There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.

Stable isotope analysis is a powerful tool that can be used to describe a population’s foraging niche by identifying basal resource use, trophic feeding levels, environmental stability, seasonal ecological variation, important shifts in life history, ontogenetic shifts, intraspecific habitat use, and population dynamics. Describing these relationships in endangered marine turtle populations and their critical foraging grounds is essential for determining informed management decisions. This study systematically describes the foraging niche of hawksbills Eretmochelys imbricata, and green turtles, Chelonia mydas in Buck Island Reef National Monument, U.S. Virgin Islands, a critical habitat for nesting and foraging. It assesses the relationships within and between the species in terms of overlap, annual and seasonal variation, and life history and feeding strategies within the community. Most importantly it describes these relationships with metrics that can be used in global comparisons or to measure change in local conditions. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

The Eurasian woodcock Scolopax rusticola (hereon woodcock) is a wader adapted to woodland and farmland habitats. It is an important quarry species, widely hunted across Europe, but owing to its cryptic plumage and elusive nature, there exists only poor information concerning its natural history. As such, the conservation status of the woodcock remains uncertain. One area that is particularly lacking is knowledge of its ecology outside the breeding season. Generally, avian ecological studies have focused on breeding season events due to the importance of reproductive success in determining fitness. However, it is now apparent that the non-breeding season represents an equally important period of the annual cycle. For example, recent studies have shown that declines in some migratory bird populations were due to events during the non-breeding season, either during migration, or on the wintering grounds. In Britain, the non-breeding woodcock population comprises both British breeding and non-British breeding birds, yet the origins and relative distribution of these sub-populations is not fully understood. Nor is it known whether ecological differences exist between them. This thesis addresses these two aspects of woodcock biology, using stable isotope and radio-tracking methods. The former was used to assign birds to their likely origins and determine population-specific distributions across Britain. The latter was used, in conjunction with the former, to determine whether ecological differences exist between locally-breeding and non-locally breeding birds residing in Hampshire in winter. A large degree of mixing between birds from different breeding populations was apparent for woodcock residing in Britain over winter. Russia and Fennoscandia comprised the most likely origins of migratory birds and regional differences in distributions were apparent. The highest proportions of birds from Russia were found in Norfolk and Wales, whilst the highest proportions of birds from Fennoscandia were found in Scotland. The presence of non-breeding residents in Cornwall and Ireland also provided strong evidence for the short-distance, south-westerly movements of resident birds, which probably originated from Scotland. Locally, the movements and behaviour of birds were found to vary with age (adult vs. juvenile) and/or predicted migratory status (resident vs. migrant), with adult residents potentially representing the dominant group. Differences in habitat use, commuting flights, home range size and activity patterns were all apparent. As such, these findings might have important consequences for the relative survival rates and breeding success of resident and migrant woodcock. This work has provided new insights into the non-breeding ecology of woodcock in Britain and contributes significantly to European efforts to better understand this bird species. Given the importance of seasonal interactions, an understanding of events throughout the annual cycle is necessary and this can only be achieved through concerted efforts. Indeed, an integrated approach is imperative to develop the conservation plans necessary to ensure the sustainability of the woodcock.

This project addressed if decaying macroalgae and leaf detritus play a major role in the detrital pool of a 7th-order karst riverine system. Decay rates, macroinvertebrates colonization patterns, and change in δ13C values of Cladophora, Platanus occidentalis, and a mix of Acer negundo and A. saccharinum were tracked during summer and autumn months for portions of multiple years. Packs of air-dried Cladophora, Acer, and P. occidentalis were placed in mesh bags and put in groups (n=4) in wire baskets. Seven baskets were submerged in riffle (0.5 m) and deeper run (2 m) habitats. Benthic organic matter was collected with each pack to see if there was a correlation with δ13C signatures of decaying macroproducers to help understand what is entering the detrital food web. Summer 2014 Cladophora and Acer were significantly faster to breakdown than Platanus in both habitats. In autumn‒spring 2014‒2015, Cladophora was significantly faster to breakdown than leaves. Isotopic values of Cladophora were not significantly different than leaves in summer 2014 but were significantly more δ13Cdepleted in the autumn‒spring 2014‒2015. There were no significant differences in macroinvertebrate abundance between the macroproducers for either season. Cladophora had significantly lower macroinvertebrate richness in both seasons, lower shredder abundance, but a significantly higher abundance of clingers. The mean δ13C values of benthic detritus were significantly different than all three macroproducers in the summer and significantly different than Cladophora in the run treatment for autumn‒spring. Seasonality had a strong influence on breakdown rates, leading to greater mass loss of all three species in the warm summer months compared to the cooler autumn‒spring months. The low macroinvertebrate richness and shredder abundance on the decaying macroalga suggests Cladophora may not be consumed by macroinvertebrates but used strictly as habitat. The implication of rapid Cladophora decay during warm seasons, plus few colonizing macroinvertebrate taxa, is that the decaying macroalgae may not pass through a decomposer food web before being remineralized as CO2.

