Low species diversity in the Arctic promotes strong food-web linkages, as changes in abundance of one species may influence many others. Using harvest records, I determined Arctic fox populations are declining in their southern distributional range due to shallower snow potentially limiting density of lemmings, their primary prey, which live and breed beneath snow. Additionally, warm fall and spring temperatures are shortening access to alternative prey, seals on sea ice. Arctic foxes also influence other species through non-trophic interactions, as lemming winter nests were found on 70% of fox dens examined. I determined warmer subnivean temperatures promoted by accumulation of thick snow leeward of tall vegetation on dens attracted lemmings to these dens. Furthermore, lemming reproduction was higher dens compared to traditional lemming habitat. This research highlights the impact of climatic variables on Arctic predator-prey interactions and the importance of understanding impacts of trophic and non-trophic interactions on species demographics. / February 2017

Fall cankerworm (FCW) outbreaks have recently increased in frequency and intensity in the mid-Atlantic region of the United States, especially around cities of Charlotte, NC and Richmond, VA. This study evaluated the effects of two landscape features associated with urbanization, impervious surface and forest cover, on population patterns of FCW and its parasitoids across eastern Virginia. Forest cover was positively related to parasitism rates while impervious surface was positively related to FCW abundance, suggesting that FCW outbreaks may be amplified in urban areas. FCW abundance declined over the two-year period of this study, but parasitism rate increased at most sites. Parasitism was highest at sites that experienced FCW outbreaks first, indicating that parasitoid populations are responding to moth abundances. It remains to be seen whether this outbreak was an aberrant occurrence, or represents a regime shift to more frequent defoliation in Virginia, similar to that in North Carolina urban areas.

Arthropod predators often use prey and conspecific cues to make foraging decisions. Calosoma wilcoxi (Leconte) is a voracious predatory beetle that specializes on lepidopteran larvae often found in the forest canopy, including the fall cankerworm. This study tested the hypothesis that C. wilcoxi uses olfactory cues to detect prey and conspecifics. A Y-tube olfactometer was used to test attractiveness to larvae, larval frass, conspecific cues, and volatiles from herbivore-damaged white oak leaves. C. wilcoxi did not preferentially choose the treatment in any of the experiments. There was no difference in mean time spent in the treatment or control arm for any of the cues assayed. The time to choose the treatment was significantly shorter in the female conspecific experiment only. I found no evidence that C. wilcoxi uses olfaction to locate prey; however, C. wilcoxi is attracted to conspecifics. C. wilcoxi may use conspecific cues to make informed foraging decisions.

The thesis results of two laboratory experiments focusing on the impacts of predation risk, prey density and habitat complexity on predator-prey interaction strengths and predator metabolic rates, complemented by a brief review of the subject. The experimental system used in the first experiment consisted of cladoceran prey, larvae of three dragonfly species (Sympetrum sanguineum, Libellula quadrimaculata, Ischnura cf. elegans) as intermediate predators, and larvae of a large dragonfly species (Aeshna sp.) as a top predator. The second experiment of investigated how predation risk influences metabolic rates of the intermediate predators.

