Showing papers in "Journal of Animal Ecology in 1994"
TL;DR: The small-population paradigm has not yet contributed significantly to conserving endangered species in the wild because it treats an erect (smallness) as if it were a cause and hence is of scant theoretical interest.
Abstract: Conservation biology has two threads: the small-population paradigm which deals with the erect of smallness on the persistence of a population, and the declining-population paradigm which deals with the cause of smallness and its cure. The processes relevant to the small-population paradigm are amenable to theoretical examination because they generalize across species and are subsumed by an inclusive higher category: stochasticity. In contrast, the processes relevant to the declining-population paradigm are essentially humdrum, being not one but many. So far they have defied tight generalization and hence are of scant theoretical interest. The small-population paradigm has not yet contributed significantly to conserving endangered species in the wild because it treats an erect (smallness) as if it were a cause
2,110 citations
TL;DR: A novel approach to modelling of metapopulation dynamics is described, constructed as a generalized incidence function, which describes how the fraction of occupied habitat patches depends on patch areas and isolations.
Abstract: This paper describes a novel approach to modelling of metapopulation dynamics. The model is constructed as a generalized incidence function, which describes how the fraction of occupied habitat patches depends on patch areas and isolations. The model may be fitted to presence/absence data from a metapopulation at a dynamic equilibrium between extinctions and colonizations. Using the estimated parameter values, transient dynamics and the equilibrium fraction of occupied patches in any system of habitat patches can be predicted. The significance of particular habitat patches for the long-term persistence of the metapopulation, for example, can also be evaluated
1,519 citations
TL;DR: Stable isotopes of nitrogen and carbon analyses suggest that lower trophic-level organisms are more important to several seabirds than was recognized previously and may be a good indicator of inshore versus offshore feeding preference.
Abstract: 1. The stable isotopes of nitrogen (δ 15 N) and carbon (δ 13 C) were analysed in 22 species of marine birds from coastal waters of the northeast Pacific Ocean. Analyses confirm that stable nitrogen isotopes can predict seabird trophic positions. 2. Based on δ 15 N analyses, seabird trophic-level inferences generally agree with those of conventional dietary studies, but suggest that lower trophic-level organisms are more important to several seabirds than was recognized previously. 3. Stable-carbon isotope analysis may be a good indicator of inshore vs. offshore feeding preference
816 citations
TL;DR: A philosophical position The gene as a unit of selection Clade selection and macroevolution Levels of selection among interactors Optimization and kindred concepts Historicity and constraint Diversity within and between clades Some recent controversies Statis Other challenges and anomalies Bibliography Appendix as mentioned in this paper
Abstract: A philosophical position The gene as a unit of selection Clade selection and macroevolution Levels of selection among interactors Optimization and kindred concepts Historicity and constraint Diversity within and between clades Some recent controversies Statis Other challenges and anomalies Bibliography Appendix.
761 citations
TL;DR: In this paper, a resource selection model is proposed to estimate the probability of a resource unit selection from a census of resource units at several points in time using the proportional hazards model.
Abstract: Introduction to resource selection studies. Examples of the use of resource selectory studies. Examples of the use of resource selection functions. Statistical modelling procedures. Studies with resources defined by several categories. Estimating a resource selection probability function from a census of resource units using logistic regression. Estimating a resource selection probability function from a census of resource units at several points in time using the proportional hazards model. Estimating a resource selection function from samples of resource units using proportional hazards and log-linear models. Estimating a resource selection function from two samples of resource units using logistic regression and discriminant function methods. General log-linear modelling. Analysis of the amount of use. The comparison of selection for different types of resource unit. References. Index.
569 citations
TL;DR: The preference of sheep for two temperate grassland species, ryegrass and white clover, was tested by releasing flocks onto swards that contained adjacent monocultures of grass and clover and the effects of physiological state on preference were considered.
