Much of the decline of the U.S. sheep industry has been attributed to losses caused by predators. Most predatory losses are inflicted on lambs rather than ewes. Losses have historically ranged from 4-8% of lamb crops, inflicting significant financial loss on ranchers. However, most research providing data on sheep predation is over 20 years old. Changes in the sheep industry as well as predation rates may make previous loss rates inapplicable to current conditions. Coyotes (Canis latrans) are the primary predator of concern when it comes to sheep losses, but increasingly, cougars (Felis concolor) and black bears (Ursus americanus) are reported to be responsible for an increased proportion of lamb losses. I replicated a sheep depredation study conducted during the early 1970s in southwestern Utah and compared the results of the two studies to reassess losses and the predator species responsible for those losses. Total lamb losses to all causes in my study were comparable to losses reported in the 1970s as well as categories of verified and estimated predator losses. There was a significant variation in lamb losses between the 2 years of my study due to an increase in predator kills on sheep. Cougar and bear depredations occurred at significantly higher rates during my study than during the 1970s but did not produce an additive effect to overall predator losses. Most lambs killed by predators were located on or near pasture bed grounds as reported by other studies, but a large number were found >500 m from bed grounds. Rough terrain and scavenging by California condors (Gymnogyps californianus) made location of missing sheep difficult. The ability of cougars and bears to remove sheep carcasses from kill sites made the finding of sheep carcasses more difficult and caused an underreporting of sheep killed by these predators. I found that the loss of sheep to predation continues to be a problem for the sheep industry and its magnitude was unchanged from historic predation levels.

During the last two decades, a broad spectrum of short- and long-term studies on different taxonomic groups has enriched our understanding about how dynamics of taxonomic and ecological diversification have changed through geologic time. There are two major issues that have impacted these studies: the quality and quantity of data used are often insufficient in various ways and the methods used may produce results that are more equivocal than supposed. To investigate these issues more fully, this dissertation focuses on studies on two major aspects: 1) short-term studies examining the nature of successful and unsuccessful predatory attacks on Plio-Pleistocene bivalves; and 2) a Phanerozoic-scale project examining trends in bivalve richness and ecological differentiation. The short-term studies, focusing on shell-breaking predation on bivalves, have shown that the existing methodologies which only study either successful or unsuccessful component of predation in isolation are fraught with potential issues in developing effective interpretations. When these two components (i.e., successful and unsuccessful) are studied in tandem as was done here, however, traces of predation can be used to better constrain potential paleoecological interpretations related to predation intensity, predator's attack strategies, and predator-prey dynamics. The long-term project includes two Phanerozoic studies on bivalves' taxonomic and ecological richness. The taxonomic study has shown how the elements included in various datasets used can affect the Phanerozoic richness trajectory of bivalves. The revised and newly compiled dataset developed here reveals that bivalves showed three major episodes of diversification - a Ordovician radiation of orders and families, a Mesozoic diversification of families, and a dramatic Cenozoic rise in the total number of genera - all of which were synchronous with ecological diversification in terms of appearances of new life forms capable of colonizing new ecospace (i.e., cubes). However, these synchronous changes in taxonomic-ecologic richness were influenced by many biotic (e.g., predation, competition, and adaptive innovations) and abiotic (e.g., nutrient availability, sea level, and temperature) components, for which I propose a multilevel mixed model such that all these components can be studied in tandem.

This study focused on the interactions between small skinks and their major predators/competitors (birds) and prey (arthropods) in core and edge areas of small, long established remnant Cumberland Plain woodlands of Richmond, New South Wales, Australia. Eight study sites were selected (4 edge and 4 core) within the peri-urban environment to compare the abundance and diversity of small skinks, birds and arthropods. Of the three taxa, only arthropods maintained a similar abundance and diversity between edge and core areas. Birds and skinks were either in lower numbers in the perimeter areas (skinks), or were interior/perimeter specialists (birds). Arthropod diversity and abundance of preferred skink prey, was also examined. It was concluded that the distribution of arthropod prey was similar between core and edge areas, and therefore, was not considered to have an influence on small skinks’ ability to inhabit edges. However, large, aggressive/noisy birds (including skink and small bird predators) dominated edge areas. Those birds encountered in the edge foraged in a variety of niches, such as on the ground or they swooped from vantage points. This, coupled with other anti competitor behaviour (e.g. noise, aggression, flocking), placed these birds in proximity to skinks in the edge areas. However, as most of these birds were also predators of skinks, it was concluded that the evidence supported a predator/prey relationship in the perimeter area, rather than a competitive one. This was supported by predation rates on skinks, using decoys. Birds preyed on small skink in greater numbers in the perimeter of woodland remnants than in their interior. This predation pressure was sustained throughout the year. It was concluded that predation and/or displacement of skinks and small birds resulted in lower numbers being observed in edge compared to core areas. This study demonstrated that old, small remnants not continually exposed to major disturbances (e.g. logging, agricultural practices) can re-establish stability in terms of environmental conditions. However, a stable environment or a single taxonomic group does not necessarily predict the response individual taxa will have to edge habitats and that this can alter the interactions between dependent groups such as prey/predator or competitors. . / Doctor of Philosophy (PhD)

