Salt marsh food webs are complex systems, with high levels of in situ primary production supporting a wealth of resident and migratory species. In this study, we use stable isotopes as a tool to trace organic matter utilization within the Nueces Marsh food web. Specifically, we were interested in (1) the use of treated wastewater as a ¹⁵N tracer, and (2) seasonal and interannual variation in food web structure. We hypothesized that treated wastewater would selectively label detrital resourse use within the food web, allowing us to trace grazing vs. detrital pathways within the marsh system. We also hypothesized that marsh consumers would exhibit distinct differences in isotopic composition between summer and winter, and between different years. We found that the Nueces Marsh food web consists of 3.5 consumer trophic levels. The [delta]¹³C values of consumer organisms were similar across the spatial extent of the low marsh, regardless of proximity to wastewater inflow. However, a majority of the organisms collected from the wastewater channel were significantly (p<0.05) enriched in ¹⁵N compared to their reference counterparts. We propose that ¹⁵N-enriched nitrogen is entering the Nueces Marsh food web through detrital rather than grazing-based pathways, making wastewater effluent an effective tracer of detrital integration into a marsh food web system. Hydrologic data indicate that isotopic shifts between seasons and between years reflected larger scale shifts between drought and wet years. During drought years, decreased production by phytoplankton and emergent plants led consumers to rely more heavily on ¹³C-enriched cyanobacterial carbon. In contrast, wet years encourage phytoplankton and emergent plant production, making cyanobacterial carbon relatively less exploited. While the Nueces Marsh food web is supported by a stable detrital carbon pool, it may still be susceptible to larger scale hydrologic events. / text

Marine mammals breeding in sympatry use resources differently depending on their time-activity budgets and prey distribution. We measured isotopic values and patterns of δ15N and δ13C in keratinous whiskers of satellite-tagged adult female Antarctic (Arctocephalus gazella) - and Subantarctic (Arctocephalus tropicalis) fur seals from three colonies at Marion Island in the Southern Indian Ocean. The three sympatric colonies were Mixed Pickle (HD_MP), Rockhopper Bay (LD_RhB), and Watertunnel (HD_WT). A comparison between two colonies of differing A. tropicalis densities will also be investigated. We investigated resource use in breeding mature females over varying time and spatial scales during summer and winter. The aim was to understand the variation in resource and habitat use at population and individual levels. The whiskers of A. gazella and A. tropicalis grow constantly at a rate of 0.16 ± 0.05 day-1 and 0.12 ± 0.05 day-1, respectively. To compare and relate behaviours, the stable isotope data and satellite tracks were grouped into winter and summer (pooled for 2010 - 2014). In summer, A. gazella from HD_WT had a larger isotopic niche width (0.85 ± 0.67‰2) compared to A. tropicalis from both HD_MP (0.18 ± 0.19‰2) and LD_RhB (0.21 ± 0.15‰2). However, the isotopic niche width of A. gazella reduced in size by more than half (0.40 ± 0.40‰2) during winter when the mature females were no longer constrained by the lactation mandate. The mean δ15N values in whiskers of both A. tropicalis and A. gazella in summer were similar (11.3 ± 0.4‰ and 11.0 ± 0.9‰, respectively). The A. gazella broadens its’ isotopic niche feeding at different trophic levels in summer (lactation period). We used a Repeatability index (R) to assess levels of intra- and inter-individual consistency. Repeatability indicated that the bigger isotopic niche width for A. gazella is attributed to high inter- and intra-individual variability in their resource use. The A. gazella individuals ranging closer to the colony consistently consumed myctophid fish. Other individuals foraged on low 15N content euphausiids (i.e., Euphausia spp. and Thysanoessa spp.) south of Marion Island in both winter and summer. The A. tropicalis from LD_RhB were repeatable in their δ15N values (trophic level) (Rglobal = 0.63; [95% CI: 0.29 – 0.80]) and δ13C values (habitat) (Rglobal = 0.69; [95% CI: 0.35 – 0.84]). At HD_MP, the A. tropicalis colony, diet was moderately repeatable (Rglobal = 0.33; [95% CI: 0.11 – 0.51]) while habitat was repeatable (Rglobal = 0.58; [95% CI: 0.33 – 0.73]). Consistency in diet (Rglobal = 0.27; [95% CI: 0.08 – 0.44] and foraging habitat (Rglobal = 0.45; [95% CI: 0.21 – 0.63] was moderate at HD_WT, the A. gazella colony. The diet varied with habitat at the individual level, across seasons. Segregation in diet and foraging habitat minimises resource-use overlap between sympatric fur seals. The behaviour of A. gazella from HD_WT (a high-density colony) might have a direct or indirect impact on the A. tropicalis from LD_RhB (a low-density colony) (i.e., competitive exclusion). Seasonality, at-sea movement, and intrinsic factors shaped the foraging behaviour and diet of adult female fur seals breeding at Marion Island. Some breeding mature females changed diets between seasons and depending on foraging habitat. / Dissertation (MSc (Zoology))--University of Pretoria, 2021. / NRF, Grantholder linked / Zoology and Entomology / MSc (Zoology) / Unrestricted

Land-use, feeding habits, and response to seasonality by Quaternary megaherbivores in Saltville, Virginia, is poorly understood. Stable isotope analyses of serially sampled Bootherium and Equus enamel from Saltville were used to explore seasonally calibrated (δ18O) patterns in megaherbivore diet (δ13C) and land-use (87Sr/86Sr). Overall, this dataset suggests an open forest with relatively constant temperatures year round that were similar to modern conditions. Neither Bootherium or Equus individuals spent a significant amount of time at higher elevations in the nearby Blue Ridge geologic province. These analyses provide a unique perspective on long-term response of large mammals to climatic shifts and their impact on local ecosystems. Results are also relevant to modern conservation decisions, especially those surrounding highland grassy balds in the Appalachians, and their maintenance by grazing pressure.

