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排序方式: 共有195条查询结果,搜索用时 15 毫秒
1.
How reliable are dung counts for estimating elephant numbers? 总被引:4,自引:0,他引:4
R. F. W. Barnes 《African Journal of Ecology》2001,39(1):1-9
Dung counts are the most commonly used techniques for estimating elephant numbers in forests, yet there is considerable scepticism concerning their accuracy. Published accounts of dung counts show that they give estimates similar to those from other methods for vertebrates ranging in size from lizards to elephants. For ungulates, macropods and elephants there are strong correlations between estimates from dung counts and other methods. Thus, dung counts are as accurate or inaccurate as other methods for estimating vertebrate numbers, including elephants. Dung counts for elephants give estimates that are as precise as, and sometimes more precise than, those from aerial surveys of elephants. This is because the variance in dung density is usually low and results in a lower than expected variance for the final elephant estimate when combined with the variances of defecation and decay rates. Dung counts may be more appropriate than aerial surveys for monitoring small or declining elephant populations. 相似文献
2.
Abstract. A technique for fine-scale vegetation mapping with the aid of low-altitude aerial photography was developed. The procedure is as follows: 1. The site is divided into a lattice pattern - in case the site is too large to fit into a single photograph with satisfactory resolution. The coordinates of every lattice point are surveyed to be used as control points for geometric correction. A photograph of each block of the lattice is taken using a remote-controlled camera system lifted by a captive helium balloon. 2. The vegetation is classified on the basis of a phytosociological survey. 3. The shapes and locations of vegetation patches appearing in the photographs are entered into a computer, using a digitizer. A geometric correction is carried out through coordinate transformation referring to the coordinates of the control points and subsequently a draft vegetation map is produced. Finally, discrepancies are corrected and the map is coloured to produce the final version of the vegetation map. This technique was applied to vegetation mapping at a bar, 500 m wide and 2 km long, in the river Yoshino in Shikoku, Japan. A fine-scale vegetation map was obtained and used to analyse the influence of plants on geomorphic processes and community-specific hydrogeomorphic conditions on the bar. 相似文献
3.
B. Meier 《Human Evolution》1989,4(2-3):223-229
Extinction of small, closed populations in captivity as well as in the wild is believed to be nearly inevitable, because inbreeding
will adversely effect reproductive success, mortality, sex ratio and also the susceptibility to epidemic diseases and environmental
stress. An ever increasing number of primate species exist only in small isolated populations, which contain only a part of
the original genetic variability. In captive breeding programs research about genetic management strategies is, therefore,
of essential importance. In 1980 we imported 9Loris tardigrdus nordicus (4 females, 5 males) from NE-Sri Lanka. The founders came from one natural breeding population. All sexual mature females
are breeding. Up to now the colony contains 36 living individuals. The main goal of our long-term genetic management plan
was to minimize inbreeding and to preserve the genetic diversity. Therefore, we try to pass the founder bottleneck rapidly
by enlarging the population to a desired minimum population size of 25 pairs and to equalize the founder representation within
any generation. The need to control the spread of sublethal genes, introduced by one of the founders, conflicts directly with
the aim of equalizing the founder representation. A solution of this problem is discussed. To produce a sufficiently large
population we intend to give animals to other institutions and to build up an exchange-system for offspring individuals, which
should lead to an international studbook. 相似文献
4.
5.
《Current biology : CB》2021,31(16):3606-3612.e7
6.
Recovery of tree and mammal communities during large‐scale forest regeneration in Kibale National Park,Uganda
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Patrick A. Omeja Michael J. Lawes Amélie Corriveau Kim Valenta Dipto Sarkar Fernanda Pozzan Paim Colin A. Chapman 《Biotropica》2016,48(6):770-779
Tropical landscapes are changing rapidly as a result of human modifications; however, despite increasing deforestation, human population growth, and the need for more agricultural land, deforestation rates have exceeded the rate at which land is converted to cropland or pasture. For deforested lands to have conservation value requires an understanding of regeneration rates of vegetation, the rates at which animals colonize and grow in regenerating areas, and the nature of interactions between plants and animals in the specific region. Here, we present data on forest regeneration and animal abundance at four regenerating sites that had reached the stage of closed canopy forest where the average dbh of the trees was 17 cm. Overall, 20.3 percent of stems were wind‐dispersed species and 79.7 percent were animal‐dispersed species, while in the old‐growth forest 17.3 percent of the stems were wind‐dispersed species. The regenerating forest supported a substantial primate population and encounter rate (groups per km walked) in the regenerating sites was high compared to the neighboring old‐growth forests. By monitoring elephant tracks for 10 yr, we demonstrated that elephant numbers increased steadily over time, but they increased dramatically since 2004. In general, the richness of the mammal community detected by sight, tracks, feces, and/or camera traps, was high in regenerating forests compared to that documented for the national park. We conclude that in Africa, a continent that has seen dramatic declines in the area of old‐growth forest, there is ample opportunity to reclaim degraded areas and quickly restore substantial animal populations. 相似文献
7.
