlands, the lowlands will remain a social and ecological sponge, destined to become uninhabitable / acase@tulane.edu

This research was designed to investigate the relationships between migratory birds and the habitats they use during the non-breeding winter season in Jamaica, West Indies. I first examined the ecological determinants of habitat relationships of canopy-foraging insectivorous migratory warblers wintering in Jamaica. Over a wide spatial scale, warbler density was correlated with food availability. In addition, warbler density changed over time in correspondence to short term and longer term fluctuations in food availability. These results suggest that migratory warblers distribute themselves with respect to food availability Second, I examined the ecological roles of migratory and resident birds in Jamaica. The ratio of migrant to resident bird abundance was significantly negatively correlated with the ratio of large (>5mm) arthropod biomass in the breeding season to total arthropod biomass in the non-breeding season. After controlling for effects of arthropod seasonality, migrant proportions remained higher in disturbed than undisturbed sites. These results suggest that the breeding productivity of resident birds may be limited in part by the availability of large, soft-bodied arthropods suitable for breeding, whereas non-breeding bird populations may be limited by total arthropod availability. These findings are consistent with the 'breeding currency hypothesis.' I hypothesize that patterns of nest predation interact with food availability in limiting populations of tropical breeding birds below carrying capacities set by non-breeding season arthropod abundance, thereby creating a set of resources (small arthropods) available only to wintering migrants Third, I compared habitat quality for a migratory warbler, the American Redstart (Setophaga ruticilla), wintering in four natural forest types versus two agricultural habitats (citrus and coffee). Demographic indicators of habitat quality (density, persistence, return rate, and body mass retention) suggest that habitats in Jamaica vary in quality for wintering redstarts, and that citrus orchards and coffee plantations lie within the variation found among natural forests. Sharp increases in arthropod biomass in the late winter in shade-coffee plantations, especially those shaded by the tree Inga vera, may have permitted redstarts inhabiting them to maintain body mass over the winter better than in other habitats. This finding suggests that shade-coffee plantations provide high quality habitat for wintering migratory songbirds, especially for species likely to feed on abundant foliage-dwelling insects Taken together, these findings help reveal two links in the chain of events causing the decline of migratory songbird populations: (1) migratory bird winter habitat relationships are influenced by food availability, and (2) some habitats confer favorable demographic traits on their inhabitants. These conclusions suggest that a more complete understanding of migratory songbird populations may best be pursued by working to reveal how human activity may affect patterns of tropical arthropod abundance and habitat quality. In addition, valuable predictions of how future tropical land conversion may affect migrant populations can be made by coupling demographic habitat quality information with land use data. (Abstract shortened by UMI.) / acase@tulane.edu

Endocrine disruption by anthropogenic chemicals has been well documented for vertebrates but has not been extensively studied for invertebrates. However, concern has been expressed over the possibility that the same environmental agents that interfere with male development in vertebrates may also perturb male development in invertebrates, for instance, cladocerans. My study with Daphnia magna has shown that the estrogenic xenobiotics diethylstilbestrol (DES) and endosulfan do not interfere with male differentiation but do inhibit molting of daphnids. Further investigation revealed that some other estrogenic agents, such as a PCB formulation Aroclor 1242, diethyl phthalate, and 2,4,5-trichlorobiphenyl (PCB29), also delay molting of Daphnia magna To gain insight into the mechanisms for the inhibition of molting caused by these estrogenic agents, a chitinolytic enzyme, chitobiase (also known as N-acetyl-beta-glucosaminidase), was used because this chitin-degrading enzyme is at the terminal of cascades of endocrine events that control molting of crustaceans and appears to be a product of genes that are regulated by the arthropod molting hormone, 20-hydroxyecdysone. I found that activity of chitobiase in the epidermis and hepatopancreas of Uca pugilator is modulated over the duration of the molting cycle with maximum enzymatic activity in both tissues occurring in late premolt, substage D3-4. This pattern of change in chitobiase activity coincides well with changes in the hemolymph titer of ecdysteroids during the molting cycle reported for the same species. Multiple injections of 20-hydroxyecdysone into premolt substage D1 fiddler crabs elevated chitobiase activity in the epidermis and hepatopancreas. These results are the first direct evidence that chitobiase is a marker for the actions of the molting hormone in a crustacean To determine whether the delay of molting in the presence of estrotrogeic xenobiotics is linked to the inhibition of activity of chitobiase, Uca pugilator was exposed up to seven days to Aroclor 1242, DES, diethyl phthalate, endosulfan, 4-octylphenol, 4-tert-octylphenol, and PCB29. Significant declines in chitobiase activity were apparent in the epidermis and hepatopancreas of Uca pugilator. The inhibition of epidermal enzymatic activity by Aroclor 1242, DES, endosulfan, and PCB29 can at least partly account for the slowing of molting in crustaceans caused by these chemicals since chitobiase is essential for degradation of the old chitinous exoskeleton. Because activity of chitobiase is regulated by 20-hydroxyecdysone, the inhibition of enzymatic activity in the presence of various estrogenic agents strongly suggests that exposure to these compounds disturbs the Y-organ-ecdysteroid receptor axis in Uca pugilator External features of a sexually abnormal fiddler crab that carries characteristics of both sexes are described / acase@tulane.edu

