Letteratura scientifica selezionata sul tema "Acinonyx jubatus jubatus (schreber 1776)"

The extant genera of fur seals and sea lions of the family Otariidae (Carnivora: Pinnipedia) are thought to have emerged in the Pliocene or the early Pleistocene in the North Pacific. Among them, the Steller sea lion (Eumetopias jubatus) is the largest and distributed both in the western and eastern North Pacific. In contrast to the limited distribution of the current population around the Japanese Islands that is now only along the coast of Hokkaido, their fossil records have been known from the middle and late Pleistocene of Honshu Island. One such important fossil specimen has been recorded from the upper lower Pleistocene Omma Formation (ca. 1.36–0.83 Ma) in Kanazawa, Ishikawa Prefecture, Japan, which now bears the institutional number GKZ-N 00001. Because GKZ-N 00001 is the earliest fossil having been identified as a species of the sea lion genus Eumetopias, it is of importance to elucidate the evolutionary history of that genus. The morphometric comparisons were made among 51 mandibles of fur seals and sea lions with GKZ-N 00001. As results of bivariate analyses and PCA based on 39 measurements for external morphologies with internal structures by CT scan data, there is almost no difference between GKZ-N 00001 and extant male individuals of E. jubatus. In this regard, GKZ-N 00001 is identified specifically as the Steller sea lion E. jubatus. Consequently, it is recognized as the oldest Steller sea lion in the North Pacific. About 0.8 Ma, the distribution of the Steller sea lion had been already established at least in the Japan Sea side of the western North Pacific.

We measured individual growth, looked for evidence of weaning, and examined the interaction of these changes with diving behavior in young-of-year Steller sea lion (Eumetopias jubatus (Schreber, 1776)) pups in Alaska, USA, during their first winter. Steller sea lions employ an income breeding strategy, in which females provision their young over an individually variable period of months to years. Thus, we set out to identify whether these young sea lions showed evidence of weaning during the challenging winter months, describe the nature of their growth during this time, and examine their behaviors in light of these changes. Between 2005 and 2008, we captured 71 pups during early winter and recaptured 33 of these pups in early spring. Mark–resight and stable nitrogen isotope ratios in vibrissae indicated most pups remained nutritionally dependent on adult females throughout the winter. All pups increased both mass and lipid mass, with half of growth contributed by lipid mass. Changes in behavior were not correlated with growth excepting a weak but significant effect on rate of vertical travel. This study demonstrated that capture–recapture of Steller sea lion pups is possible, provided seasonal timing, locations, and age classes are carefully considered for their likelihood of capture success.

Pupping-site fidelity (defined as pupping within 5.8 m of a previous location in ≥2 years) in Steller sea lions ( Eumetopias jubatus (Schreber, 1776)) was investigated during the breeding seasons from 2001 to 2005 at Chiswell Island, a small rookery in the Gulf of Alaska. Density of females was minimal with 54–80 pups born. Photo-identification of individuals and GPS points, including elevation of the rookery, were used to determine locations of 297 births. Sixty-four percentage (35/55) of the females exhibited pupping-site fidelity, and mean frequency of site fidelity was greater for females that gave birth >3 times. Fifty percentage of the births occurred at 22% of the locations for all years, indicating that multiple births occurred at some locations throughout the breeding season. Competition or aggression among females for specific pupping locations before birth was not observed, and there was no temporal order of pupping locations used, indicating that the rookery was not overcrowded and that many suitable pupping locations existed. Multiparous females gave birth at significantly greater distances from the surf zone than primiparous females. Long-term monitoring of pupping-site fidelity in combination with other measures of maternal care will ultimately determine which factors have the greatest effect on pup survival.

Identifying factors that affect the timing of parturition among annual breeders is important to aid our understanding of how variations may adversely affect population trends over both short and long temporal scales. We investigated the effect of several parameters on the timing of parturition among individual Steller sea lions (Eumetopias jubatus (Schreber, 1776)) over 6 years between 2005 and 2016 using an information–theoretic approach. In addition to the random effect of year, birth and care of a pup in the previous year had the largest effect on parturition, causing a 2.4 day delay. Maternal age was negatively correlated with timing of parturition and male pups were born nearly a day earlier than female pups, on average. There was limited support for effects of sex and mass, with heavier pups born marginally earlier than lighter ones. This study illustrates some of the complexity of variables that can influence the timing of birth in this species and which should be considered in models that attempt to identify long-term trends in changing marine ecosystems.

