Cerithium zonatum is a dominate species in an intertidal zone of Shi-Lang, Green Island. This study aimed to characterize the population dynamics, reproduction and trophic ecology of C. zonatum in this intertidal zone. Results indicated C. zonatum in rocky habitat had high density, high growth rate and small shell length. In seagrass bed it was low in population density and large in shell length. The reproductive season of C. zonatum was from spring to summer, with indirect development and short planktonic period. The C. zonatum was a primary consumer with £_13C values of -6.97 - -6.26‰ and £_15N values of 3.65 - 5.13‰. They fed on seagrass detritus and periphyton including microalgae and filamentous green algae. The major food was seagrass detritus and filamentous green algae in the seagrass beds. In the rocky and sand habitats, the major food was microalgae and filamentous green algae. The population dynamics and food sources of C. zonatum were different among seagrass bed, rocky and sand habitats. In general, the C. zonatum was an opportunistic feeder with low mobility. And, the high population density and growth rate of C. zonatum in rocky habitat might result from abundant food sources in the area.

Species invasions are regarded as one of the most serious threats to biodiversity and native ecosystems and our ability to predict and quantify the impacts of invasive species has been an arduous task. Since the 1840s, the Laurentian Great Lakes have experienced an exponential increase in the number of identified invasive species. The most recent, Hemimysis anomala, is a littoral freshwater mysid native to the Ponto-Caspian region of Eastern Europe. They have been identified in all of the Great Lakes (except Lake Superior), the St. Lawrence River downstream to Québec City, and inland lakes in New York State and have the potential to destabilize energy flow in aquatic food webs. Using stable isotopes of carbon (13C) and nitrogen (15N), I evaluated nearshore food web structure at four sites along Lake Ontario’s north shore spanning a gradient of Hemimysis density to determine: 1) if dominant nearshore food web pathways change seasonally, and 2) whether fish exhibit a dietary shift towards consumption of Hemimysis. Also, the effects of Hemimysis consumption on the growth of yellow perch (Perca flavescens) were quantified using bioenergetics modeling and four predictive feeding scenarios simulating Hemimysis incorporation into yellow perch diets. My results suggest Hemimysis are being incorporated into diets of round gobies, alewife and small yellow perch, which has resulted in a trophic lengthening of the food web. As Hemimysis populations continue to establish and stabilize, fish may incorporate this species into their diets at a higher rate. Based on the bioenergetic modeling, the incorporation of Hemimysis into the diets of yellow perch will have a negative impact on their growth. These negative impacts on fish growth will likely be exacerbated when the limited seasonal availability of Hemimysis, patchy distribution and predator avoidance behaviours, are considered. These results have implications surrounding the sustainability of the Great Lakes fishery as Hemimysis will likely increase competition with young fish for food and fish consumption of this new invasive may lead to reduced fish growth. / Thesis (Master, Biology) -- Queen's University, 2012-04-03 23:04:18.612

Our ability to predict community responses to environmental stress remains limited. To address this issue, I investigated how species abundance, community composition and food-web structure varied across abiotic gradients (principally disturbance and habitat size) in New Zealand streams. In surveys, community composition, biomass and richness were all strongly influenced by flood-related habitat disturbance, although disturbance influenced each trophic level via different mechanisms. Experiments indicated that macroinvertebrate prey communities were primarily structured by physical disturbance effects, whereas predatory fish communities were structured by physical disturbance effects and disturbance-mediated changes to prey communities. Prey community biomass and composition affected fish species identity and abundance and an in situ stream channel experiment suggested that prey communities were structured by trade-offs between resisting biotic interactions in physically stable environments and successfully exploiting highly disturbed habitats. The prey community traits associated with different disturbance regimes then directly influenced the composition and predatory impact of the resultant fish communities. In addition to disturbance-mediated biotic interactions, abiotic gradients also provided strong selection pressures on predatory fish communities. In particular, disturbance and habitat size strongly influenced predator community responses (e.g., biomass and maximum body size) in surveys and experiments. However, a habitat’s capacity to support predator community biomass was largely determined by its size. Food-web structure changed with habitat size; small streams supported more prey than predator biomass, whereas large streams had inverted biomass pyramids (i.e., more predator than prey biomass). Similar relationships between food-web structure and habitat size were found in grassland and forested streams, but terrestrial invertebrate subsidies meant that forested streams supported more predator biomass per unit area than grassland stream food webs. My results indicate that human actions resulting in habitat loss (e.g., water abstraction or river impoundment) and increases in flood-related disturbance events (e.g., climate change) are likely to have significant impacts on stream food webs, ultimately leading to habitats that support smaller fish communities (i.e., less biomass, smaller body size). This means that ecologists and managers will need to consider the separate, interactive and indirect effects of disturbance and habitat size on ecological communities if we are to accurately predict and manage food-web responses to global environmental change.