The present study is the first to use historical fish museum records and data from contemporary collections to examine effects of land use on warm-water fish communities over a large spatial (six watersheds) and temporal (15-40 years) scale. I used Geographic Information System technology and data from Halawakee Creek, Wacoochee Creek, Little Uchee Creek, Mountain Oak Creek, Mulberry Creek, and Uchee Creek of the central Chattahoochee River system to test the hypothesis that fish community structure is sensitive to land use in the surrounding watershed. I also collected in-stream habitat data to examine the relationship between land use and stream habitat structure. Land-use cover types (urban, agriculture, pine-monoculture, pine-hardwood forest, clear-cut, hydrography, and roads) were digitized from aerial photography I found a significant positive relationship between agricultural land-use and the in-stream sediment index (r$\sp2$ = 0.43, P = 0.01). Stream depth heterogeneity decreased significantly with increased sediment (r$\sp2$ = 0.39, P = 0.02). Substrate complexity tended to be lower in agricultural streams Mainstream (3rd and 4th order) Piedmont reaches draining agricultural lands had significantly lower levels of fish diversity (r$\sp2$ = 0.47, P $\leq$ 0.01). Land use was not a significant predictor of diversity in Coastal Plain or Piedmont headwater(1st and 2nd order) reaches. Agricultural land-use explained significant variation in mainstream core species abundances of Piedmont but not Coastal Plain streams Pool and riffle species that use coarse substrates (i.e. Nocomis leptocephalus, Semotilus atromaculatus) were most sensitive to the effects of agricultural land-use. Lepomis spp. were least sensitive to agriculture in the watershed Regional persistence and stability of fish communities over time were not significantly correlated with declines in pine-hardwood forest, except that the least stable fish community was observed in the watershed with the greatest decrease in pine-hardwood forest cover. Species showing signs of decline across all watersheds were Notropis hypsilepis, Lythrurus atropiculus, Luxilus zonistius, Ameiurus natalis, and Noturus gyrinus Results from this study suggest that mainstream environments and their associated communities are more susceptible than headwater reaches to the effects of agricultural land-use and this has important consequences for conservation / acase@tulane.edu

Magnolia ashei Weatherby (Ashe's magnolia) is a rare understory shrub or small tree endemic to select steephead ravine systems of the Florida panhandle. M. ashei is currently designated as Endangered by the State of Florida (Category 2 - Federal) and is subject to possible threat and litigation in the future. I present an integrated study of Magnolia ashei; including species ecology, demography, reproductive biology, and population genetics. I also compare Magnolia ashei to its more widespread sister taxon Magnolia macrophylla Michx. Historical biogeographical data indicates a decline in the overall distribution of magnolias over geological time, though the level of decline for individual magnolia species is variable. For M. ashei and M. macrophylla, reduced distributions are due primarily to loss of habitat from large-scale global climatic change and secondarily from more recent habitat destruction by man. I present demographic data showing populations of both species to be stable, relatively dense, and evenly distributed throughout suitable habitat. Rates of mortality are low due to the remarkable persistence of established plants even under adverse conditions (e.g. heavy shading, erosion, etc.). Seedlings are infrequent, however, and have low rates of survival. An investigation of floral biology indicated that the system of pollination was effective, but that one or more isolating or incompatibility mechanisms may result in relatively low percentages of viable seeds. Non-viable seeds are empty and thus may deter seed dispersal vectors from performing optimal dispersal. Genetic statistics for both M. macrophylla and M. ashei indicated low genetic diversity values when compared to species with similar life history traits, approximating instead, values of rarer endemic species. A significant portion of total genetic variability is partitioned among populations, indicating a low incidence of gene flow between populations and considerable genetic differentiation. Such genetic structuring among population lends support to the theory that these exceptional forests are 'habitat islands' with reduced gene exchange via pollen or seed Continued destruction of forests containing M. ashei and M. macrophylla is the immediate threat to populations of both species, though genetic isolating mechanisms, incompatibility factors, and low levels of genetic variability may affect long-term viability / acase@tulane.edu

