Thesis (Ph.D.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.

All animals are adapted to the environmental conditions of the habitat they chose to live in. It was the aim of this PhD-project, to show which behavioral strategies are expressed as mechanisms to cope with the constraints, which contribute to the natural selection pressure acting on individuals. For this purpose, small mammals were exposed to different levels and types of predation risk while actively foraging. Individuals were either exposed to different predator types (airborne or ground) or combinations of both, or to indirect predators (nest predators). Risk was assumed to be distributed homogeneously, so changing the habitat or temporal adaptations where not regarded as potential options. Results show that wild-caught voles have strategic answers to this homogeneously distributed risk, which is perceived by tactile, olfactory or acoustic cues. Thus, they do not have to know an absolut quality (e.g., in terms of food provisioning and risk levels of all possible habitats), but they can adapt their behavior to the actual circumstances. Deriving risk uniform levels from cues and adjusting activity levels to the perceived risk is an option to deal with predators of the same size or with unforeseeable attack rates. Experiments showed that as long as there are no safe places or times, it is best to reduce activity and behave as inconspicuous as possible as long as the costs of missed opportunities do not exceed the benefits of a higher survival probability. Test showed that these costs apparently grow faster for males than for females, especially in times of inactivity. This is supported by strong predatory pressure on the most active groups of rodents (young males, sexually active or dispersers) leading to extremely female-biased operative sex ratios in natural populations. Other groups of animals, those with parental duties such as nest guarding, for example, have to deal with the actual risk in their habitat as well. Strategies to indirect predation pressure were tested by using bank vole mothers, confronted with a nest predator that posed no actual threat to themselves but to their young (Sorex araneus). They reduced travelling and concentrated their effort in the presence of shrews, independent of the different nutritional provisioning of food by varying resource levels due to the different seasons. Additionally, they exhibited nest-guarding strategies by not foraging in the vicinity of the nest site in order to reduce conspicuous scent marks. The repetition of the experiment in summer and autumn showed that changing environmental constraints can have a severe impact on results of outdoor studies. In our case, changing resource levels changed the type of interaction between the two species. The experiments show that it is important to analyze decision making and optimality models on an individual level, and, when that is not possible (maybe because of the constraints of field work), groups of animals should be classified by using the least common denominator that can be identified (such as sex, age, origin or kinship). This will control for the effects of the sex or stage of life history or the individual´s reproductive and nutritional status on decision making and will narrow the wide behavioral variability associated with the complex term of optimality. / Das Verhalten von Tieren ist das Ergebnis eines kontinuierlichen Anpassungsprozesses im Laufe der Evolution einer Art und damit der Veränderung der Umgebung in der es lebt und der Interaktion mit anderen Arten. Dies wird besonders deutlich im Verhalten von potentiellen Beutetieren, ihre Strategien beinhalten meist ein möglichst unauffälliges Verhalten im Zusammenspiel mit reduzierter Bewegung und möglichst guter Tarnung. Dementgegen stehen essentielle Bedürfnisse, wie zum Beispiel die Nahrungssuche, die Verteidigung von Ressourcen (zum Beispiel Territorien, Futterstellen) und die Suche nach Paarungspartnern. Beutetiere leben also in einem Spannungsfeld indem sie Ihr Verhalten optimieren müssen. Hierbei stehen die Ernährung, erfolgreiche Verpaarung und andere Chancen auf der einen Seite, die Vermeidung von Begegnungen mit Prädatoren auf der anderen. Vor allem Kleinsäuger sind häufig als Beutetiere mit einer Vielzahl von Prädatoren aus der Luft und auf dem Boden konfrontiert. Sie müssen für die verschiedenen Bedrohungen adaptive Verhaltensanpassungen bereit haben und in der Lage sein, auf die optischen, olfaktorischen oder akustischen Signale, die die Gefahr durch Prädatoren anzeigen, mit plastischen Verhaltensmustern zu reagieren. Die vorliegende Dissertation beschäftigt sich mit bisher als Konstanten behandelten Faktoren und untersucht anhand von Verhaltensexperimenten mit wilden Wühlmäusen (Microtus arvalis) folgende Fragestellungen: - Wie verhalten sich Tiere, die einer homogenen Risikoverteilung ausgesetzt sind, zum Beispiel weil ihr Prädator genauso gross ist wie sie, im gleichen Habitat lebt und es keinen sicheren Ort gibt? - Mit welchen Anpassungen reagieren Tiere, wenn sie gleichzeitig verschiedenen Prädatoren ausgesetzt sind? - Wie unterscheiden sich die Nahrungssuchstrategien von Männchen und Weibchen? - Wie verhalten sich laktierende Weibchen, die einer permanenten, indirekten Gefahr, z.B. durch einen Nestprädator ausgesetzt sind? Die Ergebnisse der verschiedenen Versuche in künstlichen Arenen und Aussengehegen zeigen, dass die Mäuse in der Lage sind, adaptive Verhaltensanpassung an homogenes Risiko und verschiedene Prädationstypen abzurufen. So sind sie in der Lage, Luft- von Bodenprädatoren zu unterscheiden und jeweils das Verhalten zu zeigen, dass die größtmögliche Sicherheit mit sich bringt. Die simultane Kombination von verschiedenen Prädatoren bewirkt hierbei additive Effekte. Gibt es keine Auswahl zwischen Habitaten, sondern nur unterschiedliche homogene Risikolevel, reagieren sie auf steigendes Risiko immer mit verminderter Aktivität und konzentrieren ihre Nahrungssuche auf weniger Futterstellen, beuten diese dafür jedoch länger aus. Die Wertigkeit von Futterstellen und alternativen Optionen verändert sich also mit dem Risikolevel. Ähnliches zeigt sich auch in den unterschiedlichen Futtersuchstrategien von Männchen und Weibchen. Die untersuchte Art ist polygyn und multivoltin, dementsprechend verbinden die Männchen mit ihrer Nahrungssuche Aktivitäten wie die Suche nach Paarungspartnern und unterscheiden sich die Aktivitätsmuster zwischen Männchen und Weibchen. Zusätzlich zeigen die Ergebnisse, das laktierende Weibchen in der Lage sind, das Risiko für sich und für Ihre Jungen abzuschätzen, wenn sie mit einem Nestprädator (Sorex araneus) konfrontiert werden. Für die Interaktion zwischen diesen beiden Arten ist jedoch die Saison (und damit die Ressourcenlage), in der sie sich begegnen, von entscheidender Bedeutung. Wühlmäuse reagieren mit entsprechenden Verhaltensanpassungen zum Schutz des Nestes um die Überlebenschancen ihrer letzten Würfe im Herbst zu erhöhen. Die vorliegende Arbeit konnte grundsätzliche Probleme der antiprädatorischen Verhaltensanpassung von Beutetieren klären und wichtige Faktoren der Entscheidungsfindung unter Prädationsdruck analysieren. Sie zeigt, dass Tiere das Risiko in ihrer Umgebung nicht unbedingt über direkt Signale wahrnehmen, sondern ihre Verhaltensstrategien einem empfundenen Gesamtrisikolevel anpassen. Dies ermöglicht ihnen, adaptive Strategien zu verfolgen, auch wenn sie keine Auswahl an sicheren Habitaten haben. Sie zeigt auch die unterschiedliche Wahrnehmung von Risiken durch Männchen und Weibchen, die durch die unterschiedlichen mit der Aktivität zusätzlich wahrgenommenen Chancen verknüpft zu sein scheint. Zusätzlich wurde der Einfluss des reproduktiven Status (z.B. laktierend), sowie der Ressourcenlage (z. B. je nach Saison) nachgewiesen.