Abstract: The preference of sheep for two temperate grassland species, ryegrass and white clover, was tested by releasing flocks (of three ewes) onto swards (0.25 ha) that contained adjacent monocultures of grass and clover, and observing their intake behaviour over 6 days. The test paddocks contained either 20, 50, or 80% clover by ground area to distinguish partial preference from indifference. To test whether recent diet affected preference, separate groups of dry (non-pregnant, non-lactating) ewes grazed prior to testing on one of three diet «back-grounds»: an all-grass sward, an all-clover sward, or a 50:50 grass/clover sward by area. To consider the effects of physiological state on preference, a further group of lactating ewes, also from a 50:50 grass/clover «background», were tested
343 citations
TL;DR: The relationship between a number of constraints and female size was studied in the parasitoid Aphaereta minuta, and larger females were found to have more eggs available, have larger eggs, live longer and have a higher searching efficiency within patches than small females, but searching efficiency for patches and travel speed were finding to be independent of size.
Abstract: 1. The relationship between the size of a female parasitoid and its fitness is a major element of models of optimal clutch size, of host species selection, of the evolution of siblicide in parasitoids and of some sex allocation models. 2. In estimating this relationship, usually only size-dependent longevity and/or fecundity is considered, neglecting differences in searching efficiency for hosts, although this is an important component of fitness. The relationship between a number of constraints and female size was studied in the parasitoid Aphaereta minuta. Larger females were found to have more eggs available, have larger eggs, live longer and have a higher searching efficiency within patches than small females, but searching efficiency for patches and travel speed were found to be independent of size
328 citations
TL;DR: It is demonstrated that female fur seals invest a significantly greater effort in foraging during periods of low prey abundance by both increasing the time spent foraging and by increasing activity during foraging.
Abstract: 1. Foraging behaviour of Antarctic fur seals rearing pups at Bird Island, South Georgia, was assessed using at-sea activity patterns measured by electronic time-depth recorders. Information was obtained for a total of 75 individuals and 191 foraging trips to sea over five reproductive seasons from 1988/89 to 1992/93; this included one season (1990/91) of low prey abundance. A method was developed to divide the diving record up into logical units or bouts which differed from past methods used for defining bouts of behaviour. 2. Foraging trips were significantly longer in 1990/91 than in the other years. There were significant differences between years in the proportion of time spent foraging when at sea and in the distribution of foraging through the day and night. These differences probably represent behavioural responses to changes in prey distribution and abundance and were reflected in the frequency of occurrence of different types of foraging behaviour. 3. Four types of foraging bout were recognized using a cluster analysis. Type I (short) bouts were of short duration (17 min) and occurred mainly during daytime and at dusk. They probably represented exploratory behaviour. Type II (long) bouts occurred mainly at night and were of long duration (80 min). They increased in frequency in 1990/91 when food was scarce and 61-73% of time spent foraging was in these bouts. Type III (shallow) bouts occurred mainly at night, were of short duration (12 min) and represented feeding close to the surface, possibly in association with other, surface-feeding krill predators. Shallow bouts accounted for 8-14% of time spent foraging. Type IV (deep) bouts were of medium duration (19 min) and represented feeding at greater depth (40-50 m) than other bout types. They were most abundant around dawn. 4. Mean dive duration during bouts exceeded the theoretical aerobic dive limit on > 30% of occasions for short, long and deep bouts. There were positive correlations between mean dive duration and surface interval duration for most of these bout types in most years. This suggested that long dives incurred a cost in terms of the amount of time spent at the surface between dives. 5. The study demonstrated that female fur seals invest a significantly greater effort in foraging during periods of low prey abundance by both increasing the time spent foraging and by increasing activity during foraging. This could represent a 30-50% increase in the costs of foraging during years of low food abundance.
262 citations
TL;DR: The evolutionary history of British butterflies and its role in conservation is illustrated with case studies in evolution.
Abstract: 1. Islands, regions, ranges, and gradients 2. Adult behaviour 3. Eggs and egg-laying 4. Butterfly populations 5. Avoidance, concealment, and defence 6. Monitoring butterfly movements 7. Butterflies and communities 8. Diversity within populations 9. Case studies in evolution 10. An evolutionary history of British butterflies 11. The conservation of British butterflies Glossary Bibliography Appendices Author and subject indexes
251 citations
TL;DR: The food-provisioning strategy of a pelagic seabird, the blue petrel Halobaena caerulea was assessed on Kerguelen Island by the simultaneous recording of individual trip duration, feed mass and change in adult mass.
