DISTRIBUTION,POPULATION SIZE AND CONSERVATION OF THE SWIFT TERN STERNA BERGII IN SOUTHERN AFRICA

Cooper, J., Crawford, R. J. M., Suter, W. & Williams, A. J. 1990. Distribution, population size and conservation of the Swift Tern Sterna bergü in southern Africa. Ostrich 61: 56–65.

The Swift Tern Srerna bergü occurs commonly in coastal southern Africa, with a nonbreeding distribution extending the length of the southern African coast and into southern Angola. The known nonbreeding distribubon of the nominate subspecies S. b. bergü extends from Swakomund, Namibia to Kosi Bay, Natal, South Africa. In Natal its nonbreeding distribution overlaps with that of the subspecies S. b. enigma. The species very rarely occurs inland or far out to sea. The geedin distribution of tre nominate subspecies extends from Swakopmund to Algoa Bay, eastern Cape, South Afcnca.

Twenty-two breeding localities are known in southern Africa, but usually only six to seven are occupied. in any one year. Most breeding localities are marine islands where Swift Terns often breed in muted colonies with Hartlaub's Gulls Lorus hartloubii. In 1984 a complete breeding ansus estimated a breeding population of 4835 pairs. However, 6088 pairs were counted at only three localities in 1988. The size of the annual breeding population varies by a factor of as much as 1,6; although the overall size of the adult population is thought to be reasonably stable with no temporal trends evident. Thirteen breeding localities which are legally proclaimed nature reserves supported 72% of the 1984 breeding population. Existing and perceived threats to the Swift Tern are discussed in detail. To improve further tRe conservation status of the Swift Tern in southern Africa, it is recommended that: unprotected breeding localities be proclaimed reserves, also protecting those not on islands with adequate fences; feral cats be removed from breeding islands where they are present; and fisherman be educated to release entangled terns and not to discard lines and nets.     

POPULATION SIZE,DISTRIBUTION AND DISPERSAL OF KELP GULLS IN THE SOUTHWESTERN CAPE,SOUTH AFRICA

Steele, W.K. & Hockey, P.A.R. 1990. Population size, distribution and dispersal of Kelp Gulls in the southwestern Cape, South Africa. Ostrich 61:97-106.

There are indications that the Kelp Gull Larus dominicanus population of the southwestern Cape Province, South Africa, is increasing. It is proposed that decreased post-fledging mortality due to supplementary food from man's activities, at sites such as fishing harbours and refuse dumps, is likely to be the main cause of this population increase. Kelp Gulls aggregate, and juveniles (first-year birds) are disproportionately abundant, at sites where supplementary food is available. Juvenile dispersal from the two largest breeding colonies, 38 km apart, is in opposite directions.     

DISTRIBUTION,POPULATION SIZE AND CONSERVATION OF HARTLAUB'S GULL LARUS HARTLAUBIL

Williams, A. J., Steele, W. K., Cooper, J. & Crawford, R. J. M. 1990. Distribution, population size and conservation of Hartlaub's Gull Lorus hurtlaubii. Ostrich 61: 66–76.

Hartlaub's Gull Larus hartlaubii is endemic to southern Africa, where it breeds between Swakopmund, Namibia and Dyer Island, southwestern Cape Province, South Africa. The species has been re breeding at 48 localities within this range. Between 1984 and 1989 an estimated 12000 pain brered at 31 localities. Twenty-eet percent of the population breeds at Robben Island off the Cape Peninsula, sQuth Africa. Hartlaub's Gull frequently has low breeding success and is considered endangered in Narmbia, where 12% of the poulation occurs. However, the population is increaslng around the urbanmd Cape Peninsula where HartLub's Gull has the potential to become a pest species.     

DISTRIBUTION AND POPULATION SIZE OF THE SOUTHERN SEA LION (OTARIA FLAVESCENS) IN CENTRAL AND SOUTHERN CHUBUT,PATAGONIA, ARGENTINA

Population size and distribution of Otaria flavescens in central and southern Chubut, Patagonia were determined by aerial censuses conducted during the breeding season in 1989 and 1995 and outside the season. Pup numbers were corrected by means of a linear regression between pup and adult male (AM) numbers obtained from terrestrial censuses carried out in 1994 and 1996. During the 1989 breeding season, 10,557 sea lions occurred at 29 locations; 2,800 (26.3%) were pups. During the 1995 breeding season, 14,887 animals were censused at 32 sites; 3,311 (22.2%) were pups. The corrected pup number increased to 4,852, indicating that around 32% is lost when counting from photographs. The corrected total number increased to 16,483; this fell to less than one half between breeding seasons (November 1990 and 1995). The 1995 breeding season census represents the highest number since 1972 (8,800) and the widest historical dispersion (37 sites year round contrasting with 13 in the late 1940s and 1972). However, the present number is about one half of the 33,000 censused about 50 yr ago. Using a correction factor developed for the north Paragonian population (1.8 × censused number) the present population size in the area can be estimated at around 29,669 individuals.     

BIOLOGY OF THE BANK CORMORANT,PART 1: DISTRIBUTION,POPULATION SIZE,MOVEMENTS AND CONSERVATION

Cooper, J. 1981. Biology of the Bank Cormorant, Part 1: Distribution, population size, movements and conservation. Ostrich 52: 208–215.

The Bank Cormorant Phalacrocorax neglectus is a marine species, endemic to southern Africa. Its non-breeding range extends from Walvis Bay to Cape Agulhas. Breeding range extends from Hollamsbird Island to Quoin Rock. Its distribution is broadly similar to that of kelp beds Ecklonia maxima. A total of 44 breeding localities supports approximately 18 000 adult birds; 12 800 (71%) occur on two islands (Ichaboe and Mercury) north of large kelp beds. Adult Bank Cormorants are resident but juveniles may disperse several hundred kilometres. The species is not considered to be seriously at risk to disturbance at most breeding localities. However, modern expansion of fishing activities may affect the very large populations of Ichaboe and Mercury Islands.     

