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Showing papers in "Journal of Animal Ecology in 1980"


Journal ArticleDOI
TL;DR: It seems particularly opportune to discuss food webs and evolving views on their structure here for both their genesis and first modern treatment (Elton 1927) and much of their later development (May 1973; Pimm & Lawton 1978) has a decidedly British accent.
Abstract: It seems particularly opportune to discuss food webs and evolving views on their structure here for both their genesis and first modern treatment (Elton 1927) and much of their later development (May 1973; Pimm & Lawton 1978) has a decidedly British accent to it. The central significance of webs is derived from the fact that the links between species are often easily identified and the resultant trophic scaffolding provides a tempting descriptor of community structure. If this structure is in any fashion related to the persistence of natural communities or their stability, however defined, then we are dealing with issues of vital ecological importance. Elton's views have admirably withstood the tests of time. They were especially useful to field biologists, and encouraged the assembly and organization of feeding data into networks of trophically bonded species or higher taxa. The early emphasis was on connectedness per se. Perhaps the first significant deviation from this theme was the development of the trophic dynamic viewpoint of Lindeman (1942) and all subsequent efforts to describe energy transfer and material flow through communities. A second departure, and one I believe to be conceptually richer, was the formalization of the view that web structure and community stability were related (MacArthur 1955). May (1973) in another landmark publication questioned this relationship and called attention to four primary web features: the number of species involved, the nature of their interconnections, the number of connections per species, and the intensity of interaction between web members. This focus has stimulated application to agroecosystems (Southwood & Way 1970), new interpretations of the number of trophic levels (Pimm & Lawton 1977), and a resurgence of interest in the significance of mutualism (Vance 1978). It has not been characterized by stunning breakthroughs, ecological stability remains a frustrating issue, and to a field ecologist, the ties between model and reality at times appear remote; All but ignored in these recent developments is an insightful recognition that trophic pathways might contribute little to ecosystem stability, and that the answers lie in the spatial patterning of the environment (Smith 1972). I wish to return to the basic observations on food webs as a naturalist and experimentalist, and employing an approach advocated by Sir Arthur Tansley (Godwin 1977), ask whether we are modelling their correct properties, and if not, what modifications might be made.

1,690 citations




Journal ArticleDOI
TL;DR: Interspecific differences are related to search strategies which depend on body weight, forest levels used, social roles, etc, which suggests that interspecific competition is important in determining resource partitioning.
Abstract: (1) Fruit, leaves and animal matter form the main part of the diets of the three Cercopithecus monkeys studied. Cercopithecus nictitans eats less fruit and insects and more leaves; C. pogonias more fruit and insects and fewer leaves; C. cephus is intermediate. (2) Sex-related differences occur: males eat more fruit than females who eat more leaves and animal matter, especially when these foods are abundant. (3) Interspecific differences in food items taken are small for fruit (68% of the species are taken by the three monkeys), obvious for animal matter. Cercopithecus nictitans preys mainly on sedentary prey (caterpillars, ants), C. pogonias on mobile ones (orthoptera) while C. cephus captures both types. Sex-related differences occur in C. cephus and C. pogonias. (4) Interspecific overlap in diets is great during the main part of the year. Species diets change and overlap less when fruit, young leaves and animal matter production are short (main dry season). This suggests that interspecific competition is important in determining resource partitioning. A second decrease in diet overlap occurs at the end of the long rainy season while foods are abundant. Females are either pregnant or lactating and select protein-richer foods such as young leaves and/or insects while males eat more fruit. At this time, intraspecific competition could be the selective force in food sharing. However increasing protein-requirements could account for the reorientation in food choice of the females. (5) The intermediate trophic position of C. cephus rests upon sex-related differences. The cephus male behaves like nictitans while the cephus female behaves like pogonias. (6) Interspecific differences are related to search strategies which depend on body weight, forest levels used, social roles, etc. Differences in spatial and temporal feeding patterns are small.

