Showing papers in "Journal of Animal Ecology in 1991"

Food Hoarding in Animals

Abstract: In this first comprehensive synthesis of the literature on food hoarding in animals, Stephen B. Vander Wall discusses how animals store food, how they use food and how this use affects individual fitness, why and how food hoarding evolved, how cached food is lost, mechanisms for protecting and recovering cached food, physiological and behavioral factors that influence hoarding, and the impact that hoarding animals have on plant populations and plant dispersal. He then provides detailed coverage of hoarding behavior across taxa-mammals, birds, and arthropods-to address issues in evolution, ecology, and behavior. Drawings, photographs, and appendixes document complex and intrinsically interesting food-hoarding behaviors, and the bibliography of nearly 1,500 sources is itself an invaluable and unique reference.

Dung beetle ecology

Abstract: In many ecosystems dung beetles play a crucial role--both ecologically and economically--in the decomposition of large herbivore dung. Their activities provide scientists with an excellent opportunity to explore biological community dynamics. This collection of essays offers a concise account of the population and community ecology of dung beetles worldwide, with an emphasis on comparisons between arctic, temperate, and tropical species assemblages. Useful insights arise from relating the vast differences in species' life histories to their population and community-level consequences. The authors also discuss changes in dung beetle faunas due to human-caused habitat alteration and examine the possible effects of introducing dung beetles to cattle-breeding areas that lack efficient native species. "With the expansion of cattle breeding areas, the ecology of dung beetles is a subject of great economic concern as well as one of intense theoretical interest. This excellent book represents an up-to-date ecological study covering important aspects of the dung beetle never before presented."--Gonzalo Halffter, Instituto de Ecologia, Mexico City

Population structure of temperate zone insectivorous bats in relation to foraging behaviour and energy demand

Abstract: (1) The morphology, echolocation calls, foraging behaviour and prey distribution of two temperate zone species of insectivorous bats was studied to assess the hypothesis that sexual differences in distribution pattern are the result of differences in energy demand. (2) In an area of the eastern slopes of the Rocky Mountains (Canada) characterized by low ambient temperatures and low insect abundance, over 90%yo of the Myotis lucifugus caught during the summer were adult males while an equal sex ratio of Myotis evotis was caught. (3) M. lucifugus forage low over water on aerial prey, especially chironomids, which are abundant only for a short time after sunset. (4) M. evotis forage along paths and in forest and prey primarily on moths. They take insects from the air but laboratory studies indicate that they are also adept at gleaning prey from the ground and vegetation. This provides a broader, more predictable food resource than is available to M. lucifugus. (5) I suggest that the flexible foraging strategy of M. evotis allows reproductive females, with their high energy demand, to inhabit areas that cannot support reproductive female M. lucifugus. Males of both species can exist in such areas because of lower energy demand and, potentially, the use of torpor under adverse conditions. Selecting such areas and reducing foraging time may benefit males if there are risks incurred while they forage.

Determinants of chick survival in the lesser black-backed gull: relative contributions of egg size and parental quality

Abstract: (1) Avian egg size is commonly held to be an important index of egg 'quality' because it reflects the quantity of yolk reserves available to the chick during embryonic development and on hatching. (2) The assumption that egg size may therefore play an important part in determining chick survival overlooks the confounding variable of parental quality which may influence both egg size and fledging success. (3) In order to test the hypothesis that the abilities to produce large eggs and to rear chicks successfully may be positively related, and to investigate the relative contributions of parental quality (ability to produce large eggs) and egg size per se to chick fledging success, a clutch transfer experiment was performed in which clutches of large eggs were cross fostered with clutches of small eggs. (4) Large eggs produced chicks which were not only skeletally larger (tarsus length) but also heavier for their size than those from smaller eggs, both of which could contribute to increased chances of survival. (5) Logistic regression analysis showed that both egg size and the quality of the foster parents contributed significantly to the probability of fledging. Parental quality was more important than egg size in determining chick survival, which suggests that correlations between survival and egg size found by other workers in nonexperimental situations may be due to the confounding effect of parental quality. (6) The contribution of large egg size to chick survival in the lesser black-backed gull Larus fuscus L., appears to be mediated via advantages of increased skeletal size, rather than body condition, on hatching. (7) As large egg size is advantageous, selection for increasing egg size is implied. The likely counterbalancing forces are discussed.

