The present study investigates the impact of northern pike (Esox Lucius) on the growth of juvenile burbot (Lota lota) in northern lake ecosystems. It is hypothesized that the presence of pike will positively affect the growth of juvenile burbot by reducing interspecific competition and increasing the abundance of benthic invertebrates. To test this hypothesis, electrofishing for juvenile burbot was conducted in the littoral zones of lakes with and without pike in the region Jämtland Härjedalen, Sweden. Data on length and age of the captured burbot were used to compare growth between the two lake types. Contrary to the initial hypothesis, the results show that juvenile burbot were significantly larger at a given age in lakes where pike was absent. This outcome suggests that juvenile burbot may reduce their foraging activity in lakes with pike to minimize predation risk. Since adult burbot has shown to be of greater size in lakes with pike, future research could investigate whether the shift towards piscivory in burbot leads to changes in how they are affected by pike.

Predicting the impacts of non-native species remains one of the greatest challenges to invasion ecologists. Because of their insularity, freshwater systems are particularly vulnerable to invasions, especially from non-native predators. The research in this thesis explores the role of abiotic and biotic factors in mediating the distribution and impact of Bythotrephes longimanus, a predatory cladoceran that has been introduced to freshwater systems in North America. Although the general impacts of this invasion have been documented, little is known about the factors that modulate them. Using a combination of field surveys and experiments, I tested several hypotheses concerning the influence of interactions with native species, as well as the role of heterogeneity in the light environment, in mediating the impact of Bythotrephes. Results demonstrated that biotic resistance by native macroinvertebrate predators does not play a limiting role in the establishment success of Bythotrephes. However, the within-lake distribution of Bythotrephes was influenced by these macroinvertebrates, suggesting that the native predator context matters when trying to understand the impacts of non-native predators. This was demonstrated with a mesocosm experiment in which the impact of Bythotrephes was constrained by the native Chaoborus larvae. In terms of the abiotic environment, in situ feeding experiments demonstrated that refuges from impact could exist for some prey taxa, as the outcome of predation by Bythotrephes was dependent on light availability and some prey taxa were more successful at evading predation under low light conditions. Finally, results show that adaptive behaviour by prey is also an important determinant of impact, as migrating Daphnia can escape predation effects by Bythotrephes. The combination of light-limited predation and a shallow distribution by Bythotrephes selects for prey that occupy relatively deeper positions during the day. As a whole, this research highlights the importance of complex interactions in mediating the impact of Bythotrephes and may help to explain some of the variation that has been documented among invaded lakes. A better understanding of these complex interactions can improve our ability to anticipate impacts as Bythotrephes continues to spread, as well as provide insight on some of the long-term effects following invasion. / Thesis (Ph.D, Biology) -- Queen's University, 2013-06-17 09:26:35.221

Unlike desert rodents from North America, Allenby’s gerbil (Gerbillus andersoni allenbyi) from the Negev Desert, Israel has evolved with snakes that do not have heat-sensitive sensory pits that enhance night vision. Does this history affect their ability to assess and respond to a snake that has this ability? As a test, we exposed gerbils to risk of predation from various predators, including snakes, owls, and foxes. The snakes included the Saharan horned viper (Cerastes cerastes) and the sidewinder rattlesnake (Crotalus cerastes). The former snake lacks sensory pits and shares a common evolutionary history with the gerbil. The latter snake, while convergent evolutionarily on the horned viper, has sensory pits and no prior history with the gerbil. The gerbils exploited depletable resource patches similarly, regardless of snake species and moon phase. While the gerbils did not respond to the novel snake as a greater threat than their familiar horned viper, the gerbils were cognizant that the novel predator was a threat. In response to both snakes, giving-up densities (GUDs; the amount of food left in a resource patch following exploitation) of the gerbils were higher in the bush than open microhabitat. In response to moonlight, GUDs were higher on full than on the new moon. Based on GUDs, the gerbils responded most to the risk of predation from the red fox, least from the two snake species, and intermediate for the barn owl. Keywords:

