Showing papers in "Journal of Animal Ecology in 1985"

Identifying areas of concentrated use within the home range

Abstract: (1) Animals generally use space disproportionately within the boundaries of their home range. Areas receiving concentrated use by resident animals can be termed core areas. Identifying these core areas is an important part of understanding the ecological factors that determine use. (2) Comparison of the observed space-use pattern with that expected from a uniform pattern of use is our basis for defining core areas. The difference in ordered cumulative distribution functions can be tested using a one-sided goodness-of-fit procedure. Core areas are delineated by enscribing those areas within the home range where use exceeds that expected from a uniform distribution. (3) This method of estimating core areas is illustrated with a hypothetical data set and applied to radio-telemetry locations of a black bear (Ursus americanus, Pallas). The bear used two distinct core areas, which enclosed 34% of the total home range and included 76% of the animal locations. (4) Patterns of core area use are demonstrated for male western tanagers (Piranga ludoviciana, Wilson). Although 90% home range boundaries overlap, core areas for four adjacent males are shown to closely resemble exclusive-use territories. (5) Interspecific use of core areas of western tanagers and chipping sparrows (Spizella passerina, Bechstein) are compared. Core areas for chipping sparrows tended to be a larger proportion of the home range and intensity of core area use was greater for western tanagers. (6) The size and location of core areas depend on the method of determination of home range size. Alternative home range methods may have a substantial influence on the estimation of core areas due to differences in the estimated home range boundary and underlying use distribution.

The effects of density-dependent resource limitations on the demography of wild reindeer

Abstract: Pour une forte densite la survie des jeunes diminue mais non celle des adultes se trouvant dans la classe d'âge reproductrice et la plus abondante, la fecondite des subadultes, descend au-dessous du seuil de taille corporelle pour la maturite, la fecondite des adultes n'est pas affectee. La limitation des ressources dependant de la densite est plus apparente pour les fortes densites de population

Does Interspecific Competition or Predation Shape the African Ungulate Community

Abstract: (1) Although interspecific competition has been the suggested process producing resource partitioning and coexistence of African ungulates, recent evidence has pointed to intraspecific competition, predation, and facilitation as alternative hypotheses. (2) The ungulate community in the Serengeti-Mara region of Tanzania and Kenya was examined in the light of these hypotheses between 1980 and 1983. The wildebeest migration provided a natural experiment to alter the intensity of interspecific competition among eight other species of grazing ungulates. (3) Data on vegetation choice, habitat overlap with wildebeest, and herd spacing between species were obtained from vehicle transects in the presence and absence of wildebeest. These data were used to test the predictions derived from six hypothetical processes: (i) interspecific competition, (ii) intraspecific competition, (iii) autecological factors, (iv) predation, (v) facilitation, and (vi) random processes. (4) There was a high similarity in vegetation choice between species, and a large overlap with the competing wildebeest. (5) Most species were found closer to wildebeest than an expected random distribution would suggest. (6) Comparing these results with the predictions, they suggest that Thomson's and Grant's gazelles are strongly influenced by predation. (7) Zebra, topi, impala, waterbuck and warthog are influenced by both predation and interspecific competition and these species may be showing a mixed evolutionarily stable strategy to cope with two opposing pressures. Zebra, in particular, are using the wildebeest to obtain protection from predators. (8) In general predation appears to play as much a role as interspecific competition in structuring this community.

Fur seal diving behaviour in relation to vertical distribution of krill

Abstract: (1) Quantitative studies of predator-prey interactions depend on a knowledge of their spatial dynamics and behaviour. Studies on marine vertebrates have hitherto been precluded by the difficulty of acquiring the relevant data. (2) Continuous records of diving depths of female Antarctic fur seals on 3-8 day feeding trips to sea from South Georgia were analysed in conjunction with data on diel changes in the abundance and distribution of their main prey, krill. (3) In 36 complete days foraging by seven seals, 75% of 4273 dives were at night. Dives then were consistently shallower (dive depth < 30 m) than in daytime (mostly 40-75 m). (4) This closely matched changes in the vertical distribution of krill, nearly all of which was below a depth of 50 m from 09.00-15.00 h, with substantial quantities above 40 m only between 21.00-06.00 h. (5) Although over 40% of krill in the water column at any time of day was below 75 m, only 3% of dives exceeded this depth. We suggest that because krill migrate vertically fur seals are able to exploit them most efficiently during shallow dives at night.

