Showing papers in "Journal of Animal Ecology in 1997"

Abstract: 1. Positive relationships between the local abundance and the range size of the species in a taxonomic assemblage are very general. 2. Explanations for these relationships typically focus on two mechanisms, based on differences in the niche breadths of species, or metapopulation dynamics. Others have, however, also been suggested. 3. Here we identify and clarify all the principal mechanisms proposed to explain positive interspecific abundance-range size relationships. We critically assess the assumptions and predictions that they make, and the evidence in support of them. 4. A number of predictions are common to all of the biological (as opposed to artefactual) mechanisms, but the combination of predictions and assumptions made by each is unique, suggesting that, in principle, conclusive tests of all of the mechanisms are possible. 5. On present evidence, no single mechanism has unequivocal support. We discuss reasons why this might be the case.

Abstract: Introduction 1. The evolution and diversity of bats 2. Bat flight 3. Echolocation 4. Torpor and hibernation 5. Reproduction and development 6. Behavioural ecology 7. Community ecology and the interactions between bats and other organisms 8. Conservation References Index

Abstract: Chapter 1 - Introduction. Part I: General Principles. Chapter 2 - Parasite-mediated natural selection. Chapter 3 - Immune defence: genetic control. Chapter 4 - Behavioural defence. Chapter 5 - Parasite-mediated sexual selection: endocrine aspects. Chapter 6 - Parasitism and the evolution of host life history. Chapter 7 - Host-parasite processes and demographic consequences. Chapter 8 - The role of parasites in bird conservation. Chapter 9 - Community ecology of parasites and free-living animals. Chapter 10 - Comparative studies of host parasite communities. Chapter 11 - Host-parasite cospeciation: history, principles and prospects. Chapter 12 - Host-parasite cospeciation, host switching and missing the boat. Part II: Avian Models. Chapter 13 - Birds as habitat for parasites. Chapter 14 - Viruses, bacteria and fungi of birds. Chapter 15 - Protozoa, helminths and arthropods of birds. Chapter 16 - Avian brood parasites. Chapter 17 - Conclusion: Evolution of host-parasite interactions

Abstract: Introduction to farming and birds in Europe, D.J. Pain, J. Dixon Europe's changing farmed landscapes, C. Potter the evolution of Common Agricultural Policy and the incorporation of the environmental considerations, N. Robson priorities for bird conservation in Europe - the importance of the farmed landscape, G. Tucker extensive grazing and raptors in Spain, J.A. Donazar, M.A. Nevaso, J.L. Tella, C. Campian cereal farming, pesticides and grey partidges, D. Potts the Spanish Dehesas - a diversity in land-use and wildlife, M. Diaz, P. Campos, F.J. Pulido rice faming and water birds - integrated management in an artificial landscape, M. Fasola, X. Ruiz shrikes and the farmed landscape in France, N. LeFranc birds and wet grasslands, A.J. Beintema, E. Dunn, D.A. Stroud farming in the drylands of Spain - birds of the pseudosteppes, F. Suarez, M.A. Naveso, E. De Juana the importance of mixed farming for seed-eating birds in the UK, A. Evans conclusions - a future for farming and birds?, D.J. Pain, M.W. Pienkowski European agriculture - threats and opportunities, J. Dixon.

Abstract: 1. Intra-brood competition and parental feeding effort are considered important determinants of survival of offspring in altricial bird species because they affect accumulation of fat reserves by nestlings. However, the causal relationship between rearing conditions and post-fledging survival might also be mediated by other mechanisms ; for example, the amount and quality of food provided by parents to each nestling might affect development of immune system organs and functions and, hence, the ability of offspring to cope with parasites and pathogens. 2. The hypothesis that parental feeding effort, food quality and brood size affect immunocompetence of nestlings was tested for the first time in the barn swallow, Hirundo rustica, Linnaeus. 3. The intensity of T-lymphocyte cell-mediated immune responsiveness was evaluated after intradermal inoculation of a lectin (phytohaemagglutinin) in a large sample of nestlings from unmanipulated broods and broods whose size had been manipulated immediately after hatching. 4. In unmanipulated broods, immune response, body mass and body condition were correlated negatively with brood size and positively with the rate of parental feeding to each offspring. Nestlings in enlarged broods had smaller immune response and body mass, and received less food per capita than those in reduced broods. 5. Broods artificially provisioned with a food rich in proteins showed larger immune response, but not larger body mass, as compared to unprovisioned controls. 6. We conclude that T-lymphocyte cell-mediated immune response as well as body mass is influenced by the level of parental investment and brood size, perhaps via its effect on competition for food. Since T-lymphocytes are fundamental components of avian immunity, and parasites are known to affect survival of their avian hosts, our results suggest a new pathway through which rearing conditions might influence offspring survival.