The use of fatty acid (FA) analysis has become an important tool in recent years to investigate a broad spectrum of questions in fisheries and aquatic ecology. One of these applications has been the use of FA profiles as biomarkers for indicating diet and recent feeding history of fishes and other aquatic consumers. Differences in forage FA profiles and spatial differences in food web structure within aquatic systems may lead to corresponding spatial patterns of FA profiles in consumers, thereby facilitating the potential applicability of FA biomarkers as indicators of habitat use and origin for mobile consumers such as fishes. However, little information is available regarding differences in FA profiles among habitat types in river-floodplain ecosystems and the time-scale over which fish FA profiles change when fish move between habitats that differ in the FA profiles of prey resources. The objectives of this study were to test whether the tissue FA profiles of channel catfish (Ictalurus punctatus) differed among three reaches of the lower Kaskaskia River and its floodplain lakes, to determine the time-course of tissue FA profile turnover when fish are relocated to a new habitat type, and to compare FA profiles among muscle, liver, and adipose fin tissues in channel catfish. Fatty acid profiles of channel catfish were significantly different among sites, especially between upper and lower river sites, and between river channel and oxbow lake sites, suggesting differing energy sources among habitats and river reaches in the Kaskaskia system. More specifically, there was a significant increase in the essential FAs, 18:2n-6 and 18:3n-3, in channel catfish with increasing distance downstream, which could reflect an increase in river-floodplain connectivity at downstream sites. Channel catfish transplanted from the Kaskaskia River to ponds at Southern Illinois University Carbondale showed a significant linear decrease in n-3 and medium-chain polyunsaturated FAs (MC-PUFA), and a significant linear increase in monounsaturates (MUFA) with longer residence time in a lentic environment. Liver tissue exhibited the fastest turnover rate of the three tissue types (< 2 weeks), with muscle and adipose fin tissue both displaying similar, longer turnover times (approximately 10 weeks). Results of this study support the use of FA profiles as indicators of energy sources for fishes in large river-floodplain ecosystems, including the potential for indentifying habitat-specific (river channel vs. floodplain lake) or river reach-specific energy sources. Additionally, results of this study provide a timeline for FA turnover in channel catfish tissues when fish move among habitats with distinct FA signatures, which is crucial for detecting temporal shifts in use of habitat-specific energy sources by channel catfish. Results also suggest that adipose fin tissue samples may be a less invasive alternative to muscle tissue for analysis of FA profiles in channel catfish. Improved understanding of which habitats or river reaches provide trophic support for riverine fishes through use of FA profile analysis has potentially important implications for habitat conservation and rehabilitation in river-floodplain ecosystem.

abstract: In desert riparian ecosystems, rivers provide free water but access to that water diminishes with distance producing a steep gradient in the relative importance of water for growth and reproduction of riparian animals and hence, their biodiversity. Previous work suggests that water limited riparian predators eat more prey to meet their water demand where free water is not available. Here I explore the effect of water limitation on prey selection and per capita interaction strengths between a predatory spider ( Hogna antelucana) and two prey species occupying different trophic levels using a controlled field experiment conducted in the riparian forest of the San Pedro River, Cochise County, AZ. Lab measurements of water and energy content revealed that intermediate predators (smaller spiders in the genus Pardosa) had 100-fold higher energy: water ratios than an alternate prey species more basal in the food web (crickets in the genus Gryllus). Given this observation, I hypothesized that water-stressed predatory wolf spiders would select more water-laden crickets but switch to more energy rich Pardosa when water stress was experimentally eliminated. Additionally, I hypothesized that switching by quenched Hogna to Pardosa would reduce predation by Pardosa on Gryllus leading to increased abundance of the basal resource. Finally, I hypothesized that water mediated switching and release of basal prey would be stronger when male Hogna was the apex predator, because female Hogna have higher energetic costs of reproduction and hence, stronger energy limitation. Experimental water additions caused both sexes of Hogna to consume significantly higher numbers of Pardosa but this difference (between water and no-water treatments) did not vary significantly between male and female Hogna treatments. Similarly, strong negative interaction strengths between Hogna and Pardosa led to release of the basal prey species and positive interaction strengths of Hogna on Gryllus. Again strong positive, indirect effects of Hogna on Gryllus did not depend on the sex of the Hogna predator. However, water mediated indirect effects of Hogna (either sex) on Gryllus were the strongest for male Gryllus. These results suggest that water and energy co-dominate foraging decisions by predators and that in managing water-energy balance; predators can modify interaction pathways, sex-ratios of prey populations and trophic dynamics. / Dissertation/Thesis / Masters Thesis Biology 2015