Experimental Evidence for a Causal Relationship between Timing and Success of Reproduction in the Great Tit Parus m. major

Abstract: SUMMARY (1) We investigated experimentally whether timing of reproduction is causally involved in the seasonal decline in reproductive success in the great tit Parus m. major L. This is important because of its implications for the optimization of reproductive decisions of the individual bird. (2) Timing of breeding was manipulated by inducing repeat clutches through removal of the first clutch. The experiment was performed in 1987 in two forests (W and 0) and followed up the year after. It was assumed that parental quality was unaffected by the ex-periment. Reproductive success of the experimental and undisturbed control clutches were compared. For forest 0, reproductive success of the experimental clutches was also compared with the expected reproductive success of first clutches laid at the same time. (3) Clutch size, fledging success and nestling weight in experimental clutches were reduced as compared with controls in forest W but not in forest 0. We conclude that late breeding causes reduced pre-fledging reproductive success in forest W but not in forest 0. (4) Recruitment of fledged young in the breeding population was strongly reduced by the experiment. We conclude that late breeding caused reduced post-fledging reproductive success in both forests. (5) Survival of females was reduced by the experiment in forest 0 relative to controls and this corresponded with the natural seasonal trend. Survival of females in W and of males in both forests was unaffected. In experimental females, clutch size in the next breeding season was reduced by 16 eggs compared with controls. The clutch size of the males was unaffected, as was the following year's laying date for both sexes. We conclude that future reproductive success of females, but not of males, is also related to the timing of current reproduction. (6) Possible mechanisms underlying the relationship between date and reproductive success are discussed. It is suggested that differences in pre-fledging reproductive success induced by the experiment are related to food availability. Differences in post-fledging reproductive success are probably caused by competition between early and late young.

Individual decisions and the distribution of predators in a patchy environment. ii. the influence of travel costs and structure of the environment

Abstract: SUMMARY (1) We investigate properties of a model of predator distribution in relation to prey abundance, when the predation process is subject to:(i) non-negligible handling time and mutual interference; (ii) predator learning; (iii) intake rate maximization by individual predators. The model is a development of that of Bernstein, Kacelnik & Krebs (1988). (2) The independent variables are between-patch travel cost and structure of the environment. The outcome of the model is described in relation to the predictions of the ideal free distribution (IFD). We consider both the numerical distribution of predators and the mortality rate imposed on the prey population. (3) When travel cost is small, prey depletion is slow and interference is moderate, predators conform to the predictions of the IFD and prey mortality is densitydependent. (4) As travel cost is increased, rate-maximizing predators become more sedentary and the population settles at distributions far from the IFD. In common with all other disturbances of the predation process that impair the correlation between prey and predator densities, this causes mortality to approach density independence and later negative density dependence. (5) In semi-continuous environments where prey density is correlated between neighbouring patches, the slower the spatial rate of variation in prey density (the coarser the environmental grain), the poorer is the adjustment to the IFD. This effect is due to the predators' need for learning: when the environmental sample experienced within the reach of each individual predator is unrepresentative of the global average prey density (as it happens when the environmental grain is very coarse relative to migration range of predators), the predators cannot learn the

Host-plant selection in the holly leaf- miner: does mother know best?

Abstract: SUMMARY (1) The holly leaf-miner (Phytomyza ilicis) is a monophagous leaf-mining agromyzid that attacks holly (Ilex aquifolium). (2) Twenty-five individual holly bushes maintained six- to eightfold differences in levels of infestation over 3 years (three generations of mines), despite being in close proximity. Differences in levels of infestation were due to differential oviposition by adult flies. (3) Infestation levels were negatively correlated (nominal P < 0.05) with nitrogen levels in young foliage at the time of oviposition in one generation of flies (1988); however, this result is difficult to interpret because several significance tests were carried out. No other characteristics of the bushes were correlated with levels of infestation. (4) Contrary to expectation, larval performance and host-plant selection by adult female were not coLrelated. There were no differences in mine size, larval growth rate, or size of adult females at emergence on heavily infested or lightly infested bushes. Percentage successful emergence was low, and did not differ significantly with mine density. (5) The heaviest source of miner mortality (miscellaneous larval deaths) was density-independent. Mortality of larvae surviving miscellaneous larval deaths was significantly spatially density dependent (revealed by k-factor analysis), due to parasitism by Chrysocharis gemma. Spatially density-dependent larval parasitism, and miscellaneous larval deaths were inversely correlated. (6) We discuss these results in the context of the ideal free distribution (Fretwell 1972), speculating that high densities of animals reduce the quality of intrinsically superior habitat patches via spatially density-dependent larval parasitism, leading to equal miner performance on all bushes.

