Showing papers in "Journal of Animal Ecology in 1993"
TL;DR: In this article, age and size at maturity at maturity number and size of offspring Reproductive lifespan and ageing are discussed. But the authors focus on the effects of age and stage structure on fertility.
Abstract: Prologue Part I: Evolutionary explanation Demography: age and stage structure Quantitative genetics and reaction norms Trade-offs Lineage-specific effects Part II: Age and size at maturity Number and size of offspring Reproductive lifespan and ageing Appendices Glossary References Author index Subject index.
10,338 citations
TL;DR: Body size offers a good (though not perfect) interpretation of the ordering of animal species assumed in the cascade model, a stochastic model of food web structure, when the body sizes of different animal species are taken as log-normally distributed.
Abstract: Summary 1. We measured the body sizes (weights or lengths) of animal species found in the food webs of natural communities. In c. 90% of the feeding links among the animal species with known sizes, a larger predator consumes a smaller prey. 2. Larger predators eat prey with a wider range of body sizes than do smaller predators. The geometric mean predator size increases with the size of prey. The increase in geometric mean predator size is less than proportional to the increase in prey size (i.e. has a slope less than 1 on log-log coordinates). 3. The geometric mean sizes of prey and predators increase as the habitat of webs changes from aquatic to terrestrial to coastal to marine. Within each type of habitat, mean prey sizes are always less than mean predator sizes, and prey and predator sizes are always positively correlated. 4. Feeding relations order the metabolic types of organisms from invertebrate to vertebrate ectotherm to vertebrate endotherm. Organisms commonly eat other organisms with the same or lower metabolic type, but (with very rare exceptions) organisms do not eat other organisms with a higher metabolic type. Mean sizes of prey increase as the metabolic type of prey changes from invertebrate to vertebrate ectotherm to vertebrate endotherm, but the same does not hold true for predators. 5. Prey and predator sizes are positively correlated in links from invertebrate prey to invertebrate predators. In links with other combinations of prey and predator metabolic types, the correlation between prey and predator body sizes is rarely large when it is positive, and in some cases is even negative. 6. Species sizes are roughly log-normally distributed. 7. Body size offers a good (though not perfect) interpretation of the ordering of animal species assumed in the cascade model, a stochastic model of food web structure. When body size is taken as the physical interpretation of the ordering assumed in the cascade model, and when the body sizes of different animal species are taken as log-normally distributed, many of the empirical findings can be explained in terms of the cascade model.
661 citations
514 citations
TL;DR: Behaviour and microhabitat selection by brown trout in two streams presenting severe winter conditions, were investigated in south-central Norway, finding that trout were active throughout the night from dusk to dawn, and this behaviour was consistent throughout the winter.
Abstract: Behaviour and microhabitat selection by brown trout in two streams presenting severe winter conditions, were investigated in south-central Norway. Fish were studied by direct underwater observation in different habitat types, during day and night, and with simultaneous sampling for dietary analysis and invertebrate drift. During the day in winter, brown trout exhibited two different behavioural strategies, depending on fish size. Smaller fish (<25 cm) sheltered passively in the substrate or in submerged vegetation, and were almost never active during daylight hours. This behaviour was consistent throughout the winter until water temperatures rose in spring. Larger trout (25-60 cm) were actively aggregating in deep-slow stream areas during the day. During the night the trout exhibited a third behavioural strategy. The trout were active throughout the night from dusk to dawn, and this behaviour was consistent throughout the winter
377 citations
TL;DR: A trade-off between quality and number of offspring is feasible only in the absence of the parasitic hen flea, and in parasite-free broods fitness can potentially be gained through offspring quality or number or both, whereas in infested broods it can be gain through offspring quantity only.
