Thesis (Ph. D.)--University of Chicago, Dept. of Ecology and Evolution, August 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Abstracted in Dissertation abstracts, v. 16 (1956) no. 2, p. 410-411. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 116-121).

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

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

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.

Thesis (M.S.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 63-105). Also available via the World Wide Web.

Males produce conspicuous advertisement signals to attract mates. These signals, however, often attract eavesdropping predators as well, so the benefit of obtaining a mate is balanced by the cost of an increased risk of predation. The evolution of sexual advertisement signals can be understood only through a thorough investigation of both predator and prey. The Neotropical bat, Trachops cirrhosus, feeds on frogs and uses frog mating calls to locate its prey. On the basis of frog calls alone, bats can assess which frogs are palatable and which are poisonous. The túngara frog, Physalaemus pustulosus, produces two types of calls, simple and complex. Both female frogs and frog-eating bats prefer complex calls to simple ones, and as a result, male frogs face opposing forces of sexual and natural selection. While there has been extensive study of mate choice behavior in the túngara frog, there has been comparatively little investigation of foraging behavior in the frog-eating bat. In my doctoral research, I investigate the sensory constraints and cognitive flexibility that shape foraging success in T. cirrhosus. Specifically, I address the following questions: (1) Are predator preferences for signal complexity influenced by localization performance? Do bats show better localization performance for complex calls than simple ones in silence, in noise, or in obstacles? (2) How fixed are predator associations for prey cues? Given novel foraging contexts, can predators rapidly track prey changes and alter pre-existing associations between prey cues and prey quality? (3) What mechanisms do predators use to learn about prey cues? Do social interactions play a role in prey acquisition behavior? My results show that while T. cirrhosus is limited by biophysical constraints in its ability to localize prey, within these constraints it shows surprising flexibility. It can rapidly alter associations between prey cues and prey quality, and can quickly acquire novel foraging behavior via social learning. Together these studies offer new insights on the role of eavesdropping predators in the evolution of their sexually advertising prey, and shed new light on the role of learning in foraging success. / text

No description available.

The character and magnitude of predation by Calliopius laeviusculus on the intertidal eggs of capelin (Mallotus villosus) were examined. Average endobenthic densities at Bryant's Cove (NFLD) in 1988 for both amphipods and capelin eggs during capelin egg development (June 17-August 8) were 0.78 amphipods cm$ sp{-2}$ and 62 eggs cm$ sp{-3}$ (750 cm$ sp{-2}$) respectively. At this average capelin egg density, laboratory results suggest that, on a daily basis, only gut capacity and clearance time limit amphipod predation on eggs. In situ, C. laeviusculus biomass closely tracked capelin egg biomass indicating that reproductive cues operating for both capelin and amphipods may be linked. In 1988, ca. 50% of the annual production of C. laeviusculus resulted from predation on capelin eggs. Given the bioenergetic demands of C. laeviusculus and the annual variation in capelin spawning effort, the temporal overlap between capelin eggs and high amphipod biomass could result in predation mortalities ranging from ca. 15-30% of the total capelin egg deposition.

No description available.