Grassland birds are the most rapidly declining bird guild in North America, due in large part to extensive loss and fragmentation of grassland habitat resulting from the spread of agriculture and other human-dominated landscapes. Over the past several decades, grassland birds have increasingly become a guild of high conservation and management interest as their populations continue to decline and suitable grassland habitat becomes continually scarcer. Although studies investigating grassland bird responses to management actions and habitat structure are common, few studies are concerned with clarifying the mechanisms through which habitat structure may affect grassland birds. Filling this knowledge gap is critical for increasing our understanding of grassland bird ecology and improving the effectiveness of management and restoration actions for grassland birds. To address this knowledge gap, I took a uniquely holistic approach to traditional grassland bird-habitat studies by concurrently gathering data on multiple wildlife taxa that may interact with birds to examine how these different taxa respond to habitat characteristics across multiple spatial scales, and how those responses may in turn impact grassland birds. Research was conducted on 10 grassland sites at Burning Star State Wildlife Management Area in northeast Jackson County, Illinois, during the bird breeding season (May-July) from 2018 to 2021. My first five objectives were to determine the grassland habitat characteristics that were most highly associated with the following taxa: arthropods, an important food source for adult and nestling grassland birds; small mammals, which are occasional nest predators and an alternate prey source for more prolific nest predators; snakes; raccoons; and grassland birds. My final objective was to estimate the extent to which grassland bird habitat associations were mediated through nest predator abundance, alternate prey abundance, and food availability. In Chapter 2, I examined associations between grassland arthropod communities and habitat characteristics representing three spatial scales: local (within-patch vegetation structure and composition), patch (size, shape, edge composition), and landscape (landcover composition within a 400 m buffer). In addition to their relevance for grassland birds, arthropods play important functional roles in grasslands and are useful indicators of grassland health. I collected arthropod samples using pan traps in grassland patches at Burning Star, and used generalized linear mixed models to relate variation in arthropod biomass and diversity to habitat predictor variables. I found that arthropod biomass increased with vegetation height at the local scale and proportion of forest/shrub edge at the patch scale, while arthropod diversity responded only to local-scale variables, including a negative association with vegetation height and woody vegetation cover, and a positive association with forb cover. I conclude that local vegetation structure and composition are the main drivers shaping arthropod communities at Burning Star, and that limiting woody encroachment and increasing forb cover and variation in vegetation height within grassland patches may encourage arthropod abundance and diversity in tallgrass prairies. In Chapter 3, I estimated associations between small mammal abundance and habitat variables, again representing three spatial scales. I surveyed small mammal communities using a grid of 100 Sherman traps set out for three nights at each study site. I identified all captured individuals to genus, individually marked them with ear tags, and estimated abundance using a combination of Huggins P and C models in Program Mark and generalized linear mixed models in Program R. I found that small mammal abundance was positively related to vegetation density and negatively related to plant diversity, though variation in plant diversity affected Microtus voles more strongly than Peromyscus mice. At the landscape scale, small mammal abundance was positively associated with the amount of water surrounding a patch, and negatively associated with the amount of grassland surrounding a patch. Variation in small mammal community composition (proportions of Microtus vs Peromyscus) was mostly governed by differences in habitat structure at the landscape scale, rather than differences in vegetation structure at the local scale. I suggest that managers interested in influencing small mammal abundance in grasslands encourage dense vegetation growth by limiting disturbance if increased small mammal abundance is desired, or reduce vegetation density by increasing disturbance frequency to reduce small mammal abundance. Additionally, increasing plant diversity by sowing a high diversity of seeds may be an effective way to control Microtus vole populations. In Chapter 4, I estimated the habitat associations of snakes at Burning Star, focusing on the relative abundance of snakes among different grassland sites, as well as snake diversity and species-specific occupancy. Although snakes are prolific nest predators of grassland birds, they are also integral components of grassland systems, and there may be instances where managers and decision-makers wish to increase, rather than decrease, their abundance in grasslands. I found that snake community metrics were strongly and positively related to an increase in woody plant cover at the local (within-patch) scale. Snake relative abundance was also positively related to an increase in grass cover and a decrease in forb cover, though my occupancy results suggest that this was primarily driven by an increase in black kingsnakes (Lampropeltis nigra). At the patch scale, snake relative abundance and diversity were both positively related to the proportion of patch edge composed of roads. Habitat structure at the landscape scale had the smallest impact on snakes in this study, though the proportion of trees in the landscape was positively related to snake diversity. I suggested that managers and conservationists interested in manipulating snake abundance in grasslands focus on within-patch vegetation structure and composition. Decreasing woody cover in grasslands, or increasing the ratio of forbs to grasses, may reduce the presence of snakes, while maintaining a woody component could encourage both snake abundance and diversity. In Chapter 5, I estimated the habitat characteristics that were most strongly associated with raccoon abundance estimates in grassland patches at Burning Star. Raccoons have become increasingly important avian nest predators in midwestern grasslands due to rampant habitat fragmentation. I estimated raccoon abundance using an occurrence index from a series of baited trail cameras located in grassland sites. I found no convincing evidence of raccoon abundance being influenced by local scale habitat structure, beyond a weak association with vegetation height. At the patch scale, raccoon abundance was positively related to the proportion of patch edge composed of roads. At the landscape scale, raccoon abundance was negatively related to grassland, and positively related to water, within 400 meters of a grassland patch. I recommended that managers concerned with minimizing the presence of raccoons in grasslands should limit roads along grassland perimeters, maximize the proportion of grassland in the landscape surrounding a grassland patch, and avoid planning a grassland restoration in close proximity to open water if possible. In Chapter 6, I estimated the habitat characteristics that were most strongly associated with daily nest survival, nest density, and abundance of Dickcissels (Spiza americana), Field Sparrows (Spizella pusilla), and Common Yellowthroats (Geothlypis trichas), but also considered responses of all grassland bird species combined. I considered habitat characteristics representing four spatial scales: nest site, within-patch, patch, and landscape, though the nest site scale was only considered for nest survival analyses. I found that Dickcissels, an obligate grassland species, exhibited the strongest response to fire, as nest density drastically improved after previously undisturbed grasslands were burned. Dickcissel abundance was positively related to agriculture at the landscape scale and negatively related to woody cover. Field sparrows demonstrated a preference for woody cover and proximity to forests and shrublands, and Common Yellowthroats were positively associated with forb cover. Both Field Sparrow and Common Yellowthroat nest survival increased with greater distance from an edge, though no edge effect was detected for Dickcissel nest survival. All bird species benefitted from increased plant diversity and greater patch size. All species also responded negatively to vegetation height or litter depth, suggesting that fire, which reduces vegetation biomass and litter, may indirectly benefit the facultative grassland birds of Burning Star in addition to Dickcissels. In Chapter 7, I used structural equation models and data gathered in the previous five chapters to estimate whether the effects of habitat structure on breeding Field Sparrows is mediated through changes in predator (snake and raccoon) abundance, alternate prey availability, or arthropod biomass. I used Field Sparrows as the focal species for this chapter because they were the most common grassland bird in my dataset. I found no evidence of nest survival or nest density of Field Sparrows being directly influenced by nest predator abundance, alternate prey, or arthropod biomass, although habitat characteristics associated with increased nest survival were also associated with greater arthropod biomass and reduced predator abundance. I suggested that habitat structure at Burning Star may primarily impact breeding Field Sparrows through direct means, such as influencing nest concealment or foraging efficiency. These results also suggest that nest success and nest density are decoupled in this study area, so Field Sparrows may be preferentially selecting nest sites with structural characteristics that do not increase nest survival. Ultimately, my findings from this study indicate that while predator avoidance and food provisioning likely play an important role in determining nest survival for grassland birds, predator abundance and arthropod biomass may not necessarily predict predation risk and foraging efficiency to the extent that is often assumed.

