The condition and age of Thomson's gazelles killed by cheetahs and wild dogs

The condition and age of Thomson's gazelles ( Gazella thomsoni ) killed by two species of predators were compared. The wild dog, a coursing predator, was predicted to take a greater proportion of young, old and sick animals than the cheetah, a stalker. As measured by the marrow fat content of limb bones, wild dogs captured more Thomson's gazelles in poor condition than cheetahs. This appeared to be a consequence of their preference for male gazelles, which were in worse condition than females. Cheetahs did not capture fewer young and old gazelles than wild dogs.     

Ecological characteristics of territories of male cheetahs (Acinonyx jubatus)

Ecological characteristics of nine male cheetahs territories in the Serengeti National Park are described. Territories were centred on areas that provided cover but did not have particularly high rainfall or prey abundance. Resident male cheetahs did not occupy their territories continuously. Some territories were vacated in the dry season, others in the wet season, but in both cases this occurred when numbers of Thomson's gazelles (females' main prey) and female cheetahs seen there were low. Although changes in territory ownership appeared to be related to demographic rather than ecological factors, territories that remained vacant seemed to contain rather little prey. Over two years, evidence suggested that territories occupied by males of larger group size contained greater numbers of Thomson's gazelles.     

The biomass of game animals in Nairobi National Park, 1960–66

The large animals of Nairobi National Park have been censused intermittently once a month from mid-1960 until the end of 1966. Of the 23 species discussed, the density per kilometre has been determined accurately for the following: Grant's gazelle, Thomson's gazelle, water-buck, impala, wildebeest, hartebeest, eland, buffalo, warthog, giraffe, zebra and ostrich. From these figures the biomass has been calculated for each species each year. After a peak biomass of 12,775 kg/sq. km during the drought of 1960–61 the population declined to and remained fairly level at about 5690 kg/sq. km from 1962 to 1966. This figure includes about 1050 kg/sq. km of cattle and sheep. The large predators account for only about 1.4 % of the total biomass of wild animals while removing about 15.5% from this group annually.     

Comparing mark-recapture and constant removal protocols for estimating forager population size of the subterranean termite Coptotermes lacteus (Isoptera: Rhinotermitidae)

Forager population sizes of colonies of Coptotermes lacteus(Froggatt) in New South Wales were estimated using two methods: mark-recapture and constant removal, in two disturbed habitats: a pine plantation and cleared farmland. Mark-recapture population estimates were unrealistic and unreliable: they could be improbably large, over 200 million foragers, and they varied enormously between samples for each colony without any pattern. The constant removal population estimates could also be unrealistic: they could be negative or quite different when calculated using regression and maximum likelihood methods. However, the unrealistic results could be predicted reliably, and explained by the lack of re-contact with the sampling devices (bait stations) - a violation of an assumption of the method. This happened more frequently in the plantation than in the farmland, probably because of the greater abundance of alternative food sources in the plantation. Of the two methods, constant removal provided reasonable forager population estimates, relative to direct counts, at least some of the time, plus a mechanism by which reliability could be tested, whereas mark-recapture provided neither. Further refinement and testing of constant removal methods are urged to provide a more reliable population estimation technique for termites.     

Observations on the biology of the trochid gastropod Austrocochlea constricta (Lamarck) (Prosobranchia). I. Factors affecting shell-banding pattern

The intertidal trochid gastropod Austrocochlea constricta (Lamarck) has a variable pattern of banding, the shell ranging from white with fine black stripes, to completely black. The patterns may be classified into six arbitrarily chosen types. Populations were studied on three shores chosen to represent the range of habitat of the species (from estuarine to open coast localities) to determine the relative importance of environmental factors on shell-banding. The densities and proportions of the population in different stripe-classes were estimated from quadrat samples on the three shores. Analysis of size-frequency distributions indicates recruitment to be continuous. In all months, juveniles were at greater densities at the upper level of the distribution of the species on open coast and estuary-mouth platforms; the estuarine population was uni modal in size-frequency distribution. Growth rates of caged animals were higher on the open coast than in the estuary, and changed in animals transferred between the two localities, but did not differ between animals of different banding pattern. The proportion of the population in each stripe-class was constant on each shore, suggesting large scale selection processes do not cause the observed differences in frequencies of each banding pattern.The concentrations of the major shell pigment, uroporphyrin I, varied between stripe-classes and, within classes, between shores, with a trend for more densely pigmented shells on the open coast, a trend also evident for the proportion of the population in the darker stripe-classes. Caged animals transferred from the open coast to the estuary showed changes in banding pattern which were consistent with the differences in pigmentation of the two populations. Animals transferred from the estuary to the open coast changed pattern at the same frequency as controls from the open coast; a result of severe storms which caused the open coast population to show changes of banding pattern.It is concluded that shell-banding patterns in A. constricta are primarily governed by environmental factors.     

