Showing papers in "Journal of Animal Ecology in 1986"

Biological indicators of freshwater pollution and environmental management

Abstract: The preface of a book often provides a convenient place in which the author can tender his apologies for any inadequacies and affords him the facility to excuse himself by reminding the reader that his art is long but life, or at least the portion of it in which he has the opportunity for writing books, is short. I, too, am deeply conscious that I have undertaken a task which I could not hope to complete to my own satisfaction but I offer, in self defence, the observation that, inadequate though it is, there is no other book extant, so far as I am aware, which provides the information contained herein within the covers of a single volume. Often during the last decade, in discharging my responsibilities for the environmental aspects of the water authority's operations and works, I should have been deeply grateful to have had access to a compendium such as this. The lack of a convenient source of data made me aware of the need which I have attempted to fill and in doing so I have drawn on my experiences of the kinds of problem which are presented to biologists in the water industry. The maxim 'half a loaf is better than none' seems particularly apt in this context."

The Biology of butterflies

Abstract: Background and Identification Butterflies are in the order Lepidoptera which are insects with scaled wings. Moths are also in the order Lepidoptera. Butterflies are invertebrates, which means that they do not have a backbone, instead they have an exoskeleton, a shell that encases their soft body and protects their vital organs. Butterflies undergo metamorphosis, so that the immature and adult forms are very different.

A dictionary of birds

Abstract: A Dictionary of Birds enlists contributions from over 280 ornithologists and other specialists from around the world. Major, authoritative articles cover the field of modern ornithology and related subjects, many of them running to several thousand words. In addition there are articles on all the bird families, almost all of which are illustrated by a representative species. There are also numerous short entries defining special terms, application of names, etc. The total gives a text of over 800,000 words, supported by more than 500 photographs, drawings and diagrams. "One of the most valuable books to have been published for many years." --BTO News

The effect of a parasitic nematode on the breeding production of red grouse

Abstract: (1) The breeding success of female red grouse treated with an anthelmintic to reduce an infection of the nematode Trichostrongylus tenuis was compared over a period of 3 years with that of a control group. Treatment significantly increased the production of young per female in all years. (2) Breeding success showed a significant, negative correlation with parasite numbers in old grouse, both within and between areas (in 4 out of 5 years). (3) The role of parasitic nematodes in the population cycles of red grouse are discussed in relation to current models and previous studies.

Territoriality and mating system of California voles

Abstract: (1) In this study I used radiotelemetry to examine patterns of space use by free-ranging California voles (Microtus californicus) both before and after the provision of supplemental food (fresh carrots). In each of the study's 2 years, carrots were provided over an area (100 m2) about the size of a California vole home range. The first run was conducted at peak population density, and the second at low density. (2) Home range core areas were 30-50% larger for males than for females, but peripheral areas were nearly 100% larger for males. Home ranges of those females having access to supplemental food shrank after provisioning, whereas those of males did not. Home ranges of males were nearly 100% larger at low than at high density, whereas those of females were 30-50% larger at low than at high density (the latter difference being non-significant). (3) Home ranges of females often overlapped extensively with those of other females, and nest-sharing was not uncommon. Some females shifted their home ranges after food addition to encompass more of the provisioned area. The addition of food induced overlap between females that had not previously overlapped. (4) Males showed very little overlap with other males, and this was not affected by food addition. Males rapidly occupied home ranges abandoned by adjacent males. (5) Males and females overlapped with each other extensively, but access to females was unequal. I conclude that male M. californicus are strongly territorial, but that females are non-territorial or selectively territorial. Mating is probably polygynous, and the most likely mode is female defence.

Density dependence in suspension-feeding and deposit-feeding populations of the bivalve macoma balthica: a field experiment

Abstract: SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment. SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked clams from each treatment were then measured. (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment. SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked clams from each treatment were then measured. (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment.

Brood size in canada geese: a manipulation experiment

Abstract: SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size.

Generalist and specialist natural enemies in insect predator-prey interactions

Abstract: SUMMARY (1) The dynamics of a predator-prey, or parasitoid-host, interaction are considered where the predator or parasitoid is a generalist whose population is buffered against changes in the particular prey being considered. (2) The interaction is then broadened to include, in addition, a specialist natural enemy, and three questions are examined within this framework. (i) Under what conditions can a specialist 'invade' and persist in an existing generalist-prey interaction? (ii) How does the addition of the specialist natural enemy alter the prey's population dynamics? (c) How does the relative timing of specialist and generalist in the prey's life cycle affect the dynamics of the interaction? (3) The following conclusions emerge. (i) A specialist can invade and co-exist more easily if acting before the generalists in the prey's life cycle. (ii) A three-species stable system can readily exist where the prey-generalist interaction alone would be unstable or have no equilibrium at all. (iii) In some cases the establishment of a specialist leads to higher prey populations than existed previously with only the generalist acting. (iv) In some cases, a variety of alternative stable states are possible, either alternating between two-species and three-species states, or between different three-species states.