This thesis deals with the evolution of individuals within a species adapted to utilize specific resources, i.e. resource polymorphism. Although a well-known phenomenon, the understanding of the mechanisms behind is not complete. Considering the ruling theories, resource polymorphism is suggested to depend on severe competition for resources, the presence of open niches to be occupied leading to a reduction in competition, and disruptive selection where generalist are out-competed due trade-offs in foraging efficiency for different prey. In order to study resource polymorphism, I have used fish as the animal group in focus and the methods I have used range over laboratory experiments, field experiments, literature surveys and theoretical modelling. In my work, I have showed that different resource use induces different body shapes and that the rate of change is dependent of the encounter rate of different resources. The induced body changes partly led to increased foraging efficiency but surprisingly I did not find any trade-offs due to specialization. However, when studying predation risk in relation to resource polymorphism, my studies point towards that resource use and predation risk may act as balancing factors in such a way that disruptive selection can take place. My work also shows that population feedbacks have to be explored when considering the evolution of resource polymorphism. In pond and field experiments, I found that changes in resource densities affected the actual resource use despite previous adaptations to certain resources. By performing a literature survey, I found that cannibalism indirectly by its effect on population dynamics seems to facilitate the evolution of resource polymorphism. Modelling a size-structured population, I found that resource dynamics were stabilized, and the relative availability of different resources was levelled out due to cannibalism. Taken together, my studies strongly suggest that to understand the development of resource polymorphism in consumer populations, future studies have to include the effect of a dynamic environment both with respect to resources and predators.