The Saskatchewan River Delta (SRD) in central Canada, North America’s largest inland delta, is an important spring and fall stopover site for waterfowl with thousands flocking there annually to stage. However there is very little information on their origins prior to arrival and their feeding ecology while in the Delta. To date, band recoveries are largely from birds banded south of the SRD, mostly due to limited banding activity in productive waterfowl habitats to the north such as the Peace-Athabasca Delta and the broader boreal forest. There is also very little information on the importance of the SRD as an overall recruitment area for the North American waterfowl population. No studies have used stable isotopes to infer the origins and diets of these birds. I first used stable isotopes of hydrogen (2H) and sulfur (34S) to infer migratory origins and specifically evaluate the contribution of local and non-local birds to the staging population in the SRD during fall migration. Based on 2H, I found that few birds (34%) originated in the SRD despite its known role as breeding habitat; instead, most birds (56%) were migrants from the north of the SRD and a small fraction (10%) came from south of the SRD. Stable sulfur isotope data proved a useful tool in further delineation of birds into prairie and forest regions, respectively. Secondly, I used stable carbon (13C) and nitrogen (15N) isotopes and mercury concentrations in liver tissue ([Hg]) to trace nutrient sources of these waterfowl using the SRD prior to fall migration, and tested for differences in diets among species, sexes and age groups within species. I demonstrated the importance of macrophytes as a source of food, particularly among the American Widgeon and Northern Pintail (70% of the diet). However, there was some level of partitioning of resources at the species level, as Blue-winged Teal and Green-winged Teal used invertebrate sources, as did a distinct group of Mallards. This is likely a result of birds minimizing competition for resources during the short staging period in the SRD when waterfowl densities are high. Finally, I found that 15N values in liver, a known indicator of trophic position, can be confounded by variation in basal sources; hence, there is the need to use other isotopes or tracers such as [Hg] for verification. Overall, my results suggest an important role for northern ecosystems in central Canada in contributing to the waterfowl breeding population in the Central Flyway, and a key role for the SRD in providing fuel for waterfowl during fall migration. .

Recent observed changes in bird distributions provide an unprecedented opportunity to gain a deeper understanding of the processes that influence species' persistence. By modelling presence-absence data from the North American Breeding Bird Survey, we found evidence that the breeding range of the western burrowing owl has contracted at its northern, western, and eastern boundaries since 1967. We suggest that the species' breeding distribution is also expanding southwards to former wintering grounds into northern Mexico, facilitated by the appearance of new breeding habitat created by irrigated agriculture in the arid areas of southwestern United States and northwestern Mexico. This dissertation explores the hypothesis that burrowing owls from northern migratory populations have become resident breeders in areas of northwestern Mexico that were formerly used only by migratory owls during winter, contributing to both population declines near the northern extent of the species' breeding range and population increases in the southern half of the species' range. We used novel DNA microsatellite markers to test patterns of gene flow predicted by this migration-mediated range-shift hypothesis. We genotyped 1,560 owls from 36 study locations in Canada, Mexico, and the United States. Analyses of molecular variance provided evidence that burrowing owl populations in both northwestern Mexico and Canada are genetically different from the rest of the populations in the breeding range, lending some support to the migration-mediated range-shift hypothesis. We found evidence of subtle genetic differentiation associated with subtropical irrigated agricultural areas in southern Sonora and Sinaloa, demonstrating that land use can produce location-specific population dynamics leading to genetic structure even in the absence of dispersal barriers. We also used stable isotopes 2/H, 13/C, and 15/N in feathers to test philopatry and breeding dispersal patterns predicted by this migration-mediated range-shift hypothesis. Burrowing owl populations near the northern edge of the species' breeding range had a high proportion of immigrants compared to interior populations, while other populations had high levels of philopatry. Stable isotopes also provided evidence of breeding dispersal events from Canadian populations to northwestern Mexico in support of the migration-mediated range-shift hypothesis, but similar isotope signatures in nestling feathers between these two regions prevent stronger inferences.

The spatial ecology of a species underpins an array of important questions about the ecology and evolution of a species, relating for instance to sociality, population dynamics, geographical distribution or genetic partitioning. Furthermore, the understanding of the spatial ecology of a species also has important implications for conservation and for disease management. It is in this context that I have examined the spatial ecology of the serotine bat (Eptesicus serotinus), in Europe, and especially at the northern limit of its distribution in England, using population genetic and stable isotope analyses. Data from nuclear microsatellite markers indicated higher levels of gene flow on the continent than in England. Consistent with this, England was separated into three genetically distinct populations, inter-connected by male-driven gene flow. Substantial asymmetric gene movement over the English Channel was inferred, possibly indicating a northward and westward range expansion. Mitochondrial DNA revealed fast population expansion and strong female philopatry. Moving to finer scale, δ13C in wing tissue and fur revealed that the association of individuals at roosts is flexible and dynamic, possibly reflecting their membership to communities operating at larger geographic scales. Communities of E. serotinus seem therefore to create a network of roosts with individuals continually re-assorting among themselves both within and across breeding seasons. The integration of the genetic and isotopic data highlighted complex spatial, social and temporal interactions in this species. While individual associations within communities seem to be flexible, communities were found to be strongly segregated over the breeding season. In contrast, genetic connectivity operates on a larger geographical scale than the local summer landscape. Together, these findings help explain the apparent absence in the UK of the European Bat Lyssavirus 1 (EBLV-1) for which this species is the main host. Hence, the relative fragmentation of this low-density population may inhibit the virus’ spread. However, with regular immigration from the continent, EBLV-1 could eventually enter the UK.