Effect of food type on the acute and chronic toxicity of copper to Daphnia magna

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin-enriched algae were less sensitive to a chronic copper stress than animals fed a trout-granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r , the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal-fed animals, 0.12 for animals reared on trout-granules). In contrast to chronic toxicity, 72 h LC₅₀ values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.     

Rotavirus (reovirus-like) infection of neonatal ruminants in a zoo nursery.

An outbreak of a pneumoenteric disease occurred in neonates in a zoo nursery. Four of seven affected animals died. Rotaviruses were observed in the feces of an affected 4-day old impala (Aepyceros melampus), a Thomson's gazelle (Gazella thomsonii) and an addax (Addax nasomaculatus). Encapsulated Escherichia coli also were isolated from the feces. The recovered rotaviruses was antigenically related to bovine rotavirus. A bovine rotavirus vaccine was given orally and no adverse effects were noted.     

The natural regulation of buffalo populations in East Africa: The food supply as a regulating factor,and competition*

Evidence is presented to show that both the quality and quantity of food available to a buffalo population falls below the minimum maintenance requirements of that population at certain times of the year. In the Serengeti grasslands there was a shortage of the only good quality component, grass leaf, in the dry season, with the result that the animals consumed an increasing proportion of poor quality food such as grass stem. By the end of the dry season the diet had dropped in quality below the minimum maintenance level. In areas such as Mt. Meru where there was a more continuous growing season, the high density of animals kept the standing crop of leaf at a low level. During the cooler dry season the growth of leaf became insufficient in quantity for the maintenance requirements of the population. These two quite different situations suggested that food shortage was a more general phenomenon in eastern Africa. Various measurements of feeding behaviour were made. Total grazing time per 24 h did not differ between seasons but ruminating time may have increased as the season became drier and could have been a response to the more fibrous food. Analysis for cycles of activity showed that there was more temporal organization during the dry season. These changes in activity cycles appeared to be related to the increase in energy expenditure produced by heat stress and sweating. Old animals with poor teeth did not compensate for the poor food supply by changing their feeding behaviour. There was a positive relationship between annual rainfall and mean crude density in different areas of eastern Africa, indicating that regulation was taking place. Since rainfall determined the amount of available food, it could have operated through the food supply. On a finer scale it was found that the extent of the preferred riverine habitats was also related to density. Thus rainfall, the extent of riverine habitat and perhaps soil moisture were three limiting factors that determined mean density and all could have taken effect through the food supply. As a result of initial selective grazing the amount of available leaf declined as the dry season progressed to the extent that by the end of the season the proportion of this component in the diet fell to a very low level. The impact of the population on its limited food supply indicated that intra-specific competition was acting as the cause of regulation. Measurements of wildebeest eating the same food in the same habitats as buffalo showed that inter-specific competition was also taking place. A small proportion (7“) of the wildebeest population could have reduced the buffalo population by approximately 18^o,‘, from its potential population size. The buffalo population in the Serengeti was regulated by adult mortality which was caused by undernutrition as a result of food shortage. This food shortage was caused by intra- and inter-specific competition. The effect of predation and disease was to hasten the response of the population to changes in the food supply. The limiting factors determining the mean level of the available food were, amongst others, rainfall, soil moisture and the extent of the preferred riverine habitat. The effect of interspecific competition could result in a complex regulation of populations through their food supply. There appears to be no foundation for hypotheses which invoke over-utilization or damage as a consequence of regulation through food.     

