首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 250 毫秒
1.
A large body of studies have linked sexual segregation in dimorphic ungulates with differential resource selection and nutritional requirements of the sexes. However, detailed patterns of sexual dietary preferences have rarely been assessed as keystone mechanisms of sexual segregation. We compared diet and nutritional selection by 3 sex-age classes in the Iberian red deer (Cervus elaphus hispanicus Hilzheimer) across reproductive states and according to seasonal fluctuations in resource availability in a Mediterranean environment. Foraging segregation between sexes was found during rut when female/juvenile selection of shrubs was higher than that of males. Observed foraging patterns relate to a stronger selection of nitrogen, tannins and lignin by females and juveniles, and fibres by males. Our findings are associated to the Mediterranean climate, where rut and lactation concur with a shortage period, the particularly dry summer. Foraging segregation between sexes during the rut could be shaped by a conjunction of factors such as the low quality of resources and different fitness enhancement strategies. We highlight both the importance of including the dietary component and providing a temporal framework when documenting ungulate sexual segregation, and the interest of considering regional conditions when addressing management of ungulates with a wide distribution.  相似文献   

2.
We studied the feeding ecology of the Andean hog-nosed skunk (Conepatus chinga) in three areas with different land use in Patagonia. Two areas were heavily grazed by sheep or horses and wild exotic herbivores and the third area was lightly grazed by cattle. In each area, we assessed skunk diet, prey abundance and carrion availability. Skunks were generalist feeders, with invertebrates composing the bulk of their diet, but also consumed small vertebrates and carrion. Differences in diet composition were found among areas, mainly because skunks consumed more beetle larvae in the sheep area and more cricetines and spiders in the exotic-herbivore area. All prey but rodents were significantly more abundant in spring and summer than in fall and winter, but skunk diets were similar among seasons. In the sheep area, where the soil was most disturbed, we found reduced abundances of invertebrate prey and rodents. High consumption of beetles during autumn and winter when these were least abundant and in the sheep area indicates that skunks had a preference for beetles and their larvae. We conclude that Andean hog-nosed skunks in Patagonia might be negatively affected by reductions of their main prey due to soil and plant alterations by livestock.  相似文献   

3.
Assemblages of small bird species (<90 g body mass) from the Monte desert in Argentina were studied to analyze spatial and temporal variation in abundance and species richness. Mean species richness was higher during breeding season than in non-breeding season. The same pattern was observed in aerial insectivores, while granivores and substrate insectivores did not differ between breeding and non-breeding seasons. Overall bird abundance was similar across seasons. Species richness was positively correlated with bird abundance and negatively correlated with dominance; bird abundance and dominance were not correlated. These patterns could be explained by distinct responses of functional groups of birds; dominant species were granivores in the non-breeding season and aerial insectivores during the breeding season, and bird abundance in functional groups changed according to food supply. Most species are residents or regular migrants, while there are few nomadic and transient species. Predictable annual fluctuations in rainfall and resource availability should favor a migratory strategy more than nomadic movements. Similarly, breeding is strongly seasonal and most species start breeding when the first summer rains have generally not yet fallen. Finally, concordances in assemblage structure at local and regional scale suggest that similar mechanisms are acting on the local bird assemblages across the Monte.  相似文献   

4.
The North African houbara bustard (Chlamydotis undulata undulata) is a medium-sized steppeland bird described as omnivorous and opportunistic. Its diet reflects the local abundances of plants and invertebrates. However, comprehensive studies based on both plant and animal materials are lacking to confirm or invalidate this characterization. The diet of the species during the non-breeding season was studied based on the contents of the stomachs of 42 adults collected during 2004, 2006 and 2007 in two regions of eastern Morocco. Taxa were identified to species or genus using a herbarium, a plant epidermis reference collection, an invertebrate reference collection, and an invertebrate fragment reference collection. We analyzed variation in the diet according to sex, region and year. The diet primarily included plant material (66 ± 25% of the dry weight of the stomach contents). The relative proportions of plants and invertebrates did not differ between the sexes but showed variations in space and time. The ingested plant and invertebrate assemblages differed between year and area but not between the sexes. These results suggest that both sexes forage in similar habitats and that their diet reflects spatial and temporal variations in plant and invertebrate availability, as expected for an opportunistic feeder.  相似文献   

