Thesis (M.A.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Scott Creel. Includes bibliographical references (leaves 40-44).

No description available.

Thesis (M. Sc.)(Zoology)--University of Pretoria, 2002. / Includes bibliographical references (p. 113).

Predation is one of the basic mechanisms of population growth control. Using a mathematical model, we explore the impact of predation in a prey population structured into two age classes, juveniles and adults, assuming a generalist predator. The specific predation pressure is represented for each of the two age classes by either no predation or Holling type II or Holling type III functional responses in various combinations. We distinguish two scenarios. In the first one, we seek for potential Allee effects or multiple stable states in the prey population, and explore the conditions at which the predation is more effective on juveniles than adults and vice versa. The most interesting finding here is the occurrence of bistability, or a predator-pit-like behaviour, when predators consume only juvenile prey, via a Holling type II functional response, an observation not described previously. In case only adults or both age classes are killed by predators exhibiting a type II functional response, the Allee effect occurs frequently. Multiple positive stable states are commonly observed if one of the age classes is exploited via a type III functional response. In the second scenario, we assume that the prey feeds on a resource and that the resource together with the prey undergoes outbreak dynamics, and we examine possibilities of control of such outbreaks using age-specific predation. Predation was proven to be able to suppress the prey population successfully. In some cases, an oscillation-free resource-prey-predator coexistence was detected.

Abstract Globally, populations of several wader species are in decline. However, for most populations, information on abundance, its changes and the causes of declines is insufficient for designing successful management strategies to recover threatened populations. In this thesis I studied the status and population trends, nesting success, genetic structure and viability of a small, declining and threatened Temminck's stint population in the Bothnian Bay in the northern Baltic Sea. Historical population data, recent population counts in the early 1990s and in 1999–2002 and the demographic data showed that the decline is continuing, paralleled by declines in nesting success, recruitment and adult survival. Decline in nesting success was caused by a coincident increase in nest predation. Depredation was the main cause of nest losses. The common gull (Larus canus) and the ruddy turnstone (Arenaria interpres) were found to be the most important nest predators. I tested if an increase in nest concealment and consequent decrease in visibility lowers the efficiency of the early-departure antipredator behaviour of the species. An expected positive correlation emerged between visibility and flushing distance in the presence of alarm-giving birds, but not without them. This indicates that Temminck's stint exploits signals from other birds as early warning of an approaching predator. More nests were lost to predation on narrow than on wide shores. The nest predation rate was not related to habitat (natural vs. man-made) nor to differences in microhabitat characteristics associated with concealment. Overall variability of the mitochondrial control region was low in the one northeast Siberian and the three Fennoscandian populations studied. The occurrence of two maternal lineages in all Fennoscandian populations points to mixing of two previously isolated populations. The overall microsatellite genetic structuring (6 loci) in Fennoscandia was low. The pairwise comparison revealed a low but significant degree of differentiation between the Bothnian Bay and the two other Fennoscandian populations. However, no clear indication of genetic effects of small population size in the Bothnian Bay was detected. Matrix and Pradel-λ projection models, based on a ten year (1994–2003) capture-recapture data set, predicted a steep future decrease and a high risk of extinction within 50 years. Without immigration the decline would lead to extinction within 20 years. Population growth was the most sensitive to changes in adult survival, the rate of which declined during the study. Factors affecting adult survival most likely operate primarily during the non-breeding season in locations specific to the study population that are virtually unknown. Management efforts in the Bothnian Bay should, in addition to improving hatching success, first of all guarantee availability of wide, low-sward coastal breeding habitats for potential immigrants and recruits.

