Source: Dissertation Abstracts International, Volume: 37-07, Section: B, page: 3244. / Thesis (Ph.D.)--The Florida State University, 1976.

Source: Dissertation Abstracts International, Volume: 38-05, Section: B, page: 2021. / Thesis (Ph.D.)--The Florida State University, 1977.

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Plant interactions (e.g., competition, facilitation) are critical drivers in community development and structure. The Stress Gradient Hypothesis (SGH) provides a predictive framework for how plant species interactions vary inversely across an environmental stress gradient, predicting that facilitation is stronger with increasing levels of stress. The SGH has been supported in numerous ecosystems and across a variety of stress gradients, but recent research has demonstrated contradictory results. These discrepancies have led to SGH revisions that expand its conceptual framework by incorporating additional factors, such as other stressor types and variations in species life history strategies. In this dissertation, I examine a further modification of the SGH by proposing and testing a Multiple Stress Gradient Hypothesis (MSGH) that considers how plant interactions vary along a continuous gradient of two co-occurring stressors using mangrove and salt marsh communities as a case study. In Chapter 1, I outline the predictive framework of a MSGH, by creating a series of predictions of species interactions. The components of the MSGH predict that stressors of similar types (e.g., resource and nonresource) will have similar effects and be additive. On the other hand, varying species life history strategies and life stages will lead to extremes of plant interactions. In Chapter 2, I performed a series of experiments to test the various components of the MSGH. In Chapter 3, I performed a large-scale observational study to test whether multiple co-occurring stressors altered the cumulative effects on plant interactions, and if these stressors should be grouped (e.g., resource and non-resource, abiotic and biotic, etc.) to enhance predictability. From a series of studies conducted herein, I concluded that co-occurring stressors are important factors that control complex species interactions as shown in my MSGH modeling approach. Further, future theories need to incorporate species-specific and stressor specific grouping when modeling how species interactions shape communities. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.

The reproductive biology and residency patterns of over 800 stone crabs (Menippe mercenaria, M. adina, and their hybrid) were examined during an eight month tagging study at artificial, concrete block reefs constructed near intertidal oyster reefs and subtidal seagrass beds in Franklin and Wakulla Co., Florida. Characteristics of adult crabs occurring intertidally in the summer include a male-biased sex ratio (5M: 1F), a prevalence of M. adina and hybrids, a high frequency (71%) of molting males, and low sperm content (nine million) in males. Subtidally in the summer, the adult sex ratio was female-biased (1M: 9F), the Menippe-complex forms occurred at equivalent frequencies, and male sperm content was higher (18 million). In the fall, sex ratios became more uniform in both habitats, the intertidal male molting frequency declined (7%), and male sperm levels increased (19 million sperm). Mating among the Menippe-complex forms appeared random in both habitats. / A test of the effect of precopulatory guarding on sperm production in stone crabs revealed guarding males contained significantly more sperm (90-100 million) than non-guarding males exposed to pre-molt females or pre-molt males (40-50 million sperm). The sperm level for males held with intermolt females (20 to 30 million sperm) was consistent with background sperm levels from the field study. Male sperm number and the amount of sperm transferred to females were positively correlated. / The influence of sexual selection and predation on postcopulatory guarding durations in stone crabs was also examined. Males guarded significantly longer (126 h beyond the female's molt) when another male stone crab was present than when an intermolt female (84 h) or a blue crab (83 h) were present. In predation trials with the longest postcopulatory guarding durations, the females survived the treatment, whereas females were eaten by the blue crabs in the trials with the shortest guarding durations. The cul-de-sac morphology of the female sperm storage organ is such that sperm pre-emption is likely to occur upon multiple inseminations. Sexual selection appears important in maintaining postcopulatory mate guarding in stone crabs. / Source: Dissertation Abstracts International, Volume: 48-12, Section: B, page: 3486. / Thesis (Ph.D.)--The Florida State University, 1987.