Incidence of severe acute renal failure in adults: results of a community based study.

OBJECTIVE--To determine the age related incidence of severe acute renal failure in adults in two health districts in England. DESIGN--Prospective study of patients identified as having severe acute renal failure within a two year period; subsequent monitoring of outcome for a further two years. SETTING--Two health districts in Devon. SUBJECTS--Those adults in a population of 444,971 who developed severe acute renal failure (serum creatinine concentration > 500 mumol/l) for the first time during two years, with subsequent fall of the serum creatinine concentration below the index value. MAIN OUTCOME MEASURES AND RESULTS--125 adults (140 per million total population yearly, 172 per million adults) developed severe acute renal failure, of whom 90 (72%) were over 70. Age related incidence rose from 17 per million yearly in adults under 50 to 949 per million yearly in the 80-89 age groups. In 31 patients (25%) the cause was prostatic disease, which was related to a good prognosis (84% (26) alive at three months). Overall survival was 54% (67) at three months and 34% (42) at two years and was not significantly age related. 18 per million total population yearly (22 per million adult population) received acute dialysis. Referral rate for specialised opinion was 51 per million total population yearly with an estimated appropriate referral rate of 70 per million per year. CONCLUSIONS--The incidence of severe acute renal failure in the community is at least twice as high as the incidence reported from renal unit based studies. Prostatic disease, a preventable and treatable problem, is the most common cause. Survival figures indicate that age alone should not be a bar to specialist referral or treatment.     

Effects of sexual differences of age at maturity and survival on population sex ratio

Summary Five demographical factors influencing the sex ratio of a population are classically considered. The influence of two of them is dependent on the longevity of individuals in the population. The effect of differential age at maturity between males and females is higher for animals with low annual survival, whereas the effect of differential annual survival between males and females is higher for animals with high annual survival. Such a conclusion applied to turtles, which are long life-span animals, allows us to retain differential survival between sexes as a major factor influencing the population sex ratio.     

麦蚜和寄生蜂对农业景观格局的响应及其关键景观因子分析

大量研究表明多样性的农业景观格局能够影响蚜虫及寄生蜂的分布。本文利用并设计了两种尺度的麦田农业景观格局,依据麦蚜种群发生特点,分为迁入期、增长期与高峰期三个时期,论述了不同尺度下农业景观元素对麦蚜及寄生蜂系统的影响,通过逐步回归筛选了不同时期麦蚜及寄生蜂分布的关键景观元素,最后通过CANOCO软件模拟了麦蚜及寄生蜂的分布排序格局。结果表明不同景观因子对麦蚜及寄生蜂种群影响不同,迁入期两种尺度下裸地最有利于两种有翅蚜的迁飞入田,塑料大棚对有翅蚜种群的入田有抑制作用。增长期草地与林地生境对麦蚜种群增长率促进最大,塑料大棚同样抑制了麦蚜的种群增长率;但塑料大棚、草地与林地对蚜茧蜂的种群增长率有促进作用,非麦类作物生境对蚜茧蜂种群增长率抑制作用最大;草地与林地有利于重寄生蜂的种群增长率;高峰期裸地比例大的农业景观下麦蚜的最大种群密度较大,草地与林地对蚜茧蜂与重寄生蜂的最大种群密度均有促进作用。两种尺度下的研究结果一致。不同麦物种的对不同景观元素反应与形态学与生活史特征有关,而且景观结构中特定的植物种类、非作物植物的密度与物候期都可能影响寄生蜂群落的多样性与功能。     

Effects of dehydration and heat stress on food intake and dry matter digestibility in East African ruminants