Trophic cascades involving large terrestrial mammals are very seldom empirically demonstrated. The high species diversity often associated with terrestrial systems is thought to modulate the strength of trophic cascades. In speciose systems, species often vary in vulnerability to consumption, hence some species are less responsive to top-down pressure. African large mammalian herbivores are highly diverse and vary greatly in body size, a characteristic linked to vulnerability to predation. Moreover, Africa is one of the last places to still support megaherbivores, species that have grown large enough to be practically impervious to non-human predation. Thus an African ecosystem is the ideal setting to explore trophic cascades in speciose terrestrial systems. In this study I explored patterns in trophic interaction amongst carnivores, vulnerable mesoherbivore and predator-invulnerable megaherbivores in an intact African savanna at a variety of spatial scales. I examined the mechanistic links between trophic levels at the patch scale through fine scale empirical manipulation of predation risk. In addition, I assessed the landscape scale biological relevance of these trophic interactions through correlative observations over large spatiotemporal scales. I present the first evidence of community level trophic cascades explicitly involving megaherbivores. I demonstrate how megaherbivores’ disregard of predation risk masks the effects of predator-triggered trophic cascades and weakens their impact on the ecosystem. The risk of predation triggered a spatial response in vulnerable species, driving them into safe areas, yet did not influence the space use of megaherbivores. This species-specific spatial response had contrasting effects on nutrient distribution. Vulnerable herbivores’ fear-induced foraging behaviour led to localised nutrient accumulation whereas the foraging behaviour of predator-invulnerable megaherbivores led to nutrient redistribution across the landscape. In addition, the fear-driven spatial differences in mesoherbivore grazing impact and nutrient deposition led to landscape scale changes in the distribution and persistence of herbivore maintained grass communities, so-called grazing lawns. However, the grazing activity of the in-vulnerable megagrazer, white rhino (Ceratotherium simum) weakened the effect of this trophic cascade by creating and maintaining grazing lawns within the risky habitat avoided by mesograzers. This study contributes to our understanding of what drives the variation among patterns of trophic control and provides the first evidence of the modulating influence that megaherbivores have on predator-triggered trophic cascades.

Abstract I studied the ecology of the goshawk-grouse relationship in Oulu, northern Finland, during and outside the breeding season, by radio-telemetry. This included museum samples of goshawk to obtain a better ecological as well as a better evolutionary understanding of it. The proportion of grouse in the diet of goshawks has decreased since the 1960's, in accordance with the decline of grouse populations. The main prey groups replacing the lacking grouse were corvids, squirrels and hares. The proportion of grouse was highest in spring and it decreased towards the end of the nestling phase. The most preferred grouse species were hazel grouse Bonasa bonasia and willow grouse Lagopus lagopus. Preferences for different prey types are not explained by active choices of goshawk, but by changes in the vulnerability of the prey species. The nestling phase, when food demand is highest, is not adjusted to when prey supply is highest, but before it. The size and shape of the goshawks has changed from the 1960's. Adult males became smaller but females larger. Both became relatively longer winged and tailed. Decrease of male's size may be a response to the change in the food supply. Prey types replacing grouse are generally smaller, which may cause the change in the male's morphology. Females being less active during the breeding season may not be affected. For the female to be larger is advantageous in winter when they kill 'over large' prey like mountain hares Lepus timidus and capercaillie cocks Tetrao urogallus. Wintering goshawks were mainly females in adult plumage that tended to stay in the study area. However, only one third bred locally. More than one quarter of all hawks died during the study. Although known to be inhabitants of old forests, which this study supports, goshawks are fairly well adapted to mosaic landscape resulting from modern forestry, providing that suitable sized prey is available. Females have less problems, probably because hares, the main winter prey for females, are not affected negatively by forestry, like grouse and squirrels are, the main prey for males. Goshawks have a remarkable impact on grouse populations, especially when non-territorial hawks, 'floaters' are also included. About one half of the total mortality rate of grouse may be due to goshawk predation. Goshawk predation accords to predictions of general predation theory and may be a noticeable factor contributing to cyclicity in grouse.