Invasions from coho salmon were first reported in the Cape Horn Biosphere Reserve (CHBR) in 2019 which is the most southern distribution registered to date. The CHBR is known for its high number of endemic species and unique biodiversity, such as the native fishes Galaxias maculatus and Aplochiton taeniatus. There are now three invasive salmonid species in the rivers of CHBR and are a potential threat to the native fish taxa. Stable isotope and gut content analysis were used to understand resource utilization by both native galaxiid and invasive salmonid taxa, as well as aquatic macroinvertebrates and riparian spiders. The natural laboratory study approach applied to this research, allowed for comparisons of differences within streams that contain conditions in which fish do not occur naturally, to sites in which high densities of invasive salmonid exist. Analysis of the trophic niche and diet in this study showed the importance of marine resource use by the native galaxiid and coho salmon juveniles supported with elevated δ15N and δ34S ratios. Diet analysis also confirmed there was the highest similarity between the coho salmon juveniles and the native fish. Altered behavior and habitat use was shown through the isotope and diet analysis for the galaxiid in snow melt streams which could be due to the high density of invasive salmonids in these streams. The invasive salmonids were found to impact aquatic macroinvertebrate populations, specifically larger bodied Trichoptera abundance. Aquatic insect emergence was negatively correlated to salmonid densities. The aquatic insect emergence revealed alterations with significantly higher biomass of aquatic insect emergence in upstream sites without invasive fish. Lastly, aquatic insect predator (Hydrobiosidae: Rheochorema sp.) exhibited a suppressed trophic position in rivers with invasive salmonids. An unexpected finding from the study was the refugium stream habitat conditions that has been shown to be important for conserving the native fish in the CHBR. We conclude that the impacts from invasive species are significant enough to disrupt lower trophic levels especially aquatic insects. The altered aquatic emergence and insect behavior have the potential to disrupt food webs and ecosystem functioning in the southernmost protected ecoregion in the world.

The black bear (Ursus americanus) is an iconic species with cultural, economic and ecological importance in Vermont, USA. Bears exhibit a highly variable diet, and few studies have described bear diet in the state. Information on diet may provide insight into foraging behavior, thus allowing managers to better assess patterns of human-bear conflict. My objectives were to estimate the relative contribution of food items to bear diet and how factors including sex, habitat, food availability, and nuisance status describe patterns of consumption. I collected samples from bears and major food groups including C3 plants, white-tailed deer (Odocoileus virginianus), corn (Zea mays), and human foods, then quantified diet using stable isotope analysis. Samples were collected from 71 bears, 547 plants, and 38 deer throughout Vermont. I also collected 12 corn samples, and 20 human hair samples to represent anthropogenic foods. I determined δ13C and δ15N isotope values for all samples, then used Bayesian mixing models to estimate the contribution of foods and effect of each factor on proportional contribution estimates. Nuisance status best described patterns of diet over other factors. Median percent contributions for non-nuisance bears were 73.2% C3 plants, 23.8% corn, 1.9% human foods, and 0.5% deer. Median percent contributions for nuisance bears were 64.6% C3 plants, 28.9% corn, 3.2% human foods, and 0.7% deer. Factors such as sex, habitat, and food availability exerted less effect on diet than expected. Proportional contribution of meat was lower than in some other parts of North America, suggesting bears forage differently in Vermont. Results provide the first statewide estimate of bear diet and indicate corn may represent a much larger component of diet than previously thought. In particular, bears labeled as nuisance animals may forage on greater proportions of corn throughout the year.

Understanding energy fluxes within and between floodplain water bodies, and between rivers and their floodplains is essential for comprehending the dynamics of modern, altered river systems. Floodplain aquatic invertebrates may move between habitats deliberately (through emergence and dispersal) or through passive transport during flooding. This movement may represent a significant flux of energy and an essential food web subsidy. I assessed the usefulness of the stable isotopes of hydrogen and oxygen (D and 18O respectively) for identifying the origins and movements of macroinvertebrates in Mississippi River floodplain water bodies. I sampled water and invertebrates from the Mississippi River, intermittent and permanent floodplain wetlands, and tributaries during 2007 and 2008. Results showed consistent relationships between δD and δ18O signatures in invertebrate tissues and their home water bodies. I also investigated whether δD and δ18O could be used as a multivariate "fingerprint" to trace a captured invertebrate back to its environment of origin. Results showed that δD can be a useful tracer of the movement of floodplain invertebrates in some cases, although δ18O is likely not suitable for that purpose.