Comparative investigations were made between wild and domestic ruminants from arid and semi-arid regions and those species from non-arid areas in an attempt to evaluate the adaptations of these ruminants in terms of the effects of heat stress and dehydration on food intake and digestibility. The effect of (a) an intermittent heat load (a daily light cycle of 12 h at 22 degrees C and 12 h at 40 degrees C) compared to 22 degrees C throughout the day and (b) dehydration level of 15% weight loss, with and without the heat load, on the intake and digestibility of a poor quality hay was investigated in the Grant's gazelle, Oryx, the domestic Turkana goats, fat-tailed sheep, zebu cattle, Thomson's gazelle and wildebeest. The intermittent heat load with water available ad libitum depressed the food intake of zebu cattle and Turkana goats by more than 40%. It had no significant effect on the food intake of the other species. The Thomson's and Grants gazelle, oryx, wildebeest and fat-tailed sheep appear well adapted to withstanding a periodic heat load. Dehydration at 22 degrees C caused a marked depression on food intake of all the species investigated. Dehydration together with a heat load caused no further reduction in the food intake by the Grants's gazelle, oryx, and goats but it did cause a further reduction in the intake in the other species. The small non-domestic ruminants (i.e. Grant's and Thomson's gazelle) appear much more digestive efficient than any of their domestic counterpart.     

Antibodies against equine herpesviruses and equine arteritis virus in Burchell's zebras (Equus burchelli ) from the Serengeti ecosystem

A total of 51 sera from a migratory population of Burchell's zebras (Equus burchelli) were collected in the Serengeti National Park (Tanzania) between 1999 and 2001 to assess levels of exposure to equine herpesvirus types 1, 2, 4, 9 (EHV-1, -2, -4, -9), EHV-1 zebra isolate T965, and equine arteritis virus (EAV). Using virus-specific neutralizing antibody tests, seroprevalence was high for EHV-9 (60% of 45), moderate for EAV (24% of 51), and lower for the EHV-1-related zebra isolate (17% of 41), EHV-1 (14% of 49), and EHV-4 (2% of 50). No evidence for exposure to EHV-2 was found (0% of 51). The high level of exposure to EHV-9 is interesting because evidence of infection with this virus has not been previously described in any wild equine population. Although the epidemiology of EHV-9 in Burchell's zebras is presently unknown, our results suggest that in East Africa, this species may be a natural host of EHV-9, a neuropathogenic virus that was only recently isolated from captive Thomson's gazelles (Gazella thomsoni) in Japan. There is currently no evidence that EHV-9 induced mortality in Burchell's zebras in the Serengeti, but because of the reported virulence of this virus for more susceptible species such as Thomson's gazelles, viral transmission from infected zebras to ungulates may result in mortality.     

Changes in the expression of genetic characteristics across cohorts in skeletal deformations of farmed salmonids

Genetic analysis of disorder incidence in farmed animals is challenged by two factors. Disorders in different cohorts and environments could be caused by different factors, leading to changes in heritability and to less than unity genetic correlations across cohorts. Moreover, due to computational limitations, liability scale heritabilities at very low incidence may differ from those estimated at higher incidence. We tested whether these two dilemmas occur in skeletal deformations of farmed salmonids using multigeneration data from the Finnish rainbow trout breeding programme and previous salmonid studies. The results showed that heritability was close to zero in cohorts in which management practices maintained incidence at a low level. When there was a management failure and incidence was unusually high, heritability was elevated. This may be due to computational limitations at very low incidence and/or because deformations are induced by different factors in different cohorts. Most genetic correlations between deformations recorded in different generations were weakly to strongly positive. However, also negative correlations between generations were present, showing that high liability at one time can be genetically connected to low liability at another time. The results emphasise that genetic architecture of binary traits can be influenced by trait expression.     

Development of a Model For Estimating the Size and Dynamics of the Pet Dog Population

Abstract

A conceptual model was developed to describe the dynamics of the pet dog population. The model synthesizes existing data collected for a variety of purposes to estimate the size of the various components of the pet dog population in Washington and Iowa during 1991. The total population mortality rate was estimated as 12.4% per year. Animal shelters in Washington and Iowa handled 7.6% and euthanized 4.0% of the dog population in those two states. When these estimates were extrapolated to the entire U.S. dog population, the model predicted that the total annual turnover in owned dogs was 14.7%, or 7.71 million dogs, that 4 million dogs were handled by animal shelters, and that 2.1 million were euthanized. It was also estimated that 79% of all female dogs were spayed, that household breeding could be attributed to less than one-fifth (18.7%) of the female dogs in the reproductive pool, and that the number of owners contributing to total dog population turnover through failure to retain their dog (103,453) was approximately three times the number of owners who allowed their female dogs to be bred (32,513).     