To investigate the milk fatty acid composition of female Steller sea lions (Eumetopias jubatus (Schreber, 1776)) between and within maternal states (i.e., perinatal or foraging), milk samples were collected in 2010 and 2011 via gastric intubation from Steller sea lion pups on a small rookery in the central Gulf of Alaska. Maternal states of lactating females were determined upon reuniting with their sampled pups via remotely operated video cameras on the rookery. Milk fatty acid composition between Steller sea lion maternal states was significantly different, and thus can be utilized to distinguish between perinatal and foraging Steller sea lions of the same geographic region in the absence of direct observation. However, milk fatty acid composition remained relatively constant within perinatal Steller sea lions, suggesting steady mobilization of fatty acids from blubber to milk, and within foraging Steller sea lions, implying females forage on similar prey species within several days after their perinatal period. Differences in milk fatty acid composition between maternal states, including differences in the relative percentages of polyunsaturated fatty acids, may have important implications for growth and development of offspring.

Reduced juvenile survival caused by prey depletion is one hypothesis for the decline in the western Alaska population of Steller sea lions ( Eumetopias jubatus (Schreber, 1776)). To understand the exposure of young sea lions to these depletions, the swimming and diving behavior of pups, juveniles, and subadults was evaluated relative to prey behavior. Pups made shorter and shallower dives (13 m, 0.9 min) than juveniles or subadults, as expected based on physiological limitations, but juveniles and subadults dived to similar depths and durations (29 m, 1.7 min and 38 m, 2.0 min, respectively). Activity patterns of juveniles and subadults reflected diurnal prey migrations, while pup activity did not. Longitudinal trends in pup dive behavior reflected both physiological and behavioral development, while juvenile dive behaviors reflected seasonal changes in prey availability. Results suggest that adult females must continue to provide nutritional support to pups during winter because of the limited diving ability of these young animals. For this reason, the flexible lactation strategies that allow for longer nursing periods during periods of low prey availability and reduce female fecundity may improve juvenile survival.

Large carnivores play a key role in regulating terrestrial ecosystems and their removal can cause effects that cascade through the lower trophic levels. Despite this, the geographic range and density of most large carnivore species are declining globally due to anthropogenic factors. Large carnivores are particularly difficult to conserve because they often come into conflict with humans, have large ranges, normally occur at low densities and are not confined to protected areas. This is particularly true for Vulnerable cheetahs Acinonyx jubatus and Endangered African wild dogs Lycaon pictus that are two of the widest ranging carnivores and are threatened by killing due to conflict, habitat fragmentation and snaring. Wild dogs are further susceptible to being killed on roads and cheetahs are often traded into captivity. Conservation planning for cheetahs and wild dogs in South Africa is hampered by a lack of information on suitable habitat for conservation action and connectivity between these habitats. Ecological niche models show that there are 21 410km2 of suitable habitat for both species in South Africa, both inside and outside of their current distribution ranges. Key areas are identified for conflict mitigation work, reintroduction projects and range expansion. With the exception of the Kruger National Park, the current protected area network is inefficient in conserving cheetah and wild dog habitat. To supply relevant information for conservation action, the range use of cheetahs outside of protected areas was investigated. Male home ranges ranged from 121.5 km2 to 607 km2 while females ranged from 14.7 km2 to 703.3 km2. Cheetahs utilised several ranches and mean home ranges sizes were larger than mean ranch size. This provides valuable and relevant information on cheetahs and aids conservation practitioners in mitigating human-cheetah conflict on South African farmland. The Kruger National Park is a stronghold for cheetah and wild dog conservation in South Africa thus monitoring the status of these populations is important. Tourist photographic surveys were used to obtain data for photographic-based capture-recapture analysis for open populations. Results show that 412 (329-495; SE 41.95) cheetahs and 151 (144-157; SE 3.21) wild dogs occur in the Kruger National Park. Cheetah capture probabilities were affected by time (number of entries) and sex, whereas wild dog capture probabilities were affected by the region of the park. The cheetah population of Kruger appears to be healthy, while the wild dog population size and density are of concern. Because cheetahs and wild dogs have been extirpated from most of South Africa, reintroduction programmes have resulted in cheetahs and wild dogs being introduced into fenced reserves. These are fragmented from each other and populations need to be managed to ensure demographic and genetic integrity. The survival of cheetahs introduced into reserves from the free roaming population was examined using data from 29 reserves and 189 cheetahs: 92 adults: 59 males and 33 females, plus 94 cubs born on the reserves. The Kaplan-Meier (product limit) estimator with staggered entry (Pollock et al. 1989) was used and the mean annual survivorship for all cheetahs, including cubs born, was 82.8%. The final survivorship value for all adult cheetahs was 0.23 and for cubs was 0.04. Cubs had significantly higher survival on reserves where other competing predators were absent. The median survival time was 38 months for adult males and more than 53 months for adult females. Cheetah and wild dog conservation needs to be addressed in three key geographically areas due to the different challenges and management interventions required: 1) free roaming populations outside of protected areas, 2) the Kruger National Park and 3) reintroduced populations in fenced reserves. Each area provides unique opportunities and challenges for conservation of these species.
Thesis (PhD)--University of Pretoria, 2015.
Animal and Wildlife Sciences
PhD
Unrestricted