We performed a series of experiments to investigate the relationships between plant performance, defense, and herbivory in tropical plants with nitrogenous defenses We compared defenses among three plants, Piper cenocladum, P. melanocladum, and P. imperiale. Piper melanocladum has tough leaves and nitrogenous secondary metabolites. Piper cenocladum is defended by ant mutualists, nitrogenous secondary metabolites, and moderately tough leaves. Both species experience little herbivory. Piper imperiale has tender leaves and low concentrations of secondary metabolites and experiences a higher rate of herbivory Feeding trials assessing the effectiveness of the P. imperiale defenses showed that Spodoptera exigua feeding efficiency did not respond to plant chemicals and whiteflies showed no preference for plants with lower chemical concentrations. Leaf-cutter ants, which are abundant, damaging herbivores, avoid P. imperiale secondary metabolites. Since A. cephalotes are equally deterred by high and low concentrations of P. imperiale defenses, selective pressure from this herbivore cannot account for maintenance of variation in chemical production In order to compare the relative importance of environmental and genetic sources of variation in secondary metabolite content, we exposed clones of multiple plant genotypes to variable soil type, nutrient content, moisture content, and light availability. Genotype had a strong effect on plant chemistry. None of the environmental variables that we measured showed any relationship to plant chemical content. This species lacks phenotypic plasticity for secondary metabolism and cannot adjust defenses in response to fluctuating resource availability. Mortality was high, and was influenced by soil moisture content, plant genotype, and light availability. Genotypes with higher concentrations of secondary metabolites were better able to tolerate shade than those that produced low chemical concentrations. This genetic linkage between shade tolerance and defensive chemical production may account for the maintenance of variation in secondary metabolite production in this species We used photosynthetic capacity to estimate plant investment in primary and secondary metabolism to determine the cost of producing defenses. Higher concentrations of secondary metabolites were associated with reduced growth and photosynthetic capacity, representing a considerable cost to the plant. Selection against this cost of defense is likely balanced by selection for anti-herbivore defense and shade tolerance / acase@tulane.edu

Long-term population trends of colonial wading birds (Ciconiiformes) in Louisiana, Florida, Texas, and California were examined using data from Audubon Christmas Bird Counts (1949-1988) and Breeding Bird Surveys (1966-1989). Winter populations of most Louisiana wading birds increased over the 40-year period, with the sharpest increases occurring during the last 20 years. Increased acreage of crayfish (Procambarus) aquaculture in Louisiana appears to be the most significant factor explaining the observed population increases. First, populations of wading-bird species that use crayfish were correlated positively with the wild crayfish harvest, and more strongly with crayfish pond acreage. Second, the regularity of pond management provided a more predictable foraging habitat than did comparable natural areas. Third, the use of crayfish ponds by wading birds peaked during pond drawdowns, which may have increased reproductive success by concentrating prey available to wading birds during their nesting season. Fourth, wading bird species that specialized on crayfish showed the greatest population increases and the strongest correlation with crayfish pond acreage A field study comparing crayfish farms with natural habitats found significant differences in prey availability, and in the relative foraging success of Great Egrets, Snowy Egrets, and White Ibises. Wading birds on crayfish farms took significantly more prey for less effort, and selected more preferred prey. Wild sites had more fish $(P<0.001),$ more total prey $(P<0.001),$ and higher prey densities $(P<0.001)$ than flooded farm ponds. Farm ponds during drawdown, however, had higher densities of fish, more crayfish $(P<0.001),$ and higher prey densities than wild sites $(P<0.001).$ When foraging on crayfish farms, Great Egrets took more total prey $(P<0.05),$ Snowy Egrets took more fish $(P<0.05),$ and White Ibises took more crayfish $(P<0.01)$ than in the wild. Juvenile White Ibis foraged significantly more successfully on crayfish farms than did adult birds on farms or in the wild. Crayfish farms thus provide superior foraging habitats for wading birds during the nesting season. Recent increases in crayfish farm acreage in Louisiana appear to be a major factor causing the long-term population increases of Louisiana's colonial wading birds. These findings have important implications for the conservation and management of Louisiana's wading bird populations / acase@tulane.edu