Many organisms with complex life cycles undergo transition periods associated with increased vulnerability to predation. Several evolutionary adaptations have been proposed as antipredator defenses for organisms during risky transition periods. These include: shortening of the transition period, parental care, cryptic coloration, and synchrony of risky transitions with large numbers of conspecifics. The results of my research support the hypothesis that synchrony of metamorphosis and emergence from the water and aggregation during the period of transformation may be antipredator defenses for the western toad (Bufo boreas). For some anuran species, synchronous metamorphosis may function as an antipredator adaptation by swamping predators during the period of transformation. I examined the levels of synchrony of emergence from the water of metamorphosing western toads (Bufo boreas) in the presence and absence of a live snake predator, the common garter snake (Thamnophis sirtalis) in a laboratory experiment. To compare between the treatments, I measured the time to emergence from the water, the number of metamorphs emerging together, and the level of aggregation (before and during emergence) of the toads in each treatment. There was a difference between the treatments when all three factors were considered. I attributed these differences to a behavioral response in which B. boreas emerged sooner in the presence of the predator, regardless of whether individual toads had reached the point at which they were physically better suited to the terrestrial environment than the larval environment. Since the Pacific treefrog (Hyla regilla) is also preyed upon by T. sirtalis during the vulnerable period of metamorphosis, I conducted a laboratory experiment to test the effects of the presence of T. sirtalis on 1) aggregation of larval and metamorphosing H. regilla, 2) time to metamorphosis, 3) synchrony of metamorphosis, 4) time to emergence from the water and 5) synchrony of emergence from the water. The only significant effect observed in this experiment was a difference between aggregation levels of H. regilla throughout the experiment. There was, however, a strong trend in which the variances around the mean times to metamorphosis and emergence of the frogs in the control treatments were larger than those in the predator treatments. This could indicate a trend toward synchrony of metamorphosis and emergence for H. regilla in the presence of snake predators. / Graduation date: 1998

Thesis (Ph. D.)--University of Washington, 1985. / Vita. Includes bibliographical references.

Terrestrial mammals affect numerous aspects of plant demography, colonization, and community structure in Neotropical forests. Granivorous mammals destroy seeds via seed predation and seedlings through herbivory, negatively affecting plant fitness. Mammals can also positively affect plants by dispersing or hoarding seeds. Seed fate outcomes are contingent on the interaction between mammal seed handling strategies and the intrinsic anti-predation defenses possessed by seeds. In field experiments at La Selva Biological Station, I investigated how collared peccaries (Pecari tajacu) and Central American agoutis (Dasyprocta punctata) affect five species of large seeds that have various defenses against predation. Overall, peccaries consumed and killed most non-defended and chemically-defended seeds but they could not destroy seeds with physical defenses. Agoutis killed non-defended and physically-defended seeds, but not seeds with chemical defenses. Using seeds of Mucuna holtonii, I investigated how chemical and structural defenses deter mammal and insect seed predation respectively. I also determined how endosperm removal by invertebrates affects seed germination and seedling biomass. Chemical defenses protected seeds from rodents, but not ungulates that digest seeds via pregastric fermentation. Physical defenses protected seeds from invertebrate seed predators, and removal of endosperm negatively affected both seed germination and seedling growth. To determine how scatter-hoarding by agoutis affects seed escape from seed predators, germination, and seedling growth, I created simulated agouti hoards. I also investigated how mammals affect young seedling survival. Hoarding enhanced seed survival, germination, and seedling growth for most species of seeds. Terrestrial mammals killed some seedlings via seed predation rather than by herbivory. Overall, large mammal activity in La Selva negatively affected seed and seedling survival and this likely influences many aspects of forest dynamics.