Trap-jaw ants are characterized by high-speed mandibles used for prey capture and defense. Power-amplified mandibles have independently evolved at least four times among ants, with each lineage using different structures as a latch, spring and trigger. We examined two species from the genus Myrmoteras (subfamily Formicinae), whose morphology is unique among trap-jaw ant lineages, and describe the performance characteristics, spring-loading mechanism and neuronal control of Myrmoteras strikes. Like other trap-jaw ants, Myrmoteras latch their jaws open while the large closer muscle loads potential energy in a spring. The latch differs from other lineages and is likely formed by the co-contraction of the mandible opener and closer muscles. The cuticle of the posterior margin of the head serves as a spring, and is deformed by approximately 6% prior to a strike. The mandibles are likely unlatched by a subgroup of closer muscle fibers with particularly short sarcomeres. These fast fibers are controlled by two large motor neurons whose dendrites overlap with terminals of large sensory neurons originating from labral trigger hairs. Upon stimulation of the trigger hairs, the mandibles shut in as little as 0.5 ms and at peak velocities that are comparable with other trap-jaw ants, but with much slower acceleration. The estimated power output of the mandible strike (21 kW kg(-1)) confirms that Myrmoteras jaws are indeed power amplified. However, the power output of Myrmoteras mandibles is significantly lower than distantly related trap-jaw ants using different spring-loading mechanisms, indicating a relationship between power-amplification mechanism and performance.

Abstract I studied the structure of European breeding forest bird communities on several spatial scales focusing on heterospecific attraction among birds (i.e., the attraction of individuals to the company of interspecifics). Namely, I examined how heterospecific attraction affects habitat selection in migrant birds and the potential role of predation risk in enhancing heterospecific attraction during breeding with particular emphasis regarding the interaction between resident and migrant birds. Geographically, low densities and low relative proportions of resident titmice (Parus and Aegithalos spp.) were associated with harsh winter conditions. The densities of northern European titmice populations are suggested to be lower than expected on the basis of summer productivity potentially causing geographical variation with respect to the interactions between resident and migrant birds. As expected, the associations between titmice and migrants appear stronger and more positive in northern Europe than elsewhere. Heterospecific attraction in habitat selection among migrant species was studied both experimentally and theoretically. An increased density of titmice resulted in a higher number and abundance of migrant species than the removal treatment, suggesting that resident birds are used as cues for locating profitable breeding sites. From a theoretical perspective and under most conditions, the use of heterospecific cues proved to be a better habitat selection strategy than selection of sites based on direct assessment of the relative quality of habitat patches. Only when interactions (both positive and negative) between migrants and residents were weak and sampling costs of both strategies were about equivalent, did individuals using direct sampling gain in fitness. Heterospecific attraction during breeding in relation to predation risk was assessed by examining the spatial distribution of birds. Both experimentally increased perceived predation risk and naturally occurring predation risk created by the presence of sparrowhawk (Accipiter nisus) i.e., relative to the vicinity of nesting hawk, resulted in more clumped distribution of birds than areas of lower risk. Around sparrowhawks nest, however, clumping was apparent for only one forest type and only among study plots including both large (≥ 20 g, preferred prey) and small birds (< 20 g). To conclude, heterospecific attraction of migrants to resident birds contributes to the structure of local avian communities in forest landscapes. Heterospecific attraction among birds is strengthened by increased predation risk causing variation in species interactions when considered in a landscape perspective.

Landscape characteristics, disturbances, and temporal variability influence predator-prey relationships, but are often overlooked in experimental studies. In the Everglades, seasonal disturbances force the spatial overlap of predators and prey, potentially increasing predation risk for prey. This study examined seasonal and diel patterns of fish use of canals and assessed predation risk for small fishes using an encounter rate model. I deployed an imaging sonar in Everglades canals to quantify density and swimming speeds of fishes, and detect anti-predator behaviors by small fishes. Generally, seasonal declines of marsh water-levels increased the density of large fishes in canals. Densities of small and large fishes were positively correlated and, as small-fish density increased, schooling frequency also increased. At night, schools disbanded and small fishes were observed congregating along the canal edge. The encounter rate model predicted highest predator-prey encounters during the day, but access to cover may reduce predation risk for small fishes.