5.
Small mammals usually constitute the main prey for Leopardus geoffroyi throughout its distribution. We studied the patterns of small rodent selection by this felid in a semi-arid scrubland of central Argentina, addressing whether prey choice may be related to the availability, morphology, and distribution of the different rodent species. Cat’s diet was studied during 2005-2006 through the analysis of 182 scats, along with field estimates of rodent abundances from trapping. The cricetine rodents Akodon molinae and Calomys musculinus were predated according to the availability expected by trapping, indicating that their use was opportunistic. Akodon azarae and Graomys griseoflavus, on one hand, and Eligmodontia typus, on the other hand, were consumed in lower and higher proportion than their availabilities, respectively. Our results suggest that some cricetine rodent characteristics such as abundance, escape ability, microhabitat use, and activity period, appear to be potential factors contributing to differential vulnerability to predation by Geoffroy’s cat in central Argentina.  相似文献   

6.
Caribou and muskoxen are the only ungulate species occupying Arctic tundra environments. We analysed plant fragments found in fresh (< 4 hr old) samples of faecal material to determine the diets of Peary caribou ( Rangifer tarandus pearyi ) and muskoxen ( Ovibos moschatus ) on Banks Island, Canada. Willow was a major component of the diets of both animals, dominating the caribou diet during summer and representing substantial proportions of the muskoxen diet during at least seven months of the year. The diet of caribou was more diverse than that of muskoxen and was dominated by sedge, willow ( Salix arctica ), legume ( Astragalus spp., Oxytropis spp.) and Dryas integrifolia . The diet of muskoxen was dominated by sedge and willow. There was substantial overlap (up to 70%) in the diets of these herbivores with the similarity more pronounced in areas of high muskox density ( ca. 1.65 ani mals/km2). We discuss herbivore diets in relation to foraging behaviour and forage availability.  相似文献   

7.
In this study, we provide the first evidence of scavenging behaviour in the spiny-tailed agamid lizard (Uromastyx aegyptia microlepis), a species which heretofore has been considered a strict desert herbivore. We examined 294 faecal samples collected in the desert of Qatar and found that 84% of the faeces (n = 247) contained exclusively plant material. Grains of barley (Hordeum vulgare) were present, suggesting that Uromastyx can benefit from the food provided to livestock when wild plants are scarce. We also found remains of invertebrates, vertebrates and stones in the lizard faeces. The type of vertebrate remains found suggests scavenging behaviour and some flexibility in feeding behaviour where food resources are scarce. Overgrazing by camels and goats in the area may affect food availability for Uromastyx populations, suggesting the need for conservation measurements in the Qatar desert.  相似文献   

8.
Esophageally fistulated goats were released in a microphyll desert scrub habitat with 14.6% or 46.2% aerial cover of Atriplex canescens (induced by removal of all shrubs except A. canescens, with livestock grazing exclusion for 10 years) to determine the seasonal forage species selected by the goats. The shrub removal strongly influenced the goats’ feeding habits. The goats grazing the Atriplex-dominated site consumed 4.5 times more A. canescens than the goats on the untreated (control) pasture during all seasons. Shrubs were used heavily during all seasons by goats in both pastures, with higher percentages (75.5–82.8%) in the diets of goats grazing the control pasture than in the diets of goats grazing the Atriplex-dominated area (62.5–68.5%). No differences were found between seasons. The goats in the Atriplex-dominated pasture ate more grass than the goats grazing the control area and used more perennial graminoids during the summer (15.0%) and spring (18.3%) than the goats on the control area (6.0–7.0%). Forbs were an important component of diets. It was concluded that the successful revegetation of the treated pasture affected the goats’ feeding strategy, with an increase in the use of A. canescens, forbs and grasses in all seasons.  相似文献   

9.
Botanical composition of cattle seasonal diets (faecal sampling with microhistological analysis) was determined in a four-pasture, one-herd grazing system during a 3-year period. Diets were classified using cluster analysis. Three diet groups were identified: beginning of rainy season (spring), peak of rainy season (summer) and dry season (fall and winter). Contribution of grasses and woody species to these diet groups was significantly different (p< 0·001). Grasses were the most important component of cattle diets throughout the rainy season, while shrubs and trees were important in the dry season. The major shifts in diets occurred in response to changes in grass phenology.  相似文献   

10.
In 1988, first-year Herring Clupea harengus were the dominant prey fed to Puffin chicks on Hernyken, Røst. Puffins carrying food loads were observed at least 137 km from the colonies in July. In early August, two major feeding areas were located about 20 and 85-105 km off Røst. These long foraging ranges and an insufficient availability of food are thought to be the main reasons for the poor chick growth this year. No relationships were found between the distribution of Puffins observed at sea and survey station data on prey distribution, sea temperature or salinity, but this may have been due to inadequate sampling of these parameters. A recorded seasonal change in flight direction of adults returning to colony is discussed in relation to food quality and chick growth.  相似文献   