Abstract: 1. The effect of a haematophageous ectoparasite, the hen flea, on quality an number of offspring was experimentally investigated in the great tit. The experiment consisted of a controlled infestation of a random sample of nests with the parasitic flea and of a regular treatment of control nests with Microwaves in order to eliminate the naturally occurring fleas. 2. To assess the effects of fleas on variables related to offspring number, we considered the number of hatchlings and fledglings, the mortality between hatching and fledging, and the hatching and fledging success. For assessment of offspring quality, we measured body mass, tarsus and wing length, and calculated the nutritional condition of, nestlings as the ratio of body mass to tarsus length. A physiological variable, the haematocrit level, was also measured. 3. Hatching success and hatchling numbers did not differ between the two experimental groups. Offspring mortality between hatching and fledging was significantly higher in the infested broods (xBAR = 0.22 chicks dead per day) than in the parasite-free broods (xBAR = 0.07 dead per day). Fledging success was 83% in the parasite-free broods, but only 53% in the infested ones. The number of fledglings in infested broods (xBAR = 3.7 fledglings +/-2.1 SD) was significantly lower than in the parasite-free (xBAR = 4.9 +/- 1.1 SD) broods. 4. Body mass of chicks in the infested broods was significantly smaller than in the parasite-free broods both 14 days and 17 days after hatching. The chicks in the infested broods reached a significantly smaller tarsus length than the ones in the parasite-free broods. Close to fledging, the nutritional condition of chicks was significantly lower in infested broods. Haematocrit levels were significantly lower in the infested broods. 5. Brood size correlated differently with body mass and condition of chicks in infested and parasite-free nests. In parasite-free broods both body mass and condition of chicks at age 17 days, i.e. close to fledging, were significantly higher in small broods than in large ones. However, in the infested broods chicks were of the same body mass and condition in large as in small broods. Therefore, in parasite-free broods fitness can potentially be gained through offspring quality or number or both, whereas in infested broods it can be gained through offspring quantity only. In other words, a trade-off between quality and number of offspring is feasible only in the absence of the parasitic hen flea. 6. These results emphasize the need to study the effects of ectoparasites on ecological, behavioural and evolutionary traits of their bird hosts. A knowledge of these effects is essential for the understanding of population dynamics, behaviour and life-history traits of the hosts.
317 citations
311 citations
TL;DR: It is concluded that the results on large-scale spatial synchrony in moths and aphids are better explained by regional stochasticity than by migration.
Abstract: 1. We report patterns of intraspecific spatial synchrony (cross-correlation with lag zero) in the dynamics of British moths and aphids sampled at 57 and 21 localities throughout the UK. 2. Spatial synchrony was substantially higher in aphids than in moths. In both taxa, spatial synchrony declined with increasing distance between conspecific populations, but synchrony remained positive at all distances up to 800 km. 3. Species with large slopes (>2) of the spatial variance-mean regression had spatially asynchronous dynamics, as predicted by a theoretical model. 4. In noctuid moths and in aphids, but not in geometrid moths, there was a significant positive correlation between the degree of spatial synchrony and the level of temporal variability in local populations. 5. We discuss the two main hypotheses about the causes of spatial synchrony, migration and regional stochasticity (spatially correlated weather conditions). We conclude that our results on large-scale spatial synchrony in moths and aphids are better explained by regional stochasticity than by migration.
310 citations
TL;DR: From two enclosed populations monitored for 13 and 11 years, time- and age-specific survival rates of roe deer were estimated in relation to age and study site by recent capture-mark-recapture methods, finding that females survived better than males, the survival rate of prime-age adults were the highest, and survival decreased after 7 years of age.
Abstract: From two enclosed populations monitored for 13 and 11 years, time- and age-specific survival rates of roe deer were estimated in relation to age and study site by recent capture-mark-recapture methods. The two populations were very different. Roe deer in Trois Fontaines, a 1360 ha reserve in east France, faced severe winters. The size of this highly productive population was roughly constant during the study period. Conversely, in Chize, a 2660 ha reserve in west France with mild winters, roe deer showed density dependence in reproduction and body weight. As a general rule, females survived better than males, the survival rates of prime-age adults were the highest, and survival decreased after 7 years of age. Only the severe winters affected markedly the survivorship of roe deer
288 citations
TL;DR: In this paper, a simple randomization test is described for testing for change in community structure, which can be used in conjunction with any measure of community structure based on observed species abundances such as diversity indices.
Abstract: 1. The effect of disturbance on a biological community is commonly measured by a change in an index of community structure. When such an index is calculated from a sample from the community, it is important to assess the statistical significance of an observed change. 2. A simple randomization test is described for testing for change in community structure. The test can be used in conjunction with any measure of community structure based on observed species abundances such as diversity indices. An example is given
205 citations
TL;DR: An evolutionary interpretation of the different patterns of seasonal change in birds is suggested, and predictions by analysis of nest-record data held by the British Trust for Ornithology are tested.
