<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>

<p> Habitat loss and fragmentation (hereafter fragmentation) are some of the largest conservation threats today and will increasingly put pressure on species in the future. Maintaining population connectivity helps mitigate the negative effects fragmentation has on vulnerable species, especially those of conservation concern. In this dissertation, I elucidated the movement ecology of black-capped vireos by 1) estimating and characterizing patterns of gene flow, 2) examining the relationships between land cover and connectivity, and 3) simulating how future populations respond to climatic landscape change. I additionally characterized potential biases in family-wise error rate correction across population genetic studies, a correction important for evaluating the genetic structure of a species. I genotyped 343 individuals at 12 microsatellite loci in and around Fort Hood, Texas, which houses the largest and most stable breeding population. To characterize patterns of gene flow among black-capped vireo populations, I analyzed genetic differentiation, migration rates, number of migrants and parentage. Across these independent analyses, I found evidence for asymmetrical movements from Fort Hood to the other central Texas sites consistent with source-sink dynamics and findings from demographic studies. I used gravity models to test the relationships among Euclidean distance, land cover types (water, developed, forest, scrub, open, agriculture and wetlands), brown-headed cowbird control, and genetic similarity. My findings indicate that wetlands, likely via riparian areas, may be acting as corridors among populations. Better understanding of what factors influence connectivity will be crucial for maintaining connectivity when species of conservation concern are threatened by fragmentation.</p><p>

Increased availability of data on morphological, physiological, and behavioral traits of species has improved understanding of the processes driving community assembly and the consequences of community disassembly for ecosystem functioning. In addition, there has also been a call for advancing the multitrophic view of biodiversity- ecosystem functioning. Here I propose a trait-based framework to merge plant-herbivore interactions with biodiversity-ecosystem function relationships. This framework links plant growth and defense strategies, herbivore feeding preferences, and primary production in terrestrial plant communities. I empirically tested these proposed linkages in laboratory and field experiments carried out in the understudied grasslands of Inner Mongolia, China. I found that a dominant generalist grasshopper Oedaleus asiaticus exhibits feeding preference for plants of high palatability when equally available, but in the field feeds on nearly any graminoid which is dominant. This behavior potentially allows subdominant plants to coexist, maintaining plant diversity. To link feeding behavior to consequences for plant communities, I carried out detailed measurements of plant morphological and physiological traits in the field and experimentally manipulated grasshopper feeding intensity. Using a novel analytical tool, I found that plant communities in these grasslands exhibit high niche overlap, regardless of intensity of herbivory by grasshoppers or sheep. This result indicates that environmental filtering structures these communities more than limiting similarity. Extending the use of traits beyond the study system in Inner Mongolia, I test the how both functional and phylogenetic diversity explain the biodiversity effect on grassland ecosystem functioning. The promise for merging tools from evolutionary biology and functional ecology is great, as these diversity metrics provide superior explanatory power in a meta-analysis of biodiversity experiments. Future work should be addressed at clarifying which functional traits are most strongly reflected in measures of phylogenetic diversity, including strategies of compensating for or avoiding herbivory.

No description available.

No description available.

The Atlantic Goliath Grouper, a large, long-lived reef fish in the southeastern United States, was fished to near extinction decades ago. It is now showing signs of recovery in Florida waters due to protection from fishing in state and federal waters that started in 1990. While providing some optimism for their future, recent discovery of high mercury levels in this species is cause for concern. Indeed, I contend that such levels could not only impede their full recovery but present a human health problem if the fishery were re-opened. For my dissertation, I investigated their spawning patterns and trophic ecology, the latter of which included investigations of the organisms in their diet that lead to mercury accumulation in their tissues. Mercury presents a problem because of its neurotoxic effects and its ability to bioaccumulate in some forms. My research demonstrates that mercury levels in Goliath Grouper are not only much higher than the Environmental Protection Agency’s suggested safe levels for human consumption, but that they are likely impacting the overall health and reproductive potential of this iconic species. / A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2019. / February 25, 2019. / diet, Goliath Grouper, health, mercury, spawning patterns, trophic ecology / Includes bibliographical references. / Felicia C. Coleman, Professor Directing Dissertation; Markus Huettel, University Representative; Scott C. Burgess, Committee Member; R. Dean Grubbs, Committee Member; Thomas E. (Tom) Miller, Committee Member; Joseph L. Travis, Committee Member.

Thesis ( MSc ( Biology ) ) -- University of Limpopo (Medunsa Campus), 2012. / Tsessebe are now considered rare antelope, which once occupied much of sub- Saharan Africa. Population numbers of tsessebe in Borakalalo National Park have shrunk from 43 to 13 in just 10 years. Causing great concern for park management and creating a need to determine distribution of these animals. Five vegetation communities were identified within the tsessebe’s home range. Step point method was used to determine the veld condition index for each of the identified communities. Height classes and density of woody species was determined per community. The five communities could be grouped into four major community types with two variants for community four. Veld condition index values ranged from 43.1% to 67.8%. Data downloaded from GPS/GSM collars was used to determine home ranges, distribution patterns and spatial movements within the park. Mean home range was 248 ± 49 hectares. Core ranges occurred around and along temporary water points and drainage lines. Cross-species microsatellites were used to assess genetic diversity among the tsessebe in Borakalalo National Park. In total, 36 alleles using 12 cross-species microsatellite makers were identified. The average number of alleles was 2.71 ± 1.2. The average expected heterozygosity was 0.446 ± 0.067 and average observed heterozygosity was 0.482 ± 0.047.

acase@tulane.edu / 1 / Luke Browne