中国驼鹿种群数量及分布现状的研究

1985一1987年间,作者在中国东北大、小兴安岭林区,根据三阶抽样的原理,选择1 6块样地,设置并调查202条样带,长2476．6km,遇见309条驼鹿足迹链。由此,明确了驼鹿在中国的分布区域并确定总栖息面积为1 9万多km² ．平均分布密度为0.0519头／km²,种群数量为9955士397头(a=0．2 ）,其种群下降率年平均逃6.3 %,且呈继续下降趋势, 亟待保护。     

白暨豚种群数量及资源保护

为了了解长江中白鱀豚的分布状况及种群数量,从1978年至1983年1月止,先后9次在长江中、下游(宜昌至南通)的干流进行了白鱀豚的生态考察,并到汉江和鄱阳湖、洞庭湖等水域查访有无白鱀豚活动的情况,依据考察所得资料,对长江白鱀豚群体的数量作了初步剖析。 通过考察,到1983年初为止,中游最上是在湖北枝城,约距长江口1,613公里的江段和下游最下是江苏太仓浏河口距长江口24公里的江段都有白鱀豚的活动。白鱀豚种群约156头,20个群体,分布在长江中、下游的17个江段里,在安庆一黑砂洲南水道约170公里及嘉鱼—王家渡水道约80公里的两个江段里生活着较多的个体。根据雌、雄自鱀豚体长与年龄关系式的速度变化曲线,白鱀豚的个体发育阶段可分为:幼龄期(胎儿—雄性4龄,雌性5龄),壮年期(雄性5龄—12龄,雌性6龄—13龄),成年期(雄性13龄,雌性14龄至20龄)和老年期(20龄以上雌雄个体)4个龄期。白鱀豚种群的年龄结构是一个基部较窄,顶部相对宽的锥体,显然是一个生产较差的种群。 近些年来,由于人类对江河的开发利用,使得白鱀豚种群的补充能力和再生产能力都遭到了一定程度的破坏。分析白鱀豚资源减少的主要原因是:(1)食物条件的变化;(2)有害渔具对白鱀豚的杀伤;(3)航运业务对白鱀豚的误伤;(4)群众缺乏保护珍贵动物的知识而     

LARGE POPULATION SIZE PREDICTS THE DISTRIBUTION OF ASEXUALITY IN SCALE INSECTS

Understanding why some organisms reproduce by sexual reproduction while others can reproduce asexually remains an important unsolved problem in evolutionary biology. Simple demography suggests that asexuals should outcompete sexually reproducing organisms, because of their higher intrinsic rate of increase. However, the majority of multicellular organisms have sexual reproduction. The widely accepted explanation for this apparent contradiction is that asexual lineages have a higher extinction rate. A number of models have indicated that population size might play a crucial role in the evolution of asexuality. The strength of processes that lead to extinction of asexual species is reduced when population sizes get very large, so that the long‐term advantage of sexual over asexual reproduction may become negligible. Here, we use a comparative approach using scale insects (Coccoidea, Hemiptera) to show that asexuality is indeed more common in species with larger population density and geographic distribution and we also show that asexual species tend to be more polyphagous. We discuss the implication of our findings for previously observed patterns of asexuality in agricultural pests.     

牛背梁自然保护区羚牛的分布与数量

1998 年1～4 月对牛背梁国家级自然保护区内羚牛种群数量与分布做了调查, 结果表明, 保护区内有11 群羚牛, 总数量119～130 头(包括独牛) , 整个保护区内羚牛分布密度为0.007 3～0.007 9 头/ hm² 。在冬季, 羚牛分布于海拔1 900～2 700 m的5 块相互隔离的栖息地中, 以海拔2 200～2 600 m之间分布更为集中。在1981～1998 年的17 年间, 保护区内的羚牛种群分布范围在逐渐缩小; 从上世纪50 年代至90 年代, 羚牛最低的分布高度比历史分布高度至少上升了400 m。周边地区人为干扰、生境不断丧失和保护区内生境破碎化是导致羚牛分布现状最直接的原因。     

东海水域瓶鼻海豚种群数量和分布的初步研究

运用截线抽样法调查了北纬２５°～３０°,东经１２５°以西的东海水域中瓶鼻海豚在夏季７～９月间的种群密度和数量,得出的最小估计值分别为０．１４００头／ｋｍ２和９９４０头。瓶鼻海豚在该水域的分布特点为：随纬度增加（由南向北）密度逐渐减少,而在经度方向上则没有明显的密度变化规律。     

中国现代灵长类的分布、现状与保护

本文对中国现生灵长类类群分布和现状作了较全面的总结;对现存的种群数量进行了初步估价;并就保护和存在的问题与展望提出了概括性评述。所得结果系据作者自1975年以来的实际考察和国内外有关文献记载。     

鄱阳湖及其支流长江江豚种群数量及分布

在1997 年11 月至1998 年11 月的134 d 中, 大致按一年四季, 分4 次对鄱阳湖及其主要支流中的长江江豚种群数量、数量的季节变动、分布、行为、江豚栖息地环境、人类活动对江豚的影响进行了考察。江豚的分布主要集中在鄱阳湖湖区, 赣江、信江、抚河等主要支流的中下游和支流入湖的湖口附近。冬、春、秋3 个季节鄱阳湖水系长江江豚种群数量的估计值分别为91 头、431 头和260头。即, 鄱阳湖江豚的种群数量约为100～400 头,其种群数量随季节、水位、鱼类资源的变化而呈现出相应的变化。