Abstract: In many species of birds the mean clutch size is not constant through the breeding season: Some species show a seasonal pattern of declining clutch size, while others can show a mid-season peak. We suggest an evolutionary interpretation of the different patterns of seasonal change in birds, and test predictions by analysis of nest-record data held by the British Trust for Ornithology (BTO). We assume that conditions for breeding will show a seasonal pattern of improvement and then decline, and that the optimal clutch size (Lack 1947) is larger for each individual in the population when the conditions for breeding are better
204 citations
TL;DR: Within natural assemblages, the relationship between body size and abundance is usually polygonal, with species body size being a very poor predictor of species abundance, and the most abundant species near the upper bound slopes of assemblaging may be energy limited, because in only one assemblage does the upper Bound slope differ from energetic model predictions.
Abstract: Studies of the relationship between body weight and population abundance for animal species based on pooling data from many taxa and assemblages suggest that abundance scales with weight to the -0.75 power. Since metabolic rate scales with weight as (plus)0.75, this result has been taken as evidence that all species in assemblages used equal amounts of energy. The evidence for "energetic equivalence' is, however, equivocal, because within many individual assemblages the scaling of abundance on weight differs significantly from 0.75. The authors here examine the relationship between body size (weight and/or length) and abundance in nine previously unpublished animal assemblages, and five previously published assemblages. Twelve of the 14 assemblages show a negative relationship between log body size and log population abundance, but the proportion of variance in abundance which body size explains is always low. Plots of the relationship tend to be polygonal. Regression slopes for most assemblages differ significantly from the predictions of energetic constraint models: most species in these assemblages cannot be energy limited. However, the most abundant species near the upper bound slopes of assemblages may be energy limited, because in only one assemblage does the upper bound slope differ from energetic model predictions. Within natural assemblages, then, the relationship between body size and abundance is usually polygonal, with species body size being a very poor predictor of species abundance. Abundances of most species in assemblages are not, apparently, constrained by energetic requirements, but the commonest species in assemblages may be. -from Authors
TL;DR: The probability of colonization between 1982 and 1991 increased with patch area, and declined with isolation from source populations (maximum 8-65 km), but the probability of local extinction declined with increasing patch area and increased with isolation.
Abstract: In Britain, Hesperia comma inhabits heavily grazed calcareous grasslands When rabbits were killed by myxomatosis in the mid-1950s, this habitat became overgrown and H comma declined to 46 or fewer localities in 10 refuge regions (Thomas et al 1986) By 1982, rabbits had recovered and many former sites again appeared suitable, but had not been recolonized Between 1982 and 1991, the number of habitat patches that were populated increased by 30% in the South and North Downs Most of the increase was in East Sussex The probability of colonization between 1982 and 1991 increased with patch area, and declined with isolation from source populations (maximum 8-65 km) The probability of local extinction declined with increasing patch area, and increased with isolation
TL;DR: The aim of this study was to document the difference in age-specific mortality rates of male and female kudus, and to relate this difference to possible causes, in particular the influence of sexual size dimorphism.
Abstract: The aim of this study was to document the difference in age-specific mortality rates of male and female kudus, and to relate this difference to possible causes, in particular the influence of sexual size dimorphism. The study was conducted over 10 years in the Kruger National Park, South Africa. Female survival was estimated by following cohorts of individually recognizable animals in closed social units. Male survival was estimated from year-class ratios, adjusted for population change. Male mortality rate remained similar to that of females up to 3 years of age. Thereafter, male mortality accelerated sharply with age. A male reaching full weight at 6 years of age had only a 0-5 chance of surviving a further year. Female mortality started rising only after 6 years of age
TL;DR: Large variation was found in age of onset of reproduction among radio-collared female moose in a population in northern Norway and calf weights were significantly correlated with the biomass of the herb species in the mother's summer home-range.