Les vasières intertidales sont des environnements complexes et changeants, qui abritent des invertébrés enfouis dans le sédiment (la macrofaune benthique) et sont visités de manière saisonnière par de grands migrateurs : les oiseaux limicoles. Ce travail de recherche s’intéresse aux relations proie-prédateur entre les oiseaux limicoles et leur ressource alimentaire : la macrofaune benthique. La thèse est articulée en 8 chapitres qui présentent des études à différentes échelles spatio-temporelles : des saisons à la décennie, et de la baie à la route migratoire. Ces études sont basées sur un échantillonnage régulier des vasières intertidales du Golfe de Gascogne (France) ainsi que d’échantillonnages en mer des Wadden (Pays-Bas) et au Banc d’Arguin (Mauritanie). Les données de macrofaune (qualité, taille, densité, biomasse) sont couplées aux données de comptages de leurs prédateurs ainsi qu’à leur comportement alimentaire (reconstruction du régime alimentaire d’après les isotopes, les fécès, la modélisation ou l’observation de vidéos). Ces huit études apportent un éclairage sur l’écologie de leurs interactions (en intégrant des variables environnementales telles que le temps d’inondation, la granulométrie, la température, la production primaire, ou encore la latitude). Une attention particulière est portée à la variabilité des proies et du comportement alimentaire de leurs prédateurs, dans l’espace et le temps. Des encarts viennent illustrer pour l’un les techniques de reconstruction du régime alimentaire, pour l’autre les défenses développées par les mollusques marins, ou encore la relation entre énergie à disposition et sélection du site pour les limicoles. / Intertidal mudflats are complex ecosystems undergoing constant changes, home to infaunal invertebrates (benthic macrofauna), and migratory sites for particular birds : shorebirds. This research focuses on predator-prey interactions between shorebirds and their macrobenthic prey. The present thesis is composed of 8 chapters which illustrate different spatio-temporal scales : from seasons to the decade, and from the bay to the migratory flyway. These studies are based on regular benthic sampling of intertidal flats along the Bay of Biscay (France), as well as sampling data from the Dutch Wadden Sea and the Mauritanian Banc d’Arguin. Macrobenthic data (quality, sizes, densities, biomass) are linked with shorebird counts and data about their feeding behaviour (diet reconstruction from isotopes, faeces, modeling and video observations). These eight studies shed light on particular relationships between some prey and their predators, and the ecology of these interactions (including environmental variables such as inundation time, grain size, temperature, primary production, or even latitude). Particular attention is given to the variability of prey and predator behaviour in time and space. Inserts are included in between chapters to illustrate for instance different diet reconstruction techniques, anti-predation traits in marine molluscs, or relation between energy available and site selection in shorebirds.

I characterized dusky dolphin (Lagenorhynchus obscurus) underwater bait-balling behaviors and acoustic signals, and compared data between Argentina and New Zealand (NZ) to investigate the roles of ecology versus social learning. I quantified prey herding and capturing behaviors from video footage, and I analyzed acoustic signals from narrowband recordings. In both locations, I related bait-balling behaviors and acoustic signals to group and prey ball sizes. In NZ, I also related dolphin behaviors to prey ball escape behaviors and acoustic signal parameters to examine proximate functions. Observed herding behaviors typically involved dolphins swimming around or under a prey ball using a side body orientation, while dolphins typically captured fish from the side of a prey ball using a ventral orientation. Coordinated prey-capture behaviors may have made it easier for dolphins to capture fish by trapping fish between dolphins. Signals were categorized as click trains, burst pulses, and combinations due to a bimodal inter-click interval distribution. I observed 3 whistle-like chirp-screams, but no whistles. Sequences of burst pulses also occurred that contained 2-14 burst pulses that aurally and visually appeared closely matched. Similarities between locations suggest that ecological context related to broad behavioral and acoustic parameters, while social learning differences may occur on a finer scale. In NZ, prey balls exhibited horizontal and vertical movements, but the only behavior that preceded escape was “funneling”, the brief formation of a ball shape where the height was at least twice the width. Dolphin behaviors that related to prey balls ascending were type of herding pass, location of prey-capture attempts, and body orientation during attempts. These behavioral parameters may also be used to counter vertical prey escape behaviors. In NZ, all signal categories had a direct or indirect role in capturing prey. Click train-burst pulses were likely used for echolocating on prey, burst pulses and sequences appeared to have communication roles, and the role of click trains was ambiguous. No signal categories appeared to have a herding function, but the sheer number of signals emitted may have caused fish to cluster together more tightly and therefore facilitated capture.