Foraging and oviposition decisions in the parasitoid Aphytis lingnanensis : distinguishing the influences of egg load and experience

Abstract: (1) We used an experimental protocol that allowed us to distinguish the relative influences of egg load and experience with host contact on foraging behaviour and clutch size decisions in the gregarious parasitoid Aphytis lingnanensis Compere. Egg load was manipulated without concurrent changes in experience by exploiting sizerelated variation in fecundity and by holding parasitoids at different temperatures to vary the rate of egg production. (2) Egg load influenced the intensity of searching behaviour. Parasitoids with smaller egg loads required more time within a foraging arena to discover hosts. (3) Parasitoids with smaller egg loads and parasitoids with a prior experience with host contact deposited smaller clutches. (4) Total host handling time was inversely related to parasitoid egg load. Increased egg load had a similar accelerating influence on each of the component activities that comprise host handling, including preparation for oviposition, oviposition, and postoviposition grooming and resting. (5) The probability of successful parasitoid egg to adult development was independent of clutch size. Progeny size, however, decreased with increasing number of competing sibs. (6) A. lingnanensis clutch size decisions do not conform to the static expectations of a forager maximizing the fitness gained per egg, per host, or per unit time. Rather, clutch size decisions appeared to be fundamentally dynamic, responding to changes in parasitoid physiology (egg load) and the parasitoid's perception of host availability (experience).

Long-Term Decline in Body Size in a Snow Goose Population: Evidence of Environmental Degradation?

Abstract: (1) The effect of environmental factors on annual body size variation was investigated in a breeding population of lesser snow geese (Anser caerulescens caerulescens L.) La Perouse Bay, Manitoba, using data from 1969 to the present. The population size has increased from approximately 2000 to 10 000 pairs during this period (Cooch et al. 1989). (2) Annual mean gosling body mass, tarsus and culmen length (measured at fledging) declined significantly by approximately 16% (240 g), 4% (3.4 mm), and 2% (0.93 mm) respectively in cohorts hatching between 1976 and 1988. The decline in gosling size has led to a significant decline in size of locally bred adults. Annual mean adult female body mass, tarsus and culmen lengths declined by approximately 15% (270 g), 6% (5.4 mm), and 4% (2.3 mm), respectively, in cohorts hatching between 1969 and 1986. (3) Gosling growth and subsequent adult size was also reduced in years with cold, wet weather after hatch. (4) The decline in gosling size was not dependent on the pattern of annual variation in egg or hatch mass, nor systematic changes in annual mean hatch date or post-hatch weather. Goslings reared by individual adult females showed a decline in size over time, suggesting that the general decline reflects a non-genetic change in gosling growth rates during the fledging period. The most probable non-genetic factor is a long-term reduction in food available to the geese at La Perouse Bay. This reduction in food availability may reflect over-exploitation of primary food plants by the geese.

Breeding performance in the western gull : effects of parental age, timing of breeding and year in relation to food availability

Abstract: (1) We studied age-specific breeding success of western gulls (Larus occidentalis) on south-east Farallon Island, California in relation to annual variation in food abundance, 1983-89. We assessed yearly reproductive performance on the basis of clutch initiation date, clutch size, hatching and fledging success, and the number of chicks raised to independence. We categorized age of parent into three groups: young, middle-aged and old. (2) Mature birds initiated breeding earlier and laid larger clutches; they fledged more chicks than younger birds as a result of hatching a greater proportion of their eggs and fledging a greater proportion of their hatched chicks. The oldest birds generally did not differ from middle-aged in breeding performance. The difference in reproductive performance between young and mature birds was most apparent during years when food availability was reduced. (3) Timing of breeding influenced reproductive performance independently of parental age; reproductive performance decreased throughout the breeding season. Within-season reductions in reproductive performance were most apparent for young breeders and individuals with small clutches or broods. (4) Breeding performance varied significantly among years independently of age of the study animals. Food availability accounted for part of the yearly variation in breeding success. (5) We suggest that clutch/brood size reflects individual quality. Age-specific breeding success in western gulls is best explained by previous breeding experience and individual quality.