Abstract: Large variation was found in age of onset of reproduction among radio-collared female moose (Alces alces) in a population in northern Norway (69°N). Eight (50%) of the individuals matured at 2.5 years old, whereas age of maturity was 3.5 years or older for eight females. Onset of reproduction was closely correlated with body weight. Both calf and yearling weight was significantly higher for those females that matured as 2.5 years old, compared with the other females. Average calf weight differed significantly among females; however, this variation was not significantly correlated with the mother's body weight. Calf weights were significantly correlated with the biomass of the herb species in the mother's summer home-range
TL;DR: In this article, the effects of the haematophagous tropical fowl mite (Ornithonyssus bursa, Berlese (Macronyssidae, Gamasida)) on the within-season costs of reproduction in their swallow (Hirundo rustica L.) hosts by simultaneously manipulating the size of first clutches and the mite loads of first clutch nests were either sprayed with a pesticide or kept as controls.
Abstract: Parasites are hypothesized to increase the cost of reproduction in their hosts due to their time and energy drain. I experimentally studied the effects of the haematophagous tropical fowl mite (Ornithonyssus bursa, Berlese (Macronyssidae, Gamasida)) on the within-season costs of reproduction in their swallow (Hirundo rustica L.) hosts by simultaneously manipulating (i) the size of first clutches (which were either increased by one egg, kept as a control, or decreased by one egg), and (ii) the mite loads of first clutch nests (nests were either sprayed with a pesticide or kept as controls). The experimental treatments were successful as evidenced from the effect of the clutch size manipulation on clutch and subsequent brood size, and from the effect of the parasite manipulation on subsequent mite loads
TL;DR: An existing simple model for the dynamics of insect pathogens is used, slightly modified both to provide greater accuracy and to allow for more straightforward parameter estimation.
Abstract: 1. Biologists have made little use of recent advances in the mathematical theory of the dynamics of insect pathogens, because of difficulties with parameter estimation and misgivings about the simplicity of the models in question. 2. We use an existing simple model for the dynamics of insect pathogens, slightly modified both to provide greater accuracy and to allow for more straightforward parameter estimation. 3. Focusing on the nuclear polyhedrosis virus (NPV) of gypsy moth (Lymantria dispar (L.)), we estimated each of the model parameters independently, estimating three of the four model parameters from the literature
TL;DR: The composition of the diet varied seasonally and with the size as well as the gender of the snakes, showing extreme sexual dimorphism in body length, body shape, relative head size, head shape, foraging habitat and diet.
Abstract: Sex-based differences in diets are widespread among animals, but may often reflect sex differences in body size or in the times and places that feeding occurs, rather than sex-specific prey-selection behaviour. We examined these hypotheses with detailed information on the types and sizes of fishes consumed by filesnakes, Acrochordus arafurae McDowell, 1979, based on a 4-year field study in the Wet-Dry tropics of northern Australia. These aquatic snakes show extreme sexual dimorphism in body length, body shape, relative head size, head shape, foraging habitat and diet. The composition of the diet varied seasonally and with the size as well as the gender of the snakes
TL;DR: Data collected in 1983-89 from cereal fields was analysed to elucidate the relationships between the primary parasitoids and hyperparasitoids of cereal aphids and establish whether or not hyperparASitoids interfere with the impact of primary Parasitoids on cereal aphid populations.
Abstract: 1. We analysed data collected in 1985-89 from cereal fields to elucidate the relationships between the primary parasitoids and hyperparasitoids of cereal aphids. The analysis aimed to establish whether or not hyperparasitoids interfere with the impact of primary parasitoids on cereal aphid populations. 2. From more than 10000 parasitized aphids, 14 primary parasitoid and 18 hyperparasitoid species were reared. The five most common hyperparasitoids attacked the five most common primary parasitoids, which, in turn, parasitized most frequently the most abundant aphid species, Sitobion avenae (F.). 3. Levels of aphid primary parasitism never exceeded 33%, whereas levels of hyperparasitism often reached 100% in the latter part of the season. However, the low rates of aphid primary parasitism could not have been solely the result of hyperparasitism: if primary parasitoid females which emerged early continued to deposit eggs before the collapse of the aphid populations, those females should have been numerous enough to parasitize large numbers of their hosts before hyperparasitoid pressure became high. 4. We hypothesize that primary parasitoid females leave areas which develop high hyperparasitoid densities. A multiple linear regression model was used to test the hypothesis. The observed declines of aphid primary parasitism were quantitatively related to hyperparasitoid density. 5. The results of this study and additional theoretical considerations are in favour of the above hypothesis. However, other factors such as mortality other than that due to hyperparasitoid attack, and aestivation acting together may also contribute to the low abundance of primary parasitoid females later in the season.