230 citations


Journal ArticleDOI
TL;DR: Drawing on a number of alternative approaches, the null hypothesis that real food webs are not significantly more compartmented than chance alone dictates is tested.
Abstract: SUMMARY compartmented. (3) Alternative food web models are briefly described. These incorporate biologically more realistic assumptions, and do not neccessarily predict that food webs are more likely to be stable if they are divided into blocks. (4) Compartments exist in food webs if the interactions within the web are grouped into subsystems: that is, if species interact strongly only with species in their own sub- systems, and interact little, if at all, with species outside it. (5) Drawing on a number of alternative approaches, we test the null hypothesis that real food webs are not significantly more compartmented than chance alone dictates. (6) Analyses of published food webs show that subsystems can only be detected where the webs span major habitat divisions, for example a forest and a prairie, or adjacent freshwater and terrestrial habitats. These compartments are imposed by the natural histories of the component species. There are no grounds for believing that dynamical constraints, i.e. a requirement for persistent natural food webs to be stable, play any part in imposing compartments.

218 citations




Journal ArticleDOI
TL;DR: While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.
Abstract: SUMMARY (1) The general feeding biology of Morter obscurus is described. (2) First instar larvae, because they use a different pit construction technique, have steeper-walled pits than later instars. Pit diameter and larval length are linearly related. (3) Capture success is determined mainly by the relative sizes of predator and prey. For a given relative size instar 1 larvae are more successful because of the steep-walled pits. Capture success drops to zero when ants can place some of their legs outside the pit. Third instar larvae were more successful than second instar larvae in pits of the same size. Capture success, particularly for large larvae, is 100% over much of the prey size range. (4) Successful attacks on ants with thick exoskeletons occurred almost exclusively via the gaster whereas mandible insertion for ants with thin exoskeletons frequently occurred elsewhere. (5) Differences in pit morphology and prey capture behaviour in Macroleon lynceus are documented and related to habitat differences. In Morter, pit morphology is crucial for prey capture, while strength is more important for the larger Macroleon. (6) Handling time was divided into time to capture (Ta), time to death (Td), and time to extract body contents (Te). T, was constant for small prey but increased rapidly for larger prey. Td was constant for all sizes of predator and prey. Te increased with prey size and decreased with increasing predator size and temperature. Te seems to depend not only on the amount of extractable food but also on the shape of the victim. (7) Hunger has no effect on prey handling time or food extraction efficiency. However hungry larvae are more likely to move their pits. Ant-lions can capture prey falling into the pit when already feeding and so increase their food supply. (8) Growth rates of larvae feeding on different sized prey were measured. Large larvae grew more slowly than small ones when fed on the same sized prey because of higher maintenance costs. For a given sized predator, growth per unit weight of prey received declined with increasing prey size because of increased feeding costs. Each size of ant-lion had a prey size for which the costs per unit return were a minimum, this size changing abruptly from very small prey for the first two instars to large prey for the final instar. (9) The feeding biology of the three instars is compared and contrasted. First instar larvae are adapted to achieve a high capture success rate on a small prey size range because feeding costs are high and escapes therefore expensive. For large larvae, maintenance costs are more important and selection has favoured a large size range of catchable prey. While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.

161 citations


Journal ArticleDOI
TL;DR: The population was found to be increasing at a fairly steady rate of about 120 per annum, and females within reproductive units were in close reproductive synchrony, partly due to the environmental control of conceptions; however, social factors also played an important role in bringing females into synchrony.
Abstract: SUMMARY (1) Demographic parameters of a free-ranging population of gelada baboons were determined during a field study in Ethiopia. (2) The annual birth rate varied inversely with the severity of the rainfall around the period of conception. The distribution of births within the year, however, was timed so as to minimize the exposure of the neonates to the severe wet season conditions. (3) Females within reproductive units were in close reproductive synchrony, partly due to the environmental control of conceptions; however, social factors also played an important role in bringing females into synchrony. (4) After the first year of life, mortality fell most heavily on the oldest age classes; exposure to severe wet season conditions, old age and parasitic infestations were the main causes of death. Age-specific mortality and fecundity rates were estimated. (5) The population was found to be increasing at a fairly steady rate of about 120 per annum. Migration by entire sub-sections of the population at aperiodic intervals helped to maintain the actual density of animals within the study area around a longterm mean value.

