Showing papers in "Journal of Animal Ecology in 1979"
TL;DR: Methods for assessment of fish production in fresh waters, Methods for assessing fish production of fresh waters as discussed by the authors, Methods for assessing fish production from fresh waters in the Persian Gulf, Iran.
Abstract: Methods for assessment of fish production in fresh waters , Methods for assessment of fish production in fresh waters , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
2,191 citations
TL;DR: The locomotory responses which influence patch time allocation were investigated for the parasitoid, Nemeritis canescens (Grav.).
Abstract: (1) The locomotory responses which influence patch time allocation were investigated for the parasitoid, Nemeritis canescens (Grav.). Arrestment in patches was brought about by orthokinetic and klinotactic responses to a host-produced chemical and, indirectly, by oviposition. (2) A series of ovipositions increased patch time in a manner dependent on their rate rather than their absolute number. (3) A behavioural model is developed for the duration of a patch visit at different host densities. The aggregative response predicted is compared with experimental findings. (4) The effect of experience on patch time is investigated. Nemeritis avoids already visited patches. More long-term effects of conditioning on patch time are also suggested. (5) The manner in which Nemeritis forages is compared to that predicted by foraging models, and the nature of the parasitoid foraging process is discussed.
456 citations
Journal Article•
367 citations
286 citations
268 citations
TL;DR: It is concluded that differences between habitats in climate, body size, perch height, and acoustic competition from other species are unimiportant in accounting for the observed differences in song.
Abstract: (1) We recorded the territorial songs of great tits at ten different geographically separated sites. Five of the sites were in dense deciduous or coniferous forest, and five in open woodland, parkland or hedgerows. (2) Forest birds from England, Poland, Sweden, Norway and Morocco had songs with a lower maximum frequency, narrower frequency range and fewer notes per phrase than woodland birds from England, Iran, Greece, Spain and Morocco. (3) We also measured acoustic attenuation for each habitat type; and for each study site we noted; body size of the birds, tree density, territory size, song of other species, song perch height, temperature and humidity. (4) We suggest that the differences in song between habitats, and striking similarities of songs from the same habitat type are at least in part related to differences in acoustic attenuation and territory size. Birds living in dense forests have to broadcast songs through more vegetation and over greater distances than do woodland birds. (5) We conclude that differences between habitats in climate, body size, perch height, and acoustic competition from other species are unimiportant in accounting for the observed differences in song. (6) If it is accepted that forest songs are better suited for long distance transmission, we cannot explain why woodland birds use less well designed songs, although we offer some suggestions.
262 citations
TL;DR: The most important finding of the study was that double- Brooded females survived less well (especially if they bred early) than single-brooded ones and this did not apply to males and there was no age-specific change in mortality for double brooded birds of either sex.
Abstract: (1) The aim of the study was to identify costs of reproduction in house martins and to make an assessment of the value of life-history theories and qualitative differences between individuals for interpreting intraspecific variation in reproductive output. (2) Breeding statistics for house martins in central Scotland were similar to southeastern England (except laying was 8 days later and II Y. fewer had a second clutch). There was a correlation between arrival date at the colony and the start of breeding for each individual. Females invariably arrived after their mates. (3) Older males were heavier, tended to pair with older, double-brooded females, laid earlier and reared more young. (4) Older females bred earlier and reared more young but were not heavier. (5) Adults lost weight when food was scarce and also during the most demanding (middle) phase of nesting growth. Laying anomalies (a stop to laying due to food shortages) probably led to significant weight losses in females. (6) Laying interruptions wasted time, reduced the chance of a second brood and marginally lowered the size of the first. (7) First brood fledglings survived equally over winter, irrespective of brood size and (less convincingly) parent age. (8) Older parents tended to be more successful in bringing clutches to independence. (9) Mortality of adult house martins occurred mainly outside the nesting period and averaged 57%. The most important finding of the study was that double-brooded females survived less well (especially if they bred early) than single-brooded ones. This did not apply to males and there was no age-specific change in mortality for double brooded birds of either sex. (10) Food supply limits the start of breeding and can account for some of the changes in output through the season. For a full explanation of intraspecific differences in output within first and second broods however, it is useful to invoke qualitative differences between individuals. They may be considered as proximate mechanisms whereby the attributes of individuals (females in particular) (i.e. weight, size and ability) interact with resources leading to a reproductive pattern which is optimal for each individual. The advantage of early breeding for males was much greater than for females (as indicated by the reproductive value of different breeding patterns) in which the benefits of early laying and double broodedness were largely offset by the mortality costs experienced by female parents.