The significance of limiting and regulating factors on the demography of moose and white-tailed deer

Abstract: SUMMARY (1) I examined the significance of food competition, wolf predation (Canis lupus), and snow accumulation as limiting or regulating factors of moose (Alces alces) and white-tailed deer (Odocoileus virginianus). That is, I assessed the contribution of those factors in creating year-to-year variations in animal abundance, or in generating density dependence. (2) I used long-term data on the demography of moose on Isle Royale, Michigan, and deer in the National Superior Forest, north-eastern Minnesota. (3) Wolf predation and food competition explained 80% of the interannual variation of moose abundance. Snow accumulation had no quantifiable effect on moose numbers. Competition for food, but not wolf predation and snow, had a regulatory impact on moose. (4) Wolf predation was inversely related to moose density and the relationship differed between periods of moose expansion and reduction. The dual density relationship of wolf predation may explain population cyclicity of moose at elevated densities. (5) Significant inverse relationships were found between deer population growth and relative wolf density, as well as with deer density. Snow had no measurable effect on deer numbers, possibly because of extremely low deer densities and the predominant impact of wolf predation. (6) A previous suggestion that snow accumulation during consecutive winters creates a cumulative impact on the nutritional status of deer and moose was not supported.

Territory infidelity in the polygynous great reed warbler acrocephalus arundinaceus: the effect of variation in territory attractiveness

Abstract: SUMMARY (1) We studied breeding dispersal in male and female great reed warblers (Acrocephalus arundinaceus L.) at lake Kvismaren in South Central Sweden from 1984 to 1990. In the two study plots, Marsh A and Marsh B, the numbers of breeding birds increased over the years. (2) About 55% of the breeding birds returned to the study site between years and 80% returned to the same breeding marsh. Birds that had bred successfully were more likely to return to their breeding marsh than those that had failed. (3) Between years, 18% of females and 6% of males returned to breed in their former territories and males tended to move further than females. Less than 15% of the females with their previous year's mate alive, re-established the pair bond. (4) The order of territory settlement was similar between years. Both males and females settled earlier in yeart,j in territories that were occupied early in yeart, than in territories occupied late or in territories that had been unoccupied. (5) Males and females that arrived relatively earlier than they did the year before occupied a territory of higher rank. Such males increased their reproductive success significantly whereas females did not. (6) The attractiveness of territories was fairly constant over the study period. By dividing the territories into two groups, attractive and less attractive, based on the average order they became occupied by males, we show that males became mated with more females and had higher reproductive success in the attractive territories. Reproductive success of females did not differ between attractive and less attractive territories. (7) The high marsh fidelity for both males and females cannot be explained by benefits from optimal inbreeding, re-mating with former mates or breeding in the same territory. Instead, we suggest that the adaptive significance of returning to their breeding marsh (neighbourhood fidelity) is that the birds can use knowledge about the quality of several territories, gathered in yeart, and settle in the best

Conservation of Australia's forest fauna

Abstract: The editor Dan Lunney and the council supporting members of the Royal Zoological Society of New South Wales are to be congratulated and encouraged for the production of a valuable journal that helps bridge the ever-increasing chasm between the interested public and the enthusiastic scientist. Like most Royal Societies, the emphasis is on rigorous communication of research findings to a broader and often lay audience. Increasingly, ecologists are shouldering their social responsibilities and applying their expertise more widely. The Australian Zoologist will continue to play a key role in this process and will continue to exploit the huge niche successfully and opportunistically in response to the rapid changes in the physical, scientific and social environments in Australia. REFERENCES

Living in a patchy environment

Abstract: Introduction: Patchy environment - an overview 1 Starvation and predation in a patchy environment 2 The response of plants to patchy environments 3 Dynamic stability of a single-species population in a divided and ephemeral environment 4 Variance and patchiness in rates of population change - a planthopper's case history 5 Coexistence in a patchy environment 6 Population dynamics and community structure of parasitic helminths 7 Dung and carrion insects 8 Patchiness and community structure 9 Extinction of finite metapopulations in correlated environments 10 Conservation in a variable environment - the optimal size of reserves 11 Does interdemic group selection occur in commensal house mice (Mus domesticus)? 12 Sex determination and sex ratios in patchy environments