Abstract: Preface.- Principles.- Models of Systems.- The Modeling Process.- Qualitative Model Formulation.- Quantitative Model Formulation: I.- Quantitative Model Formulation: II.- Numerical Techniques.- Parameter Estimation.- Model Validation.- Model Analysis.- Stochastic Models.- Applications.- Photosynthesis and Plant Growth.- Hormonal Control in Mammals.- Populations and Individuals.- Chemostats.- Diseases.- Spatial Patterns and processes.- Scaling Models.- Chaos in Biology.- Cellular Automata and Recursive Growth.- Evolutionary Computation.- Bibliography.- Index.

Abstract: 1. Phylogenetics in behavior 2. The statistical analysis of interspecific data 3. How to study comparative methods for discrete characters 4. The mechanistic bases of behavioral evolution 5. Geographic variation in behavior 6. Phylogenetic liability and rates of phenotypic evolution 7. Comparing behavioral and morphological characters as indicators of phylogeny 8. The phylogenetic content of avian courtship display and song evolution 9. Comparative analysis of the origins and losses of eusociality 10. Using comparative approaches to integrate behavior and population biology 11. Phylogenetic interpretations of primate socioecology 12. Using cladistic analysis of comparative data to reconstruct the evolution of cognitive development in hominids

Abstract: 1. There were marked changes in the relative lipid content of somatic and visceral tissues during the course of upstream migration and spawning. The lipid content per 100 g wet tissue mass was high in maturing salmon in July (soma, pooled sexes: 12.1 g; viscera: 11.4g in males and 7.3 g in females) and decreased to a minimum after spawning in November (soma: 2.1 g; viscera: 1.6 g). Percentages of protein in the soma and viscera were relatively stable during the study period, ranging from 21.9 g (soma) and 16.3 g (viscera) 100 g -1 tissue in maturing fish in September-October, to 17.1 g (soma) and 16-1 g (viscera) in spent salmon. The carbohydrate content was relatively small, ranging between 0.27 and 2.4 g 100 g -1 wet tissue mass. 2. Application of energetic coefficients suggested that the somatic energy content decreased from 814 kJ 100 g -1 wet tissue mass in maturing salmon (pooled sexes) caught in coastal waters in July, to 370 kJ in spent fish in the river in November. Visceral energy density decreased in the same period, from 706 kJ in males and 570 kJ in females to 340 kJ and 360 kJ, respectively. 3. Mean gonadosomatic index (GSI) values, in terms of energy of males, in July and just prior to spawning were 0.4 and 3.2, respectively. The corresponding figures for females were 2.8 and 28.6. 4. Gonadal energy contents per unit tissue mass were estimated to be higher in females than males, except for spent fish. Prior to spawning energy content was 845 kJ 100 g -1 gonad wet mass in females and 375 kJ in males. After spawning the gonadal energy contents were 280 kJ and 385 kJ 100 g -1 wet mass, respectively. 5. The relative energy, lipid and protein contents of somatic, visceral and gonadal tissues were highly correlated with percentage tissue water. 6. Total energy loss due to migration and spawning was between 60% and 70% of the body reserves prior to upstream migration. It was similar for males and females, but higher in large than small salmon. Estimated energy investment due to reproduction correlated significantly with estimated survival rates in 12 Norwegian populations of Atlantic salmon.

Abstract: Part One: Rarity and rare-common differences. Introduction: on the causes and consequences of rare-common differences. Rare-common differences: an overview. What is rarity. Who is rare: Artefacts and complexities of rarity determination. Part Two: Mechanisms creating rare-common differences. Who gets the short bits of the broken stick? Speciation and rarity: separating cause from consequence. How do rare species avoid extinction: A paleontological view. Extinction risk and rarity on an ecological timescale. Population biology and rarity: on the complexity of density dependence in insect-plant interactions. Genetic consequences of different patterns of distribution and abundance. Evolved consequences of rarity. Rarity and evolution: some theoretical considerations. Part Three: Future directions. Predicting and understanding rarity: the comparative approach. Concluding comments. Index.

