Unattached benthic algae are a common component of seagrass meadows and other benthic systems. I used a series of field experiments to investigate (1) whether competition by algal mats represents a disturbance force capable of opening gaps in the seagrass canopy, (2) the extent of associated indirect effects on mobile fauna, (3) the extent to which algal patches are isolated epifaunal islands, and (4) whether algal clumps serve as a dispersal mechanism for benthic animals. Algal mats proved to be a powerful disturbance mechanism which killed most of the above-ground and half of the below-ground biomass of seagrass underlying the algae. Total faunal abundance increased on experimental algal plots, although relative dominance of various taxa changed considerably. The algal mats, despite supporting large numbers of animals, should provide a poor substitute for seagrass because of algal ephemerality. In situ staining and mark-recapture techniques showed that algal clumps were not isolated islands; rather, there was extensive exchange of fauna between algal masses and the surrounding habitat, although there was greater insularity for are dispersed by tumbling benthic algae. Transport of animals by algae proved to be considerable, and observations of tagged algae indicated that clumps can tumble up to 0.5 kilometers per day. This dispersal mechanism should be particularly important for species with direct development or abbreviated larval phases and should entail lower risk than other adult dispersal stratagems such as vertical migration or rafting. The pattern of non-shifting mosaic disturbance and mobility present in this system result in unusual patch dynamics and provide some alternative views of plant-plant and plant-animal interactions in the benthos. / Source: Dissertation Abstracts International, Volume: 53-07, Section: B, page: 3267. / Major Professor: Robert J. Livingston. / Thesis (Ph.D.)--The Florida State University, 1992.

Genetic models of female-biased sex ratios in subdivided populations include individual selection (inbreeding and sib mating, dispersal, and local mate competition (LMC) that assumes restricted mating among the progeny of a few females) and group selection. I examined two genetic assumptions of these models in a parasitic wasp, Muscidifurax raptor (Hymenoptera: Pteromalidae), a solitary ectoparasitoid of dipteran pupae. These assumptions are (1) sex ratio genotypes produce similar phenotypes over a range of environmental conditions (no genotype-environment interactions), and (2) sex ratio is genetically uncorrelated with other life history traits. / I found variation among five strains in sex ratio and daily fecundity, but there were no strain-environment interactions. The strains all increased the proportion of males with increasing density of ovipositing females. M. raptor is not a pure LMC species. Males emerge before females and await them for mating, but emergence spans 8 days and males are winged and capable of dispersal. Alternative models for sex ratio variation in M. raptor include differential dispersal by males and females and group selection models. / In a diallel analysis of three strains, I found that the genetic variance in sex ratio and other life history traits includes directional dominance, indicating that inbreeding will reduce the bias in sex ratio. I also found dominance genetic correlations and maternal effects correlations among sex ratio, daily fecundity, and development time. Females that develop quickly have higher fecundity and produce more female-biased sex ratios. The correlation is a result of the sequence of sex allocation during an oviposition bout: male eggs are oviposited early whereas females are oviposited later. / Sex ratio in M. raptor is a composite trait that reflects variation in fecundity as well as the propensity to fertilize eggs. The genetic correlations between sex ratio and other life history characteristics indicate that sex ratio may not evolve freely, but is constrained by selection on other traits. / Source: Dissertation Abstracts International, Volume: 51-11, Section: B, page: 5125. / Major Professors: Joseph Travis; Daniel Simberloff. / Thesis (Ph.D.)--The Florida State University, 1990.