Parasitoid foraging: should parasitism be density dependent?

Abstract: Presentation d'un modele mathematique; nombreux exemples pris parmi les insectes. Suivant la densite de l'hote, le parasitisme est ou non dependant de la densite du parasite

The effect of larval density on adult longevity of a mosquito, aedes sierrensis: epidemiological consequences

Abstract: SUMMARY (1) A 3-year field study of larval populations of Aedes sierrensis, a common North American tree-hole mosquito, produced no evidence for density-dependent larval mortality, but revealed that pupal weight of females was inversely correlated with larval density. (2) Sampling of a wild adult population indicated that, in general, larger adults lived longer than smaller ones. The interval between blood meals in nature was estimated as 8 days. (3) The total expectation of infective life (for transmission of a nematode, Dirofilaria immitis) for females was estimated within the range of larval densities observed in nature. As these estimates may be maximal at intermediate population densities, reduction of larval density may result in an increase in the capacity of the adult population to transmit disease. Accurate assessment of the longevity of adult female mosquitoes has long been recognized as prerequisite to quantification of the ability of a species to transmit disease (MacDonald 1957; Garrett-Jones & Grab 1964; Garrett-Jones 1964). In no case, however, has it been shown that intraspecific variation in adult longevity may be related in a simple fashion to larval density, and that this relationship has important epidemiological consequences. The present study shows that for a wild mosquito population (i) pupal size is inversely related to larval density and (ii) adult longevity is positively correlated with adult size. Equations describing these relationships are linked by an equation relating pupal weight to adult size, then used in conjunction with MacDonald's (1957) equation describing adult survivorship to explore the relationship between the total expectation of infective life of females arising from a given population and the larval density of that population. The treehole-breeding Aedes sierrensis (Ludlow) is an appropriate species for this kind of study because: (i) it is common and easily identified; (ii) as its larval habitat is confined, sampling is simplified; (iii) it is univoltine, allowing easy estimation of larval mortality; (iv) it is the only common mosquito inhabiting tree-holes throughout most of its range (Zavortink 1985); and (v) it is a vector of a nematode parasite of canids, Dirofilaria immitis (Leidy) (Weinmann & Garcia 1974; Walters & Lavoipierre 1982). Life history of A. sierrensis Aedes sierrensis is prevalent on the west coast of North America from southern California to British Columbia. Winters in this region are mild and wet, while summers are

Variability in feeding rate and meal size of Leach's storm-petrel at Kent Island, New Brunswick

Abstract: (1) Feeding rate and meal size of Leach's storm-petrel at Kent Island, New Brunswick, were studied by analysing mass increments of the chicks. (2) Meal size, estimated by mass increments over short periods during the night, averaged 10.0 g (S.D. = 2.3 g, range approximately 5-13 g). (3) Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 3-h intervals during the night (SUM) by the equation NET = -6.04 + 0.92 SUM (r2 = 0.88). With knowledge of meal size and of this relationship, we estimated the number of feeds per night (0, 1, or 2) from NET. (4) During August in both 1962 and 1983, each parent fed its chick on 43% of nights. Each parent fed independently of the other. Percentages of nights with 0, 1, and 2 feeds were 35, 44, and 21%, which do not differ significantly from the binomial probability function with P = 0.43. (5) The probability of a parent feeding its chick (p) did not vary with respect to date (i) in 1983. In 1962, P, was significantly below average on 3 nights and above average on 3 nights. Periods between feeds by either or both parents were 57% = 1 day, 31% = 2 days, and 11% = 3 days in 1983, and 45%, 43%, 9%, 2% (4 days), and 1% (5 days) in 1962. (6) We estimated that intervals between feedings by an individual parent were 22% = 1 day, 38% = 2 days, 23% = 3 days, and 17% = 4 days in 1983. Meal size was independent of the number of days since the previous feeding. (7) After removing variation attributable to date in season (hence age) and difference between chicks, variance in chick mass was 47.8 g2. This was approximately equal to the variance in NET (51.6 g2), indicating that short-term variance in chick mass is generated anew each night by variation in amount fed. Furthermore, the covariance between NET on one night and the next is negative and about half the value of the variance, demonstrating short-term regulation of food delivery. (8) Variability in feeding rate and meal size indicates that intervals between feeds rarely are so long as the period over which chicks could survive utilizing only their substantial fat reserves. This calls into question the prevalent idea that the purpose of the fat deposits is to guarantee survival through periodic fasts resulting from unpredictable food supplies or feeding conditions. Furthermore, food provisioning in storm-petrels appears to be regulated by the requirements of the chicks, rather than by variation in food resources available to adults.