Abstract: The food-provisioning strategy of a pelagic seabird, the blue petrel Halobaena caerulea was assessed on Kerguelen Island by the simultaneous recording of individual trip duration, feed mass and change in adult mass. Dietary analysis provided information on the energetic value of meals and on the spatial distribution of adults at sea. Males and females brought large meals (average 62 g), representing 36% of their unladen mass, and contributed equally to the feeding of the chick. Adults regularly alternated long trips (LT, average duration 7.2 days) over oceanic waters with short trips (ST, 1.8 days) probably restricted to the Kerguelen shelf. They systematically gained mass during LT, but lost this stored energy during the following ST
240 citations
TL;DR: A two-dimensional difference equation model is developed that relates the average quality of individuals to patterns of abundance and suggests that complex dynamics, i.e. cycles or deterministic chaos, may be more prevalent than once thought, and that higher-dimensioned models are necessary.
Abstract: Many species of forest Lepidoptera have cyclic population dynamics. Although there are numerous potential causes, including interactions with predators, parasitoids, pathogens, and food-plant quality, strongly density-dependent interactions are often difficult to demonstrate. Both autocorrelation analysis and attractor-reconstruction methods have recently been applied to a number of species' time series. Results suggest that complex dynamics, i.e. cycles or deterministic chaos, may be more prevalent than once thought, and that higher-dimensioned models are necessary. We develop a two-dimensional difference equation model that relates the average quality of individuals to patterns of abundance
TL;DR: The total estimated biomass of diurnal primates, ruminants, pigs, elephants and squirrels in the five sites varied between 998 and 5866 kg km −2, and forest elephants dominated the biomass in all sites.
Abstract: 1. Densities of mammals in five sites in lowland semi-evergreen tropical rain forest in the Lope Reserve, central Gabon, were estimated using standard line-transect methods. Biomass was calculated using weights taken from the literature. 2. The total estimated biomass of diurnal primates, ruminants, pigs, elephants and squirrels in the five sites varied between 998 and 5866 kg km −2 . Forest elephants (Loxodonta africana cyclotis Matschie) dominated the biomass in all sites, making up 52-89% and primates accounted for 6-30%. 3. Statistically significant differences in density were detected for most species in at least two of the sites. Some of these differences could be related to vegetation structure and composition, but the reasons for others were unclear
TL;DR: The influence of reproductive effort on host susceptibility to parasitism was examined in great tits, Parus major, by comparing the prevalence of haematozoan parasites with respect to clutch size in male and female parents.
Abstract: 1. The influence of reproductive effort on host susceptibility to parasitism was examined in great tits, Parus major, by comparing the prevalence of haematozoan parasites with respect to clutch size in male and female parents. 2. Observational and experimental studies were conducted. Observational studies documented the relationship between clutch size and parasite prevalence in males and females in unmanipulated nests. Reproductive effort was manipulated by exchanging complete clutches between pairs of nests during incubation. Parents experienced a maximum manipulation of ± 5 eggs. 3. Observational studies showed that the prevalence of parasites was higher in females than males. The prevalence of parasites in males increased with both increasing clutch size and increasing age
TL;DR: The reproductive performance of older, experienced Antarctic fur seals was greater than that of younger, inexperienced animals because they had higher natality rates, gave birth to heavier pups earlier in the season, had greater weaning success and were more likely to pup the next season.
Abstract: 1. The reproductive performance of female Antarctic fur seals was examined in relation to age, reproductive experience and environmental variation over 10 consecutive years (1983-92) at Bird Island, South Georgia. 2. The age at which females first gave birth varied from 3 to 6 years; over 90% of these females were 3 or 4 years of age. We found no evidence to suggest that age at primiparity had significant effects on subsequent reproduction; however, 3-year-old primiparae were less likely to be seen in subsequent years than 4-year-old primparae which may indicate a cost, in terms of survival, for females that first give birth at an early age. 3. Age-specific reproductive rates increased rapidly from ages 2 to 6 years, reached a peak of 0.80 at 7-9 years, remained above 0.75 until 11 years and then began to decline with increasing age. 4. The mean duration of foraging trips in the current year (which was used as a measure of the availability of food resources) consistently improved models of the likelihood of pupping and of weaning success. When these trips were long (indicating reduced local food resources), females returned to the breeding beaches later, fewer females pupped, they gave birth to lighter pups and weaning success was reduced. 5. The reproductive performance of older, experienced Antarctic fur seals was greater than that of younger, inexperienced animals because they had higher natality rates, gave birth to heavier pups earlier in the season, had greater weaning success and were more likely to pup the next season.