153 citations


Journal ArticleDOI
TL;DR: A population model based on that of May (1978), but with k from the negative binomial now a function of host density as observed for Cyzenis, is analysed and the stability properties displayed.
Abstract: SUMMARY (4) A population model based on that of May (1978), but with k from the negative binomial now a function of host density as observed for Cyzenis, is analysed and the stability properties displayed. (5) This general model for parasitism is included in a more detailed model for the winter moth and Cyzenis at Wytham Wood. It shows Cyzenis to play a minor part in the winter moth population dynamics, which is largely governed by the destabilizing effects of the key-factor and the stabilizing effects of the density dependent soil mortality. (6) A model for the winter moth and CyzeMis in Nova Scotia is developed. Cyzenis is assumed to search in the manner found for Wytham Wood, but the other components are derived from the studies of Embree (1965, 1966). The model predicts the successful biological control of the winter moth that has been observed in Nova Scotia following the introduction of Cyzenis. The reasons for the very different performances of Cyzenis at Wytham Wood and Nova Scotia are discussed.

152 citations



Journal ArticleDOI
TL;DR: It is suggested that species' behaviour is a major component of spatial stability, being the only common property in all the environmentally varied samples, and mean population density accounted for more than 70o of the spatial variance in more than 90/ of species.
Abstract: (1) Ninety-seven species of aphids, 263 species of moths and 111 species of birds were sampled simultaneously over an area of about 2300 km2, for up to eleven, thirteen and fifteen years at up to twenty-four, 126 and 210 sites, respectively. (2) Aphid sites were uniform farmland; bird sites were segregated into farmland and woodland; moth sites were highly diverse. (3) Aphids were sampled by suction traps, moths by light traps and birds by direct observation. (4) By analogy with temporal variance, spatial variance (S2) was used as a measure of spatial stability and in most species was found to be proportional to a fractional power of mean population density (ms). (5) Estimates of the parameter b, in S,2 = amb, ranged from 1.29 to 2-95, 0.95 to 3.32 and 1.19 to 2.69 in aphids, moths and birds respectively, and from 1.20 to 3.32 within a single genus (Apamea). (6) Estimates of the parameter a (in S2 = amb) were different in farmland and woodland for nearly half the bird species examined. This difference may be due to environmental components of variance. (7) Taylor's (1961) power model fitted well in 95/ of species and, on logarithmic scales, mean population density accounted for more than 70o of the spatial variance in more than 90/ of species. This suggests that species' behaviour is a major component of spatial stability, being the only common property in all the environmentally varied samples. No species showed evidence of reaching an upper limit of density constraining variance.




Journal ArticleDOI
TL;DR: Empirical results from birds for which food abundance varies strongly between breeding seasons support several predictions, but the need for further studies of movement patterns in banded adults is stressed.
Abstract: SUMMARY (1) Adult nomadism is compared to site tenacity, using a model which relates the fitness of an individual to its clutch size and mortality rate, and to the pattern of food production. (2) The model predicts that the relative merit of nomadism is higher with cyclic than with random fluctuations in food abundance. The merit increases with the interval between successive good years in an area. (3) With cyclic food production, nomadism is favoured by large clutch size, high juvenile survival, and low adult survival. (4) Although the relation between juvenile and adult survival is important, the general level of the survival rate does not influence the optimal tactic. (5) Empirical results from birds for which food abundance varies strongly between breeding seasons support several predictions, but the need for further studies of movement patterns in banded adults is stressed.

Journal ArticleDOI
TL;DR: The varied structure of oak galls provides a basis for a partitioning of resources between polyphagous parasites and may explain the co-existence of many cynipid species on oak trees.
Abstract: (1) Indices of species diversity are applied to parasite communities associated with cynipid gall-wasps and Phyllonorycter leaf-miners, their performances are examined, and it is concluded that they provide a useful measure of community composition. (2) Communities include more polyphagous than specific parasite species and they are more diverse on trees than on shrubs or herbaceous plants. In the latter situation communities are usually dominated by specific parasites whilst polyphagous parasites achieve their highest representation in tree communities. (3) Community diversity is highest in situations where most species of primary hosts occur. This is on trees in the cases of both gall-wasps and Phyllonorycter. (4) The varied structure of oak galls provides a basis for a partitioning of resources between polyphagous parasites and may explain the co-existence of many cynipid species on oak trees. Polyphagous parasites in Phyllonorycter mines do not, in general, discriminate between primary hosts on the same plant species and numbers of co-existing species of Phyllonorycter are restricted.