Traces of unsuccessful predatory attacks can be found in the hard parts of shell-bearing organisms as repaired shell injuries and are often preserved in the fossil record. These repaired shell injuries can help to deduce the relationship between predator and prey in the past. Gastropods afford an excellent opportunity for study since their shells are easily recognized from the Cambrian onwards, and usually preserve a full record of their life history. Predation is a phenomenon which has led to a great variety of adaptations among prey organisms in their quest to avoid being eaten. Increased predation pressure seems to have been one of the factors that has fueled the evolution of predation-resistant shell morphologies. Individual case studies examine the frequency of shell repair in assemblages of Palaeozoic gastropods from different geological periods. The Silurian species Poleumita discors showed a shell repair frequency of 10 %, while only 4 % of the Devonian species Praenatica gregaria have been repaired. The Palaeozoic bilaterally symmetrical bellorphontiform molluscs also showed low levels of shell repair. Similar shell morphologies in the long-lived group of pleurotomarioid gastropods were examined and shell repair frequenceis calculated to investigate potential variation through geological time. The Palaeozoic species showed repair frequencies of 17.1 % and 4.2 %. The frequency increased in the Mesozoic to between 28.8 % and 46.6 %, while all shells of Recent pleurotomarioids in the study showed repaired injuries. The repaired injuries found do not change in appearance through time, which is probably a reflection of the presence of the slit in the apertural margin. Which type of injury is the most abundant can be seen to change with time, and there is also an increase in size with time. This may be a defensive strategy taken up by the pleurotomarioids as a response to more abundant predators.

Landscape effects on species performance currently receives much attention. Habitat loss and fragmentation are considered major threats to species diversity. Deciduous forests in southern Sweden are previous wooded pastures that have become species-rich communities appearing as islands in agricultural landscapes, varying in species composition. Actaea spicata is a long-lived plant occurring in these forests. In 150 populations in a 10-km2 area, I studied pre-dispersal seed predation, seed dispersal and pollination. I investigated spatio-temporal dynamics of a tritrophic system including Actaea, a specialist seed predator, Eupithecia immundata, and its parasitoids. In addition, effects of biotic context on rodent fruit dispersal and effects of flowering time and flower number on seed set, seed predation and parasitization were studied. Insect incidences of both trophic levels were related to resource population size and small Eupithecia populations were maintained by the rescue effect. There was a unimodal relationship between seed predation and plant population size. Seed predator populations frequently went extinct in small plant populations, resulting in low average seed predation. Parasitoids were present in large plant populations but did not affect seed predator density. Seed predators aggregated at edges, relaxing seed predation in patch interiors. Flowering phenology was unrelated to seed set and insect incidence. A higher flower number did not influence seed predation but was associated with higher seed set and a tendency for a higher parasitization rate. In the study on fruit dispersal more fruits were removed inside than outside populations. Within plant populations more fruits were removed from large aggregations. Overall, this thesis underlines the importance of plant-animal interactions during different phases of the life cycle. The spatial configuration of host plants plays an important role for the outcome of plant-animal interactions and trophic cascades.