TL;DR: The extent to which seasonal changes in offspring survival were caused by environmental changes was assessed experimentally by cross-fostering clutches of differing age between pairs of nests in Bagley Wood, Oxfordshire.
Abstract: In blue tit (Parus caeruleus L.) populations the numbers of surviving young from a clutch generally declines the later in the season it hatches, but hatching too early also reduces productivity. The extent to which seasonal changes in offspring survival were caused by environmental changes was assessed experimentally by cross-fostering clutches of differing age between pairs of nests in Bagley Wood, Oxfordshire. This manipulation had the effect of advancing or delaying the hatch date experienced by parents. Productivity of experimental nests could then be compared with the productivity of control pairs breeding at the same time, and with seasonal trends in long-term data from a blue tit population nesting in a similar habitat at Wytham, Oxfordshire
TL;DR: Age of male parents was positively correlated with fledging success, suggesting that aspects of parental quality play an additional role, and the results were consistent only with the date hypothesis.
Abstract: 1. We investigated the relationship between hatching date and fledging success in the European coot (Fulica atra). 2. The production of fledglings per brood increased in the first half of the season and decreased in the second half, independent of clutch size or egg size. We tested experimentally whether this convex seasonal pattern is causally related to date. 3. The timing of parental care was manipulated by exchanging complete first clutches that differed in stage of incubation. Our experiments tested whether the natural variation in fledging success was due to (i) factors related to date (date hypothesis), (ii) factors related to parental and/or territory quality (parental quality hypothesis), or to a combination of both factors. 4. In the first half of the season, an experimental advance of the timing of parental care reduced fledging success, while an experimental delay raised it. In the second half of the season the opposite was found. Fledgling production by experimental pairs did not differ systematically from that of control pairs raising young at the same time. 5. Thus, the results were consistent only with the date hypothesis, and we conclude that timing of breeding and fledging success are causally related in the coot. 6. Independent of date, age of male parents was positively correlated with fledging success, suggesting that aspects of parental quality play an additional role.
TL;DR: In this article, an ecological landscape consisting of discrete interconnected patches was constructed in the laboratory and each patch in the landscape was a 1-litre aquatic microecosystem containing producers and consumers.
Abstract: 1. An ecological landscape consisting of discrete interconnected patches was constructed in the laboratory. Each patch in the landscape was a 1-litre aquatic microecosystem containing producers and consumers. 2. Species invaded and spread throughout the landscape in a specific sequence following prescribed invasion pathways. 3. Species distribution among landscape patches was heterogeneous and converged to one of several alternative states despite identical initial conditions. 4. Differences in structure which developed among patches were the result of the assembly processes which occurred in each patch and among interconnected patches
TL;DR: It is shown that G. d.
Abstract: 1. Following introductions in the 1950s, Gammarus pulex has replaced the native Irish freshwater amphipod G. duebeni celticus in several river systems. We show that G. pulex has eliminated and replaced G. d. celticus in lower sections of the River Lagan system, N. Ireland, although G. d. celticus maintains pure populations upstream from G. pulex. More rarely, the two species may be found together. 2. We investigate the potential roles of cannibalism and mutual predation in explaining these replacement patterns. G. d. celticus was significantly more cannibalistic on moulted conspecifics than G. pulex
TL;DR: Pelagic juvenile Arctic charr had larger age-specific lengths than their epibenthic counterparts, and few juvenile Arcticcharr moved from epIBenthic to pelagic areas in the presence of large brown trout, the main potential fish predator present.
Abstract: 1. Arctic charr Salvelinus alpinus underwent phenological and ontogenetic habitat shifts between the epibenthic and pelagic zones in five Norwegian study lakes. Juveniles exploited epibenthic areas until they reached a body length of 13-18 cm when many moved into pelagic waters during summer. 2. Pelagic juvenile Arctic charr had larger age-specific lengths than their epibenthic counterparts, and few juvenile Arctic charr moved from epibenthic to pelagic areas in the presence of large brown trout, the main potential fish predator present
TL;DR: Bite weight and intake rate of wildebeest and topi were similar despite the difference in breadth of their incisor rows, and Wildebeest had a faster bite rate than either topi or hartebeest on swards with low biomass and high protein content of green leaf.