Abstract: 1. Ants are known to compete in transitive hierarchies, where the superior competitors behaviourally exclude subordinate species. Nevertheless, in Mediterranean communities, where environmental factors show important daily and seasonal variations, the limited thermal tolerance of behaviourally dominant species compared with that of subordinates disrupts the expected transitive hierarchies. 2. This thermal tolerance allows a far greater dominance in the ecosystem by subordinate species than might be expected from their relative abundance and fighting abilities. 3. In the studied areas, activity curves of dominants and subordinates did not overlap because the latter were less temperature-limited and active during the day, while the former were more temperature-limited and active during the afternoon and night periods. 4. The lower thermal limitation of subordinate activity not only increased their exploitative ability, but also altered the outcome of interspecific interactions at food resources, i.e. modified the interference hierarchy. 5. These temporal changes in the foraging abundance of species lead to increasing diversity: more competing species may co-exist as a result of changes in the environment that periodically reverse the order of competitive prevalence among the species.

Abstract: 1. I present a conceptual model that predicts the proximate and ultimate factors that determine whether a mammal species has the potential to be regulated by intrinsic (behavioural) or extrinsic factors. The model is based on three behavioural phenomena that purportedly regulate mammal populations: female territoriality, dispersal, and reproductive suppression. 2. The model predicts that intrinsic regulation can occur only in those species in which females are territorial, offspring-rearing space (or alpha status) is limited, and young females exhibit reproductive suppression. Female territoriality should occur in species that have altricial young and serve as a counter-strategy to infanticide from conspecific females. Female mammals that have precocial young or mobile altricial young that are not vulnerable to infanticide should not commit infanticide and should not be territorial. Thus, developmental state at birth would be an ultimate factor that determines whether offspring-rearing space potentially can be limited. 3. Dispersal should be density-independent in nonterritorial species and inversely density-dependent in territorial species and thus has limited potential to regulate population density in any species. 4. Behavioural reproductive suppression of young females is proposed as an adaptive mechanism to avoid inbreeding or to conserve reproductive effort in response to the threat of infanticide. 5. Intrinsic regulation should be most likely to occur in monogamous territorial species in which daughters grow up in the presence of male relatives (such as in canids and some primates). Polygynous species, in which females are territorial such as most rodents, have the potential for self-regulation; however, exposure to unrelated males and the fact that young females can breed on their mothers' territories usually preclude benavidural reproductive suppression. 6. Intrinsic regulation should not occur in species with precocial young, nonterritorial species, or in species in which daughters do not associate with male relatives, such as the ungulates, marine mammals, bats and marsupials. 7. The model predicts that female territoriality, the threat of infanticide, and the presence of male relatives in the natal home range are the proximate mechanisms for intrinsic population regulation in mammals. These factors apparently occur only under a limited set of conditions; therefore, most mammal populations are probably controlled by extrinsic factors. The model is presented with a series of a priori predictions from which hypotheses can be formulated and tested.

Abstract: 1. The reproduction of the golden eagle Aquila chrysaetos was studied in southwestern Idaho for 23 years, and the relationship between eagle reproduction and jackrabbit Lepus californicus abundance, weather factors, and their interactions, was modelled using general linear models. Backward elimination procedures were used to arrive at parsimonious models. 2. The number of golden eagle pairs occupying nesting territories each year showed a significant decline through time that was unrelated to either annual rabbit abundance or winter severity. However, eagle hatching dates were significantly related to both winter severity and jackrabbit abundance. Eagles hatched earlier when jackrabbits were abundant, and they hatched later after severe winters. 3. Jackrabbit abundance influenced the proportion of pairs that laid eggs, the proportion of pairs that were successful, mean brood size at fledging, and the number of young fledged per pair. Weather interacted with prey to influence eagle reproductive rates. 4. Both jackrabbit abundance and winter severity were important in predicting the percentage of eagle pairs that laid eggs. Percentage laying was related positively to jackrabbit abundance and inversely related to winter severity. 5. The variables most useful in predicting percentage of laying pairs successful were rabbit abundance and the number of extremely hot days during brood-rearing. The number of hot days and rabbit abundance were also significant in a model predicting eagle brood size at fledging. Both success and brood size were positively related to jackrabbit abundance and inversely related to the frequency of hot days in spring. 6. Eagle reproduction was limited by rabbit abundance during approximately two-thirds of the years studied. Weather influenced how severely eagle reproduction declined in those years. 7. This study demonstrates that prey and weather can interact to limit a large raptor population's productivity. Smaller raptors could be affected more strongly, especially in colder or wetter climates.