Our earth is currently undergoing unprecedented human induced climate change, which is expected to drive widespread changes in species distributions and abundances that will affect natural pest suppression. Recent studies have suggested that climate change may cause changes to predator and herbivore assemblages in ways that alter multi-trophic food webs and affect the stability of ecosystems. Moreover, higher temperatures and increased climatic variability are expected to induce differential responses from predators and their prey that will undoubtedly disrupt species interactions. This thesis aims to test how climate change will impact the ability of natural enemies to continue to control pests in agroecosystems, and how they will continue to survive and function. In a field experiment using 13 farm sites across a natural temperature gradient, I found that temperature had direct positive effects on the abundances of the dominant parasitoid (an aphid specialist) and hyperparasitoid species, highlighting the importance of specific species responses in shaping larger communities. I also found that overall community composition was affected by temperature, with composition in warmer sites changing more throughout the season than cooler sites. In a future of inevitable climatic changes this result tells us we can expect arthropod community structure to change, which will have questionable impacts on overall population dynamics. To build on the field experiments, I used laboratory experiments to test differential responses of species to both drought and temperature and found that natural enemies responded to drought and temperature in a non-additive way, suggesting that the interaction between various climate change drivers is more important than their singular effect. Also, different species of natural enemies responded differently to abiotic factors, highlighting the importance of conserving natural enemies that can maintain important functional attributes in the face of climate change. Although biodiversity can be important for ensuring ecosystem functioning, response diversity, rather than species richness, may better promote ecosystem resilience, especially in the face of changing climate. The mechanisms underlying biodiversity effects are often difficult to disentangle, however, by manipulating the diversity of climate responses exhibited by ecosystem service providers, I tested how the rates and stability of prey suppression by predators are affected by climate warming and drought. I found that predator combinations with different individual responses to climate change maintained greater and less variable (i.e. more stable) prey suppression, compared with single predator species or combinations of predators with similar climate responses. This response complementarity became strongest through time and under drought or high temperature treatments. I suggest that response complementarity provides ‘insurance’ effects, which may be more important than previously envisaged for maintaining ecosystem functions such as biological control under global environmental change. Overall, the non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggests that predicting future pest outbreaks will be more challenging than previously imagined.

Hatchery supplementation of declining fish populations is used for increasing year-class strength, particularly when fish are released with knowledge of local predators. The ability of young-of-the-year lake sturgeon (Acipenser fulvescens) to avoid predation, as well as their vulnerability to predation, remains undocumented. The objective of my thesis was to determine: 1) whether hatchery-reared, predator-naive juvenile sturgeon would respond to alarm cues from injured conspecific cues, a reliable indicator of predation risk in other fishes; and 2) if sturgeon would learn to identify unknown predators through a Pavlovian-like conditioning with conspecific alarm cues. Releaser-induced recognition learning is a variant of Pavlovian learning in which recognition of a previously neutral stimulus is acquired through the experience of pairing a behaviourally active releasing stimulus and a novel stimulus. Sturgeon were initially conditioned using a behaviourally active stimulus of sturgeon alarm cue, paired with a behaviourally neutral stimulus of novel northern pike (Esox lucius) odour, or were pseudo-conditioned with distilled water paired with pike odour. Following conditioning, sturgeon were tested for recognition of the predator odour 24 hours later. The first population of fish (Rainy River) showed a dramatic antipredator response to alarm cues from the skin of conspecifics, but failed to exhibit learning of a novel predator through conditioning with alarm cues obtained from the skin of conspecifics. However, when Rainy River fish were conditioned with alarm cues from the whole body of conspecifics, they showed strong learning of the predator. Conditioning Wolf River fish to recognize predators with whole body extract had no effect on response to predator odours. However, when the fish were conditioned multiple times there was evidence of predator learning. These results highlight potential opportunities and limitation to life-skill training of artificially reared sturgeon for future conservation initiatives.

The ecological importance of introduced mammalian predators is well acknowledged in New Zealand, however, little research has focused on the ecology of native avian predators and their role in communities. This study investigated the ecology of moreporks (Ninox novaeseelandiae) on Ponui Island, Hauraki Gulf, New Zealand between August 2007 and April 2008. The primary aim was to investigate the functional response of moreporks to availability of their prey. The contents of regurgitated morepork pellets were compared with relative abundance of prey taxa (invertebrates, small birds and rodents) over the study period. The diet consisted primarily of a range of invertebrate prey, particularly weta (Anostostomatidae and Raphidophoridae) and beetles (Coleoptera). Small numbers of vertebrate prey were recorded including rodents and birds. A positive relationship between the percentage contribution to pellet samples of certain taxa and their relative availability was found, and there were peaks in the occurrence of seasonally abundant taxa including cicadas (Cicadidae), and huhu beetles (Prionoplus reticularis). The tendency of moreporks to prey on abundant taxa indicates that they are unlikely to depress prey populations to low levels, and may have some degree of stabilising influence. A significant increase in the rodent component of the diet in April indicated that the risk to moreporks of secondary poisoning during mammalian pest control operations may vary considerably with the time of year. The secondary aims were to collect data on roost site characteristics and breeding success. Moreporks roosted at a mean height of 4m, and foliar cover at the 4-6m height tier appeared to be the most important characteristic of roost sites when compared with control sites. These findings suggested that moreporks were selecting roost sites with high overhead cover. Possible reasons for this include predator avoidance, avoidance of mobbing passerines, and the microclimate provided. None of three established pairs and two other birds were observed to establish a nest or breed successfully. Additionally, only three juvenile moreporks were sighted or heard across the 90ha study area suggesting low breeding success in 2007-08. This may have been influenced by a range of factors including 1), predation by the high densities of ship rats on Ponui, or other predators 2), a lack of suitable nest sites such as tree hollows in some areas or 3), competition for invertebrate prey with high densities of ship rats and North Island brown kiwi (Apteryx mantelli).