Drifting territoriality in the red fox Vulpes vulpes

Abstract: (1) The spatial organization of a population of red foxes, Vulpes vulpes L., living in the city of Oxford was investigated and contrasted to that of a neighbouring population in the surrounding suburbs. (2) Both populations were organized in social groups, each of which occupied an exclusive territory. While territories in the suburbs were spatially stable, those in the city drifted in location continually, but they did so in such a way that the juxtaposition of neighbouring groups remained essentially unaltered across generations of occupants. (3) The hexagonal pattern of city ranges moved at a rate equivalent to the complete displacement of an average range (38·8 ha) every 13 months (3·01 ha month-1), although drifting was more pronounced from November to April. City and suburban foxes had comparable diets and ranges of the same order of magnitude; the mobility of city foxes was associated with social instability due to a higher turnover of the population and a lower proportion of barren vixens. (4) As a response to constraints of the city environment not encountered in the suburbs, synchronous drifting of city ranges represents a rapid modification of behaviour since the urban niche first became occupied by foxes in the 1930s.

An Experimental Study of the Effects of Timing of Breeding on the Reproductive Success of Common Guillemots (Uria aalge)

Abstract: SUMMARY (1) The reproductive success of 474-574 pairs of common guillemots was studied from 1985 to 1987 on Skomer Island, Wales. (2) Laying was highly synchronized, and within years productivity decreased seasonally from shortly after the period of peak laying. (3) The timing of breeding of one group of forty-five pairs was experimentally delayed by 13 days to test whether timing of breeding relative to calendar date or relative to other pairs was the factor causing the seasonal decline in productivity. The results showed that timing relative to other individuals rather than calendar date was important. (4) Naturally late breeders provisioned chicks at a lower rate than early breeders, but there was no evidence for a seasonal deterioration in food availability. (5) The effects of physical characteristics, breeding density and synchrony on productivity were examined in a logistic regression analysis for 567 breeding sites. Only density and synchrony had significant effects. Productivity increased with density and decreased for late breeders. (6) Predation was the main cause of breeding failure. High-density breeding reduced vulnerability to predators. Synchrony was important for the benefits of highdensity breeding to apply throughout the breeding period, and also for swamping predators.

Breeding biology of white-fronted bee-eaters at nakuru: the influence of helpers on breeder fitness

Abstract: SUMMARY (1) Among white-fronted bee-eaters (Merops bullockoides) near Nakuru, Kenya, helpers dramatically increased the fitness of breeders. Using 5 years of data, we examine the relative importance of food availability, breeder attributes and group size on reproductive success. (2) Both food availability and size of the group attending the nest had significant effects on productivity, while the characteristics of breeders (age, experience) did not. Helpers had their effect almost entirely through increased productivity per nesting attempt, each helper on average increasing the number of fledglings by 0 50 (+0.06 S.E.). The activities of helpers did not affect either breeder survival or the number of nesting attempts per year. (3) The presence of helpers did not affect clutch size, had no influence on the probability of successful hatching, but dramatically increased the rate of provisioning per nestling. As a consequence of their feeding contributions, helpers significantly decreased both the probability of nestling starvation and the degree of nestling developmental retardation due to food stress. More young fledged, and fledged in better condition, from helped nests. (4) The mechanisms by which helpers have their effects are largely ecologically determined. The ability of bee-eater helpers to increase fledging success through their feeding contribution is related to the environmentally unpredictable, and often harsh, conditions at Nakuru. Nestling starvation rates were high (48% of all hatchlings), whereas predation losses were low (4% of eggs laid). In other, cooperative breeding species where helper feeding contributions have increased nestling growth and survival, sparse or unreliable food resources have also been the rule. In contrast, predation has been implicated as the major source of mortality in many other cooperative breeding species, and it is in these species that the anti-predator activities of helpers have been reported to have an important impact on nesting success. (5) Helper effects of the magnitude recorded in the Nakuru population of beeeaters are unusual. The presence of one helper effectively doubled the fledging success of an unaided pair, and the effect of increasing numbers of helpers was linear across all commonly observed group sizes. This large helper contribution has important implications for the behavioural options of both breeders and helpers. Not only should the presence/absence of helpers influence the decision to breed, but breeders are expected to compete for potential helpers. From the perspective of a potential