Journal ArticleDOI
TL;DR: Information from South Sweden and North America supported the hypotheses that: (a) most summer species make mineral cases whilst autumn species preferably construct organic cases; (b) the final larval length of mineral case makers is small compared to that of organic case makers, and (c) the tendency to use case enlargement is most pronounced among the organic case maker.
Abstract: SUMMARY (1) Young larvae of Potamophylax cingulatus construct their cases of leaf discs, but as the larvae grow, the material used to construct the cases changes to pieces of bark and then to mineral particles. The relative amount of secretion used for the construction of the leaf cases was low compared to that used for cases of older larvae. As the larvae grew and the cases changed, there was an increase in the pressure which the cases could withstand before collapsing. (2) Larvae with leaf cases were more often taken by trout when they were on a sandy bottom than when they were on a leaf bottom, while the predation on larvae with mineral cases was the same, irrespective of bottom type. Larvae inhabiting natural leaf cases were more vulnerable to trout predation when the portions of the cases extending beyond the tube inhabited by the larvae were cut off. Larvae with mineral cases suffered a much lower predation than did those with leaf cases. (3) Information from South Sweden and North America supported the hypotheses that: (a) most summer species make mineral cases whilst autumn species preferably construct organic cases; (b) the final larval length of mineral case makers is small compared to that of organic case makers, and (c) the tendency to use case enlargement is most pronounced among the organic case makers. These adaptations could all be related to the selection pressure by predation.




Journal ArticleDOI
TL;DR: Food habits of Formica rufa L. in a limestone woodland in north Lancashire are studied and dry weight studies show honeydew to be the most important food in these terms.
Abstract: SUMMARY (1) Food habits of Formica rufa L. in a limestone woodland in north Lancashire are studied. Use is made of a semi-automatic collecting device which solves some of the problems inherent in manual sampling. (2) The main food items are shown to be aphids (mainly Drepanosiphum platanoides Schr.), Diptera (mainly Bibionidae), Lepidoptera larvae (mainly Operophtera brumata L.) and honeydew. (3) Aphids, Lepidoptera larvae and honeydew are brought in in greatest quantities in spring and early summer, Diptera throughout the year. Differences in food income at two study sites are discussed in relation to differences between the two sites. (4) Many ants are shown to be involved in the collection of building material or are apparently unladen. (5) Dry weight studies show honeydew to be the most important food in these terms. (6) Honeydew was also found to be the most important food in terms of energy content. Up to 15 200 kJ/5 min of honeydew are carried in on a single trail. The maximum intake of solid food on the same trail was 13 287 kJ/5 min. (7) Formica rufa is shown to utilize particular species of tree at different times of year. Sycamore is important in the early season with scots pine and oak increasing in importance in summer and autumn. This is related to the food being obtained from these species. (8) The present results are discussed in relation to previous data on wood-ant feeding habits and its more general applications are discussed in terms of work done on food selection in birds. The importance of assessing the impact of large ant colonies on the ecosystem via studies of their food income, etc. is stressed.

Journal ArticleDOI
TL;DR: In this paper, Pied flycatchers Ficedula hypoleuca on a migration stopover in Portugal were accumulating reserves at a rate of 0.34 g d-1 for a trans-Saharan flight.
Abstract: (1) Pied flycatchers Ficedula hypoleuca on a migration stop-over in Portugal were accumulating reserves at a rate of 0.34 g d-1 for a trans-Saharan flight. Marked birds occupied limited feeding ranges which were defended against conspecifics but not other species. (2) The flycatchers foraged for active arthropods with the predominant items of diet being ants, wasps and beetles. Capture attempts were clumped in time which was taken to mean that prey were clumped in space. (3) Within a tree a bird's feeding rate declined exponentially the longer it foraged there. (4) For one bird the time taken to find a new feeding place varied four-fold between observation sessions. This could not be explained by time of day or temperature and was taken to reflect prey availability. In poor feeding conditions the bird stayed longer in each tree or nearby after encountering food. To this extent variations of feeding strategy appeared consistent with optimal foraging theory though direct measurements of prey dispersion were lacking. (5) The recovery of prey patches following a bird's departure was such that most occurred within 10-15 min. Birds did not move round their territories on a random walk but tended to proceed in a circuit (albeit with many reversals). Probably as a result, trees tended to be revisited after intervals of about 12 min. (6) Territory circuiting behaviour spaced repeat visits to trees in such a way as to enhance the birds' rate of encounter with prey. It was not possible to assess the net benefit of exclusive territoriality and circuiting to the flycatchers since the costs of defence could not be estimated.


