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Ungulate Populations (ungulate + population)
Selected AbstractsSpatial Association in a Highly Inbred Ungulate Population: Evidence of Fine-Scale Kin RecognitionETHOLOGY, Issue 2 2008Jorge Cassinello We present the first evidence of fine-scale kin recognition, based on a continuous measure of relatedness, in ungulates. The spatial association between herdmates of a captive population of aoudad (Ammotragus lervia), where all the individuals are related, is analysed during resting time. Our goal was to estimate which factors influence individuals' associations. The study population is highly inbred, although it does not show serious deleterious effects caused by consanguinity. It comprises a single captive herd, reproducing freely and in good conditions for more than 10 yr. It emerges that kin, measured as the coefficient of relationship between two given herdmates, is the main factor determining the spatial association (e.g. average distance) of male,male and female,female dyads, as more-related individuals tend to rest closer to each other than less-related ones. As for male,female dyads, individuals of a similar age tend to stay closer. To rule out any familiarity confounding effects, individuals' cohabitation time in the herd was added as a random factor in the analyses. Concerning the type of dyad, mother,calf dyads are characterized by higher proximity than others, particularly during the suckling period, whereas males tend to stay closer to each other than females or male,female dyads, being also more kin-related. Female social rank does not influence spatial association between herdmates. These results are related to group composition of the species in the wild, which are characterized by intense mother,calf bonds and all-male groups that are probably kin-related. It is seen that adult male,female associations are not related to kinship, but to age similarity, which is in accord with the assumption that main family groups in the wild are formed by matrilineal lines, whereas males are the dispersing sex. [source] On harvesting a structured ungulate populationOIKOS, Issue 3 2000E. J. Milner-Gulland Variation in demographic rates within a spatially structured population could have important consequences for management decisions, harvesting strategies and offtake rates. Although there is a growing body of evidence suggesting that demographic rates vary within populations over a range of spatial scales, there has been little research investigating the consequences of this variation for population management. In this paper, data on the dynamics of two female red deer sub-populations on Rum are analysed, and evidence is presented for differences between the fecundity and mortality rates of the two sub-populations. A simple harvesting model is developed to represent the dynamics of the two sub-populations, including density-independent migration between sub-populations and spatially correlated environmental variability. The highest monetary yield in the model is obtained by harvesting the more resilient sub-population at a higher rate. Surprisingly the losses involved in harvesting both sub-populations at the same rate are insignificant. However, if migration were density-dependent, the size of one sub-population would be more relevant to harvesting policy for the other sub-population. The results of this empirical study are compared to theoretical work on spatially structured populations; it is shown that when a species has complex age- and sex-structured population dynamics, previous theoretical results may not hold. [source] Estimating the growth of a newly established moose population using reproductive valueECOGRAPHY, Issue 3 2007Bernt-Erik Sæther Estimating the population growth rate and environmental stochasticity of long-lived species is difficult because annual variation in population size is influenced by temporal autocorrelations caused by fluctuations in the age-structure. Here we use the dynamics of the reproductive value to estimate the long-term growth rate s and the environmental variance of a moose population that recently colonized the island of Vega in northern Norway. We show that the population growth rate was high (,=0.26). The major stochastic influences on the population dynamics were due to demographic stochasticity, whereas the environmental variance was not significantly different from 0. This supports the suggestion that population growth rates of polytocous ungulates are high, and that demographic stochasticity must be assessed when estimating the growth of small ungulate populations. [source] Individual variation in reproductive costs of reproduction: high-quality females always do betterJOURNAL OF ANIMAL ECOLOGY, Issue 1 2009Sandra Hamel Summary 1Although life-history theory predicts substantial costs of reproduction, individuals often show positive correlations among life-history traits, rather than trade-offs. The apparent absence of reproductive costs may result from heterogeneity in individual quality. 