Winter activity of pipistrelle bats

Abstract: (1) Pipistrelle bats leave hibernation to feed in all winter months. (2) Winter activity is most likely on warm and calm nights. (3) Bat feeding rates are highest on warm calm nights. (4) The behaviour of the bats shows a good qualitative fit to a simple energetic model of winter activity, but the response of the bats to temperature does not form the predicted step-function. (5) Males seem more often active in winter than females, and more males are active on warmer nights than on cold ones.

Changes in the Biology of the Kittiwake Rissa tridactyla: A 31-Year Study of a Breeding Colony

Abstract: Etude des changements a long terme de la biologie de la reproduction de R. t. dans une colonie du nord-est de l'Angleterre

Problems in estimating age-specific survival rates from recovery data of birds ringed as young

Abstract: SUMMARY (1) The life table model is frequently employed in the analysis of ringed samples of young in bird populations. The basic model is biologically unrealistic and of little use in making inferences concerning age-specific survival probabilities. (2) This model rests on a number of restrictive assumptions, the failure of which causes serious biases. Several important assumptions are not met with real data and the estimators of age-specific survival are not robust enough to these failures. (3) Five major problems in the use of the life table method are reviewed. Examples are provided to illustrate several of the problems involved in using this method in making inferences about survival rates and its age-specific nature. (4) We conclude that this is an invalid procedure and it should not be used. Furthermore, ringing studies involving only young birds are pointless as regards survival estimation because no valid method exists for estimating age-specific or time-specific survival rates from such data.

A quantitative study of the life history of a fairy shrimp (Branchiopoda: Anostraca) in relation to the temporary nature of its habitat, a Kenyan rainpool

Abstract: L'etude porte sur 2 cohortes de Streptocephalus vitreus qui vivent pendant 19 et 32 jours dans un etang temporaire

Annual variation in reproduction in snakes in a fluctuating environment

Abstract: Etude sur une periode de 2 a 15 ans, des variations d'une annee sur l'autre de la taille de la couvee (ou de la portee) chez 5 populations de quatre especes d'Amerique du Nord: Diadophis punetatus, Thamnophis radix, T. sirtalis, Ag

Coastal waders and wildfowl in winter

Abstract: Preface List of contributors Part I. Bird Populations: The Influence of Food Resources on the Use of Feeding Areas: Introduction P. R. Evans 1. Coastal birds: numbers in relation to food resources P. R. Evans and P. J. Dugan 2. Balancing the budget: measuring the energy intake and requirements of shorebirds in the field M. W. Pienkowski, P. N. Ferns, N. C. Davidson and D. H. Worrall 3. Relations between the distribution of waders and the intertidal benthic fauna of the Oosterschelde, Netherlands P. Meire and E. Kuyken 4. How Oystercatchers and Curlews successfully deplete clams L. Zwarts and J. Wanink 5. Waterfowl movements in relation to food stocks M. R. van Eerden 6. Diving duck populations in relation to their food supplies O. Pehrsson Part II. Bird Populations: Social Behaviour and the Use of Feeding Areas: Introduction J. D. Goss-Custard 7. Why do birds roost communally R. C. Ydenberg and H. H. Th. Prins 8. The unsociable plover - the use of intertidal areas by Grey Plovers D. J. Townshend, P. J. Dugan and M. W. Pienkowski 9. Age-related distribution of Dunlin in the Dutch Wadden Sea T. M. van der Have, E. Nieboer and G. C. Boere 10. Differences in quality of roosting flock of Oystercatchers C. Swennen 11. Feeding ecology, winter mortality and the population dynamics of Oystercatchers on the Exe estuary J. D. Goss-Custard and S. E. A. le V. dit Durell Part III. Introduction W. G. Hale 12. The Danish Wadden Sea K. Laursen and J. Frikke 13. The German Wadden Sea P. Prokosch 14. The Dutch Wadden Sea W. J. Wolff and C. J. Smit 15. The Dutch Delta Area R. J. Leewis, H. J. M. Baptist and P. L. Meininger 16. The British Isles P. R. Evans 17. The Atlantic coast of Morocco M. Kersten and C. J. Smit 18. The Banc d'Arguin (Mauritania) M. Engelmoer, T. Piersma, W. Altenburg and R. Mes 19. The changing face of European wintering areas W. G. Hale Index.