Ecological drivers of change at South Georgia: the krill surplus,or climate variability

Macaroni penguins Eudyptes chrysolophus are thought to be one of the most important mesopredators in the Southern Ocean having a greater impact on prey availability and abundance than any other seabird species. Their population centre has long been held to be South Georgia where populations were thought to comprise many million animals. Here we report the results of a recent census of the macaroni population at South Georgia undertaken using aerial survey methods. We report dramatic declines in numbers (～1.0 million breeding pairs) compared to numbers observed in the late 1970s (～5.4 million pairs), but show that these reductions have occurred principally at sites where numbers had previously been very large. During the breeding season, the main foraging grounds of birds from these sites overlap with the foraging grounds of Antarctic fur seals Arctocephalus gazella, a major competitor for their principal prey, Antarctic krill Euphausia superba. We suggest that the redistribution of the macaroni penguin population at South Georgia reflects the recent recovery of fur seal populations and thus the ongoing consequences of human intervention at South Georgia, a process which started more than 2 centuries previously. The implied resource competition and the observed population changes may also be exacerbated by recent reductions in Antarctic krill abundance which have been linked with reductions in seasonal sea ice following recent, rapid, regional warming in the Antarctic; however, the recovery of fur seal populations, and the ongoing recovery of krill‐eating whale populations argues that tropho‐dynamic interactions may be sufficient to explain the observed changes.     

The effects of gastropod shell availability and habitat characteristics on shell utilization by the intertidal hermit crab Pagurus longicarpus Say

The shell utilization patterns of two intertidal populations of the hermit crab, Pagurus longicarpus Say, were studied. The populations differed with respect to the physical characteristics of their habitats and the availability of empty gastropod shells. The first population was in an estuary connected to Narragansett Bay. This population had few, if any. empty shells available in the area. The second population was in a rock-cobble area directly on Block Island Sound. There were large numbers of empty gastropod shells available for this population. The consistently high gastropod mortality on this shore appears to be caused by the animals being washed up on the beach, where they die due to desiccation.Data from samples collected from June to November of both 1974 and 1975 showed that there were distinct differences in the shell utilization patterns of the two populations. A greater proportion of the animals collected from the estuary population inhabited damaged shells and/or shells with symbionts compared to the individuals from the population with large numbers of empty shells available.The results of shell selection experiments indicated that individuals from both populations inhabited less than preferred shells. The population with large numbers of empty shells available was qualitatively shell-limited because of the effect of physical factors on the morphology of the gastropod species of that area. In addition, the shell selection experiments showed that individuals from the two areas had significantly different shell preferences. This result may be explained by the effects of the environment on the growth rates of the hermit crabs and/or as an indication that shell preferences may vary in response to the physical factors of a given habitat.     

暮鼠越冬种群结构的年间变化

自1984年4月至1999年8月,我们沿铁路轨道检测了农田中暮鼠(Calomys venustus)的多度,研究了种群密度、越冬种群结构和繁殖期长度之间的关系,发现种群具有增长、高数量和下降年份。将动物按照同生群(种群内在相同时间内出生的一些个体)分开,利用2×2列联表卡方检验对不同性别的越冬种群结构与数量(高数量和种群下降)间的关联性进行了分析。就高密度与种群密度下降年份中的同生群组成而言,不同密度的年份显示种群结构有显著差异。在数量增长和高密度的年份里,在繁殖季节的起始期,前一年秋季出生的个体比同年夏季出生的个体在数量上要占优势,而在同生群数量下降年份则相反,特别是雌性。高密度年份具有繁殖期缩短的特征,而种群增长年份繁殖期延长。结果表明,这些变化不能只归结于繁殖期长或繁殖率引起密度变化。我们的结论是:解释C·venustus种群消长不能仅考虑动物同生群本身,需要考虑其社会和环境因子的作用。