A restauração ecológica visa a recuperação de ecossistemas que foram degradados, assegurando o seu restabelecimento estrutural e funcional. Porém, avaliar a funcionalidade do ecossistema ainda é um desafio, e vem sendo foco de trabalhos científicos a fim de desenvolver metodologias aplicáveis. Investigar as redes de interações ecológicas é uma forma adequada para avaliar a funcionalidade do ecossistema. As redes de interações são utilizadas na avaliação de habitats e já evidenciaram alterações na estrutura da comunidade que não foram detectadas pelas métricas tradicionais de riqueza, abundância e composição. Os macrofungos podem ser indicadores relevantes, pois realizam a decomposição e ciclagem de nutrientes e servem de alimento para diversos grupos de organismos, dentre eles os Coleoptera, que também podem utilizar a estrutura fúngica para nidificação. Este trabalho teve por finalidade construir redes tróficas formadas pela interação entre besouros fungívoros (Coleoptera) e macrofungos (Polyporales e Hymenochaetales) a fim de testar a aplicabilidade de redes ecológicas para avaliar a restauração quando comparadas às métricas tradicionais de abundância, riqueza e composição das espécies. O estudo se realizou em duas áreas sobre restauração florestal comparados às áreas de referência pareadas. A primeira área está em restauração há oito anos e a segunda há dez anos, sendo que até o momento, somente a segunda área teve sucesso na restauração da comunidade de plantas. No total, coletamos 512 macrofungos, representando 87 espécies, mas somente 181 indivíduos de 36 espécies apresentaram interações com besouros. Destes, foram obtidos 11.414 besouros de 53 espécies. Em ambas as áreas, as métricas de descritores de comunidade e também as métricas de redes não diferiram entre os tratamentos, indicando que a estrutura e também a funcionalidade das comunidades de macrofungos e besouros fungívoros está sendo recuperada nas áreas em restauração. Apesar de não haver diferença na composição de espécies, a espécie rara Falsocis brasiliensis e alguns exemplares da família Erotylidae somente foram encontradas em áreas de referência. Os processos de restauração diferiram qualitativamente entre as áreas, como podemos perceber através das interações realizadas. As áreas de restauração de dez anos estão mais próximas às áreas de referência, pois foram deixados troncos de madeira que serviram de substrato para os macrofungos, principalmente para o Ganoderma australe e suas interações, encontrado em árvores mortas da floresta de referência de ambas as áreas. Enquanto que as áreas de restauração de oito anos apresentaram pouco substrato lenhoso e baixa umidade, onde Pycnoporus sanguineous predominou em abundância de basidiomas e suas interações em relação à floresta de referência. / Ecological restoration aims to recover degraded ecosystems, ensuring both structural and functional restoration. Assessing ecosystem functionality is still a challenge, and current work is focusing on the development methods. Investigating networks of ecological interactions is a potential tool to assess ecosystem functionality. Interaction networks are used in the assessment of habitat change and have already evidenced differences in community structure that were not detected by the traditional metrics of richness, abundance and composition. Macrofungi are especially relevant indicators, due to their function in decomposition and nutrient cycling in the ecosystem, and as they serve as food source for several groups of organisms, among them the Coleoptera, which can also use the fungal structure for nesting. Here we aimed at building trophic networks formed by the interaction between fungivorous beetles (Coleoptera) and macrofungi (Polyporales and Hymenochaetales), in order to test the applicability of ecological networks for the evaluation of restoration when compared to the traditional metrics of abundance, richness and species composition through the macrofungi-beetles system. Research was conducted in two areas under forest restoration, compared to paired reference areas. The first area is under restoration process for 8 years and the second for 10 years, and in the second area the restoration success has been achieved based on plant community evaluation. During the study, we collected 512 macrofungi individuals, representing 87 species, but only 181 specimens from 36 species showed interactions with beetles. A total of 11,414 beetles from 53 species were obtained. For both areas, traditional community descriptors did not differ between treatments, nor did network metrics, indicating that the structure and also the functionality of the communities of fungivorous beetles and macrofungi are being successfully recovered in restoration areas. Although there is no difference in species composition, the rare species Falsocis brasiliensis and some specimens of the Erotylidae were found only in reference areas. The processes of restoration differ qualitatively between areas, as we can perceive through the interactions. The ten year-long restoration areas are more similar to the reference areas, due to the presence of wood logs that served as substrate for the macrofungus, mainly Ganoderma australe and its associated beetles, occurring on dead trees found in the both reference forest areas. On the other hand, the eight year-long restoration area had less woody substrate, composed mostly of thin branches, and less humidity, where Pycnoporus sanguineous predominated in basidiome abundance and their interactions compared to the reference forest.