Studies of variability in the processes that structure animal communities have focused on the impact of catastrophic physical disturbances, but have largely ignored the more subtle variability associated with biological phenomena, like predation and colonization. I addressed these questions in a North Florida lake using a bluegill sunfish--macroinvertebrate predator--prey system. Underwater time-lapse photography and diver observations provided estimates of predation within and among habitats, which were then incorporated in a unique set of caging experiments where predation fluctuated in one treatment. Prey community structure was then monitored for 1 year under variable, constant, ambient, and no predation treatments. Prey colonization rates were also monitored among habitats and seasons. / During the summer, predation by bluegill was patchy in middepth and deep water habitats and homogeneous in the shallow littoral zone; in winter, bluegill were only present in shallow water. Predation was most variable among sites within the middepth habitat and between biweekly (i.e., every 2 weeks) observations. Prey colonization was initially patchy at scales $>$30m and $<$2m, but became homogeneous after ten days. Colonization varied significantly among seasons and habitats, reaching the highest levels within the shallow habitat during the fall. / Caging experiments revealed that the variable predation treatment mimicked natural conditions better than conventional constant predation treatments. Variable predation tended to increase (1) prey abundances, (2) the spatial patchiness and temporal fluctuation in prey abundances, and (3) the size range of prey, as compared to the constant predation regime. These results suggest that variable predation may create much of the heterogeneity observed in freshwater macroinvertebrate prey communities, theoretically enhancing prey community diversity and stability. / Source: Dissertation Abstracts International, Volume: 49-06, Section: B, page: 2038. / Major Professor: William F. Herrnkind. / Thesis (Ph.D.)--The Florida State University, 1988.

Toxic effects of pentachlorophenol on polychaete assemblages inhabiting a seagrass meadow were studied and analyzed in various ways. Examination of the effects proceeded from a more general approach (following changes of the structure of the polychaete group) to more specific ones, which included analyses at a functional and species-specific level. The study took place in a Gulf coast seagrass meadow located at Turkey Point Shoal. The shoal is dominated by mixed stands of Thalassia testudinum and Syringodium filiforme. The effects of two PCP concentrations (10 ppm and 100 ppm) were tested, in addition to sedimentation effects due to the dosing procedure. Samples were taken for chemical, granulometric, and infaunal analyses. / This experiment showed that pentachlorophenol was highly toxic to polychaete. It was possible to determine acute toxic effects and that such effects were concentration-dependent, as they were found related only with the high dose. Detrimental effects were found when using different ecological approaches. Community-type parameters were the least sensitive to changes induced by the chemical, mainly represented by density reductions, rather than effects on number and species composition. From a functional point of view, pentachlorophenol had negative toxic effects on several polychaete functional groups. Deposit feeders in general (i.e., surface and subsurface feeders) were found to be the most affected, showing strong density reductions in the high dose treatment. Other functional groups were also affected, such as scavengers and predators, suggesting that toxic effects were generalized over the polychaete group, rather than specific on determined groups. / Species-specific toxic effects were also evident. Species such as Prionospio heterobranchia, Onuphis eremita oculata and Sphaerosyllis taylori showed significant negative effects. However, other deposit feeders, such as Mediomastus ambiseta, Aricidea philbinae did not show any adverse effects to the chemical. Moreover, some species were more affected in the juvenile stages whereas other species were more affected in the adult stages. These differences in response to pentachlorophenol were attributed to a wide range of vertical distribution of some species within the sediment matrix, reducing the probability of exposure. / Source: Dissertation Abstracts International, Volume: 49-03, Section: B, page: 0619. / Major Professor: Robert J. Livingston. / Thesis (Ph.D.)--The Florida State University, 1987.

I investigated selective feeding by juvenile pinfish, Lagodon rhomboides, on seagrass-meadow epifauna by comparing stomach contents of fish to available prey in a seagrass meadow in St. George Sound, Florida, and observing feeding behavior in laboratory experiments. Actively feeding pinfish were collected using a drop-net that was released by an underwater observer, allowing the simultaneous capture of fish and prey. Juvenile pinfish were diurnal foragers that consumed both animals (amphipods, decapods, copepods, isopods, polychaetes, tunicates and hydroids) and plants (diatoms, algae, and seagrass) in varying proportions. Pinfish fed mainly in the morning and evening, biting at prey on surfaces of seagrass blades (Syringodium filiforme and Thalassia testudinum). Amphipods and cumaceans were found in small (20-29 mm standard length (SL)) pinfish stomachs in greater amounts than would be expected based upon relative proportions of prey dry weight biomass in the environment; polychaetes, decapods and isopods were found in smaller amounts. Larger pinfish (40-49 mm SL) consumed these same prey in amounts proportional to their biomasses in the environment. Comparisons of the sizes of prey in the diet and the environment suggest that the observed selectivity by the smallest pinfish could have been caused by gape-limitation: small fish may have been unable to efficiently consume the relatively large shrimp, polychaete and isopod prey. Laboratory observations on pinfish did not completely support this hypothesis, because only the smallest fish tested (30-39 mm SL) were unable to consume the largest shrimp, Tozeuma carolinense; all other sizes of fish (40-79 mm SL) were able to consume large T. carolinense, the small shrimp Hippolyte zostericola and the large polychaete Amerionuphis magna. Visual and chemical stimuli from natural, uninjured prey enclosed in clear / glass tubes with open tops elicited predatory attacks by pinfish in laboratory experiments, suggesting that detection depends upon both chemoreception and vision. Fish prevented from using either chemical or visual cues attacked prey at lower rates. Although significant prey attack preferences were not found for four prey types (amphipods, shrimp, polychaetes and hydroids), live prey were preferred over dead prey. Thus, selectivity in the laboratory depended upon prey size and motion. / Source: Dissertation Abstracts International, Volume: 48-12, Section: B, page: 3486. / Thesis (Ph.D.)--The Florida State University, 1987.