Lakes play an important role in the global carbon (C) cycle as they process carbon from terrestrial (allochthonous) and within lake (autochthonous) sources and may store C over long periods of time. Some arctic lakes contain high concentrations of dissolved organic carbon (DOC) that does not absorb light and thus remains colourless. The origin of this DOC remains unknown, but the sediment of these lakes have been suggested to accumulate primarily autochthonous (algal) C. I developed an experimental chamber for hydrogen (H) isotope pre-treatments and applied a novel H isotope tracing approach to determine the origin of the DOC and sediment C of a lake on SW Greenland known to contain colourless DOC. I hypothesized that autochthonous C was the prime source of DOC and sediment C, in line with previous theories. Analyses of algae and soil samples from the catchment revealed that local allochthonous and autochthonous C sources had a δ2H composition of -139 ‰ and -209 ‰, respectively. In contrast to my hypothesis, the analysed DOC had a mean δ2H isotopic composition of -147 ‰ indicating a dominance (ca 80-90 %) of allochthonous C. Similarly, the sediment had a mean δ2H isotopic composition of -155 ‰, suggesting that about 84 % of the C accumulating in the sediment was derived from terrestrial sources. The terrestrial origin was supported by field observations of high DOC seepage water (up to 70 mg L-1) with uncharacteristically low light absorption values entering the lake during high precipitation events. My results indicate that terrestrial processes are fundamental C sources for arctic lakes, even in regions with very low precipitation.

To evaluate the niche of coastal fish populations in the Beaufort Sea, stable isotopes (SI) and fatty acids (FA) were used to characterize species-specific niches, niche overlaps and resource partitioning (nicheROVER) of the Shingle Point fish populations. Fishes were grouped into three isotopic groups: marine, coastal, and freshwater (Ward’s clustering analysis), and five dietary groupings (using FA), where benthic feeding strategies were prevalent (correspondence analysis). Niche metrics were used to evaluate if total mercury (THg) could contribute complementary trophic information (residual permutation procedure (RPP)). Three THg groups (high, intermediate, low) were identified (boxplot analysis). High THg was identified in high trophic and benthic feeders, high THg ranges were observed in species with large niche sizes, high trophic feeding, and freshwater influences (RPP). The bioavailability of freshwater introduced THg to marine biota was assessed, however further research needs to be performed. Combining dietary indicators SI, FA, and THg, allowed for the characterization of the diet and habitat use of coastal fish populations, better understanding of the niches of these species, and developed baseline information for future monitoring in an MPA, as climate change continues to effect the Beaufort coastal environment. / February 2017

Capelin (Mallotus villosus (Müller, 1776)) is an important marine forage fish species that typically inhabits sub-Arctic and temperate circumpolar waters. Capelin have recently been reported in greater abundance in Arctic regions, and are considered an indicator for warming climate in the northern marine ecosystem. The goal of this thesis is to examine intrinsic factors among capelin populations, and whether niche overlap among sympatric capelin and Arctic cod (Boreogadus saida (Lepechin, 1774)) will affect the abundance and persistence of capelin in the Arctic as temperatures continue to rise. Life history comparisons of capelin from two Arctic regions (Western Beaufort Sea, Cumberland Sound) relative to a sub-Arctic population (Newfoundland) show that body size, body condition, growth rate and age-at-maturity vary among these regions. Life history characteristics that are adapted to northern environments and increasing temperatures will allow the presence and persistence of this species to increase in the Arctic. The consequence of increased abundance of capelin in the Arctic environment could be competition between capelin and Arctic cod, an Arctic species within a similar dietary niche. Stomach contents indicated that both species feed primarily on calanoid copepods and this result was corroborated with high dietary overlap in isotopic bivariate space (carbon and nitrogen stable isotopes). The occurrence of capelin is expected to increase in the Arctic with rising temperatures, thus adaptation in life history traits in capelin specific to each region may facilitate increased abundance and persistence, and possibly contribute to competitive pressure on Arctic cod. Potential competition will be particularly important in nearshore and shelf habitats where shifts in availability of intermediate trophic level taxa will influence diet and distribution of key predators such as beluga, sea birds, and anadromous fishes. As the Arctic environment changes with climate shifts, newly adapted or dispersed species from sub-Arctic systems are expected to drive shifts in ecosystem structure and function in the marine environment. / October 2016