2Using detailed longitudinal data from three contrasted ungulate populations (mountain goats, Oreamnos americanus; bighorn sheep, Ovis canadensis; and roe deer, Capreolus capreolus), we assessed how individual quality affects the probability of detecting a cost of current reproduction on future reproduction for females. We used a composite measure of individual quality based on variations in longevity (all species), success in the last breeding opportunity before death (goats and sheep), adult mass (all species), and social rank (goats only). 3In all species, high-quality females consistently had a higher probability of reproduction, irrespective of previous reproductive status. In mountain goats, we detected a cost of reproduction only after accounting for differences in individual quality. Only low-quality female goats were less likely to reproduce following years of breeding than of nonbreeding. Offspring survival was lower in bighorn ewes following years of successful breeding than after years when no lamb was produced, but only for low-quality females, suggesting that a cost of reproduction only occurred for low-quality females. 4Because costs of reproduction differ among females, studies of life-history evolution must account for heterogeneity in individual quality. [source] Feedback effects of chronic browsing on life-history traits of a large herbivoreJOURNAL OF ANIMAL ECOLOGY, Issue 4 2008M. Anouk Simard Summary 1Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4Rumen nitrogen content declined 22% between two time periods, 1977,79 and 2002,04, indicating a reduction in diet quality. 5After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977,79 than in 2002,04. Hind foot length did not vary between time periods. 6The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002,04 and in 1977,79. 7Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption. [source] Variable age structure and apparent density dependence in survival of adult ungulatesJOURNAL OF ANIMAL ECOLOGY, Issue 4 2003Marco Festa-Bianchet Summary 1Large herbivores have strongly age-structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density-dependent changes in age structure could lead to apparent density-dependence in adult survival. 2To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1 year at Chizé, France, ranged from 157 to 569. 3We used recent developments of capture,mark,recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account. 4Survival rates were 10,15% higher during the prime-age stage than during the senescent stage for all sex-species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account. 5In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure. [source] The role of males in the dynamics of ungulate populationsJOURNAL OF ANIMAL ECOLOGY, Issue 6 2002Atle Mysterud Summary 1In this review, we focus on how males can affect the population dynamics of ungulates (i) by being a component of population density (and thereby affecting interpretation of log-linear models), and (ii) by considering the mechanisms by which males can actively affect the demographic rates of females. 2We argue that the choice of measure of density is important, and that the inclusion or exclusion of males into models can influence results. For example, we demonstrate that if the dynamics of a population can be described with a first-order auto-regressive process in a log-linear framework, the asymmetry between the effects of females on the male dynamics and vice versa can introduce a second order process, much in the same way that the interaction between disease and host or predator and prey can. It would be useful for researchers with sufficient data to explore the affects of using different density measures. 3In general, even in harvested populations with highly skewed sex ratios, males are usually able to fertilize all females, though detailed studies document a lower proportion of younger females breeding when sex ratios are heavily female biased. It is well documented that the presence of males can induce oestrus in females, and that male age may also be a factor. In populations with both a skewed sex ratio and a young male age structure, calving is delayed and less synchronous. We identify several mechanisms that may be responsible for this. 4Delayed calving may lower summer survival and autumn masses, which may lead to higher winter mortality. If females are born light, they may require another year of growth before they start reproducing. Delayed calving can reduce future fertility of the mother. As the proportion of calves predated during the first few weeks of life is often very high, calving synchrony may also be an important strategy to lower predation rates. 