A model of a three species intraguild predation community is proposed. The model is realized as a system of cross-diffusion equations which allow the intraguild prey species to adjust its motility based on local resource and intraguild predator densities. Solutions to the cross-diffusion system are shown to exist globally in time and the existence of a global attractor is proved. Abstract permanence theory is used to study conditions for coexistence in the ecological community. The case where the intraguild prey disperses randomly is compared to the case where the intraguild prey disperses conditionally on local ecological fitness and it is shown that the ability of the intraguild prey to persist in the ecological community is enhanced if the intraguild prey utilizes a movement strategy of avoiding areas with negative fitness. A finite element scheme is used to numerically simulate solutions to the system and confirm the analytical results.

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

Nesting success is an important vital rate affecting the reproductive fitness of birds, and predation typically is the single most important factor affecting nesting success. Presumably, birds should nest in locations that maximize nest survival. If specific nest characteristics increase the probability that a nest will hatch, natural (phenotypic) selection could favour use of sites with these features, producing nonrandom patterns of nest site use. Alternatively, birds that are highly selective in nest site choices might be at a disadvantage if predators learn to forage preferentially in these locations and improve their efficiency in depredating nests; in this case, random nesting patterns could be favoured. Finally, it has been hypothesized that predation pressure can influence nest site selection patterns of entire bird communities. If predators develop a search image to hunt for bird nests, then nests that are most similar to each other, irrespective of species, should sustain higher mortality. To evaluate these hypotheses, I quantified nest site selection patterns of multiple species of ground-nesting dabbling ducks in areas where predation pressure was normally high, and compared these patterns to those on areas where predation was relaxed. Predation pressure was experimentally reduced by removing common predators of duck nests and females (mainly red foxes, coyotes, skunks and raccoons) on some study areas and not on others (controls). Predator removal and natural causes produced a 10-fold difference in duck nesting across study sites, allowing for investigation of effects of predation pressure on nest site selection of ducks. Coarse scale habitat selection patterns were similar to results reported in previous studies; blue-winged teal and northern shoveler were found more often in native grassland than in other habitat types, while gadwall and mallard nests occurred more frequently in shrub patches when compared with other habitat patches. A difference in nest site characteristics was observed between hatched and depredated nests for gadwall and northern shoveler but not for blue-winged teal and mallard. However, in all species, the nest site selection patterns were non-random. Thus, the process of nest predation did not shape patterns of nest site choice. Contrary to predictions, inter-specific overlap in nest site features was not related to predation pressure: nests that overlapped most with features of other species did not suffer higher predation, nor did inter-specific overlap in nest characteristics decrease during the nesting season. These findings were inconsistent with the hypothesis that community-level patterns of nest site use are differentiated as a result of predation pressure. Long-term work on nest site use by individually marked females of numerous ground-nesting bird species would be informative, as would experimental studies of other hypotheses about factors affecting nest site choices in birds.

The geographical distribution of the Gulf of Bothnia zooplankton species is presented together with observations of abundancies and vertical distributions. The historical development of this plankton community in the last 70 years is discussed.Spring and summer development of the plankton fauna was studiedin the Bothnian Bay. Compared to in southern parts of the Balticit could be shown that the start of development in spring formany species was only moderately later in the Bothnian Bay. Theperiod of maximal biomass was in late summer and autumn.In a study of horizontal distribution large between-station variations were found. These variations were not random as close stations formed homogenous groups. Several cases of patchiness were established. Systematically appearing differences in age-distributions were proposed as a factor in the formation of patchiness.The selective prédation on zooplankton by Baltic herring was studied in the Bothnian Bay. Besides chosing certain species herring selects the older and larger stages of these species. Egg-bearing Eurytemora females were more heavily preyed upon than the males.From literature information and own observations it was proposed that in sence of production the Bothnian Bay and the Bothnian Sea are two very different systems. Climatic effects cause a delay of primary production in spring enabling the pelagic consumers to develop in phase with the producers in the Bothnian Bay. Contrary to systems with a spring peak in phytoplankton growth this situation will lead to high pelagial efficiency leaving little to feed the benthic communities. / digitalisering@umu