TL;DR: A quickly decelerating type II functional response that, in the absence of a numerical response, implicates an anti-regulatory effect of wolf predation on barren-ground caribou dynamics.
Abstract: 1. We investigated the functional response of wolves (Canis lupus) to varying abundance of ungulate prey to test the hypothesis that switching from alternate prey to preferred prey results in regulation of a caribou (Rangifer tarandus) population at low densities. 2. We determined prey selection, kill rates, and prey abundance for four wolf packs during three 30-day periods in March 1989, March 1990 and November 1990, and created a simple discrete model to evaluate the potential for the expected numerical and observed functional responses of wolves to regulate caribou populations. 3. We observed a quickly decelerating type II functional response that, in the absence of a numerical response, implicates an anti-regulatory effect of wolf predation on barren-ground caribou dynamics
TL;DR: The effect of a varying risk of predation by sparrowhawks on choice of overwinter feeding site was studied for redshank, on a small Scottish estuary at low tide.
Abstract: 1. The effect of a varying risk of predation by sparrowhawks (Accipiter nisus L.) on choice of overwinter feeding site was studied for redshank (Tringa totanus L.), on a small Scottish estuary at low tide. 2. Adult and juvenile redshank segregated into two areas, a mussel bed and a salt-marsh area, respectively. Juveniles were excluded from the mussel beds by the adults, but there were no aggressive interactions on the salt-marsh. Adults occasionally fed on the salt-marsh, particularly late in the winter. 3. A redshank on the salt-marsh was 4.8 times more likely to be killed on the salt-marsh than on the mussel beds. Redshank on the salt-marsh fed closer to cover, than those on the mussel beds: sparrowhawk attack success rate declined as redshank fed further from cover
TL;DR: Connectance and quantitative parasitoid webs are described for a community of leaf-mining insects and their parasitoids in regrowth tropical dry forest in Costa Rica, where leaf-miners were highly host-specific.
Abstract: 1. A parasitoid web is a subset of a food web containing data on parasitoids and their hosts; connectance parasitoid webs embody information only about the presence or absence of an interaction, while quantitative parasitoid webs include information about the relative densities of all species. 2. Connectance and quantitative parasitoid webs are described for a community of leaf-mining insects and their parasitoids in regrowth tropical dry forest in Costa Rica. The webs were centred on a study site that contained 88 species of plants, 92 species of leaf miners and 93 species of parasitoids. 3. An average of 1.22 species of miner were found per species of plant, with more species on monocots than on plants with other growth forms. Leaf-miners were highly host-specific
TL;DR: Preliminary results indicate that annual fluctuations in the synchrony between host and parasitoid populations can have a major effect on the persistence of the interaction.
Abstract: Populations of hosts and parasitoids with discrete generations frequently show imperfect phenological synchronization resulting in some hosts experiencing reduced or even no risk of parasitism. The population dynamic consequences of phenological asynchrony are explored by modelling within-generation dynamics by a set of delay-differential equations. Phenological asynchrony can stabilize an otherwise unstable interaction. The influence of the interaction between phenological asynchrony and other stabilizing forces on the stability and equilibrium population densities of hosts and parasitoids is studied. Preliminary results indicate that annual fluctuations in the synchrony between host and parasitoid populations can have a major effect on the persistence of the interaction
TL;DR: Hatching date and hatching order each had a strong, negative effect on survival in the natal stage of western gulls Larus occidentalis, and after controlling for hatching date there was a significant negative effect.