Newly settled Caribbean spiny lobsters, Panulirus argus, undergo an ontogenetic habitat shift from vegetation (algal phase) to crevice shelters (postalgal phase). I experimentally observed the nocturnal behavior and diurnal shelter choice of juveniles across this size range in the absence and presence of conspecifics. Activity and shelter choice was not influenced by conspecifics during the algal phase. Postalgal phase juveniles, in the presence of conspecifics, were induced to greater locomotory activity and shelter sharing. Conspecifics influence produced an ontogenetic habitat shift at a smaller size. / Den sharing behavior by postalgal spiny lobsters has been postulated as a form of cooperation. I examined four hypotheses of how lobsters might benefit from sharing dens and/or being gregarious. By sharing dens, lobsters may increase survival (H$\sb{\rm A1})$ through group defense against predators, or (H$\sb{\rm A2})$ through group defense against interspecific competitors. By being gregarious, lobsters may increase survival (H$\sb{\rm B3})$ through the dilution effect, or (H$\sb{\rm B4})$ through decreased exposure while searching for shelter (guidepost effect). The first two hypotheses provide a benefit for den sharing and constitute cooperation. The last two hypotheses suggest that den sharing is a coincidence of congregation. Each hypothesis makes specific predictions which I tested by den monitoring field surveys, field manipulations and mesocosm experiments. / I found (1) lobsters did not consistently utilize the most defensible dens nor occupy dens to capacity. (2) Den sharing was not correlated with predator or competitor density, but was positively correlated with conspecific density. (3) Lobsters were more often aggregated at a spatial scale larger than a single den. (4) Lobsters did not have higher survival when sharing dens. (5) Lobsters were not better competitors when sharing dens. (6) Lobsters did not have higher survival with higher conspecific density, but (7) lobsters were able to find dens twice as often and three times faster when conspecifics were present. These results support only the guidepost effect (H$\sb{\rm B4})$ hypothesis. Den sharing is a non-advantageous outcome of gregariousness but is not cooperation during the ontogenetic phase when the behavior is first observed. / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6513. / Major Professor: William F. Herrnkind. / Thesis (Ph.D.)--The Florida State University, 1995.

The structural complexity of a habitat dictates the availability of shelter, and shelter may affect population and community structure in many systems. I test a specific hypothesis of the effects of habitat structure, the demographic bottleneck hypothesis, which proposes that shelter limitation can control population size structure and recruitment density by acting strongly on only one size class. To test this hypothesis, I first experimentally manipulated the size-specific availability of shelter for stone crabs in St. Joseph Bay, Florida, and I found evidence for a bottleneck that affects the growth and fecundity of large stone crabs. / These results provide support for the demographic bottleneck hypothesis, but they do not address its generality. It is a common problem in ecology that we rely on singular tests of hypotheses and the scientific generalization of these results. To address this problem, I suggest that we repeat experiments and use random factors more often in experimental designs. The use of random factors can lead to an unbiased estimate of the generality of patterns and to an understanding of the mechanisms that underlie these patterns. / To address these concerns, I repeat the shelter supplementation experiments in St. Joseph Bay and in three additional haphazardly-selected bays in the northeast Gulf of Mexico in a mixed-model experimental design. In addition to the shelter manipulations, which test the bottleneck hypothesis at the individual level, I use observational and experimental techniques to examine five biotic factors (habitat structure, food, predation, settlement, and competition) that may contribute to population-level differences among bays. / I find differences among bays in the natural population-level parameters of stone crab size structure and density and in crab responses to shelter supplementation. The demographic bottleneck hypothesis best accounts for these differences. I show that there are demographic consequences of shelter limitation on stone crab growth and fecundity at the individual level, and that these effects appear to explain population-level differences among bays. However, the demographic bottleneck hypothesis does not explain all the differences in crab populations. The bottleneck effects are mediated by differences in food, competition, and settlement among bays. / Source: Dissertation Abstracts International, Volume: 56-11, Section: B, page: 5894. / Major Professor: Daniel S. Simberloff. / Thesis (Ph.D.)--The Florida State University, 1995.

The lower Calcasieu estuary, located in southwest Louisiana, has received industrial, municipal, and agricultural discharge for the last several decades, resulting in the contamination of distinct regions of the system. This paper coordinates existing environmental data from the analyses of surface waters, sediments, and tissues of higher trophic level aquatic organisms collected by several state and federal agencies, attempting to detect spacial trends in contaminant distribution. Selected industrial facilities were examined with respect to process, effluent parameters, and wastewater treatment equipment. Surface water quality in areas has been impacted by the presence of volatile organic compounds (VOCs), and sediment contaminants detected include chlorinated benzenes, polynuclear aromatic hydrocarbons, and phthalates. State analyses of both edible portions and whole body samples of seventeen aquatic species show a very wide spacial distribution of individuals carrying elevated body burdens of hexachlorobutadiene (HCBD) and hexachlorobenzene (HCB), two of the more prevalent chlorinated hydrocarbons found in the system. While found in animals from throughout the system, HCB and HCBD were detected in only a very limited spacial range in sediments and surface waters of the system. In an attempt to understand potential mechanisms of uptake in various species, middle trophic level organisms were collected and analyzed for whole body burden concentrations of HCB and HCBD. All organisms captured in the area of localized sediment contamination showed a detectable level of these compounds, with concentrations decreasing with distance from the source. Dialysis tubing filled with iso-octane was employed as a biological surrogate to determine relative bioavailability of water-solubilized HCB and HCBD from various regions in the system. Detectable levels of both compounds were found in areas downstream, upstream, and lateral to the area of known sediment contamination. No correlation between exposure time and uptake were found, indicating that system-specific conditions (either meteorological or man-made) were affecting the relative availability of HCB and HCBD at any given time period. No correlation was found to exist between body burden concentrations of middle trophic level organisms and surrogate concentrations / acase@tulane.edu