The comparative biology of parasite species diversity: internal helminths of freshwater fish

Abstract: SUMMARY (1) This paper describes and analyses the mean number of parasitic helminth species per host individual among Canadian freshwater fish. (2) Helminth diversity varies among host species. (3) The diversities of different taxa of helminths are correlated both within and among host species. (4) Helminth diversity is positively correlated with host size, longevity, diet and geographical range. Size (or longevity) produces the strongest correlations; when the effect of size is removed, only diet remains correlated with helminth diversity. Size and diet together explain about 40% of variance in helminth diversity among host species; the model is most successful for cestodes, where about 60% of the variance is explained. (5) Most of the ecological covariance of helminth diversity is displayed at rather high taxonomic levels, perhaps because of lag between host evolution and parasite adaptation.

Time budgets and foraging characteristics of lactating antarctic fur seals

Abstract: SUMMARY (1) We investigated time allocation to parental care ashore and foraging at sea by lactating Antarctic fur seals at Bird Island, South Georgia, during 1988-89 and 1989-90 and related this to foraging behaviour measured in terms of diving performance at sea and growth of pups. (2) The mean duration of foraging trips was 121 h and 100 h in 1988-89 and 1989-90, respectively, while periods ashore were 55 h and 45 h, respectively in the two years. There was a significant difference between these variables in the two years but there was no significant difference in the percentage of time spent at sea. In both years, there was significant variation between individuals in the foragingattendance time budget. (3) There was a positive correlation between mean time spent ashore and mean time spent at sea for individual seals. The foraging-attendance patterns of seals changed significantly with time through lactation in one year of the study but not in the other. There was no effect of maternal age or size on foraging-attendance time budget. Duration of foraging trips or the period spent ashore had no effect on pup growth rate. (4) During short foraging trips (1-2 d) seals dived for a greater proportion of the time available for foraging than during longer foraging trips (>3 d). Seals fed predominantly on krill during both years. Most foraging occurred at night and this was reflected in diel variation in times of arrival and departure of seals from the pupping colony. Based on estimated swimming speed and travel times to and from Bird Island, it was estimated that seals were normally feeding between 60 and 90 km from Bird Island.

Species conservation: a population-biological approach.

Abstract: "The source of this book is a symposium on 'Populationsbiologische Aspekte des Artenschutzes' held in October 1989 at the Akademie der Wissenschaften und der Literatur in Mainz, FRG"--Pref.

Variation in sexual size dimorphism and maximum body size among adder populations : Effects of prey size

Abstract: (1) Geographic variation in maximum body size of male and female adders, Vipera berus, was documented over one mainland locality and six groups of islands in the Baltic Sea. Males varied more in body size among localities than females, although not significantly so. (2) Geographic variation in prey (field vole, Microtus agrestis) body size explained 68% and 40% of the variation in maximum body size of male and female adders, respectively. Body size of adders increased with body size of prey. (3) Adders were smaller on islands where there were three prey species than where there were two. It is suggested that selection for fasting endurance where there are few prey species and a high risk of starvation may have produced this pattern. (4) Growth rates of individual adders were faster where mean field vole body weight was large (47 g) than where it was small (26 g). Maximum body size of adders was large where growth rate was fast and vice versa. (5) Female adders were larger than males at all localities. Females also had faster growth rates than males. (6) The degree of sexual size dimorphism of adders varied among localities and was negatively correlated with size of males. There was no relationship between sexual dimorphism and size of females. (7) There was no significant relationship between sexual size dimorphism of adders and mean body size of field voles. Nor was there any relationship between sexual dimorphism and number of prey species or size distribution of field voles. (8) I argue that optimal body size for survival is locally determined by prey availability and size of prey items. However, due to the fecundity advantage of large size in females, female adders deviate from the optimum size for survival, and more so when this optimum size is small. Thus, local variation in properties of the food resource, e.g. prey size, can give rise to variation in sexual size dimorphism.