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.

<p>Native submerged aquatic vegetation (SAV) provides critical habitat for estuarine nekton. Relatively high nekton densities also are often associated with the nonnative, Eurasian Watermilfoil (Myriophyllum spicatum), a widely-distributed species in estuaries of the northern Gulf of Mexico. The goal of my study was to assess the habitat value of Myriophyllum with that of a common native SAV (Ruppia maritima) and SNB using two metrics (nekton density and growth of juvenile white shrimp Litopenaeus setiferus). Including estimates of vital rates such as growth together with density can give a more complete assessment. The nursery habitat provided by Myriophyllum for juvenile white shrimp appeared to match or exceed that of naturally occurring habitat types (Ruppia and SNB) in the oligohaline study area. Juvenile white shrimp densities in Myriophyllum (2.2 ? 0.47 m-2) were higher than those in Ruppia (1.0 ? 0.36 m-2). Similarly, white shrimp growth rates were higher in Myriophyllum (1.0 ? 0.07 mm TL d-1, 28.2 ? 2.83 mg d-1) than in Ruppia (0.6 ? 0.09 mm TL d-1, 14.1 ? 2.51 mg d-1). Myriophyllum also supported a nekton assemblage similar to that of Ruppia. Though differences were detected between SAV species, other factors derived from differences in SAV biomass may have driven differences in white shrimp growth rates and nekton densities. My study indicates that nonnative habitat forming species like Myriophyllum can provide an alternative to native habitat, though more research is needed to fully understand the mechanisms at work.

<p>Interactions between species are dynamic and are likely to shift with changes in species ranges due to climate change. With the expansion of new species into incumbent ecosystems a variety of abiotic and biotic factors shape the rate, pattern, and method of invasion. This dissertation utilizes one such boundary of transition, the salt marsh-mangrove ecotone, located in the northern Gulf of Mexico. This dynamic coastal wetland has recently seen the expansion of sub-tropical mangrove species into a previously salt marsh dominated system. This collection of works provides pointed case studies seeking to understand local and patch scale dispersal dynamics, expansion, recruitment, growth, and survival rates along an elevational gradient, and understanding interactions both above- and belowground between mature mangroves and the surround salt marsh. We find that dispersal is overwhelmingly dominated by propagule export, that black mangrove and smooth cordgrass differ in their ability to provide structural provisioning in the short term after restoration, and that mature mangroves have much greater belowground extent than aboveground. By better understanding species-specific interactions at the salt marsh-mangrove ecotone, a greater understanding of future expansion rates can be gained.

<p> Phytoplankton groups use different forms of nitrogen (N) and show distinct responses to physical drivers. This study aimed to resolve the N cycling roles of phytoplankton size classes and major taxa in a tidally influenced salt marsh. We used a whole ecosystem ¹⁵NO_3^&ndash; tracer experiment to determine interactions among phytoplankton community structure, N biogeochemistry, and hydrodynamics over an 11-day mid/neap tidal cycle in a salt marsh creek, Plum Island, Massachusetts. During the study period (10 to 20 July, 2016) the creek experienced marsh platform flooding and non-flooding tides. Phytoplankton biomass and &delta;¹⁵N were quantified for three size classes corresponding to microphytoplankton (microP, 20&ndash;200 &micro;m), nanophytoplankton (nanoP, 3&ndash;20 &micro;m), and picophytoplankton (picoP, &lt; 3 &micro;m). All three size classes showed minimal direct assimilation of the ¹⁵NO_3^&ndash; tracer; however, each size class also used distinct N sources. MicroP appeared to use internal N stores assimilated outside of the estuary throughout the experiment, despite a shift in taxonomic community composition from mid- (diatoms) to neap-cycle (dinoflagellates) as quantified by microscopy. NanoP appeared to switch from internal N stores to recycled ¹⁵NH_4⁺ over the mid/neap cycle, exhibiting maximal biomass and ¹⁵N use during the neap tide and flood tides therein. PicoP consistently used recycled N that was largely not derived from the ¹⁵N tracer, and they appeared to use different recycled sources during flood versus ebb tide. Our results suggest a dominant role of smaller phytoplankton size classes (picoP and nanoP) in salt marsh N cycling, and possibly increased N transfer through the microbial food web during neap tide. This study also demonstrates changing interactions among phytoplankton communities, physics, and N biogeochemistry over tidal cycles, showing that to understand estuarine planktonic N processing and growth, highly temporally resolved nutrient and physical conditions both within and outside of the estuary need to be considered. </p><p>

Source: Dissertation Abstracts International, Volume: 40-02, Section: B, page: 0577. / Thesis (Ph.D.)--The Florida State University, 1978.