The Impact of Hairy Wood Ants, Formica lugubris, on the Guild Structure of Herbivorous Insects on Birch, Betula pubescens

Abstract: (1) A grease-banding experiment and a background survey of ant and non-ant sites provided evidence that the presence of wood ants changed the guild structure of the herbivorous insect community on birch. (2) In the presence of ants the abundance of free-living chewing insects was reduced more than that of leaf tie-ers, which in turn was reduced more than that of fully internal feeders such as leaf-miners. (3) Total species richness of the herbivorous insect community on birch was reduced by ants.

Interspecific competition and niche shifts in tits and the goldcrest - an experiment

Abstract: (1) In coniferous forests in Central Sweden willow, (Parus montanus) and crested tits (P. cristatus) forage in the inner canopy while coal tits (P. ater) and goldcrests (Regulus regulus) forage on the outer, needled tree parts. (2) To test if interspecific competition affects foraging site selection of the two latter species, we reduced the numbers of willow and crested tits by more than half in three 40 ha study plots in the beginning of winter. (3) Later in winter, coal tits and goldcrests increased their foraging in inner canopy in the experimental plots in comparison with three control plots. (4) An experiment is powerful in excluding alternative explanations only if it is based on a sufficient number of repetitions. Observations within a plot may be dependent because they are derived from animals inhabiting the same environment. The simplest way around the problems is to use each plot as a single observation in test. Both coal tits and goldcrests exploited inner tree parts more in all of the three experimental plots than any of the three control plots, which alone is a significant difference. (5) The experiment indicates that interspecific competition affects foraging site selection of sympatric tits and goldcrests, as has been previously suggested by many nonexperimental studies.

Population regulation for different life-stages of migratory trout Salmo trutta in a Lake District Stream, 1966-83

Abstract: Etude menee de 1966 a 83 dans le Black Brows Beck (District des lacs). La population existe rarement en equilibre dynamique par suite des perturbations liees au milieu comme la secheresse

Lake Chad : ecology and productivity of a shallow tropical ecosystem

Abstract: Historical background.- I. The lacustrine environment and its evolution.- 1. Paleolimnology of an upper quaternary endorheic lake in Chad Basin.- 2. The lacustrine environment.- 3. Physical and chemical characteristics of the waters.- 4. Hydrochemical regulation of the lake.- II. The main types of communities and their evolution during a drought period.- 5. The aquatic vegetation of Lake Chad.- 6. The phytoplankton.- 7. The zooplankton.- 8. The benthic fauna: ecology, biomass and communities.- 9. The fauna associated with the aquatic vegetation.- 10. Fish communities of Lake Chad and associated rivers and flood-plains.- III. The balance of a lacustrine ecosystem during `Normal Chad' and a period of drought.- 11. Phytoplankton production.- 12. Secondary production (zooplankton and benthos).- 13. The exploitation of fish stocks in the Lake Chad region.- IV. Trophic relations.- 14. Trophic relations between the phytoplankton and the zooplankton.- 15. Trophic relations of fishes in Lake Chad.- 16. The impact of birds on the lacustrine ecosystem.- V.- 17. The lacustrine ecosystem during the `Normal Chad' period and the drying phase.- Systematic index.- General index.