Abstract: 1. Despite a wealth of studies for a wide variety of animal assemblages, the form of the interspecific relationship between abundance and body size is still contentious. At least three different patterns have been suggested, which can broadly be characterized as negative and linear, negative but non-linear, and polygonal. At least eight different mechanisms have been suggested whereby the linear (or non-linear) and polygonal patterns can be reconciled. 2. We collated data from the literature on over 500 interspecific plots of the abundance-body size relationship with two aims. First, to examine the extent to which published studies support the different forms proposed for the relationship; and secondly, to test whether any of the mechanisms that have been suggested to reconcile linear and polygonal patterns actually do so. 3. The data revealed that abundance-body size relationships commonly assume both linear negative and polygonal forms. Around 25% of all plots of the relationship show a positive regression slope. 4. Of the eight mechanisms that have been suggested to reconcile linear and polygonal patterns, we were able to test five. Of these, only the measure of density used by a study explains none of the observed variation in abundance-body size relationships. Variation in the regression slope between studies is only explained by the type of data used (compilations vs. samples) and the scale of study (local vs. regional): compilation studies at regional scales show more linear negative relationships, while sample studies performed at local scales show more polygonal patterns. General linear modelling indicates that study scale is the most important factor influencing when different relationships are likely to arise. 5. Our results show that different patterns tend to arise at different scales of study, but say nothing about whether the patterns are real or artefactual. Polygonal relationships potentially contain an artefactual component, resulting from sampling methodology inadequate to elucidate the abundances of the less common species in any given assemblage. However, the presence of a sampling artefact does not indicate the shape of the underlying relationship from which a sample is taken, or indeed whether samples would exhibit any other shape were artefacts excluded. 6. Linear and polygonal patterns are not necessarily mutually exclusive, but may both indicate the 'true' abundance-body size relationship at different spatial scales. We conclude by suggesting that much more attention be paid to the effect of spatial scale on this relationship, especially given that scale of measurement can have subtle but severe consequences.

Abstract: 1. We studied the effect of parasitism on snowshoe hare (Lepus americanus) survival through a field experiment that reduced natural burdens of sublethal nematodes in a free-ranging hare population. We treated half the hares on each of six study areas year-round with an anthelminthic drug, and the other half with a placebo. Potential interactive effects of parasitism and nutrition were examined by supplementing the natural food supply on three of the six study areas during two winters. Survival was measured by radio-collaring a total of 612 hares with mortality-sensitive transmitters and monitoring survival daily between April 1991 and June 1993. 2. Overall, nematode burdens in hares were highest between March and October, and Obeliscoides cuniculi was the most abundant of the five species present. The proximate cause of 95% of mortalities (n = 318) during the study was predation. Predators killed hares with heavy burdens of O. cuniculi disporportionately during May-June, but burdens of the four other species (Nematodirus triangularis, Trichuris leporis, Dirofilaria scapiceps, Protostrongylus boughtoni) were similar between predator-killed hares and the live population. 3. During May-October 1991, the anthelminthic treatment did not affect hare survival, but during May-October 1992 survival of parasite-reduced hares was 2.4-times higher than that of controls. During November 1991-April 1992 survival of food supplemented hares was 21% higher than food-normal animals, but survival was similar during November 1992-April 1993. 4. The effect of parasite-reduction on hare survival was apparently contingent on overwinter food supplies between November 1991 and April 1992, with survival being highest in hares subjected to both treatments, intermediate in those receiving only food supplementation, and lowest in unfed hares. We conclude that the effect of sublethal nematode parasitism on hare survival can be important if interactive with predation, and that synergistic effects of parasitism and nutrition may affect hares if food availability is limited.

Abstract: 1. Information on the approximate number of individuals released is available for 47 of the 133 exotic bird species introduced to New Zealand in the late 19th and early 20th centuries. Of these, 21 species had populations surviving in the wild in 1969-79. The long interval between introduction and assessment of outcome provides a rare opportunity to examine the factors correlated with successful establishment without the uncertainty of long-term population persistence associated with studies of short duration. 2. The probability of successful establishment was strongly influenced by the number of individuals released during the main period of introductions. Eight-three per cent of species that had more than 100 individuals released within a 10-year period became established, compared with 21% of species that had less than 100 birds released. The relationship between the probability of establishment and number of birds released was similar to that found in a previous study of introductions of exotic birds to Australia. 3. It was possible to look for a within-family influence on the success of introduction of the number of birds released in nine bird families. A positive influence was found within seven families and no effect in two families. This preponderance of families with a positive effect was statistically significant. 4. A significant effect of body weight on the probability of successful establishment was found, and negative effects of clutch size and latitude of origin. However, the statistical significance of these effects varied according to whether comparison was or was not restricted to within-family variation. After applying the Bonferroni adjustment to significance levels, to allow for the large number of variables and factors being considered, only the effect of the number of birds released was statistically significant. 5. No significant effects on the probability of successful establishment were apparent for the mean date of release, the minimum number of years in which birds were released, the hemisphere of origin (northern or southern) and the size and diversity of latitudinal distribution of the natural geographical range.