5We argue that the effects of males on population dynamics of ungulates are likely to be non-trivial, and that their potential effects should not be ignored. The mechanisms we discuss may be important , though much more research is required before we can demonstrate they are. [source] Range expansion of the globally Vulnerable Karamoja apalis Apalis karamojae in the Serengeti ecosystemAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Philip Shaw Abstract The underlying causes of change in geographic range size are less well understood in African birds than in north temperate species. Here, we examine factors associated with range expansion in the Karamoja apalis (Apalis karamojae), a globally Vulnerable warbler confined to north-east Uganda, north-central Tanzania and southern Kenya. In Tanzania, it was originally known only from the Wembere Steppe, but since 1993 (and possibly as early as 1983) has extended its range into the Serengeti ecosystem, c. 140 km to the north, reaching southern Kenya by 2004. Changes in the warbler's range within the Serengeti have broadly reflected a cyclical change in the density of its main habitat, Acacia drepanolobium woodland, which was low in the 1970s, high during the 1980s and 1990s, and declined in the early 2000s. Karamoja apalis records in the Serengeti showed a 5 year time lag behind A. drepanolobium density, which was in turn negatively correlated with the area of grassland burnt 10 years earlier. Previous studies in the Serengeti have also linked Acacia regeneration to changes in grazing pressure, as increasing wildebeest (Connochaetes taurinus) numbers have reduced the volume of combustible material present, and hence the frequency of damaging ,hot burns'. We conclude that this globally threatened warbler appears to have benefited from changes in ungulate populations in the Serengeti, which have influenced burning intensity and hence tree regeneration. The warbler's range now appears to be declining, however, following a recent reduction in the density and annual survival of A. drepanolobium in the northern Serengeti. Résumé Les causes sous-jacentes du changement de la taille d'une distribution géographique sont moins bien connues pour les oiseaux africains que pour les espèces du nord tempéré. Nous examinons ici des facteurs liés à l'expansion de l'aire de répartition de l'apalis de Karamoja Apalis karamojae, un sylviidé classé comme Vulnérable au niveau mondial, confiné au NE de l'Ouganda, au centre-nord de la Tanzanie et au sud du Kenya. En Tanzanie, on ne le connaissait à l'origine que dans la steppe de Wembere mais depuis 1993, et peut-être même dès 1983, il a étendu son aire de répartition dans l'écosystème du Serengeti, environ 140 km plus au nord, et atteint le sud du Kenya en 2004. Les changements de l'aire de répartition de ce sylviidé dans le Serengeti reflètent largement un changement cyclique de la densité de son habitat principal, la forêt d'Acacia drepanolobium, qui était faible dans les années 1970, forte pendant les années 1980 et 1990, et qui a diminué au début des années 2000. Les rapports sur l'apalis de Karamoja au Serengeti montrent un retard de cinq ans par rapport à l'évolution de la densité d'A. drepanolobium, elle-même étant négativement liée à la zone de prairie brûlée 10 ans plus tôt. Des études antérieures faites au Serengeti lient aussi la régénération des acacias aux changements de la pression du pâturage, étant donné que le nombre croissant de gnous, Connochaetes taurinus, a réduit le volume des matières combustibles restantes et donc la fréquence des feux trop chauds qui causent beaucoup de dégâts. Nous concluons que cet oiseau menacé au niveau mondial semble avoir bénéficié des changements des populations d'ongulés au Serengeti, qui ont influencé l'intensité des feux et donc la régénération des arbres. L'aire de répartition de ce sylviidé semble pourtant en train de se réduire suite à une récente réduction de la densité et de la survie annuelle d'A. drepanolobium dans le nord du Serengeti. [source] Possible causes of decreasing migratory ungulate populations in an East African savannah after restrictions in their seasonal movementsAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Margje M. Voeten Abstract In many areas in Africa, seasonal movements of migratory ungulates are restricted and their population numbers decline, for example in the Tarangire region, Tanzania. Here, agriculture restricts migration of ungulates to their wet season ranges. We investigated whether low forage quality or supply are possible causes of population decline of wildebeest and zebra when access to these wet season ranges is restricted and migratory herds have to reside in the dry season range year-round. We simulated grazing through a clipping experiment in the dry season range during the wet season. Clipping negatively affected forage supply and had a positive effect on forage quality by increasing proportions of live and leaf biomass as well as nutrient concentrations in the leaves. However, increase in forage quality in the dry season range due to grazing was not as such that requirements of wildebeest during the wet season, when females are lactating, could be met. We conclude that low forage quality in the dry season range during the wet season could cause the decrease in migratory ungulate populations in the Tarangire region. With this study, the necessity of protecting wet season ranges from expanding human activities to safeguard migratory systems is supported. Résumé