Most studies of species diversity in habitat fragments are conducted either implicitly or explicitly within the context of the island model of population dynamics, or of species-specific metapopulation models. Whether such equilibrium models are generally applicable to tropical forest understory birds in recently fragmented landscapes remains unknown. In this dissertation, I investigated whether local populations of an understory rainforest bird (Myrmeciza exsul, Chestnut-backed Antbird) are connected via dispersal. Local populations tend to be temporally stable: Mean annual apparent survival of M. exsul was approximately 0.80 in both sexes within a large tract of forest in northern Costa Rica, and breeding dispersal was minimal. Thus, natal dispersal is the main mechanism of gene flow. I used population genetic methods to investigate dispersal and population genetic structure of five populations of M. exsul in relation to forest fragmentation. Mean natal dispersal distance was approximately 1 km, with no evidence of direct dispersal between any of the five populations sampled. Population genetic structure was significant, especially considering the small geographic scale (10-30 km), short time since putative isolation (40-60 years), and generally large populations (often > 100 pairs), all of which generally prevent genetic drift- and population differentiation. The smallest (80 ha), most isolated forest fragment population provided the strongest genetic evidence for complete isolation of populations in forest fragments. Individuals in this population exhibited significantly elevated pairwise relatedness compared to other sites, indicating a reluctance to disperse out of the site. I found no evidence of sex-biased dispersal in any of my genetic or field-based analyses. The patterns of dispersal documented here are consistent with expectations of both prevalent hypotheses for the evolution of dispersal (i.e., inbreeding avoidance and kin competition avoidance), and a null model of natal dispersal -- wherein birds settle on the first available territory they encounter -- cannot be rejected. The presence of significant population structure even between populations separated by intact forest suggests naturally short dispersal distances of M. exsul, even within continuously forested landscapes. Evidence from my studies, as well as published observations of M. exsul in Panama, suggest that this species exhibits non-equilibrium metapopulation structure in highly fragmented landscapes. These results challenge the assumption that species persisting in fragmented landscapes must have better dispersal capabilities than those that disappear from fragmented landscapes, and strongly supports hypotheses of weak dispersal capacity in some tropical forest understory birds / acase@tulane.edu

The vast majority of aquatically feeding tetrapods rely on suction feeding or filtration mechanisms, which is generally achieved via a robust hyoid apparatus that, when depressed, acts to increase the volume of the buccal cavity, thereby increasing the pressure differential between the buccal cavity and the surrounding water. In snakes, however, the hyoid apparatus is largely reduced as a consequence of its specialization for chemoreception, and hence cannot be used to expand the oral cavity and generate suction. Consequently, snakes must strike at aquatic prey in a manner similar to that used in terrestrial environments. As snakes are unable to generate suction, aquatic strikes will likely involve high drag forces and will be subjected to substantial bow-wave generation. Previous authors have thus predicted that aquatically feeding snakes should have relatively small heads that taper towards the back in order to minimize these hydrodynamic constraints. Yet, snakes are gape-limited predators (predators that do not mechanically reduce their prey before ingestion), and thus a relatively small head will influence the maximum prey size that can be ingested. These functional demands on the snake feeding apparatus predict that (1) aquatically feeding snakes will exhibit slowed head growth with increasing body size, and consume relatively smaller prey; and (2) aquatic strikes will be markedly slower than terrestrial strikes A second related issue is the fact that little data exists on which prey dimensions are the most functionally difficult to ingest for gape-limited predators such as snakes. Although numerous studies have used predator-prey mass ratios to shed light on issues such as optimal foraging theory, community level trophic relationships, ontogenetic dietary shifts, mass ratios are likely an overly simplistic view of the dynamic relationship between predators and their prey. Instead, data are needed that explore which prey dimensions are the most functionally difficult to ingest and most strongly influence feeding performance. Such data could be used to more clearly formulate optimal foraging models and could shed light on community level trophic relationships A third related issue is the influence of foraging mode (sit and wait versus active foragers) on the sensory modalities used for prey detection. (Abstract shortened by UMI.) / acase@tulane.edu