Abstract: 1. The population dynamics of colonies of nettle aphids (Microlophium carnosum Buckton) were studied on potted nettle plants placed beside plots of grass on some of which outbreaks of grass aphids (Rhopalosiphum padi L.) had been induced by fertilizer application. 2. Nettle aphid colonies adjacent to grass aphid concentration suffered an earlier population decline, and produced fewer alate dispersers, than control colonies. 3. The reduced performance of nettle aphids in the vicinity of grass aphid was due to increased predation by Coccinellidae, attracted into the area by the large concentrations of grass aphids. The indirect interaction between the two species of aphids is an example of apparent competition. 4. Because predators pre-emptively exploited nettle aphids on plants in the grass aphid treatment, the numbers of nettle aphids attacked by parasitoid wasps was greatly reduced in these sites compared to the controls.

Abstract: 1. We tested the hypothesis that protein availability rather than energy availability constrains egg formation in great tits (Parus major L.) by providing them with two food supplements of different protein content in the prelaying and laying period of 1991 and 1992. 2. Timing of breeding, clutch size and egg size did not differ between the two food supplements. Thus, the hypothesis that a low protein content of supplement restricts laying in great tits cannot be supported. 3. Food supplementation, independent of food type and year, led to an advancement of laying by 5.6 days. Average clutch size of supplemented birds, corrected for laying date and year, was 0.55 eggs above the population average. 4. Supplementary fed great tits did not breed more successfully than controls. This suggests that by adding food early in laying, birds were induced to lay at a less favourable time and/or produced clutches that were too large to care for successfully under normal food condition. Thus food early in the season might not only energetically restrict laying birds, but also provide clues about future conditions during chick rearing. 5. The comparison of results of published supplemental feeding experiments shows that the birds responded more strongly to additional feeding in poor environments. Almost two-thirds of the variation in changes of clutch size due to experimental treatment can be explained by year quality. Thus, only in poor environments do reproductive traits seem to be limited by energy availability early in the season, but other factors become more important in good environments [KEYWORDS: clutch size, egg formation, food quality, food supplementation, Parus major]

Abstract: 1. Little is known about long-term effects of brood size on fitness components of offspring. This is unfortunate because such information is needed to predict optimal brood size. Furthermore, ontogenetic circumstances are potentially important in explaining the large individual differences in lifetime reproductive success documented in many species. 2. In a laboratory study the long-term effect of brood size manipulation on mortality and morphological development of offspring was investigated. Young zebra finches Taeniopygia guttata were reared in small or large broods. Young were exchanged in such a way that natural siblings from different rearing conditions could be compared. 3. Manipulated brood size affected offspring morphology permanently (measurements were taken up to the age of 12 months). Individuals reared in small broods were heavier, had longer tarsi and wings, higher beaks, were in better condition, and males had redder beaks. The experiment did not affect beak length or female beak redness. Individuals from large broods had caught up on wing length and males from large broods on beak redness by 6 months of age, which may reflect priority of investment in traits important to fitness. 4. Mortality of offspring raised in large broods was higher both before and after independence. After independence the effect of manipulated brood size on mortality was sex specific; females were most likely to die. This suggests that the optimal sex ratio of offspring may depend on brood size. 5. The effect of brood size on mortality after independence was probably partly mediated by size and condition during the nestling phase and possibly by peer aggression among adult offspring. Sex-linked mortality could not be explained by a sex difference in morphological development. Why females are more vulnerable remains to be discovered.

Abstract: 1. In order to predict the spatial distribution of 'ideal' and 'free' predators, one needs to know how food intake rate of an individual predator is related to characteristics of the population of the prey as well as the predators themselves. 2. Surprisingly, a systematic theoretical investigation of models for the basic case, where both prey and predators are best characterized by their 'standing stock' density, is lacking. In these models intake rate is supposed to decrease with increasing predator density as a result of interference among predators, instead of immediate consumption of the prey. 3. This paper compares the various ways applied so far of incorporating interference in Holling's functional response model. It is shown that the different models of interference result in qualitatively different predictions for 'ideal' and 'free' predators on: (i) the form of the aggregative response; (ii) the trajectory of the aggregative response as prey is depleted; and (iii) the change in the aggregative response following an influx of predators. This sheds doubt on the general relevance of any one of these models, particularly if the mathematical formulation of interference is phenomenological and merely based on convention, instead of being derived from the underlying mechanism of interactions between predators. 4. Our results underline the need for detailed knowledge about the components of the predation process in order to arrive at predictions for a specific case.