本研究在甘肃兴隆山国家级自然保护区马麝繁育场展开,分别于2012年7月和2013年8月,针对374只圈养马麝,采用基于量表的个性评价法进行评价调查。结果表明:可建立包含17个个性项目的圈养马麝个性量表,因子分析显示每个项目公因子方差和载荷均大于0. 4,各因子累计贡献率为60. 33%,表明此量表具有较好的结构效度。此外Cronbach’sα系数为0. 787,表明量表具有较高的内部一致性信度,量表设计合理;因子分析和聚类分析结果显示,可将圈养马麝划分为五大个性维度:侵略性、社会性、刻板性、温顺性、活跃性。研究发现,圈养马麝个性维度与野生个体的个性类型划分存在差异,主要是受圈养条件和人为干扰等影响。圈养马麝个性量表和五大个性维度的建立对指导马麝繁育管理具有重要实践价值,填补了马麝个性研究的空缺,并为进一步进行麝类动物个性研究奠定了基础。另外,此类个性层次研究方法具有较好区分度,可为其他动物个性的初期研究提供参考。 相似文献
8.
John O’Brien Gary F. McCracken Ludovic Say Thomas J. Hayden 《Conservation Genetics》2007,8(5):1073-1082
Fruit bats of the genus Pteropus are important contributors to ecosystem maintenance on islands through their roles as pollinators and seed dispersers. However,
island faunas are the most prone to extinction and there is a real need to assess the possible genetic implications of population
reductions in terms of extinction risk. An effective method of ameliorating extinction risk in endangered species is the establishment
of captive populations ex situ. The effectiveness of captive breeding programmes may be assessed by comparing the genetic
variability of captive colonies to that of wild counterparts. Here, we use polymorphic microsatellite loci to assess genetic
variability in wild, critically endangered Rodrigues fruit bats (Pteropus rodricensis, Dobson 1878) and we compare this variability to that in a captive colony. We document remarkable conservation of genetic
variability in both the wild and captive populations, despite population declines and founder events. Our results demonstrate
that the wild population has withstood the negative effects of population reductions and that captive breeding programmes
can fulfil the goals of retaining genetic diversity and limiting inbreeding. 相似文献
9.
10.
In the wild, primate foraging behaviors are related to the diversity and nutritional properties of food, which are affected by seasonal variation. The goal of environmental enrichment is to stimulate captive animals to exhibit similar foraging behavior of their wild counterparts, e.g. To extend foraging time. We conducted a 12-month study on the foraging behavior of Japanese macaques in a semi-naturally forested enclosure to understand how they use both provisioned foods and naturally available plant foods and what are the nutritional criteria of their consumption of natural plants. We recorded time spent feeding on provisioned and natural plant foods and collected the plant parts ingested of their major plant food species monthly, when available.We conducted nutritional analysis (crude protein, crude lipid, neutral detergent fiber-'NDF', ash) and calculated total non-slructural carbohydrate - 'TNC' and total energy of those food items. Monkeys spent 47% of their feeding time foraging on natural plant species. The consumption of plant parts varied significantly across seasons. We found that leaf items were consumed in months when crude protein, crude protein-to-NDF ratio, TNC and total energy were significantly higher and NDF was significantly lower, fruit/nut items in months when crude protein and TNC were significantly higher and crude lipid content was significantly lower, and bark items in months when TNC and total energy were higher and crude lipid content was lower. This preliminary investigation showed that the forested enclosure allowed troop members to more fully express their species typical flexible behavior by challenging them to adjust their foraging behavior to seasonal changes of plant item diversity and nutritional content, also providing the possibility for individuals to nutritionally enhance their diet. 相似文献