Dans de nombreuses régions d'Afrique, les déplacements saisonniers des ongulés migrateurs sont entravés et leurs populations déclinent, comme par exemple dans la région de Tarangire, en Tanzanie. Ici, c'est l'agriculture qui limite la migration des ongulés vers les domaines qu'ils fréquentent en saison des pluies. Nous avons étudié si la mauvaise qualité ou la faible quantité du fourrage étaient des causes possibles du déclin des populations de gnous et de zèbres lorsque l'accès à leur domaine de saison des pluies est limité et que les troupeaux migrateurs doivent rester dans les domaines de saison sèche toute l'année. Nous avons simulé le pâturage en menant, en saison des pluies, une expérience de tonte dans l'aire fréquentée en saison sèche. Couper l'herbe avait un effet négatif sur l'apport de fourrage et avait un effet positif sur la qualité du fourrage parce que cela augmentait la proportion de biomasse vivante et de feuilles ainsi que la concentration de nutriments dans les feuilles. Cependant, augmenter par le pâturage la qualité du fourrage dans le domaine de saison sèche n'était pas suffisant pour satisfaire les besoins des gnous en saison des pluies, lorsque les femelles sont allaitantes. Nous concluons qu'en saison des pluies, la qualité médiocre du fourrage dans le domaine fréquenté en saison sèche pourrait causer la diminution des populations d'ongulés migrateurs dans la région de Tarangire. Cette étude conforte la nécessité de protéger les domaines fréquentés en saison des pluies contre l'expansion des activités humaines, afin de sauvegarder les systèmes migratoires. [source] Restoring a keystone predator may endanger a prey species in a human-altered ecosystem: the return of the snow leopard to Sagarmatha National ParkANIMAL CONSERVATION, Issue 6 2009S. Lovari Abstract Twenty-five years ago, the snow leopard Uncia uncia, an endangered large cat, was eliminated from what is now Sagarmatha National Park (SNP). Heavy hunting pressure depleted that area of most medium,large mammals, before it became a park. After three decades of protection, the cessation of hunting and the recovery of wild ungulate populations, snow leopards have recently returned (four individuals). We have documented the effects of the return of the snow leopard on the population of its main wild prey, the Himalayan tahr Hemitragus jemlahicus, a ,near-threatened' caprin. Signs of snow leopard presence were recorded and scats were collected along a fixed trail (130 km) to assess the presence and food habits of the snow leopard in the Park, from 2004 to 2006. Himalayan tahr, the staple of the diet, had a relative occurrence of 48% in summer and 37% in autumn, compared with the next most frequent prey, musk deer Moschus chrysogaster (summer: 20%; autumn: 15%) and cattle (summer: 15%; autumn: 27%). In early summer, the birth rate of tahr (young-to-female ratio: 0.8,0.9) was high. The decrease of this ratio to 0.1,0.2 in autumn implied that summer predation concentrated on young tahr, eventually altering the population by removing the kid cohort. Small populations of wild Caprinae, for example the Himalayan tahr population in SNP, are sensitive to stochastic predation events and may be led to almost local extinction. If predation on livestock keeps growing, together with the decrease of Himalayan tahr, retaliatory killing of snow leopards by local people may be expected, and the snow leopard could again be at risk of local extinction. Restoration of biodiversity through the return of a large predator has to be monitored carefully, especially in areas affected by humans, where the lack of important environmental components, for example key prey species, may make the return of a predator a challenging event. [source] Effective size of harvested ungulate populationsANIMAL CONSERVATION, Issue 5 2009B.-E. Sæther Abstract The harvest of ungulate populations is often directed against certain sex or age classes to maximize the yield in terms of biomass, number of shot animals or number of trophies. Here we examine how such directional harvest affects the effective size of the population. We parameterize an age-specific model assumed to describe the dynamics of Fennoscandian moose. Based on expressions for the demographic variance for a small subpopulation of heterozygotes Aa bearing a rare neutral allele a, we use this model to calculate how different harvest strategies influence the effective size of the population, given that the population remains stable after harvest. We show that the annual genetic drift, determined by , increases with decreasing harvest rate of calves and increasing sex bias in the harvest towards bulls 1 year or older. The effective population size per generation decreased with reduced harvest of calves and increased harvest of bulls 1 year or older. The magnitude of these effects depends on the age-specific pattern of variation in reproductive success, which influences the demographic variance. This shows that the choice of harvest strategy strongly affects the genetic dynamics of harvested ungulate populations. [source] | ||||||||||