Abstract: 1. Recent reports indicate that microparasites might play an important role in the ecology and evolution of freshwater zooplankton. To quantify the impact of parasitism on Daphnia in natural populations we studied the microparasites of D. magna, D. pulex and D. longispina in three ponds in southern England for a 1-year period. Parasite prevalence and richness, epibiont prevalence and density of host food (planktonic algae) were quantified and their effect on host fecundity analysed. 2. Seventeen parasite species were detected, including eight microsporidia, one haplosporidium, one ameoba, three fungi, three bacteria and one unidentified parasite. The mean proportion of infected adults across the year and the three ponds was 84.7% for D. magna, 53.6% for D. pulex and 38.6% for D. longispina for the 11 most common parasites. Body size was generally positively correlated with parasite prevalence and richness. This relation was found both across and within host species. Multiple infections by different parasite species were common. 3. In all three Daphnia species, parasitism was associated with a reduction in fecundity. The small D. longispina was less affected per parasite compared to the two larger host species, D. magna and D. pulex. Clutch presence was more strongly reduced than clutch size, and the effect increased with parasite richness. The data suggest that parasites castrated their host completely, rather than reducing clutch size. 4. Host specificity varied between parasite species. Two parasite species infected only one or two of the three hosts investigated, and six parasite species showed differences in their specificity between ponds. 5. Four different epibiont groups were distinguished; algae, Protozoa, one fungus and one bacterium. Epibiont prevalence differed between ponds and species. Overall, epibionts were not host specific, but intensity of infection differed strongly between species and the three ponds. Epibiont infection was independent of parasite infection. The presence of epibiontic algae reduced clutch size in D. magna significantly. 6. Our results suggest that parasites can have important effects on Daphnia ecology and evolution. Differential susceptibility of the three host species to parasites suggests that parasites might play a role in determining competition and coexistence in our three study sites.

Abstract: 1. Niche theory predicts that the stable coexistence of species within a guild should be associated, if resources are limited, with a mechanism of resource partitioning. Using extensive data on diets, the present study attempts: (i) to test the hypothesis that, in sympatry. the interspecific overlap between the trophic niches of the sibling bat species Myotis myotis and M. biythii-which coexist intimately in their roosts-is effectively lower than the two intraspecific overlaps; (ii) to assess the role played by interspecific competition in resource partitioning through the study of trophic niche displacement between several sympatric and allopatric populations. 2. Diets were determined by the analysis of faecal samples collected in the field from individual bats captured in various geographical areas. Trophic niche overlaps were calculated monthly for all possible intraspecific and interspecific pairs of individuals from sympatric populations. Niche breadth was estimated from: (i) every faecal sample; (ii) all the faecal samples collected per month in a given population (geographical area). 3. In every population, the bulk of the diets of M. myotis and M. blythii consisted of, respectively, terrestrial (e.g. carabid beetles) and grass-dwelling (mostly bush crickets) prey. All intraspecific trophic niche overlaps were significantly greater than the interspecific one, except in Switzerland in May when both species exploited mass concentrations of cockchafers, a non-limiting food source. This clearcut partitioning of resources may allow the stable, intimate coexistence observed under sympatric conditions. 4. Relative proportions of ground- and grass-dwelling prey, as well as niche breadths (either individual or population), did not differ significantly between sympatry and allopatry, showing that, under allopatric conditions, niche expansion does not take place. This suggests that active interspecific competition is not the underlying mechanism responsible for the niche partitioning which is currently observed between M. myotis and M. blythii.

Abstract: 1. The grasshopper Bryodema tuberculata requires open and dry habitats. In Central Europe, it survives only on gravel bars along braided rivers in the Northern Alps. Even there, many populations of B. tuberculata have become extinct in the last 50 years. 2. The dynamics of braided rivers are characterized by succession and floods. Catastrophic floods occur at irregular intervals. They are capable of washing away entire gravel bars and of building new, vegetation-free gravel bars. Succession eventually leads to an almost complete loss of habitat suitable for B. tuberculata on each single gravel bar. 3. Bryodema tuberculata can persist only as metapopulations, i.e. when local extinctions due to succession or flood events are compensated for by colonization of newly created gravel bars. 4. A simulation model was used to examine how the spatial and temporal dynamics of succession, flood regime and colonization determine the ability of B. tuberculata to survive in flood-plains. 5. The results show that small populations on relatively old gravel bars are important to the persistence of B. tuberculata, even though they usually only survive for a short time, due to demographic noise. 6. The effect of catastrophic floods is ambivalent: persistence is low if time intervals between floods are too short or too long. If floods are too frequent many subpopulations are extinguished at the same time and if floods are to infrequent, local populations are eliminated by succession. 7. It is concluded that most extinctions of B. tuberculata populations in the Northern Alps are due to changes in the flood regime caused by humans. 8. Many other spatially dynamic animals and plants occupy successional habitats. We suggest that the form of model outlined in this paper, based on a dynamic habitat mosaic, be used for such organisms.