The population demography, population genetics and reproductive ecology of Sabal minor (N. J. Jacquin) Persoon were investigated over four years in an effort to understand the reproductive dynamics of this palm. A review of the current knowledge of palm systematics and ecology as they relate to these topics is presented to provide an appropriate context in which to interpret the results. Results from the demographic studies indicate that establishment of the seedling from fruit is the most critical stage in the life history of Sabal minor. Mortality is quite low for mature individuals; the principle cause is apparently tree or branch falls. The study population's finite rate of growth was found to be quite near unity but significant differences between the observed stage structure and the predicted stable stage structure suggest that transition matrix parameters are not consistent beyond the duration of this study. A sensitivity analysis found that changes in the probability of seedling establishment and survival of the largest stage class have the greatest effect on population growth rate. The estimated life span of Sabal minor is in excess of 250 years and may exceed 400 years Investigations of the population genetics of Sabal minor found that genetic diversity in this species is low in comparison to most seed plants. Low genetic diversity may be typical in palms or the evolutionary history of Sabal minor may include events (such as population bottlenecks) which have lowered genetic diversity. Low gene flow is indicated between populations while intrapopulation gene flow is high enough that most populations are probably panmictic. The flowers of Sabal minor were found to be slightly protogynous, to produce a small quantity of sucrose dominant nectar, and to have a pollen/ovule ratio near 1100. Wasps were found to be the principle pollinators. The rate of self-fertilization is high in S. minor (between 77 and 92%) and contributes to significant deviations from Hardy-Weinberg genotypic proportions in populations. These results for Sabal minor are discussed in relation to closely related palm taxa and palm species for which similar data is available / acase@tulane.edu

The fields of sexual selection and physiological ecology have traditionally remained separate throughout much of the history of evolutionary biology, despite the surge of interest in integrative biology over the last decade. However, a growing literature is showing that whole-organism performance abilities (including locomotor ability) influences the outcomes of competitive male-male interactions in several territorial lizard species. These findings raise the possibility that fighting ability, a previously undefined trait also referred to as resource-holding potential, may be rooted in measureable, functional concepts such as speed or endurance. Furthermore, if performance capacities do comprise an appreciable component of fighting ability, than those capacities might have become linked over time to the evolution and expression of male secondary sexual characters used during fights (i.e. armaments) I show here that whole-organism performance capacities (in particular, bite force) play a major role in resolving agonistic encounters between males in territorial Anolis lizard species, but may have little or no effect on determining male fight outcomes in non-territorial anole species. I also show that whole-organism performance traits used during male combat are linked to secondary sexual trait expression in male Euoniticellus intermedius dung beetles in an independent test of the performance signalling hypothesis. By contrast, although the size of the Anolis male secondary sexual character (the throat-fan, or dewlap) is linked to bite force in some territorial anoles, dewlap size does not influence fight outcomes in this species. However, dewlap size does influence fight outcomes in non-territorial anoles that do not rely on performance capacities to win fights. This puzzling role of dewlap size in resolving male-male conflicts is a cautionary note for future behavioural studies. I also show that male performance abilities appear to have no effect on male mating preferences in the green anole Anolis carolinensis, and find no evidence for performance as part of a suite of male traits preferred by choosy females Finally, I review previous studies integrating elements of sexual selection, physiology, and performance, and point out several important areas where further integration of physiological ecology and sexual selection techniques might yield important insights into the evolution of animal mating systems / acase@tulane.edu

I employed a combination of vegetative sampling, GIS mapping, and radiotelemetry to examine habitat availability, habitat selection, and movement patterns of the invasive nutria on a freshwater floating marsh at Jean Lafitte National Historical Park and Preserve (JLNHPP) in southeastern Louisiana. I found that the floating marsh is both spatially and temporally dynamic at the plant species level. Nutria at this study site had larger home ranges than reported for most other nutria studies. This finding could be attributed to a low to moderate population density, patchy resource distribution, and/or improved telemetry techniques. I evaluated habitat selection at three different scales, or orders of selection; the home range, the location point habitat type, and the individual plant species composition at location points. Nutria did not select habitat at the home range or habitat type level; i.e. they did not select based upon broad-scale habitat characteristics or by dominant plant species. Across all seasons, nutria selected habitats that were significantly different from those available to them at the plant species level. Male and female nutria did not differ significantly in their overall patterns of habitat use and movement. These findings suggest that nutria occupy a spatially and temporally dynamic habitat and that their utilization of this habitat depends heavily upon the individual plant species present at a specific locale / acase@tulane.edu