11.
A major focus in population ecology is understanding factors that limit rare species. We used stable isotope approaches to diet to determine whether remaining rare antelope populations in Kruger National Park (KNP), South Africa experience i) nutritional stress; ii) competition with sympatric bulk grazers; iii) reduced habitat heterogeneity. Rare species consumed near-pure C4 grass-based diets throughout the seasonal cycle, in contrast to field observations that reported significant levels of C3 consumption (browse) by these taxa. This finding, coupled with low faecal %N at the height of the dry season, may indicate nutritional stress, but recent isotopic studies of the same species elsewhere in Africa suggest that field observations overestimated levels of browse consumption. We find little evidence for diet niche overlap between rare antelope with bulk grazing species. This partitioning of resources (interpreted mainly as tall- versus short-grass grazing, respectively), is consistent with reported differences in observed diet, and comparative oral morphology. Last, we find less seasonal diet variations amongst bulk grazers feeding in rare antelope habitats compared with other landscapes. We propose that loss of functional heterogeneity, apparently brought about by high densities of artificial waterholes, limits recovery of diet- and habitat-selective rare antelope populations in KNP.  相似文献   

12.
Grey brocket deer diet selection was studied during a period of water scarcity in the arid Chaco of Córdoba province, Argentina. Sampling took place during the dry season in and around Chancaní Provincial Reserve (Pocho department). Forty-eight fresh fecal samples were collected from 85 sampling plots located at random. Plant cover and abundance were used to estimate food availability. Diet composition was determined using microscopic analysis of brocket feces and resource selection was calculated using Ivlev’s Selectivity Index. Thirty-three plant species were identified in the diet. Fruits were found in high proportion (12.4%). Woody plants made up 67.7% of the diet; the most consumed species were Castela coccinea (23.1%), Maytenus spinosa (10.2%), Condalia microphylla (9.5%), Schinus fasciculatus (8.5%) and Ximena americana (7.4%). Mazama gouazoubira selects woody and succulent plants, while herbs are consumed according to availability and grasses in a proportion that is below what is available.  相似文献   

13.
Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle.  相似文献   

14.
The diets of euros or hill kangaroos (Macropus robustus), domestic sheep (Ovis aries) and feral goats (Capra hircus) in hilly, shrub rangeland in southern Australia were examined in a 12-year study. Levels of dietary overlap between these herbivores, their foraging in relation to resource availability, and the potential for competition in different conditions were also examined. The diet of euros was based around grasses. In dry seasons some shrubs were also eaten but in severe drought grass formed more than 80% of their diet. While grass was important to sheep in wetter conditions, they ate much shrub in dry conditions. Feral goats had broad diets but their preference for browse was high. In drought, euros had only a modest dietary overlap with sheep and goats. Data for dietary niche breadths and electivities pointed to only limited competition between the herbivores.  相似文献   

15.
The diet of the pichi armadillo (Zaedyus pichiy) was determined based on analysis of stomach contents of 26 dead individuals confiscated from poachers near Cerro Nevado, Mendoza Province, Argentina. Sand accounted for 66 ± 24% of stomach contents' dry weight. Beetles were the predominant food item in 14 and ants in 5 stomachs, while 5 animals had mainly ingested plant material. The remainder had mostly fed on fly larvae and arachnids. Coleoptera (mainly adults and Scarabeidae larvae) and plant material (seeds, leaves, and roots) were found in all stomachs examined. All pichis had fed on ants of different species and stages, suggesting that pichis eat any ant species they can find and actively prey on nests. Scorpions and spiders were observed in over 60% of stomachs but represented a low aggregate percent weight. Vertebrates were rarely found. Based on these results, the pichi of Mendoza Province can be described as an opportunistic omnivore that mainly feeds on insects and seems to be the least carnivorous of all carnivore–omnivore armadillos.  相似文献   

16.
We studied how features of thermal resources affect the patterns of activity of predator (Callopistes maculatus) and its prey (Gyriosomus batesi and Gyriosomus subrugatus) during the phenomenon of the Flowering Desert in Chile. We predict that restrictions or variations in temperature affect mainly the activity of insects, and that this variation in the activity of insects affects the patterns of activity of the predator. The daily activity of the three species was bimodal, but both prey species disappear when temperatures exceed 40 °C. According to our results, the prey are thermoconformers to air and substrate temperature, whereas the predator is a thermoregulator to environmental conditions by their independence of air and substrate temperature.  相似文献   