Density dependence and magpie food hoarding

Abstract: Description d'un modele de repartition des caches presentant le meilleur compromis entre la necessite de dissimuler les reserves de nourriture et celle de ne pas passer trop de temps en deplacement pour les constituer

Spatial distribution and behavioural movements of migratory trout (Salmo trutta) in a Lake District Stream

Abstract: SUMMARY (1) As the sample variance to mean relationship for 18 year-classes (1967-84) of migratory trout, Salmo trutta L., followed Taylor's Power Law, their spatial distribution was density-dependent. As expected, there were significant changes in the relative level of clumping at different stages in the life cycle. (2) The first spatial change, a decrease in relative clumping soon after the end of the alevin stage in April, was related to the behavioural movements of the fry emerging from the nest, usually at night. About 81% of fry in field experiments rarely fed, soon lost weight after their yolk was exhausted, drifted downstream chiefly at night and died. The others started to feed and either remained near their birthplace or migrated, usually upstream. The proportion migrating was density-dependent, increasing from < 1% to c. 12% as the number of fry per nest increased. Few fry emigrated out of the stream and therefore population losses in spring were chiefly due to mortality. (3) The second spatial change, an increase in relative clumping in the first winter of the life cycle, was related to the behavioural movements of first-year trout when they migrated to deeper pools in the stream. A few first-year trout emigrated out of the stream in winter, but population losses in the first summer and winter of the life cycle were chiefly due to mortality, usually within the stream, rather than migration. (4) There were no major spatial changes for second-year trout in the second spring, summer and winter of the life cycle. The third spatial change, a slight increase in the relative clumping of third-year trout, was related to their increased mobility just before they emigrated from the stream as smolts. Few second and third-year trout died in the stream and most moribund fish moved out of the stream. (5) The implications of this investigation are discussed and it is concluded that the parameters of the Power Law are not only species-specific but also life-stage specific. The present investigation has shown that such parameter changes can be used to detect major spatial changes that can be related to behavioural movements.

Maternal investment and neonatal growth in phocid seals

Abstract: (1) This paper draws together information on neonatal size at birth, weaning mass, growth rates during the nursing period and duration of lactation of phocid seals in order to examine similarities and differences in these aspects of life-history patterns within the group. Broader interspecific comparisons are also made in order to evaluate the adaptive developmental responses of phocid seals during the period of maternal investment in contrast to terrestrial carnivores and to mammals generally. (2) Individual phocid offspring of most species are large and precocial, but female phocid seals as a group do not invest more energy per litter than many other carnivores and not substantially more than mammals generally at the time of parturition. (3) The relative mass of individual phocid seals at weaning is more uniform within the group than is mass at birth. This similarity is achieved by compensatory variation of growth rates and the duration of lactation. (4) Although data are limited, it appears that maternal investment differs between the sexes in all species which are sexually dimorphic with respect to body size.

Interspecific interference competition ― Nest sites for blue and great tits

Abstract: SUMMARY (1) Interspecific competition for nest sites was studied in blue and great tits nesting in boxes in Wytham Woods, Oxfordshire. (2) The breeding density of both blue and great tits was dependent on the density of nest boxes over the range of two to eight boxes per hectare. (3) Changes in blue and great tit densities, from one year to the next, were negatively correlated at low densities of nest boxes and positively correlated at high nest-box densities. The relative density of blue tits increased as the density of available nest sites increased. The spatial variance of blue tit mean density was dependent on great tit density over the same range of nest-box densities. The spatial variance of the great tit population was independent of blue tit density. (4) Blue and great tits do not maintain interspecific territories or space out their nest sites. They do compete for the same favoured nest sites. (5) Great tits are good interference competitors and are relatively more successful than blue tits where nest sites are limiting. Blue tits are good exploitation competitors and are successful where high breeding densities result in competition for food during the breeding season.