Abstract: We examined survival and recruitment (into the breeding population) in three cohorts of western gulls Larus occidentalis (Audubon) in relation to brood size at hatching, hatching order and hatching date. We divided the pre-breeding period into four stages: (i) the natal stage ― «pre-fledging» from hatching to independence; (ii) the juvenile stage ― the period from independence to age 1 year; (iii) the subadult stage ― the second and third years of life; and (iv) the recruitment stage ― the period when adults breed for the first time. Hatching date and hatching order (in order of importance) each had a strong, negative effect on survival in the natal stage. Brood size had little effect on natal survival; however, after controlling for hatching date there was a significant negative effect
TL;DR: Experimental provision of extra food before egg-laying resulted in blue tit females starting to breed significantly earlier than unmanipulated females, and females manipulated to start breeding early started to incubate significantly later in relation to clutch completion.
Abstract: Experimental provision of extra food before egg-laying resulted in blue tit females starting to breed significantly earlier than unmanipulated females. When the females had laid their first egg, the experimental food source was withdrawn and females were thus manipulated to lay, incubate and feed nestlings at lower food levels than unmanipulated females. Although tricked into breeding earlier, the experimental females laid the same number of eggs, had no more laying gaps and produced eggs of equal size as the unmanipulated females. Females manipulated to start breeding early started to incubate significantly later in relation to clutch completion than did controls
TL;DR: The relationship between the yearly densities of avian predators and their microtine prey in western Finland was studied and Tengmalm's, Ural and hawk owls overwinter in Fennoscandia, long-eared owls are partially migratory, and short-eared owl and kestrels are migratory.
Abstract: 1. The relationship between the yearly densities of avian predators and their microtine prey in western Finland was studied. Predator densities were determined by checking nest-boxes in forests [Tengmalm's owl (Aegolius funereus), hawk owl (Surnia ulula) and Ural owl (Strix uralensis)] and by searching for nests in farmland [short-eared owl (Asio flammeus), long-eared owl (Asio otus) and kestrel (Falco tinnunculus)]. Tengmalm's, Ural and hawk owls overwinter in Fennoscandia, long-eared owls are partially migratory, and short-eared owls and kestrels are migratory. 2. Prey densities were estimated by snap-trapping in spring (early May) and autumn (mid-September), and by snow-tracking in late February to early March (early spring) and late November to early December (late autumn)
TL;DR: This paper analyses territory locations of individually marked fathers and sons during a big cyclic-type population fluctuation in 1969-77 and finds that some animal populations comprise distinct sub-populations or demes.
Abstract: Previous work on red grouse (Lagopus lagopus scoticus) on a north-east Scottish moor showed that recruitment of young to the territorial population in autumn largely determined changes in numbers between springs. This paper analyses territory locations of individually marked fathers and sons during a big cyclic-type population fluctuation in 1969-77. In years of increasing numbers, sons took territories close to their fathers. When fathers did not keep their territories for another year, sons took territories on or close to their natal territories. In years of declining numbers, kin moved further from their natal areas to establish territories. This fits ideas that some animal populations comprise distinct sub-populations or demes
TL;DR: An analysis of British ringing recoveries found no evidence that survival after the first year of life was age-dependent, and two weather variables explained 69% of the variation in adult survival rates between 1961 and 1979.
Abstract: In many parts of Britain and in other parts of western Europe, the lapwing Vanellus vanellus is declining. In order to determine if the decline in numbers was associated with a reduction in adult or first-year survival rates, an analysis of British ringing recoveries was conducted. There was no evidence that survival after the first year of life was age-dependent. Mean annual adult survival (1930-88) is estimated at 0.705 ± 0.031 (±95% confidence intervals). Since 1960, adult survival has increased to 0.752 ± 0.046. Two weather variables (mean winter soil temperature and total winter rainfall) explained 69% of the variation in adult survival rates between 1961 and 1979. Mean first-year survival (1930-87) is estimated at 0.595 ± 0.040 (±95% confidence intervals)
TL;DR: The duration of the period that females spent inshore with young pups was positively related to female body size, suggesting that the species'small size may demand that they feed to maintain lactation.