Understanding how commercial forests can be managed to benefit wildlife has important conservation implications, as silvicultural landscapes occur globally and have high economic value. In this study, I compared two habitat types in southeastern Louisiana, even-aged loblolly pine ( Pinus taeda) and bottomland hardwood forests, both used for breeding by Swainson's Warbler (Limnothlypis swainsonii; SWWA). I investigated habitat quality and habitat selection patterns of SWWA to (1) assess the conservation value of pine plantations for understory-nesting birds, (2) identify ecological factors important in habitat selection at multiple scales, and (3) contribute needed information on the natural history and status of a species of conservation concern The density of breeding pairs, timing of nesting, clutch size, hatching rates, and reproductive success of SWWA did not differ significantly between habitats. These results, coupled with similar patterns of habitat use at the nest site, suggest that the habitats are ecologically analogous for breeding. Similarities in morphology and behavior also suggest that ecotypic variation does not account for differences in ecological success or patterns of habitat selection in the two forest types Predictions about habitat selection mechanisms were tested based on the foraging behaviors and nesting requirements of SWWA at specific scales. I found support for four hypotheses (Foraging Substrate, Potential Nest Site, Nest Decoy, and Nest Concealment), demonstrating that SWWA use different cues at the habitat, territory, nest patch, and nest site scales, but consistently across habitat types. Vegetation characteristics contributing to the nesting and foraging needs of this species served as mechanisms for habitat selection These results support the conclusion that SWWA has expanded its breeding range into an anthropogenic habitat that meets its basic nesting requirements, despite structural and floristic differences between the two forest types. The implication of these findings is that the conservation value of the enormous area of commercial pine plantations in the southeastern United States can be significantly augmented by appropriate management choices / acase@tulane.edu

Habitat fragmentation impacts on bird communities are relatively well studied in the temperate zone, where brood parasites and non-forest predators are the main causes of declining avian biodiversity. However, life history traits of tropical species suggest different and more diverse effects of habitat fragmentation on tropical bird communities. This dissertation used historical data and quantitative comparisons of fragmented and control sites to infer causes and patterns of tropical avian community response to fragmentation in Central America. Particular ecological guilds, namely forest understory insectivores, mixed-species flock participants, and birds that nest on or near the ground declined or disappeared from La Selva Biological Station, Costa Rica since the 1950s as the site became increasingly isolated from other forest. Spot-maps of twenty-two insectivorous bird species at La Selva in the 1970s indicate that insectivore populations were probably never large enough to be viable, emphasizing the need for larger reserves given the low density of many tropical forest species. Comparisons of four forest sites (24.6-1200 ha) to an non-fragmented control site in southeastern Nicaragua show significant reduction in biodiversity, corresponding decline in total bird abundance, and changes in community composition, even in the larger sites. Lack of change in the Nicaraguan control site suggests landscape changes rather than climate change is the most parsimonious explanation for community changes in the fragments. Finally, comparison of community changes in two large isolated forest reserves, La Selva and Barro Colorado Island, Panama, demonstrate similar patterns of losses of insectivores and low nesting species. However, landscape level and climatic differences between the two sites also affect the ability of some species to persist in remaining forest. Overall, this dissertation suggests that deterministic factors, especially ecological characteristics, put particular species at risk to landscape changes. No single mechanism appears to explain all the patterns, but small population size, poor dispersal ability, and increase in nest depredation are implicated by this study. Further investigation is needed to assess the relative importance of these and other mechanisms. Moreover, trophic cascades involving other taxa are predicted as a result of the lack of ecological replacement of disappearing specialized forest insectivores / acase@tulane.edu