首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 140 毫秒
1.
In many ungulates, female fecundity is influenced by weather, population density and body condition. Based on a six-year survey of the reproductive tracts of adult female roe deer (Capreolus capreolus) harvested in the province of Pisa (Tuscany, central Italy), we evaluated the influence of weather, population density and individual characteristics on pregnancy rates. Eighty-five percent of females were pregnant, with a median litter size of two (range one—three). We found that pregnancy rate was positively correlated with summer rainfall and body mass of females, whereas early-winter conditions, spring rainfall, the age of females and density-dependent factors did not appear to influence pregnancy rate. These results reflect the particular seasonal variation in the abundance and quality of resources in Mediterranean habitats and show that heavier females (high-quality mothers) are more productive than lighter females.  相似文献   

2.
Summer diet, summer temperature, length of the growth season and animal density appeared to best explain annual and regional differences in calf and yearling body mass in moose from southeastern Norway. In general animals inhabiting steep, alpine landscapes had less body mass than animals using flat, low-altitude habitats. Autumn body mass of calves and yearlings decreased with increasing snow depth during the preceding winter and spring. However, calf body mass was more influenced by the summer range and less by the winter range than was body mass of yearlings. There was no indication that the effect of snow depth on autumn body mass was greater in moose living on poor than on good summer ranges. Body mass decreased with increasing competition for summer forage, while the winter range mainly had an density-independent effect. Habitat quality, expressed as regression lines between calf and yearling body mass and animal density (hunting yield), differed between regions. On ranges of medium and high altitude where birch (Betula spp.) rowan (Sorbus aucuparia) and bilberry (Vaccinium myrtillus) dominated moose summer diet, body mass decreased at a rapid rate with increasing animal density. Body mass decreased at a slower rate at low-altitude ranges and at high-altitude ranges where willow (Salix spp.) and forbs dominated the diet. Body mass of lactating cows decreased with increasing animal density, but animal density did not affect body mass of non-lactating cows. There was no indication that the decrease in autumn body mass with increasing moose density over the last 25 years has caused a decrease in animal condition (ability to survive the winter). The results are discussed in relation to the effect of summer and winter range on population regulation in moose. It is concluded that a density-dependent effect is apparent on the summer range even at low and intermediate population densities. On the winter range, on the other hand, density-dependence is likely to occur only at high levels of population density. Received: 4 February 1997 / Accepted: 1 February 1999  相似文献   

3.
A capture-recapture design was applied between January 1989 and June 1991 in a 37 5 ha area located in the central valley of the Tiber River (Latium), aimed at estimating the demographic parameters of a coypu population in the Mediterranean climate and at preliminarily investigating the factors that regulate its numbers in this region The population fluctuated between 27 and 137 individuals and followed a seasonal pattern It decreased after the winter and increased between summer and winter Density remained almost stable during a particularly mild winter Survival rates remained relatively high over the entire study period, reproductive activity and additions to the population from in situ reproduction, however, showed minimum peaks following colder winters Evidence of immigration was detected during periods of increasing density Key factor and preliminary density dependence analyses showed that pregnancy failure and newborn losses are cumulatively the most important factor contributing to varation in total mortality, and are positively related to coypu numbers in previous periods The failure to realize maximum potential fecundity is inversely related to previous coypu abundance We show that post-recruitment losses play only a minor role in determining population decline  相似文献   