Nearshore marine habitats provide critical nursery grounds for juvenile fishes, but their functional role requires the consideration of the impacts of spatial connectivity. This thesis examines nursery function in seagrass habitats through a marine landscape (“seascape”) lens, focusing on the spatial interactions between habitats, and their effects on population and trophic dynamics associated with nursery function to rockfish (Sebastes spp.). In the temperate Pacific Ocean, rockfish depend on nearshore habitats after an open-ocean, pelagic larval period. I investigate the role of two important spatial attributes, habitat adjacency and complexity, on rockfish recruitment to seagrass meadows, and the provision of subsidies to rockfish food webs. To test for these effects, underwater visual surveys and collections of young-of-the-year (YOY) Copper Rockfish recruitment (summer 2015) were compared across adjacent seagrass, kelp forest, and sand habitats within a nearshore seascape on the Central Coast of British Columbia. Recruitment was positively influenced by the structural complexity of seagrass and adjacency to kelp forest sites, however a negative interaction between seagrass complexity and kelp forest adjacency suggests that predation modifies Copper Rockfish recruitment densities. In addition, using δ13C and δ15N isotopes to determine the basal contributions to seagrass food webs, kelp-derived nutrients were on average 47% ± 0.4 of YOY Copper Rockfish diets, which was 3x and 67x greater than the contribution of autochthonous seagrass production (seagrass epiphyte and seagrass blades, respectively). YOY Copper Rockfish diets in seagrass adjacent to sand habitats had the greatest amounts of kelp-derived nutrients and harpacticoid copepods, and concurrently had lower body condition compared to rockfish in the seagrass kelp edges and interior, feeding predominantly on seagrass epiphytes and calanoid copepods. This thesis provides further evidence that temperate seagrasses are nurseries for rockfish and that spatial elements of seascapes, including connectivity via habitat adjacency and variability in habitat structure, alter the recruitment and diets of rockfish in seagrass habitats. These seascape nursery effects are important considerations for marine planning, especially given the global decline of nearshore habitats. / Graduate

Doctor of Philosophy / Department of Biology / Anthony Joern / Aboveground and belowground food webs are linked by plants, but their reciprocal influences are seldom studied. Because phosphorus (P) is the primary nutrient associated with arbuscular mycorrhizal (AM) symbiosis, and evidence suggests it may be more limiting than nitrogen (N) for some insect herbivores, assessing carbon (C):N:P stoichiometry will enhance my ability to discern trophic interactions. The objective of this research was to investigate functional linkages between aboveground and belowground invertebrate populations and communities and to identify potential mechanisms regulating these interactions using a C:N:P stoichiometric framework. Specifically, I examine (1) long-term grasshopper community responses to three large-scale drivers of grassland ecosystem dynamics, (2) food selection by the mixed-feeding grasshopper Melanoplus bivittatus, (3) the mechanisms for nutrient regulation by M. bivittatus, (4) food selection by fungivorous Collembola, and (5) the effects of C:N:P on invertebrate community composition and aboveground-belowground food web linkages. In my analysis of grasshopper community responses to fire, bison grazing, and weather over 25 years, I found that all three drivers affected grasshopper community dynamics, most likely acting indirectly through effects on plant community structure, composition and nutritional quality. In a field study, the diet of M. bivittatus was dominated by forbs with grasses constituting only a minor fraction of their diet under ambient soil conditions, but grass consumption approximately doubled as a result of changes in grass C:N:P. M. bivittatus was found to rely primarily on selective consumption of foods with varying nutritional quality, rather than compensatory feeding or altering post-ingestive processes, to maintain C:N homeostasis in a laboratory experiment. In a soil-based mesocosm study, I show that Collembola feed on both saprophytic and AM fungi, in some cases exhibiting a slight preference for AM fungi. In the final study, although I did not find the expected indirect relationship between soil Collembola and aboveground herbivory as mediated through host plant quality, there were significant effects of root C:N and AM colonization on Collembola density and of plant C:N on aboveground herbivory. Overall, this research shows that host plant C:N:P stoichiometry can influence both above- and belowground invertebrate population, community, and food web dynamics.