Timing of Nesting by Canada Geese in Relation to the Phenology and Availability of Their Food Plants

Abstract: (1) This study examined seasonal variation in the foraging behaviour of cackling Canada geese (Branta canadensis minima) and in the nutrient content and availability of tundra grasses and sedges (graminoids) and arrowgrass during the nesting and brood-rearing periods, 1977-79 on the Yukon-Kuskokwim Delta, Alaska. (2) Nitrogen concentrations in nearly all graminoids and arrowgrass began to decline either prior to, or during, hatching of cackling goose clutches. Grazing or clipping of vegetation resulted in higher and prolonged peaks in nitrogen concentration but peak nitrogen levels in these plants still occurred within a week of the end of the hatching period. (3) Standing crops of graminoids increased until early August while the standing crop of arrowgrass (the most nutritious plant in the diet) in preferred foraging habitat began to decline in mid-July due to grazing by geese. (4) Peck-rates of adult cackling geese tended to decline as brood-rearing progressed, indicating that preferred foods declined in availability during this period. Also, late in brood-rearing, preferred foraging areas were used less and arrowgrass comprised a smaller proportion of the diet. (5) Changes in plant nutrient levels and shifts in diet and habitat use reduced the nutritional quality of the diet as brood-rearing progressed. Thus, as a result of both the natural phenology of tundra plants and grazing by geese, late hatching broods were at a nutritional disadvantage compared to those hatching early. (6) We conclude that a seasonal decline in the quality of foraging conditions is probably an important factor favouring early nesting by geese.

Temperature-Induced Shift in Foraging Ability in Two Fish Species, Roach (Rutilus rutilus) and Perch (Perca fluviatilis): Implications for Coexistence between Poikilotherms

Abstract: (1) The effects of temperature on capture probability, attack coefficient (or instantaneous search rate), handling time, swimming speed and capture rate of two fish species, roach (Rutilus rutilus) and perch (Percafluviatilis), were studied in the laboratory. (2) The attack coefficient increased exponentially for both species. Handling time decreased asymptotically with temperature for perch and in a sigmoid way for roach. Roach had a longer handling time and lower capture rate than perch at low temperatures (12-18 ?C), while the reverse was the case at high temperatures (18-21 ?C). The results suggest a shift in the species having the highest competitive ability at a temperature around 18 ?C. The increased capture rate and decreased handling time of roach at high temperatures was attributable to an increase in swimming speed and capture success. (3) The temperature region (17-19 ?C) within which capture rate and handling time intersected for perch and roach in the laboratory study was compared with the vertical distribution of the species in thermally stratified lakes. A high correspondence between the predictions from the laboratory data and the actual field distribution of the species was found. (4) It is argued that including temperature in foraging models will improve both the predictions of prey selection and of resource partitioning in poikilothermic animals. Temperature may also mediate coexistence between poikilotherms in environments in which temperature varies spatially and temporally.

Structure of bat guilds in the Kimberley mangroves, Australia

Abstract: (1) Deterministic guilds have been predicted to occur in stable, persistent communities. Mangrove communities in the Kimberley of Western Australia include large, isolated stands that are stable in terms of floristic composition and vegetation structure. A selection of stands was sampled for bats belonging to the insect foraging guild. (2) The potential foraging niche of each bat species was estimated in terms of the bat's flight morphology (aerodynamic characteristics) at minimum wing loading. These estimates were used to analyse the structure of the guild observed in each mangrove stand. (3) The observed guilds had a deterministic structure. The flight morphologies of species that foraged in the same stand showed almost no overlap even though each of these observed guilds occupied almost the same total area of morphological space as the entire pool of potential colonizers. In contrast, guild structures generated stochastically from the pool of potential colonizers included significant overlap. (4) Available flight space in the mangal was arbitrarily divided into five foraging microhabitats so that species' realized foraging niches could be estimated from field observations and used to interpret the morphological analysis. (5) Differences in species' flight morphologies could be related to vertical and horizontal foraging microhabitats but the morphological data indicated that a narrower partitioning of foraging zones actually occurred.

Resource utilization, overlap and temporal community dynamics: a null model analysis of an epiphytic chironomid community.

Abstract: (1) Temporal patterns in resource utilization in a community of epiphytic chironomid larvae were investigated for a year in a small river in eastern England. (2) Null resource utilization models were constructed by Monte Carlo simulations and used for evaluating the significance of the observed temporal and dietary overlap amongst nine chironomid species. (3) The observed mean overlap in temporal resource utilization in this community was significantly larger than expected from null models. Temporal pattern in community dynamics, especially in terms of production, was strongly influenced by diatom abundance. (4) Dietary overlap was significantly larger than expected from a null model in some months, due mainly to limited choice of food and lack of selective feeding by different species of chironomids. No significant dietary partitioning (observed overlap significantly smaller than expected in the model) occurred throughout the year. (5) The results indicate that competition is not an important factor in the temporal organization of the epiphytic chironomid community. (6) The relationship between overlap and resource availability was discussed in a wider context.