<p>The aim of this thesis was to identify general structuring mechanisms in benthic food webs within the framework of ecological stoichiometry theory. Ecological stoichiometry is defined as the balance of multiple chemical substances in ecological interactions and explicitly considers the combined dynamics of key elements such as carbon (C), nitrogen (N) and phosphorus (P). Ecological stoichiometry theory was developed for pelagic environments, thus it must be tested whether the same mechanisms are applicable to benthic environments. </p><p>In this thesis, ecological stoichiometry theory was used as a framework to investigate nutrient pathways in benthic littoral ecosystems. I conducted one invertebrate field sampling and six experiments. In the experiments, factors such as grazing, light, nutrients and fish presence were manipulated.</p><p>The results showed that stoichiometric variability in consumers could mostly be explained by taxa. However, there was some stoichiometric variability due to sampling season, site, and nutrient enrichment. </p><p>Grazing mostly increased periphyton N and P content, although nutrient recycling effects were dependent on grazer stoichiometry. Grazing changed benthic algal community composition by increasing the proportion of grazing resistant algae species. Additionally, grazing decreased algal diversity, especially under nutrient poor conditions. The manipulation of fish presence revealed that fish affected primary producer biomass and stoichiometry through nutrient recycling. </p><p>The manipulation of abiotic factors, such as light and nutrient addition could affect periphyton nutrient content, biomass and benthic algal chlorophyll a content. The separate addition of N or P led to an increase of the added nutrient in the periphyton. Increased light intensities led to a decreased cellular chlorophyll a content and increased C:nutrient ratios. </p><p>This thesis arrives at the conclusion that periphyton-grazer-predator interactions in the benthic are bound by stoichiometric constraints. Nutrient recycling by benthic invertebrates and fish are important mechanism in benthic littoral ecosystems.</p>