248 citations
222 citations
222 citations
206 citations
TL;DR: In this article, a model of competition in a divided environment is presented, where the competition coefficients, a, are reduced by a term, 0, which measures the amount of overlap between species.
Abstract: SUMMARY (1) Models of competition in divided or heterogeneous environments are reviewed. (2) A model of competition in a divided environment is presented. The competition coefficients, a, are reduced by a term, 0, which measures the amount of overlap between species. (3) Actual values of 0 are presented for two Drosophila communities. (4) 0 depends on the degree of aggregation of the competing species and on their densities. The outcome of competition in a divided environment must, then, be density dependent. (5) Low values of 0 improve the stability of a multi-species community and allow more
TL;DR: Variations in outcome were significantly correlated with the encounter angle formed by the intersection of the growth direction vectors of interacting colonies, and rankings of species' competitive abilities will rarely, if ever, form simple hierarchical sequences.
Abstract: (1) The outcome of overgrowth interactions and the spatial relationships between interacting colonies were determined for fifteen cheilostome species encrusting the undersurfaces of nine foliaceous corals collected from Rio Bueno, Jamaica. (2) Ranking of competitive overgrowth abilities of the seven commonest cheilostome species does not form a simple hierarchical sequence but instead forms competitive networks. Outcome of overgrowth interactions between colonies of the same two species was not always the same, and none of the cheilostome species won in all of its overgrowth interactions. (3) Overgrowth interactions between encrusting cheilostomes are complex. Variations in outcome were significantly correlated with the encounter angle formed by the intersection of the growth direction vectors of interacting colonies. Colony surface condition in the immediate vicinity of overgrowth interaction was also a significant factor for interactions involving the commonest species. (4) Redirection of growth of a pre-existing growing edge, formation of a new growing edge, and formation of specialized barriers to overgrowth are three growth responses of encrusting cheilostomes that also affect the outcome of overgrowth interactions. (5) Similar complexity in overgrowth interactions appears to exist between all other major groups of sessile colonial animals and sponges. Under such conditions no species is likely to win all of its competitive interactions and rankings of species' competitive abilities will rarely, if ever, form simple hierarchical sequences.
TL;DR: It is suggested that net-spinning sites are in short supply and that differences in their use are necessary for stable coexistence, and both sequential distribution patterns and ecological distinctions between species in the same river section could effectively partition the supply of net- Spinning sites or food between the species.
Abstract: SUMMARY (1) Six species of Hydropsychidae were found to coexist in the River Usk and its tributaries (South Wales). There is a marked downstream sequence of species. Some of them have disjunct distributions, others have zones of overlap. On the basis of extensive temperature records from three river systems it appears that this succession is related to sequential differences in temperature. Experimental observations on respiration rates of three species suggest that they are adapted to their own characteristic temperature regimes. (2) Hydropsyche pellucidula and Hydropsyche siltalai coexist in most of the main river. They exhibit differences in their water velocity preferences, life cycles, microhabitat preferences and diet. Hydropsyche siltalai and Hydropsyche instabilis coexist in some sites. No ecological differences between them were revealed. (3) Both sequential distribution patterns and ecological distinctions between species in the same river section could effectively partition the supply of net-spinning sites or food between the species. It is suggested that net-spinning sites are in short supply and that differences in their use are necessary for stable coexistence.
TL;DR: It is concluded that the quality of available food can exert a strong influence on the density of herbivores and accounted for greater peak densities of vole populations, but it did not prevent population declines.