17.
The diet of a species can help us to understand its natural history, ecological requirements, and strategies involved in searching for food. Liolaemus pseudoanomalus is a rare desert lizard where previous studies showed no seasonal, ontogenetic or sexual differences observed in microhabitat use; however the sexual dimorphism is evident in the number of precloacal pores and in the snout-vent length. In this work, we investigate if there are differences in the diet composition between sexes and age groups. Herein we describe the diet of L. pseudoanomalus, of the Central West Monte desert of Argentina, based on the analysis of 63 stomach contents. We found that ants are the most important food item and some characteristics of foraging behavior suggest similarities with other ant-eating lizards.  相似文献   

18.
Food processing and consumption by herbivores are affected differently by the availability of forage quality and quantity per unit of time. This demonstrates the “Allometric response concept”, and it is considered a significant determinant in habitat use for foraging by grazers. The relevance of this approach has comprehensively been applied to herbivores of different body sizes, but little is known about its demonstration to explain patch use in herbivores with different digestive physiology and body size. We explain the use of patches by grazing herbivores of different digestive physiology and body sizes, Hippopotamus amphibius (hippopotamus, mega non-ruminant) and cattle (ruminant), by integrating foraging relationship herbivores. We analysed the significant relationships between species dropping densities and environmental variables across forty-eight 100 m×100 m plots in Bui National Park, Ghana, during the wet and dry seasons. We found that both species utilised areas closer to the river in the wet season, but the H. amphibius foraged further away from the river during the dry season. Sward height also determined patch use by both species, with the H. amphibius utilising shorter swards than the cattle. Considering the quality of food resources, the study revealed that patch selection of ruminants (cattle) was significantly influenced by nitrogen content. In contrast, acidic detergent fibre content was positively related to non-ruminant species (H. amphibius). The high seasonal effect of sward height and food quality on patch use is primarily due to the species digestive physiology and body size of hippopotamus and cattle at the Bui National Park.  相似文献   

19.
The paper is a study of vegetation exploitation and the effect of food availability on the diet and behaviour in barnacle geese breeding at Storholmen, Svalbard. Detailed vegetation mapping was used to estimate the availability of food to individual pairs of geese. Diet composition was assessed through analysis of plant fragments in droppings. The behaviour of geese in relation to snowmelt patterns was recorded. Most vegetation types were exploited by the geese either for feeding or as nest substrate. Nest density was highest and territories were smallest on early, snow-free ridges, although late breeding individuals also nested in moss tundra vegetation. Most geese pairs exploited a mosaic of vegetation types in their territories, which extended the feeding period when plants were nutritionally most profitable to the geese. Territory size increased with decreasing density of the highest preferred food plants. Female geese preferred plants with high nutrient quality, and the diet during incubation consisted of 41% flowers of forbs, 19% grasses, 6% leaves and buds of forbs, and 34% mosses. When the availability of grasses was <5%, geese switched to a diet dominated by the abundant, but nutrient-poor, mosses. The nutrient-poor diet resulted in more time off the nest and less time being alert or searching for food during feeding bouts. Because nests are exposed to predators when females feed or search for food, a low availability of nutrient-rich food within the territory can affect hatching success.  相似文献   

20.
This paper provides global and seasonal estimates of the “practical” wind power obtained with a 3-D numerical model (GATOR-GCMOM) that dynamically calculates the instantaneous wind power of a modern 5 MW wind turbine at 100-m hub height at each time step. “Practical” wind power is defined as that delivered from wind turbines in high-wind locations (year-average 100-m wind speed ≥ 7 m/s) over land and near-shore, excluding both polar regions, mountainous, and conflicting land use areas, and including transmission, distribution, and wind farm array losses. We found that seasonal variations in the global practical wind resources are significant. The highest net land plus near-shore capacity factors globally are found during December–January–February and the lowest during June–July–August. The capacity factors in the transitional seasons (March–April–May and September–October–November) are rather similar to one another in terms of geographical patterns and frequency distributions. The yearly-average distributions of capacity factors, whether in terms of geographic patterns or frequency distributions, differ from those in all four seasons, although they are closest to the transitional seasons. Regional practical wind resources are sensitive to seasons and to thresholds in year-average wind speed and bathymetry, but are more than enough to supply local electricity demand in all regions except Japan.  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