Cues for Oviposition by Ladybird Beetles (Coccinellidae): Response to Aphids

Abstract: (1) Reproductive responses of predatory insects to spatial variation in prey density are poorly understood, yet may contribute significantly to stability of the predator-prey interaction. To explore the nature of such responses for ladybird beetles in particular, the sensitivity of ovipositing females of Coccinella septempunctata L. to local prey conditions was examined in the laboratory. (2) Previously well-fed coccinellids laid significantly fewer eggs when removed temporarily from aphids than when kept with aphids. The drop in egg production resulted from beetles delaying oviposition for several hours when aphids were absent. (3) The coccinellids did not delay oviposition when exposed to aphid odours and honeydew (but not to aphids). (4) Female beetles were more active when aphids were absent than when they were present. Females were also more active when only aphid odours and honeydew were present than when aphids were present. Thus, the females' delay in ovipositing in the absence of prey did not result simply from their increased activity. (5) The reluctance of coccinellids to oviposit, coupled with these females' increased activity when aphids are not nearby, enhances the ability of these predators to oviposit at particularly favourable sites.

Insect species richness of the british rosaceae: the importance of host range, plant architecture, age of establishment, taxonomic isolation and species-area relationships

Abstract: SUMMARY (1) The number of species of Lepidoptera, Hymenoptera, Homoptera and Diptera feeding on British Rosaceae generally increases with the size of the geographic range of the host species, and with the complexity of the host's morphology. (2) Within the Rosaceae, trees support more insect species than shrubs which in turn support more insect species than herbs. In addition, trees have more insect species within each insect guild and taxonomic grouping associated with them than shrubs, which in turn have more than herbs. (3) Although shrubs and herbs begin to accumulate insect species at a lower level of abundance than trees, trees accrue species at almost twice the rate of herbs and shrubs. The species-accrual rate for different guilds of insects (chewing, sucking and gall-forming) and for the four taxa of insects considered (Lepidoptera, Hymenoptera, Diptera and Homoptera) is greatest on trees except in the case of gall-forming insects and Diptera, where the rate is similar for trees, shrubs and herbs. (4) The older the plant's history of establishment, based on the number of Quaternary records, the more insect species that are associated with it. Also, more recent less widespread plants have a greater polyphagous insect fauna than older more widespread plants. (5) Various analyses enabled 83%, 83% and 45% of the variation in insect species richness between trees, shrubs and herbs to be accounted for, respectively. The low variation accounted for in the case of the herbs may be the result of the poor quality of insect records for this group of plants. (6) Within given genera of plants, increases in geographical range and plant complexity are associated with an increase in the number of insects feeding upon them. When each genus within the Rosaceae was considered as a separate entity a similar pattern was seen. (7) Of the six plant genera with at least three members (Prunus, Sorbus, Rubus, Rosa, Cotoneaster, and Potentilla), Prunus has the most insect species associated with it and

Distribution and abundance of tsetse flies (glossina spp.)

Abstract: SUMMARY (1) Two approaches are used to understand the distribution of tsetse. In the first, empirical, approach the distribution of Glossina palpalis and G. fuscipes in West and Central Africa is superimposed on a map showing 'contours' of average annual temperature and saturation deficit. The northern distributional limits of both species correspond best with the joint condition that temperature and saturation deficit do not exceed 27 ?C and 14 mmHg respectively, while the southern, cooler, limit is set by the line of 6/7 mmHg saturation deficit. (2) In the second, analytical, approach mortality rates calculated from fly-round catches of G. morsitans, G. palpalis and G. tachinoides have been related to the local climograms for the fly-round sites. A reproductive plane added to these mortality climograms allows the identification of both the bioclimatic limits (where reproduction just balances mortality) and the bioclimatic optimum (where reproduction exceeds mortality by the greatest amount) for each species. (3) The above three species show very different responses to a similar range of climatic conditions, which explains their differential distribution and may also account for the ability of G. palpalis and G. tachinoides to coexist, despite competition, in West Africa. (4) The abundance of flies, and the risk of disease transmission, may be greatest at the bioclimatic optimum for each species. Several areas of Africa with known current problems of trypanosomiasis correspond well with the bioclimatic optimum for G. morsitans. (5) Field data on the abundance of G. palpalis and G. tachinoides in northern Ivory Coast are compared with the predictions based on the mortality climograms for these species. The low availability of hosts in (forest) regions corresponding to the bioclimatic optimum of G. palpalis appears to have a significant impact on the abundance of this species. (6) The future use of the relationships established between tsetse distribution and abundance and climate in forecasting the changing risks of trypanosome transmission is discussed.