Abstract: SUMMARY (1) Nutrition and demographic characteristics of three populations of prairie voles were compared in adjacent, but distinctly different, habitats in central Illinois. (2) Live trappings from 1972 to 1976 provided data for two cyclic fluctuations in density. Densities reached higher levels in all habitats during the first cycle (prairie-38/ha, bluegrass-128/ha and alfalfa-244/ha) than during the second cycle (10/ha, 60/ha and 102/ha, respectively). (3) Voles had greater reproduction and survival and higher body weights in the alfalfa than in the bluegrass or prairie habitats. Data obtained by snap-trapping indicated that litter sizes and fat reserves were also greater in the alfalfa habitat. (4) Examination of stomach contents showed that dicotyledons comprised a major portion of the vole diet in all habitats even though grasses dominated the vegetation in the bluegrass and prairie habitats. Voles in the latter habitats supplemented their diet with seeds and insects. (5) Analysis of nutrients in three common food items (alfalfa, clover and bluegrass) revealed that legumes not only contained more digestible energy than bluegrass but also higher levels of crude protein, calcium, phosphorus and sodium. Moreover, voles grew more rapidly, bred earlier and produced more young when fed alfalfa than when fed dandelions and bluegrass. (6) When released in enclosures, voles grew faster and reproduced sooner in the alfalfa than in the bluegrass or prairie habitats. (7) We conclude that the quality of available food can exert a strong influence on the density of herbivores. Higher forage quality accounted for greater peak densities of vole populations, but it did not prevent population declines.
TL;DR: Analysis of published studies generally indicates that ecological succession can be considered as a non- random process, and complex non-random or Markovian processes are likely to characterize ecological successions.
Abstract: SUMMARY (1) Analysis of published studies generally indicates that ecological succession can be considered as a non-random process. (2) Two examples are discussed in detail, termite succession on baitwood blocks in Ghana (Usher 1975) and predator-prey dynamics of mites in a complex universe of oranges (Huffaker 1958), and both indicate that succession is a non-stationary Markovian process. (3) The discussion considers that complex non-random or Markovian processes are likely to characterize ecological successions, the transition probability matrix elements not being constant but being functions either of the abundance, or of the rate of change of abundance, of a recipient class. (4) Tests of various hypotheses, using x2 criteria, are given.
TL;DR: Although optimal foraging is important to parasitoid reproductive fitness, the resulting dynamics are qualitatively similar to those produced by the model of Hassell & May (1973) in which the parasitoids do not forage optimally but have a fixed aggregation strategy.
Abstract: (1) Our aim in this paper is to bridge the gap between optimal foraging models and predator-prey or parasitoid-host population models. (2) The parasitoid optimal foraging model that we derive assumes each individual parasitoid to maximize its rate of encounter with healthy hosts in a patchy environment. (3) The model is used to generate the searching strategy of a population of parasitoids, from which their overall searching efficiency can be calculated. (4) We then explore the dynamics of a difference equation population model in which the parasitoids forage optimally. The conditions for local stability are derived and some global properties discussed. (5) We conclude that although optimal foraging is important to parasitoid reproductive fitness, the resulting dynamics are qualitatively similar to those produced by the model of Hassell & May (1973) in which the parasitoids do not forage optimally but have a fixed aggregation strategy.
TL;DR: The coexistence of seven species of Drosophila in the fruit and vegetable market was explained by the partitioning of breeding sites and by the fact that the community may never reach equilibrium.
Abstract: (1) This paper investigates the occurrence of larval competition in several domestic species of Drosophila in a fruit and vegetable market. (2) Regular seasonal changes in body size were demonstrated in D. melanogaster Meigen. (3) The heritability of body size in the field was negligible and so the seasonal changes must have been due to the environmental effects of temperature and larval density. (4) Multiple regression analysis was used to separate the effects of temperature from the effects of larval density. Density was found to account for a significant amount of the variation in body size in D. melanogaster. This is evidence of intraspecific competition. (5) Interspecific competition was demonstrated by the fact that the density of D. melanogaster was found to affect the body size of several other species. (6) The coexistence of seven species of Drosophila in the fruit and vegetable market was explained by the partitioning of breeding sites and by the fact that the community may never reach equilibrium.
TL;DR: It is suggested that the number of agromyzid species on many common and widespread umbellifers is considerably below the number that could finally evolve to exploit these plants, and that guilds of specialized leaf-miners are not 'equilibrium assemblages'.