For ectotherms living in seasonal environments, time available for development and growth is often constrained by the length of the growth season. Declining season length towards higher latitudes often select for latitudinal clines in development and growth rates, exhibiting increasing growth and developmental rates towards the north. However, the physiological and ecological factors enabling these clines are poorly understood. Our study system included eight populations of Rana temporaria along a 1500 km latitudinal gradient. We found increased growth rates in populations at higher latitudes to be the result of higher growth efficiency, partly due to increased relative gut length. Populations with higher growth rates also exhibited lower standard metabolic rates, implying that fast-growing individuals are able to achieve high growth rates by spending less energy on maintenance metabolism under low activity conditions. Predator densities, and antipredatory defenses in prey, are assumed to decrease towards higher latitudes. While all study populations responded to predator presence by decreasing activity and foraging, high latitude populations maintained higher activity levels in the presence of the predator. In trials with a free-ranging predator, high latitude tadpoles experienced higher mortality than those from the low latitudes. The higher activity level in the northern populations increases mortality under predation risk, but is probably needed to maintain high growth and development rates. When competing over resources, tadpoles from the low latitude population were inferior competitors, as indicated by their longer development time when raised together with high latitude tadpoles. We found no effect of latitude on size-corrected burst speed. The general effect of predator presence on burst speed depended on food availability, with well fed tadpoles being faster in the absence, and food restricted being faster in the presence of a predator.

Management of wolves is a complex issue, and molecular genetics is an important tool in this work. Molecular genetics can provide important information at the species, population and individual level, which can be essential for the development of management programs aiming at the long term survival of wolf populations. In this thesis I developed new genetic markers on the canine Y chromosome to estimate the number of founders of the Scandinavian wolf population. This knowledge is important to reconstruct the history of the population and to design the most appropriate conservation strategies. Next, genetic markers with different pattern of inheritance have been used to identify hybrids between wolves and dogs. This allowed us to determine the direction of hybridization and to evaluate its possible impact on the gene pool of a wolf population. Furthermore, I also developed a method for a more reliable identification of the predator responsible of an attack by using saliva remains left on the prey. Since predation on livestock is perhaps the main reason for the negative opinions about the predator, the correct identification of the responsible for an attack (wolf, dog or hybrid) is essential. Finally, this thesis has also been focusing on the domestication of dogs. By using Y chromosome markers (paternally inherited), it has been possible to complement previous studies based on mtDNA sequences (maternally inherited) and autosomal markers (inherited from both parents). In this way I have obtained a more complete picture of the domestication process and of the origin of breeds. This has shown that there has been a bias in the contribution of the two sexes in the origin of dog breeds (fewer males then females contributing to each breed) and that the origin of dogs was not marked by extensive backcrosses with male wolves over the entire species range.

Recent studies show that populations of the freshwater isopod Asellus aquaticus L. can rapidly become locally differentiated when submerged stonewort (Chara spp.) vegetation expands in lakes. In the novel Chara habitat, isopods become lighter pigmented and smaller than in the ancestral reed stands. In this study, I used laboratory experiments to investigate if selective predation by fish could be a possible explanation for these phenotypic changes. Predation from fish is generally considered to be a strong selective force on macroinvertebrate traits. In the first experiment I measured perch (Perca fluviatilis L.) handling time for three size classes of Asellus to see which size of those that would be the most profitable to feed upon. No difference in handling time was detected between prey sizes, hence the largest size would be the most beneficial to feed upon. In a second experiment I let perch feed on a mixture of Asellus phenotypes in aquaria manipulated to mimic the substrates in either the Chara or the reed habitats. Remaining isopods were significantly smaller and lighter pigmented in the fish aquaria than in the controls, showing that the perch preferred to feed on large and dark individuals. In the Chara habitat, selection on isopod pigmentation was according to what could be expected from background matching, but in the reed habitat selection was quite the opposite. These results support the hypothesis that predation from fish is a strong selective force behind the rapid local adaptation seen in Asellus populations in the novel Chara habitat.