Abstract: 1. We develop an individuals-based model that predicts the strength of interference between foraging animals from basic elements of their behaviour. The model is based on the same principles as previous behaviour-based interference models, but extends and adds further realism to these models. One key difference is that in our model the responses of animals to competitors are not fixed, as is assumed in previous models. Instead, animals use optimal decision rules to determine responses which maximize their intake rate. 2. The general shape of interference function generated by the model is similar to that predicted by previous behaviour-based models. Interference is insignificant at low competitor densities, but steadily increases in intensity as density rises. However, comparison with the observed level of interference between oystercatchers, Haematopus ostralegus, feeding on mussels, Mytilus edulis, shows that the model's predictive power is substantially increased through the addition of optimal decision rules. When animals have a fixed response to encounters, too much interference occurs because dominant animals waste time avoiding subdominants and subdominants waste time attempting, but failing, to steal prey from dominants. When animals use optimal decision rules, only subdominants avoid, and only dominants initiate attacks. Interference is therefore reduced and is much closer to that observed. 3. The conditions under which optimal decision rules will lead to interference are described in terms of basic elements of foraging behaviour. Interference is predicted to occur when handling time and the probability of winning fights are high, and when prey encounter rate and the duration of fights are low. These parameters are used to predict successfully the presence or absence of interference in a range of shorebird-prey systems. 4. We suggest that behaviour-based interference models will need to incorporate optimal decision rules if they are to predict accurately the strength of interference observed in real predator-prey systems.

Abstract: 1. Man has increased the input of carrion to marine communities worldwide through the practice of discarding fisheries-derived material. A large proportion of discarded material sinks to the sea bed and becomes available to benthic scavengers. Carrion from fisheries discards will subsidize marine food webs, which can sometimes result in the enhancement of consumer populations. 2. This study examines the benthic scavengers that feed on fisheries discards in three habitats in the Irish Sea. We investigated the relationship between the abundance of scavengers feeding on carrion in terms of numbers of each species and the density of those scavenger species in the surrounding area. 3. Observations with baited time-lapse cameras at a site offshore from Anglesey showed that the hermit crab Pagurus bernhardus was attracted to carrion in greatest abundance and aggregated at densities of up to 330 m -2 . At Red Wharf Bay a wider range of species was observed: starfish Asterias rubens, hermit crabs P. bernhardus, whelks Buccinum undatum and swimming crabs Liocarcinus spp. There was relatively little scavenging activity at the Walney Island site where the edible crab Cancer pagurus appeared to consume the greatest proportion of the carrion. 4. Numbers of each scavenger species at the bait were only partially related to the background population density of each species at each site. The rate of consumption of carrion varied between sites and could be related to the abundance of different scavenger species at the bait. 5. Baited traps were used to investigate those benthic scavengers that were too small to be observed by time-lapse photography. The traps caught a variety of amphipod and isopod species. Some species were habitat-specific, whereas others were ubiquitous, but specialized in eating a particular type of carrion; for example, Orchomene nanus, which was only caught in traps baited with crab. 6. The results demonstrated that the responses of scavengers to fisheries discards varied between different habitats. The responses of hermit crabs, P. bernhardus, were particularly variable, with large aggregations of individuals occurring at one site but not at others, despite similar background population densities.

Abstract: 1. Individuals in many social species are attracted to feeding conspecifics. The profitability of conspecific attraction is negatively frequency-dependent and can be modelled as a producer-scrounger (PS) game for which the ESS solution predicts some mixture of producer (no attraction) and scrounger (attraction) tactics in the population. Current models for the spatial distribution of rate-maximizing foragers, which learn the quality of habitats as they exploit patches, ignore the possible effect of conspecific attraction on the stable distribution of foragers. 2, We used simulations of a population with ESS levels of attraction to investigate the effect of conspecific attraction on the spatial distribution of learning foragers which incur travel costs. In habitats where patches depleted slowly, ESS levels of attraction helped foragers which experienced no interference reach the expected ideal free distribution (IFD) by facilitating aggregation to the richest patches. Large aggregations also occurred with interference and thus reduced the fit to the IFD, which in this case predicts a scatter of foragers across patches of varying quality. 3. In habitats where patches depleted rapidly, ESS levels of attraction prevented foragers from reaching the IFD, irrespective of interference levels. Foragers failed to learn habitat quality and thus often aggregated in poor patches, especially in large populations which depleted patches faster and had fewer opportunities to learn quality. 4. Predictions of the model in habitats where patches deplete slowly are supported by several studies. More work is needed for habitats where patches deplete more rapidly. We conclude that conspecific attraction can have important, and often disruptive effects on spatial distributions.