Abstract: (1) The number of species of larval agromyzids (Diptera: Agromyzidae) mining plants in the family-Umbelliferae within the British Isles is reviewed. (2) A regression of the number of agromyzid species (S) on the geographical range of each plant (measured in 10 km squares, A) (leS + 1 vs leA) is highly significant, but explains only 32% of the variance. Several other 'species-area' curves are similar in this respect. (3) Geometric mean size of the plants, leaf-form (both measures of plant 'architecture'), and whether or not they grow in aquatic habitats explains some of the residual variation, but approximately 50% remains unexplained. (4) A wide variety of other characteristics of the plants, and their associated fauna (potential competitors and natural enemies) had no detectable influence on the number of Agromyzidae. Factors examined include taxonomic isolation, whether the plants were annual, biennial or perennial, the number of species of potentially competing microlepidoptera, and the number of species of parasitoids. (5) We suggest that the number of agromyzid species on many common and widespread umbellifers is considerably below the number that could finally evolve to exploit these plants, and that guilds of specialized leaf-miners are not 'equilibrium assemblages'.
TL;DR: A simple model is used to describe the outcome of a series of trials investigating frequency-dependent selection of prey types, relating the relative frequencies of the various prey types eaten to therelative frequencies available.
Abstract: (1) Predators sometimes eat disproportionately more of the more abundant forms of their prey, thus promoting diversity in the prey population. (2) Such selection may be investigated by exposing a series of prey populations with different relative frequencies of the various types to a series of predators. (3) We use a simple model to describe the outcome of such a series of trials, relating the relative frequencies of the various prey types eaten to the relative frequencies available. Frequency-independent and frequency-dependent components of selection are separated in the model. (4) Previous criticism of the model does not appear to be valid. An alternative model due to Manly seems a priori unrealistic and potentially misleading. (5) We have investigated the fit of our model to all the available data. In most cases it is good. Manly's model is also a good fit to most of the data, except at extreme prey frequencies. (6) Experiments of the type considered need to be carefully designed if the results from different experiments are to be comparable. (7) They are more useful than most of the other types of experiment and observation that have been used for investigating frequency-dependent selection. (8) Appendix 1 describes two techniques for fitting our model to the data from experiments with two prey types. (9) Appendix 2 describes an approximate technique for fitting our model to the data from experiments with more than two prey types and illustrates it with a worked example.
TL;DR: Evidence is presented which suggests fecundity is reduced the day after an aphid disperses, and the significance of dispersal by apterous aphids is discussed in the light of evidence presented.
Abstract: SUMMARY (1) This paper examines the influence of predators on the dispersal of apterous pea aphids in the laboratory and field. (2) Individual pea aphids can be placed in one of two categories, searchers and runners, depending upon the behaviour they exhibit after dropping from their host plant. (3) In field cages, pea aphids readily disperse to new host plants in the presence of predators. Dispersal of apterous aphids is rare when active predators are absent. (4) Evidence is presented which suggests fecundity is reduced the day after an aphid disperses. (5) The distance dispersed by aphid nymphs is positively correlated with the density of aphids on the plant the aphid leaves. (6) The significance of dispersal by apterous aphids is discussed in the light of evidence presented.
TL;DR: In this article, simulation models were combined with a test of equal catchability to quantify the effect of heterogeneity of catchability on survival estimates obtained by capture-recapture methods from an actual population.
Abstract: (1) Simulation models, in combination with a test of equal catchability, were used to quantify the effect of heterogeneity of catchability on survival estimates obtained by capture-recapture methods from an actual population. (2) The biases in the estimates were found to be negligible although the test revealed a considerable degree of heterogeneity. (3) This suggests that the use of such tests to determine the appropriatene8s of particular estimation models to actual data may be highly misleading. (4) Simulation may often be a useful and relatively inexpensive method for exploring alternative models.
TL;DR: Vole numbers showed a 4-year cycle of abundance during the course of the study and most populations were in phase, and changes in vole numbers were negatively related to the vole consumption by the weasel population the preceding year.
Abstract: (1) Numbers of voles, weasels and the diet and reproductive performance of the weasel population were measured on a large area (25 kM2) of farmland in the south of England. (2) Vole numbers showed a 4-year cycle of abundance during the course of the study and most populations were in phase. Peak populations were fourteen times the density of low populations. (3) Weasel numbers varied annually and peak numbers were over twice the minimum number. Relative changes in weasel numbers lagged behind changes in vole numbers. (4) Female weasels failed to breed during the year of lowest vole numbers. (5) The diet of male weasels showed distinct seasonal changes; females showed less seasonal variation than males. The difference is attributed to large differences in home range size between the sexes. (6) The proportion of voles in the diet increased with increasing vole density and was 16% in the lowest years and 54%? in the highest. (7) When vole numbers were low birds were the main alternate food for weasels. (8) Changes in vole numbers were negatively related to-previous changes in weasel numbers. (9) Changes in vole numbers were negatively related to the vole consumption by the weasel population the preceding year.