Journal ArticleDOI
TL;DR: The size of prey taken by D. aruanus is influenced by the social habit of this species, and the relative position of an individual within its social group influences its subsequent prey intake.
Abstract: SUMMARY (1) Field observations were made on the feeding behaviour of individuals amongst social groups of D. aruanus. The sizes of prey taken were investigated by the analysis of stomach contents. There was a clear relationship between the size of prey taken and the rank of an individual within its social group. On removal of the larger individuals from a social group, the smaller individuals began to take prey previously destined for the former. (2) These results are related to what is known from previous work about the movements of D. aruanus whilst feeding as a social group. It is concluded that the size of prey taken by D. aruanus is influenced by the social habit of this species. The relative position of an individual within its social group influences its subsequent prey intake.

Journal ArticleDOI
TL;DR: This method of studying animal movement overcomes several flaws inherent in previous methods, but is restricted to distances of a few km at most.
Abstract: (1) Adult female butterflies were bred on artificial diet containing dye so that they laid coloured eggs, and the distribution of eggs was used as an amplifier for the distribution of adults. (2) The butterflies were released in a 1 km square grid of cabbage plants. The observed pattern of coloured eggs agrees with independent predictions based on Jones's (1977) rules for short-distance movement. (3) Each butterfly flies about 700 m per day over the ground, and ends the day 250600 m from where she started. (4) Each butterfly maintains a preferred direction throughout one day, but the direction changes unpredictably from day to day. (5) The butterflies in these experiments laid only 10%? of their daily complement of eggs, because they could not find enough host plants. (6) This method of studying animal movement overcomes several flaws inherent in previous methods, but is restricted to distances of a few km at most.


Journal ArticleDOI
TL;DR: Overall mean handling time was found to increase with decreasing prey density, as predicted by both optimal feeding and gut-filling models, and a positive correlation was demonstrated between handling time and intercatch interval, supporting a gut- filling model.
Abstract: SUMMARY (1) The feeding behaviour of two species of the freshwater heteropteran Notonecta was examined with respect to the factors influencing prey handling time. (2) Overall mean handling time was found to increase with decreasing prey density, as predicted by both optimal feeding and gut-filling models. (3) A positive correlation was demonstrated between handling time and intercatch interval (the time from discarding one prey item to capturing another), supporting a gut-filling model. (4) A decay in the handling time per item through the catch sequence was found, irrespective of prey density, which adequately described the overall mean handling time for each prey density. (5) A similar decrease was demonstrated in the intercatch interval through the catch sequence, suggesting an increase in searching efficiency, which could be based on the

Journal ArticleDOI
TL;DR: Activity patterns and certain life-history characteristics suggest that this species is a 'time-minimizer' and that both intra- and inter-specific predation significantly influence foraging patterns.
Abstract: SUMMARY Population density and surface activity of marked individuals of the desert scorpion, Paruroctonus mesaensis Stahnke (Vaejovidae) were monitored on over 225 nights during a 5 year period. (1) Although scorpions appeared on the surface during all bimonthly periods of the year, surface densities were highest in spring and fall, and lowest in mid-winter and midsummer. (2) Emergence from burrows at dusk is correlated with decreasing levels of ambient light. Surface density rapidly increases in early evening and then significantly decreases in late evening (early morning). Adults are relatively more active and young relatively less active in early evening as compared with late evening. (3) Low surface densities of scorpions occur during and immediately after periods of precipitation. Although moonlight does not affect surface density, both mating and feeding occur significantly less frequently during periods of full moon. (4) The surface density of adults was highly correlated with insect abundance. There are no correlations between the surface density of the two younger age groups and insect abundance. Further, adult surface density was high during the mating season and low during the mid-summer period of birth and brooding of newborn. (5) There exist age-specific differences in seasonal and nightly patterns of surface activity. These patterns tend to minimize co-occurrence on the surface with a subsequent decrease in intraspecific interactions (cannibalism and possible competition for food). It appears that adult activity is an evolutionary response to periods of high prey density, whereas the activity of the two younger age groups reflect long-term avoidance of adults and/or competition for food. Age-specific seasonal patterns are maintained by a differential response to surface temperature by each age group. (6) Low levels of overall surface activity are characteristic: only about one-half the individuals in any age group were present on the surface during an average night for any bimonthly period. These activity patterns and certain life-history characteristics suggest that this species is a 'time-minimizer' and that both intra- and inter-specific predation significantly influence foraging patterns.