4.
We assessed body condition, diet quality (indexed by fecal nitrogen), and stress levels (using fecal glucocorticoid metabolites) in mule deer Odocoileus hemionus in southeastern Idaho, USA, during a mild (2007) and a harsh winter (2008) to evaluate spatial overlap and potential competition with North American elk Cervus elaphus. We used data from GPS telemetry to construct spatially explicit maps of local population density of elk for January–April. Loss of body condition over winter in yearling and adult female mule deer was not related to elk density but to winter severity. Fecal nitrogen increased as winter progressed in both winters, was significantly lower during 2008 than in 2007, but was not related to local population density of elk. In the mild winter of 2007, a significant positive relationship existed between local population density of elk and fecal glucocorticoid metabolite levels of mule deer, indicating increased physiological stress among mule deer wintering in close proximity to elk. Fecal glucocorticoid metabolite levels in deer were lower in 2008 than in 2007 and exhibited no significant relationship with elk density. Declining fecal glucocorticoid levels through winter may be typical of northern cervids. No difference existed in levels of fecal glucocorticoids between sexes of deer. A reduction in elk populations may not improve diet quality, physiological stress levels, or body condition of mule deer on winter range, especially during severe winters. Consequently, management and conservation of winter habitat are more likely to benefit mule deer than would altering density of elk.  相似文献   

5.
Don R. Levitan 《Oecologia》1988,76(4):627-629
Summary This study documents size- and density-dependent growth (positive and negative), in the sea urchin Diadema antillarum. In the summer of 1983, an inverse relationship was found between Diadema test diameter and population density at seven sites in Lameshur Bay, St. John, United States Virgin Islands. The regression of this relationship improved when test diameter was plotted against density per unit grazing area. A field experiment demonstrated that 1) Diadema has the ability to reduce skeletal body size, and 2) direction (growth or shrinkage) and rate of growth can be predicted accurately based on the urchin's body size and population density. The ability to adjust body size as density fluctuates may allow Diadema to persist when density increases, by shrinking and reducing metabolic costs, and to take advantage of decreases in density, by increasing in size and fecundity.  相似文献   

6.
Dynamics of a harvested moose population in a variable environment   总被引:8,自引:1,他引:7  
1. Population size, calves per female, female mean age and adult sex ratio of a moose ( Alces alces ) population in Vefsn, northern Norway were reconstructed from 1967 to 1993 using cohort analysis and catch-at-age data from 96% (6752) of all individuals harvested.
2. The dynamics of the population were influenced mainly by density-dependent harvesting, stochastic variation in climate and intrinsic variation in the age-structure of the female segment of the population.
3. A time delay in the assignment of hunting permits in relation to population size increased fluctuations in population size.
4. Selective harvesting of calves and yearlings increased the mean age of adult females in the population, and, because fecundity in moose is strongly age-specific, the number of calves per female concordantly increased. However, after years with high recruitment, the adult mean age decreased as large cohorts entered the adult age-groups. This age-structure effect generated cycles in the rate of recruitment to the population and fluctuations introduced time-lags in the population dynamics.
5. An inverse relationship between recruitment rate and population density, mediated by a density-dependent decrease in female body condition, could potentially have constituted a regulatory mechanism in the dynamics of the population, but this effect was counteracted by a density-dependent increase in the mean age of adult females.
6. Stochastic variation in winter snow depth and summer temperature had delayed effects on recruitment rate and in turn population growth rate, apparently through effects on female body condition before conception.  相似文献   

7.
Reindeer/caribou (Rangifer tarandus), which constitute a biological resource of vital importance for the physical and cultural survival of Arctic residents, and inhabit extremely seasonal environments, have received little attention in the global change debate. We investigated how body weight and growth rate of reindeer calves were affected by large-scale climatic variability [measured by the North Atlantic Oscillation (NAO) winter index] and density in one population in central Norway. Body weights of calves in summer and early winter, as well as their growth rate (summer to early winter), were significantly influenced by density and the NAO index when cohorts were in utero. Males were heavier and had higher absolute growth than females, but there was no evidence that preweaning condition of male and female calves were influenced differently by the NAO winter index. Increasing NAO index had a negative effect on calves' body weight and growth rate. Increasing density significantly reduced body weight and growth rate of calves, and accentuated the effect of the NAO winter index. Winters with a higher NAO index are thus severe for reindeer calves in this area and their effects are associated with nutritional stress experienced by the dams during pregnancy or immediately after calving. Moreover, increased density may enhance intra-specific competition and limits food available at the individual level within cohorts. We conclude that if the current pattern of global warming continues, with greater change occurring in northern latitudes and during winter as is predicted, reduced body weight of reindeer calves may be a consequence in areas where winters with a high NAO index are severe. This will likely have an effect on the livelihood of many northern indigenous peoples, both economically and culturally.  相似文献   