Abstract: The niche separation of three species of alcelaphine antelope (wildebeest, topi and hartebeest) with similar body size was compared by measuring bite weight, bite rate, intake rate and selectivity of tame animals in plots containing grass at different growth stages. On growing swards, hartebeest had a smaller bite weight and lower intake rate, and were also less selective of green leaf, than either topi or wildebeest. On senescent swards, hartebeest were more selective of leaf than the other two species. Wildebeest had a faster bite rate than either topi or hartebeest on swards with low biomass and high protein content of green leaf (green flush). Bite weight and intake rate of wildebeest and topi were similar despite the difference in breadth of their incisor rows
TL;DR: Both colony size and the density of birds using brood-rearing areas increased over the duration of the study, and mean proportion of marked goslings in a brood that survived from hatch to ringing declined from approximately 65% prior to 1980 to 35-40% in recent years.
Abstract: Long-term changes in pre-fledging gosling survival, in relation to food availability, were investigated in a population of lesser snow geese (Anser caerulescens caerulescens) at La Perouse Bay, Manitoba. Both colony size and the density of birds using brood-rearing areas increased over the duration of the study (the former from 2000 to 8-9000 pairs). Annual mean size of broods using traditional brood-rearing areas (as a proportion of initial brood size) declined significantly between 1979 and 1991, from 0.9-1.0 to 0.6-0.8. Mean proportion of marked goslings in a brood that survived from hatch to ringing (5-6 weeks of age) declined from approximately 65% prior to 1980 to 35-40% in recent years
TL;DR: In this article, the history of the landscape, the climate, the vegetation, the vertebrate animals, Aboriginal association with the land, and conservation and the future are discussed in detail.
Abstract: This work covers the history of the landscape, the climate, the vegetation, the vertebrate animals, Aboriginal association with the land, and conservation and the future.
TL;DR: There was little day-to-day variation in feeding rate, and no relationship with ambient light conditions over a half lunar cycle, in Cory's shearwater Calonectris diomedea.
Abstract: We examined the pattern of chick feeding in Cory's shearwater Calonectris diomedea on Selvagem Grande by weighing 50 chicks at 4-h intervals throughout nine successive nights, then daily for a further 11 days (20 days in all). Meal sizes were estimated from the sum of positive mass increments recorded over 4-h intervals (SUM). Mass increments over 24-h (NET) were linearly related to SUMs by the equation NET = 0.83 SUM −40.1 (r 2 = 0.82). Individual meals fed to chicks averaged 74 g (SD = 26.4 g, range = 20 - 100 g). A mean of 79% of chicks were fed each night and the mean interval between feeds was 1.3 nights, with a maximum of four nights. There was little day-to-day variation in feeding rate, and no relationship with ambient light conditions over a half lunar cycle
TL;DR: This work examined the habitat selection of a Negev desert web-building spider Stegodyphus lineatus in two adjacent habitats differing in vegetation structure and prey availability and investigated the choice of web-sites by spiders in terms of both vegetationructure and expected availability of prey.
Abstract: We examined the habitat selection of a Negev desert web-building spider Stegodyphus lineatus in two adjacent habitats differing in vegetation structure and prey availability. We investigated the choice of web-sites by spiders in terms of both vegetation structure and expected availability of prey. Spiders built their webs preferentially in shrubs with dense branch architecture and chose the parts of shrubs with greatest potential availability of prey. We conducted food-supplementation experiments to determine the effects of food supply on time to reproduction and number of offspring produced. Spiders in the habitat with greater prey availability and more abundant annual vegetation grew larger and reproduced earlier
TL;DR: The effects of intra-patch experiences, such as contact with kairomone, ovipositions and rejections on the searching behaviour of individual female parasitoids of the species Leptopilina clavipes are considered.
Abstract: 1. This paper considers the effects of intra-patch experiences, such as contact with kairomone, ovipositions and rejections on the searching behaviour of individual female parasitoids of the species Leptopilina clavipes. 2. Behavioural records were analysed by means of the proportional hazards model (Cox 1972) taking effects of fixed as well as time-varying covariates into account. 3. Analyses were carried out at three levels of resolution: (i) patch leaving and return tendencies; (ii) tendencies to stop and start searching while on the patch; and (iii) the encounter rate during search bouts