Abstract: 1. The role of food in avian reproduction is generally studied from the perspective of the protein and energy demand of birds, This study provides the first experimental evidence that calcium availability may limit reproduction in wild birds as well. 2. Data are presented showing that a large proportion of great tits Parus major on calcium-poor soils in the Netherlands produce eggs with thin and porous shells and desert the clutch before hatching. About 10% of the females do not lay at all. 3. Free-living great tits were supplied with an additional calcium source, i.e. snail shells and chicken eggshells. This treatment reduced the number of females without eggs, the frequency of clutch desertion, the proportion of nests with defective eggshells and the proportion of non-hatched eggs in clutches that produced young. The calcium supplements did not affect clutch size or laying date. 4. We suggest that possible adaptations to a limited calcium supply are not yet evident because the low calcium availability is a recent phenomenon caused by acid deposition and because a large part of the breeding population consists of immigrants from calcium-rich areas. 5. We provide evidence that calcium limitation in avian reproduction may be widespread on calcium-poor soils. 6. The results imply that the costs of egg formation in calcium-poor areas can be much higher than is currently estimated and that food conditions during egg-laying have a greater impact on avian reproduction than is presently believed. [KEYWORDS: eggshell; food availability; limiting nutrients; Parus major L reproduction Brown-headed cowbirds; tit parus-major; great tit; nutrient reserves; quelea-quelea; clutch-size; food; reproduction;birds; limitation]

Abstract: 1. We experimentally set adult mortality rates, μ a , in laboratory cultures of the flour beetle Tribolium at values predicted by a biologically based, nonlinear mathematical model to place the cultures in regions of different asymptotic dynamics. 2. Analyses of time-series residuals indicated that the stochastic stage-structured model described the data quite well. Using the model and maximum-likelihood parameter estimates, stability boundaries and bifurcation diagrams were calculated for two genetic strains. 3. The predicted transitions in dynamics were observed in the experimental cultures. The parameter estimates placed the control and μ a = 0.04 treatments in the region of stable equilibria. As adult mortality was increased, there was a transition in the dynamics. At μ a = 0.27 and 0.50 the populations were located in the two-cycle region. With μ a = 0.73 one genetic strain was close to a two-cycle boundary while the other strain underwent another transition and was in a region of equilibrium. In the μ a = 0.96 treatment both strains were close to the boundary at which a bifurcation to aperiodicities occurs; one strain was just outside this boundary, the other just inside the boundary. 4. The rigorous statistical verification of the predicted shifts in dynamical behaviour provides convincing evidence for the relevance of nonlinear mathematics in population biology.

Abstract: 1. Simple models of optimal foraging, such as ideal free distribution models, are based on the assumption that foragers are omniscient with respect to the quality of all patches in the environment; they know how much food and how many competitors are present in each patch. 2. In contrast, simple population dynamic models treat predator-prey distributions in a phenomenological way, and do not take fitness consequences for individual foragers into account. Yet, the precise way in which these distributions come into being is what really matters to population dynamics. It is therefore necessary to study the behavioural mechanisms underlying the distributions of foragers over patches. 3. We studied the behaviour of a predatory mite, Phytoseiulus persimilis, in response to prey patches occupied by conspecifics. It is well known that high predator densities in prey patches promote dispersal of these predatory mites. Our question was to what extent predators can assess the presence of conspecifics from a distance. 4. Experiments with a Y-tube olfactometer showed that predatory mites avoid patches occupied by conspecifics. 5. This avoidance cannot be attributed to odours of conspecific predators, or of prey damaged by predation, as these odour sources both appear to be attractive. 6. Separating the prey patch from the conspecific predators in the odour source led to the avoidance response only when the predators in the odour source were positioned upwind from the prey patch, and not when they were positioned downwind. This suggests that predators release an odour that elicits the production of yet another odour by the prey. This was supported by the observation that removal of adult prey led to a quick disappearance of the avoidance response. 7. We argue that distant discrimination between patches with and without competing conspecifics may be quite common among predators and parasitoids, and that the use of odours instead of physical inspection of patches allows predators to instantaneously integrate information on the distribution of food and competitors. 8. This behavioural mechanism may bring predators and parasitoids closer to behaving as ideal free foragers than was previously thought possible.