8.
Density dependence of reproduction has generally been proposed to be caused by habitat heterogeneity and by the individual response of reproductive output. However, a further mechanism might generate density dependence of average reproductive rates. High density situations might be associated with a high proportion of first-season breeders which often show a principally lower reproductive performance. We tested for the existence of the latter mechanism as well as for density-dependent individual changes of reproductive effort in a population of European rabbits living in a homogeneous grassland habitat. The study was conducted over a period of eleven years. Overall, a strong relationship between mean reproductive rates and the breeding density of females was apparent. All necessary conditions for the presence of a density-dependent effect caused by age-dependent reproduction were fulfilled: Fluctuations of breeding density were paralleled by variations in the proportion of one-year-old females. These one-year-old, first-season breeders showed a consistently lower reproductive performance than older females, which might be caused by their lower body mass and their lower social rank. However, we also found strong evidence for density-dependent response of individual reproductive effort: Individual changes in fecundity over successive years were explained by changes in the breeding density of females. The results suggest that density dependence of reproduction in European rabbits is due to an interaction of age-dependent reproductive performance together with short-term fluctuations in breeding density, and a density-dependent, individual based response of reproductive rates. We further conclude that the lower reproductive performance of first-season breeders in age-structured animal populations may contribute substantially to interannual, and under particular circumstances to density-dependent variations of mean reproductive rates.  相似文献   

9.
Theory on density-dependent habitat selection predicts that as population density of a species increases, use of higher quality (primary) habitat by individuals declines while use of lower quality (secondary) habitat rises. Habitat partitioning is often considered the primary mechanism for coexistence between similar species, but how this process evolves with changes in population density remains to be empirically tested for free-ranging ungulates. We used resource-selection functions to quantify density effects on landscape-scale habitat selection of two sympatric species of ungulates [moose (Alces alces) and elk (Cervus canadensis manitobensis)] in Riding Mountain National Park, Manitoba, Canada (2000–2011). The density of elk was actively reduced from 1.2 to 0.4 elk km?2 through increased hunting effort during the period of study, while moose density decreased without additional human influence from 1.6–0.7 moose km?2. Patterns of habitat selection during winter by both species changed in accordance to expectations from density-dependent habitat-selection theory. At low intraspecific density, moose and elk did not partition habitat, as both species selected strongly for mixed forest (primary habitat providing both food and cover), but did so in different areas segregated across an elevational gradient. As intraspecific density increased, selection for primary habitat by both species decreased, while selection for secondary, lower quality habitat such as agricultural fields (for elk) and built-up areas (for moose) increased. We show that habitat-selection strategies during winter for moose and elk, and subsequent effects on habitat partitioning, depend heavily on the position in state space (density) of both species.  相似文献   

10.
Life-history traits are influenced by environmental factors throughout the lifespan of an individual. The relative importance of past versus present environment on individual fitness, therefore, is a relevant question in populations that face the challenge of temporally varying environment. We studied the interacting effects of past and present density on body mass, condition, and survival in enclosure populations of the bank vole (Myodes glareolus) using a reciprocal transplant design. In connection with the cyclic dynamics of natural vole populations, our hypothesis was that individuals born in low-density enclosures would do better overwintering in low-density enclosures than in high-density enclosures and vice versa. Our results show that the effect of summer (past) density was strong especially on survival and body mass. The response of body mass to summer density was negative in both winter (present) density groups, whereas the response of survival probability was nonlinear and differed between the winter density groups. In particular, our data show a trend for higher overwintering success of individuals originating from the lowest summer densities in low winter density and vice versa. We therefore conclude that the capacity of individuals to respond to a change in density was constrained by the delayed density-dependent effects of environment experienced in the past. These effects have the potential to contribute to vole population dynamics. Possible mechanisms mediating the effects of past environment into present performance include both intrinsic and environmental factors.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号