Abstract: Adult female harbour seals from NE Scotland were radio-tracked to follow changes in their distribution and activity during the breeding season. Seals foraged up to 45 km from haul-out sites, but females with pups restricted their range markedly during the early part of the lactation period. However, foraging trips resumed before the expected weaning date, indicating that female harbour seals do not fast throughout lactation. The duration of the period that females spent inshore with young pups was positively related to female body size, suggesting that the species'small size may demand that they feed to maintain lactation. Foraging in late lactation results in females becoming highly dispersed during the mating period and it is clearly uneconomic for males to monopolize females
TL;DR: Observations on the behaviour and movements of 11 foxes from seven neigh-bouring groups in an urban area of Bristol were combined with post-mortem data on levels of bite wounding throughout the entire Bristol fox population to quantify the importance of encounters in the maintenance of group cohesion and territory.
Abstract: Observations on the behaviour and movements of 11 foxes from seven neigh-bouring groups in an urban area of Bristol were combined with post-mortem data on levels of bite wounding throughout the entire Bristol fox population to quantify the importance of encounters in the maintenance of group cohesion and territory, and to address the social subordination hypothesis (Christian 1970) regarding dispersal behaviour. Inter-group encounters were uncommon and almost always aggressive, and occurred significantly more often in the winter months, when resident males trespassed into neighbouring ranges. Each fox had on average 0.77 inter-group encounters each day in winter, compared with 0.05-0.23 in spring, summer and autumn
TL;DR: Five blue tit Parus caeruleus populations were analysed and birds that divorced laid significantly later and tended to have raised fewer young in the year before the divorce compared to pairs that stayed together.
Abstract: 1. Two hypotheses to explain why divorce in birds may be adaptive are the «incompatibility hypothesis» and the «better option hypothesis». At least two more, non-adaptive, hypotheses exist: the «accidental loss» and the «forced divorce» hypothesis. We propose a third non-adaptive hypothesis «the musical chairs hypothesis». 2. After making predictions to make it possible to distinguish between these hypotheses we analysed five blue tit Parus caeruleus populations. Divorce rates varied between 8 and 85%. 3. Birds that divorced laid significantly later and tended to have raised fewer young in the year before the divorce compared to pairs that stayed together. These latter did better than the population mean
TL;DR: In this article, the authors developed a model to assess the risk of decline of the southern California spotted owl metapopulation by incorporating distance-dependent dispersal and correlation among the population growth rates.
Abstract: 1. The California spotted owl Strix occidentalis occidentalis is found in the Sierra Nevada and in a series of isolated populations in the mountains of southern California. 2. We developed a model to assess the risk of decline of the southern California spotted owl metapopulation. We modelled the spatial structure of this metapopulation by incorporating distance-dependent dispersal and correlation among the population growth rates. 3. Demographic characteristics of the largest insular population were estimated from colour-ringing the majority of the territorial population. This owl population declined dramatically during the study period, 1987-93
TL;DR: In this study, foraging information is used to produce a guild classification for birds of forests and woodlands of central Victoria, Australia.
Abstract: 1. The feeding guild is a useful tool for analysing community structure. Unfortunately, although there has been much work done on guilds of forest and woodland birds, there have been few studies in which differences between habitats have been assayed for consistency of guild structure. This can be done only by surveying replicate sites of each habitat type because this yields an indication of similarity between sites of the same class of habitat. If guild structure differs little between each replicate site, then one has confidence that that structure meaningfully characterizes the habitat type in question. 2. In this study, foraging information is used to produce a guild classification for birds of forests and woodlands of central Victoria, Australia
TL;DR: A priority model showed that traditional priority (both species arrive on average together, but with a range of priorities, does not significantly contribute to coexistence and had a clear effect upon three components of «fitness».
Abstract: 1. Priority experiments were carried out using the fungal-breeding species Drosophila phalerata and D. subobscura and the mushroom Agaricus bispora forma albida. 2. Field experiments showed that an oviposition window exists for these species and that priority in increments of 1 day are suitable for laboratory experiments. 3. Priority (arriving first) had a clear effect upon three components of «fitness». When a species arrived late it had lower survival, smaller size and longer developmental time. 4. A priority model [based upon the «aggregation model» of Atkinson & Shorrocks (1981)] showed that traditional priority (both species arrive on average together, but with a range of priorities) does not significantly contribute to coexistence