Lowland England abounds with shallow lakes subject to different levels of eutrophication. In the absence of long-term water chemistry records, palaeolimnology provides an alternative means of assessing the onset and extent of the nutrient enrichment process at a site. The diatoms preserved in lake sediments are extremely sensitive indicators of both past nutrient levels and of eutrophication-related changes in macrophyte-phytoplankton interactions. However the success of diatom-based palaeoecology depends upon a sound knowledge of the taxonomy, environmental requirements, and taphonomy of contemporary diatom communities. This thesis has focused on aspects of the diatom ecology, taphonomy and palaeolecology of three, small (< 22 ha.), shallow (< 3 m), alkaline lakes of contrasting nutrient and macrophyte status in the English Midlands. These lakes, Tween and Clifton Ponds and Groby Pool, were monitored on a monthly basis (Jan-Oct) for key water chemistry parameters. At the same time samples were collected from the diatom plankton and periphyton and in turn compared with the diatom assemblages which accumulated in sediment traps and at the sediment surface. The small centric diatoms that were found in these lakes were initially difficult to identify using the light microscope (LM), and a scanning electron microscope (SEM) study of the 'problematic' forms revealed considerable ecophenotypic and life-cycle related morphological plasticity. However with careful LM analysis it was possible to confidently distinguish between the different species in the samples. The ecological studies revealed strong associations between the presence or absence of submerged macrophytes and the seasonality and relative competitiveness of planktonic and periphytic diatom species. The relationship between the present-day diatom communities and the diatoms found in the traps and surface sediments of the lakes was relatively good, although there were some problems related to the dissolution of delicate forms. The timing of surface sediment sampling was found to be a critical factor affecting the sedimentary representation of species associated with different periods of the year. The eutrophication histories of Tween Pond (approx. last 30 yrs) and Groby Pool (approx. last 250 yrs) were inferred by comparing the fossil diatom record with the available historical records of lake disturbance, changing catchment land-use and submerged plant communities. The available modern data were used to assist in this process and using a simple life-form based approach it was possible to reconstruct past changes in the relative competitiveness of phytoplankton and submerged plants in both lakes. In Tween Pond the diatom stratigraphy clearly traced the dramatic increase in nutrient loading and the loss of submerged plants from the lake following the diversion of the Erewash in 1972. Similarly, in Groby Pool it was possible to identify the much slower transition- from a mesotrophic, diverse plant dominated state to a eutrophic, tall plant dominated situation. The implications of this study are discussed in relation to modern numerical methods of reconstructing past nutrient loadings.

Although the autumn phenology of plants is important for a wide range of processes including primary production, carbon sequestration and food availability for herbivores, few studies have addressed spatial variation of autumn phenology and how it changes with climate change. The greatest increase of temperature is predicted near the pole and therefor it is important to estimate how this change will affect Arctic ecosystems. The phenology of vegetation is a valuable indicator of climate change and knowledge about phenology will give indications how the Arctic terrestrial ecosystems will react on climate changes. So far, the spring phenology is well-known compared to the autumn phenology. The aim of this study was to examine how autumn phenology varies among and within locations in forest-tundra ecotone in Northwestern Sweden. The phenology of the plant communities was measured spectrally with the Normalized Difference Vegetation Index [NDVI]. This allow me to directly compare the results of this study with the results from large scale studies using satellite-derived indices. I found that the timing of the autumn senescence varies among locations, topographic positions and vegetation types. These results are important because they contribute to a more nuanced understanding of the processes regulating primary production and food availability for herbivores in the Scandinavian mountains, and provide important information for forecasting the responses of these ecosystems to future climate changes.