In this thesis I have investigated the effects of invading top and intermediate consumers in a size-structured fish community, using a combination of field studies, a lake invasion experiment and smaller scale pond and aquaria experiments. The lake invasion experiment was based on introductions of an intermediate consumer, ninespine stickleback (Pungitius pungitius L.), in to allopatric populations of an omnivorous top predator, Arctic char (Salvelinus alpinus L.). The invasion experiment was performed in two tundra lakes and in two birch forest lakes to investigate the effect of climate on the invasion success. I found that the effect of sticklebacks on char was size dependent. Small char suffered reduced growth from resource competition with sticklebacks whereas the maximum size of adult char increased from the addition of a larger prey resource, stickleback. The negative effect of sticklebacks on the growth of small char suggests that sticklebacks may be a better resource competitor than char, which was also supported by the pond and aquaria experiments. The pond experiments also suggested that char were more efficient cannibals than interspecific predators on sticklebacks. Cannibalism in char may limit the recruitment of char and decrease both their predatory and competitive effect on coexisting species and thereby also promote the coexistence of char and sticklebacks. The successful invasion by sticklebacks and their subsequent increases in density suggest that the absence of sticklebacks in char lakes in this region is not caused by biotic interactions with char. Instead, it may be suggested that co-occurrence of sticklebacks and char in the region is limited by dispersal. The char – stickleback system resembles an intraguild predation system with char as the top consumer and stickleback as the intermediate consumer. The effects of the stickleback invasion is also contrasted with a field study of a northern pike (Esox lucius L.) invasion into a system with coexisting char and stickleback, where pike can be viewed as the top consumer and char as the intermediate consumer both feeding on sticklebacks. In this case pike excluded char. The identity of the invading species and the relative strength of the predatory and competitive interactions in the two contrasting systems are discussed in relation to coexistence in intraguild predation systems. I found that the identity of the invading species is of crucial importance for the response at the ecosystem level, and that the inherent size dependency of competitive and predatory interactions in fish communities is important for attaining a mechanistical understanding of the effects of invasive species in lake ecosystems.

Cougar (Puma concolor) predation has been identified as being one of several factors contributing to the decline of mule deer (Odocoileus hemionus) throughout the Western United States. In order to better understand how these elusive felines utilize their surroundings and prey, I examined and analyzed cougar predation behavior in North-Central Utah, using global positioning systems (GPS) data from 2002-2010. Twenty-three cougars were fitted with GPS collars and monitored for prey caching behavior. In total 775 potential cache sites were visited and 546 prey remains found. Mule deer comprised the majority of prey at cougar cache sites, but 11 other species were also found. Collectively, adult female mule deer were killed more than any other demographic class. Proportionally there was no difference in the sex or age class of deer killed by cougars in three different population segments, but seasonal differences were found in the number of kills made between cougar groups. Female cougars with kittens had a higher predation rate than males or solitary females, and seasonally more kills were made in the winter vs. summer. Cougars spent an average of 3.3 days on deer kills, and 6.2 days on elk kills. Habitat analyses suggested that cougars preferentially used Gambel oak (Quercus gambelii) over other land cover types when caching prey, as well as selected unburned over burned areas for caching and foraging on prey. These results suggest that cougars utilize dense stands of vegetation cover when stalking and concealing their prey. Wildlife managers may want to consider the use of prescribed burns in areas of high cougar predation on mule deer. This habitat manipulation tool could simultaneously help mule deer populations by reducing the percent of stalking cover afforded to cougars when attempting to kill prey, along with increasing nutrient levels of newly burned foliage and allow for an increased diversity in forb and shrub species available to mule deer.