Aquatic microbial food webs are in general size structured. Phytoplankton, which constitute the base of the food web, are grazed by protozoa and mesozooplankton, which in turn are consumed by planktivorous fish. Food web efficiency (FWE) is a measure of how efficiently energy is transported up the food web. FWE is low if the phytoplankton is inedible by the grazers, while FWE is higher if the phytoplankton community is dominated by edible phytoplankton. Recently, the presence of microfungi in aquatic food webs have been suggested to facilitate energy transfer up the food web, via the “mycoloop”. The aim of the study was to set-up a model system of phytoplankton – zooplankton food chains, relevant to the Baltic Sea, and to test FWE in diatom and flagellate-based food webs. Further, I wanted to introduce microfungi in the system and observe their impact on FWE. After many phytoplankton and zooplankton species tests, I decided to perform grazing experiments using one grazer, the ciliate Tetrahymena pyriformis, and two phytoplankton species: a diatom (Skeletonema marinoi) and a flagellate (Rhodomonas baltica). I hypothesized that T. pyriformis would more efficiently feed on flagellates than on diatoms. I performed a grazing experiment where the increase in ciliate abundance was measured, the consumption of the phytoplankton monitored and the FWE estimated. The diatom-based food web led to 14 times higher FWE than the flagellate-based food web. The variation in FWE may be explained by a difference in initial abundances introduced in the experimental treatment, which created unequal grazer:prey ratio between treatments. Further, the swimming behaviour of the flagellate might have reduced the capture efficiency by the ciliate. Microfungi were introduce in an experiment, from a natural seawater sample, but fungal infection was not observed for any of the tested phytoplankton species. Further development is needed to test the effects of microfungi on marine FWE.

The Sacramento River watershed provides important rearing habitat for key aquatic species, including juvenile Chinook salmon (Oncorhynchus tshawytscha). Salmon rearing in the watershed may inhabit the mainstem river channel or a corresponding floodplain, the Yolo Bypass, before migrating to the ocean. Studies of juvenile salmon have indicated that floodplain rearing may be beneficial in terms of growth and survival, likely related to different trophic pathways of the river and floodplain. However, fish also encounter many anthropogenic stressors in these habitats, such as pesticides, which have well-documented use and environmental presence in the region. Rearing individuals are potentially exposed to pesticides via trophic transfer, which may vary based on utilized food webs due to hydrophobic pesticide fate and transport. To examine the food web structure of each system and the potential for pesticide exposure through dietary routes, a two-year field study was completed. First, to characterize dietary contributions, a three-tiered approach incorporating stable isotopes (δ13C, δ15N and δ34S), essential fatty acids and gut content analyses was employed. Subsequently, pesticides were extracted from prey items and salmon and analyzed to determine contaminant residues. Stable isotope analyses indicated that critically important components of juvenile Chinook diet were amphipoda and adult diptera in 2019 and 2020, respectively. Amphipoda groups had higher concentrations of the fatty acid docosahexaenoic acid (DHA), an important component for fish development, than juvenile diptera or oligochaeta. Diptera (larvae and adults) were frequently found in juvenile Chinook stomachs from both areas and years. Throughout the pesticide examination, organochlorines including the DDT group (p,p’-DDT, p,p’-DDD and p,p’-DDE) were prevalent in all examined biota. There were a significantly greater number of pyrethroid and phenylpyrazole detections and concentrations in zooplankton as compared to macroinvertebrates (Poisson regression, p < 0.05) across regions and years. Additionally, significantly higher concentrations of organochlorines were exhibited in floodplain rearing fish as compared to the Sacramento River (ANOVA, p < 0.05). These findings suggest that juvenile Chinook feeding primarily on zooplankton may be exposed to a greater range of pesticides than those exhibiting benthic feeding, but these pelagic prey were not demonstrated as a major dietary item during the two-year study. Additionally, the previously inferred benefits of floodplain rearing may come at a cost of increased organochlorine exposure. This research has allowed for a robust assessment of potential trophic transfer of pesticides to juvenile salmon, which may help inform future floodplain restoration efforts.

Biotic interactions are known to shape natural community assemblages and biodiversity. Positive interactions such as facilitation have recently received attention in ecological food webs. Mechanistic models have improved our understanding of these complex food web interactions. Here, focus is given to a three-species food web system with a beach dune natural community in mind. In the last decade, there has been a series of studies investigating intraguild predation between two major loggerhead sea turtle nest predators, North American raccoons and Atlantic ghost crabs. Studies have also highlighted that ghost crab predation assists raccoons in finding nests (i.e., facilitated predation). However, the combined effects of these two intraguild interactions and their consequences on nests have not been examined explicitly. The aims of this study were to (i) develop a three-species, ordinary differential equation model (ii) implement a sensitivity analysis to understand the influence of facilitation and other factors in driving species richness and abundance and (iii) characterize the dynamic interactions between intraguild predators and their effects on a shared resource. Interactions between ghost crabs and sea turtle eggs and facilitation can yield a wide variety of species abundance responses and were influential factors in the model. I found that high secondary sea turtle egg depredation and low facilitated predation by raccoons led to three species co-existence regions in the model. Controlling for nest predators at higher abundance levels showed that ghost crabs had a larger negative effect on sea turtle egg abundance responses when compared to raccoons. This suggests that interactions between sea turtle eggs and ghost crabs appear to be important and potential sea turtle nest management implications are discussed such as the use of ghost crab exclusion devices.