TL;DR: A method based on Moran curves is presented for determining monthly changes in density independent mortality acting on tsetse fly populations under natural conditions and it is suggested that the possibility of tsete control in, or eradication from, any area is related to the distance of the mean environmental conditions from the predicted optimum at the same mean temperature.
Abstract: SUMMARY (1) A method based on Moran curves is presented for determining monthly changes in density independent mortality acting on tsetse fly populations under natural conditions. (2) The method of analysis is tested on the output of a simple population model for tsetse and predicts qualitative changes in mortality under all conditions and quantitative changes when the mortality acts equally on all life stages. (3) Fly round records for female G. morsitans submorsitans from the Yankari Game Reserve, N. Nigeria, for the period 1964-73, are analysed using the new method. Mean monthly density independent mortalities are calculated and are shown to be most closely related to mean monthly saturation deficit. (4) Values of density independent mortality are superimposed on an annual climogram for Bauchi, near the study site, and mortality contours are drawn enclosing regions of equal mortality. This procedure identifies an environmental optimum for the subspecies, between 24 and 26? C and 5-13 mm Hg saturation deficit. (5) Less complete data from Zambia are also analysed and identify a similar optimum for G. m. morsitans, at between 22 and 23? C and 7-11 mm Hg saturation deficit. These two optima are compared with previous estimates derived by quite different methods. (6) Vertical sections taken through the mortality contours give rise to mortality profiles w~hich, in conjunction with the population model, can be used to define the bioclimatic limits of the species. (7) Weather records for ninety-one sites throughout tropical Africa, in both tsetse and non-tsetse areas, are summarized: 9400 of the sites within the present or recent known distribution of G. morsitans fall within the predicted bioclimatic limits, whilst only 5000 of non-tsetse areas (an average of less than 200 km away from the tsetse area nearest to each of them) do so. (8) The construction of bioclimatic limits also identifies an optimum saturation deficit at each temperature. It is suggested that the possibility of tsetse control in, or eradication from, any area is related to the distance of the mean environmental conditions from the predicted optimum at the same mean temperature. (9) Finally the problems of applying the analytical method to other data are briefly discussed.
TL;DR: Comparisons of observed and computed maximum growth rates suggest that growth rates are generally between 60 and 90?4 of the computed maximum for that temperature regime and that this percentage is no higher in chalk streams.
Abstract: (1) The maximum growth rates of brown trout have been computed from temperatures in rivers and streams of contrasting character and location, using the growth model of Elliott (1975a) for trout on maximum ration. The high growth rates of trout in chalk streams may be largely explained by their ambient temperature regime, principally its relatively homothermous character. (2) Comparisons of observed and computed maximum growth rates, for the few locations where contemporaneous temperature and growth data are available, suggest that growth rates are generally between 60 and 90?4 of the computed maximum for that temperature regime and that this percentage is no higher in chalk streams.
TL;DR: It seems that the delay between arrival and laying may be caused by the need to build up food reserves for egg formation, and it is suggested that this period may be required for the development of the reproductive organs.
Abstract: SUMMARY (1) The breeding success of migrant wheatears studied on Skokholm Island, Dyfed, Wales, showed a seasonal decline. The timing of breeding of females was very closely related to the date of their arrival on Skokholm, there being a delay of about 3 weeks between arrival and the laying of the first egg. (2) Certain territories consistently tended to be used by early breeding birds, others by late breeding birds, and this was not due to their occupation, in different years, by the same individuals. (3) The territories in which early breeding occurred were occupied in a greater proportion of the 4 study years. They were also occupied by older (as opposed to first summer) males and they were the first territories to be taken up at the start of the breeding season. (4) I suggest that the territories in which early breeding occurred were those better suited to the wheatear's feeding technique. (5) Feeding rate and time budget data were collected from females in the period from arrival through incubation. It seems that the delay between arrival and laying may not be caused by the need to build up food reserves for egg formation. Instead I suggest that this period may be required for the development of the reproductive organs.