Source: Dissertation Abstracts International, Volume: 40-06, Section: B, page: 2508. / Thesis (Ph.D.)--The Florida State University, 1978.

Sailfin mollies, Poecilia latipinna, display dramatic interdemic variation in average male body size. Size at maturity in sailfin mollies is a one locus Y-linked trait with a minimum of four alleles; males are the heterogametic sex and grow little after maturing. / Most of the variation in male size is expressed among local demes. I sampled from sixty molly populations from the eastern third of their range and found regional differences explain 6% of the total variation in male size, local differences 20%, and seasonal differences 5%. Furthermore, there is no correlation of habitat type to average male size or spread of male sizes. I constructed an index of the habitat experienced by each population through principal components analysis. The index proved to be uncorrelated with male size variation using Mantel's method. / I found sailfin mollies to have a high migration rate among demes such that stochastic population genetic processes are an unlikely explanation of their extensive local size variation. I determined this though a survey of allozyme variation at thirty presumptive loci. Approximately 20% of allozyme variation is among geographic regions, while only 3% of allozyme variation occurs within regions. / I have found both environmental and genetic bases for size variation through reciprocal transplant experiments conducted in field cages. Most of the genetic variation in size at maturity is present among family groups within demes. A laboratory factorial experiment allowed me to determine that male size at maturity is conserved across a range of temperatures, salinities, and food levels. Males matured later, but at the same size under relatively cool conditions. / The discrepancy in geographic variation of allozymes and size indicates selective intensities differ for these traits. I argue that this suggests selection shapes size variation. I found independent evidence for the operation of selection on size in my field experiment; relatively large fish at three weeks of age were more likely to survive to maturity under some conditions. Also, I reared large males in the lab from one population where large mollies have never been collected. The laboratory results exclude environmental influence as an explanation for this discrepancy. / Source: Dissertation Abstracts International, Volume: 47-12, Section: B, page: 4755. / Thesis (Ph.D.)--The Florida State University, 1986.

Adults and nymphs of three species of mites (Unionicola abnormipes, U. fossulata, and U. serrata) co-occur in the bivalve hosts, Villosa villosa, V. vibex, and Uniomerus declivis, in St. Mark's River, north Florida. Monthly samples of mussels at three sites over three years established that mean infrapopulation sizes, prevalences, and frequency distributions of mites among hosts varied greatly between mite species. Adults of only one mite species fitted predictions derived from one published model of population regulation. All other mites exhibited characteristics of two different models because of variation between sites, years, and host species, indicating that current models of regulation of parasite populations are inappropriate for these mites. / Mite species had frequently higher abundances in one host species. De-mited mussels placed out monthly at each site showed that these higher abundances are achieved within a month. Recruitment varied greatly between sites, years, and months but, because it was consistently high, did not have a significant, final effect on mite abundances with two exceptions: no recruitment by U. abnormipes at one site and no recruitment by adult U. fossulata, which enter mussels as nymphs and remain in the same mussels after metamorphosis. Consequently, the significance of any interactions between mites depends on locality and time of year, but models often assume that recruitment rates do not vary significantly. / Two field experiments indicated that the low abundance of U. abnormipes in the larger host species, Uniomerus declivis, was caused by competitive, and possibly predatory, interactions with U. serrata. However, U. serrata did not occur in Villosa villosa, in which U. abnormipes reaches its highest abundance, because most of these mussels are too small. Numbers of U. abnormipes are reduced also by adult U. fossulata but there is no evidence that U. fossulata prey upon U. abnormipes or exclude them from hosts. / Interactions between mites did not occur as predicted by either simple, theoretical models or more biologically-realistic ones developed for other systems but did demonstrate that experimental tests of models are essential. / Source: Dissertation Abstracts International, Volume: 49-06, Section: B, page: 2039. / Co-Major Professors: Daniel S. Simberloff; William H. Heard. / Thesis (Ph.D.)--The Florida State University, 1988.