Made available in DSpace on 2017-07-10T18:01:54Z (GMT). No. of bitstreams: 1 Tiago Birck.pdf: 505982 bytes, checksum: 4b6847150900887efe0c63ffd60125ee (MD5) Previous issue date: 2015-07-27 / Fundação Araucária / The practice of introducing species has brought great trouble to natural environments as a new species cause imbalance to the ecosystem and evolutionarily established his control has been one of the challenges for ecologists today. Thus, in mesocosms were experimentally analyzed the potential of juveniles of three species of piscivorous fish native (Salminus brasiliensis, Pseudoplatystoma corruscans and Brycon orbignyanus) in population control of Nile tilapia (Oreochromis niloticus) and the role of habitat complexity in this predator-prey interaction. The invasive species Oreochromis niloticus was offered in 2,000L tanks as prey for predators in 1:10 rate (predator:prey) with four levels of habitat complexity (0%, 50%, 100% and natural) without food supply. The number of exemplary preyed was evaluated with 6, 12, 24, 36, 48, 60, 72, 84, 96 and 108 hours after started of the experiment. Salminus brasiliensis showed the highest efficiency of predation, whereas the complexity of habitat did not influence the consumption of prey. In this sense, the sample results indicate that S. brasiliensis species is most effective to control of O. niloticus populations, thus constituting an alternative to implementations of management actions on aquatic environments of the Paraná River. / A prática da introdução de espécies tem trazido grandes problemas aos ambientes naturais, pois a nova espécie causa desequilíbrio ao ecossistema estabelecido evolutivamente e seu controle tem sido um dos desafios de ecologistas na atualidade. Com isso, foram analisados experimentalmente em mesocosmos o potencial de juvenis de três espécies de peixes piscívoros nativos (Salminus brasiliensis, Pseudoplatystoma corruscans e Brycon orbignyanus) no controle populacional da tilápia do Nilo (Oreochromis niloticus) e o papel da complexidade de habitats nesta interação predador-presa. A espécie invasora Oreochromis niloticus foi oferecida como presa para os predadores em tanques de 2.000 L na proporção de 1:10 (predador:presa) com quatro níveis de complexidades de habitat (0%, 50%, 100% e natural). Foi avaliado o número de indivíduos predados em 6, 12, 24, 36, 48, 60, 72, 84, 96 e 108 horas. Salminus brasiliensis apresentou a maior eficiência de predação, enquanto que a complexidade de habitats não influenciou no consumo das presas. Neste sentido, os resultados indicam que a espécie S. brasiliensis é a mais eficiente no controle de populações de O. niloticus, constituindo dessa forma uma alternativa para implementações de ações de manejo em ambientes aquáticos no rio Paraná.

Body size is a fundamental structural characteristic of organisms, determining critical life history and physiological traits, and influencing population dynamics, community structure, and ecosystem function. For my dissertation, I focused on effects of body size on habitat use and diet of important coastal fish predators, as well as their influence on faunal communities in Bahamian wetlands. First, using acoustic telemetry and stable isotope analysis, I identified high variability in movement patterns and habitat use among individuals within a gray snapper (Lutjanus griseus) and schoolmaster snapper (L. apodus) population. This intrapopulation variation was not explained by body size, but by individual behavior in habitat use. Isotope values differed between individuals that moved further distances and individuals that stayed close to their home sites, suggesting movement differences were related to specific patterns of foraging behavior. Subsequently, while investigating diet of schoolmaster snapper over a two-year period using stomach content and stable isotope analyses, I also found intrapopulation diet variation, mostly explained by differences in size class, individual behavior and temporal variability. I then developed a hypothesis-testing framework examining intrapopulation niche variation between size classes using stable isotopes. This framework can serve as baseline to categorize taxonomic or functional groupings into specific niche shift scenarios, as well as to help elucidate underlying mechanisms causing niche shifts in certain size classes. Finally, I examined the effect of different-sized fish predators on epifaunal community structure in shallow seagrass beds using exclusion experiments at two spatial scales. Overall, I found that predator effects were rather weak, with predator size and spatial scale having no impact on the community. Yet, I also found some evidence of strong interactions on particular common snapper prey. As Bahamian wetlands are increasingly threatened by human activities (e.g., overexploitation, habitat degradation), an enhanced knowledge of the ecology of organisms inhabiting these systems is crucial for developing appropriate conservation and management strategies. My dissertation research contributed to this effort by providing critical information about the resource use of important Bahamian fish predators, as well as their effect on faunal seagrass communities.