Host behavior, age, sex, diet, and condition, as well as variation in parasite specificity, drive variation in parasite infection, and ultimately determine the host parasite community. The objectives of this thesis were to 1) examine intraspecific variation in arctic fox parasites, 2) determine relationships between diet and parasites in sympatric arctic and red fox, and 3) compare wolf parasites and diet. Male arctic fox had more cestodes than females and juveniles had more nematodes than adults, likely due to diet and exposure. Red fox carried fewer parasites than arctic fox, likely due to diet, evolved resistance behaviors and higher immune investment, but diet affected cestode abundance in both species. Wolves that ate more white-tailed deer had more cestodes, suggesting increasing deer populations could enhance parasite transmission to moose. However, body condition was unaffected by parasites, suggesting northern canids may have not reached a threshold of infection.

Bythotrephes longimanus is an invasive, macroinvertebrate from Eurasia that was introduced into the Great Lakes region in the mid 1980s. Bythotrephes introductions into lake ecosystems have resulted in substantial changes in zooplankton communities, including declines in species richness, abundance, biomass and production. Changes in zooplankton communities may alter the quantity and quality of prey to other predators such as cisco (Coregonus artedii), a pelagic forage fish. Here, I conduct a current day comparison of cisco populations to determine if prey consumption by cisco differs in the presence of Bythotrephes, and whether changes in diet result in energetic consequences (changes in growth and condition) for cisco. Effects of Bythotrephes on native zooplankton communities have resulted in substantial changes in the variety and proportion biomass of zooplankton and macroinvertebrate prey types in cisco stomachs, which have in turn modified growth of cisco. Cisco taken from invaded lakes achieve greater total lengths but changes in condition were not detected. This effect may be driven by improved growth in the second and subsequent growing seasons, suggesting that growth consequences for young fish (that do not feed on Bythotrephes) are different than for older individuals. Length-at-structure age data indicate that by the end of the first growing season (age 1) cisco achieve comparable total body lengths in invaded and reference lakes, suggesting that food consumption by young cisco remains unchanged by Bythotrephes. Alternatively, young cisco forage may be reduced in the presence of Bythotrephes, resulting in decreased survival and similar growth among individuals that survive to age 1. In contrast, despite changes in the zooplankton community; growth of older fish (≥ age 2) was enhanced in lakes that have Bythotrephes. Improved growth among older cisco (≥ age 2) in invaded lakes may be related to the presence of a newly attainable, high energy prey source (Bythotrephes). Alternatively, enhanced growth may be explained by lower competition due to reduced recruitment of young cisco (≤ age 1) in invaded lakes. Increased knowledge regarding the effects of Bythotrephes on growth of cisco is important in furthering our understanding of its impact on lake ecosystems. / Thesis (Master, Biology) -- Queen's University, 2010-04-28 22:46:07.756

Host behavior, age, sex, diet, and condition, as well as variation in parasite specificity, drive variation in parasite infection, and ultimately determine the host parasite community. The objectives of this thesis were to 1) examine intraspecific variation in arctic fox parasites, 2) determine relationships between diet and parasites in sympatric arctic and red fox, and 3) compare wolf parasites and diet. Male arctic fox had more cestodes than females and juveniles had more nematodes than adults, likely due to diet and exposure. Red fox carried fewer parasites than arctic fox, likely due to diet, evolved resistance behaviors and higher immune investment, but diet affected cestode abundance in both species. Wolves that ate more white-tailed deer had more cestodes, suggesting increasing deer populations could enhance parasite transmission to moose. However, body condition was unaffected by parasites, suggesting northern canids may have not reached a threshold of infection.