Showing papers in "Journal of Animal Ecology in 1988"

Nutritional ecology of insects, mites, spiders, and related invertebrates

Abstract: Nutritional Ecology of Forb Foliage-Chewing Insects Nutritional Ecology of Insect Folivores of Woody Plants: Nitrogen, Water, Fiber and Mineral Considerations Nutritional Ecology of Grass Foliage-Chewing Insects Nutritional Ecology of Phytophagous Mites Nutritional Ecology of Lichen/Moss Arthropods Nutritional Ecology of Arthropod Gall-Makers Nutritional Ecology of Bruchid Beetles Nutritional Ecology of Seed-Sucking Insects Nutritional Ecology of Stored-Product Insects Nutritional Ecology of Stored-Product and House Dust Mites Ecology of Nectar and Pollen Feeding in Lepidoptera.

Individual decisions and the distribution of predators in a patchy environment

Abstract: SUMMARY (1) The theoretical distribution of non-omniscient predators in a heterogeneous multipatch environment is studied by numerical simulation. Although various relative densities are explored, we mostly attend to environments where prey density is approximately one order of magnitude higher than predator density. (2) Predators are assumed to follow the rule of abandoning their current patch when local capture rate is lower than estimated capture rate in the environment as a whole. This rule was chosen because it is known to maximize long-term capture rate in many foraging situations. For convenience, we assume that after abandoning a patch, predators arrive at random at any patch in the environment. (3) Predators detect precisely the capture rate in their current patch but 'learn' about the environmental average. Learning is simulated using a linear operator model which estimates global capture rate as a weighted average of past and current experienced capture rate. Following a common approach is psychological models of simple learning, the relative weight of past and present capture rate is controlled by a parameter denominated the 'memory factor'. (4) In the absence of depletion, the predators distribute themselves close to the predictions of the Ideal Free Distribution model. This result indicates that the IFD prediction is not dependent on assuming omniscient predation, but instead can be jointly derived from reasonable assumptions about learning and optimal foraging at individual level.

The impact of predation on boreal tetraonids during vole cycles: an experimental study

Abstract: Les populations de Tetraonidae de 2 iles similaires du Nord de la Suede ont ete etudiees pendant 9 ans.L'enlevement experimental des renards (Vulpes vulpes) et des martes (Martes martes) montre que la predation qu'ils exercent non seulement reduit le succes reproducteur des oiseaux mais reduit aussi le nombre d'adultes et est responsable de la synchronisation entre la productivite des Tetraonidae et l'abondance des campagnols

Estimating Primate Densities from Transects in a West African Rain Forest: A Comparison of Techniques

Abstract: (1) We used two line-transect survey techniques and five analytical methods to assess the densities of social groups of seven diurnal primate species resident on Tiwai Island, Sierra Leone, West Africa. (2) A modified standard species-specific strip-width estimation technique was applied to data from twenty-eight single-observer transect samples, each 6 km in length. (3) The second method employed seventeen sweep samples where three observers simultaneously walked parallel transects 100 m apart and 1 km in length. This method used both sightings and localization of vocalizations for density estimation. (4) The third method transformed sighting rates from the single-observer samples into density estimates by incorporating sighting rates and densities from sweep samples into calibration factors. (5) We used long-term data on home-range size and overlap to estimate density for three species for which we had sufficient data. (6) The fifth method employed the hazard-rate model of Hayes & Buckland (1983) which involved transforming estimates of distance to the first sighted individual into estimates of distance to the group centre. (7) The rank orders by species of density estimates produced by all analytical techniques were identical except for the sweep-quadrat method. We found no significant differences among density estimates produced by different analytical methods, except for the C. diana density produced by the sweep samples. (8) We recommend the use of both relatively long single-transect samples and also more localized multi-observer sweep samples. These techniques allow use of a variety of analytical methods.

Feeding intensity, growth rates, and the establishment of life-history patterns in juvenile atlantic salmon salmo salar

Abstract: SUMMARY (1) Under good growing conditions, populations of juvenile Atlantic salmon develop a bimodal size-frequency distribution by late autumn of their first year; the larger fish in the upper modal group (UMG) will metamorphose into the sea-going phase the following spring, a year ahead of fish in the lower modal group (LMG). The feeding behaviour and growth rates of individually-marked fish from a sibling laboratory population were studied during the period when these two distinct life-history patterns become apparent. (2) The length-frequency distribution of the laboratory population was unimodal in August, significantly skewed by September, and clearly bimodal by December. Bimodality was a result of fish which joined the UMG putting on a brief growth spurt in late September/early October, at a time when water temperatures were falling and growth rates of LMG fish were decreasing. (3) Studies of the feeding behaviour of single fish in laboratory flume tanks revealed that the growth rate changes could be linked to changes in appetite rather than any external factors. The appetites of the two types of fish were initially similar in August, but then diverged: UMG fish showed a marked increase in appetite through to October, whereas the appetite of LMG fish decreased, with a small peak in October. (4) The results indicate that the fast and slow developing life-history patterns become fixed prior to September of the first year, and the corresponding changes in appetite and growth rate are thereafter under internal control. The October peak in appetite does not appear to be related to natural food availability, and may instead allow fish to obtain nutritional reserves prior to the winter when feeding is constrained.

Feeding ecology of great tits (parus major) and blue tits (parus caeruleus), breeding in suburban gardens

Abstract: SUMMARY (1) The nestling diet of great tits, Parus major L. (ten pairs), and blue tits, Parus caeruleus L. (eight pairs), breeding in suburban gardens, was recorded using camera nestboxes. (2) Birds breeding in gardens fed their nestlings at a similar rate, and with similar sized prey, to birds breeding in woodland. (3) There was no difference in the type of prey brought by males and females in either species. However, there were significant differences between the species: great tits brought more spiders (Araneae) and Diptera; blue tits more aphids (Hemiptera). Both species brought approximately 15% of the nestlings' food from bird tables (artificial food), although great tits brought significantly more peanuts than blue tits. (4) There was no relationship between the amount of artificial food in the diet, and nestling survival, in either species. (5) The diet of nestljing blue tits changed over a 13-day period. Proportionately more spiders were fed to young nestlings (3-9 days), whilst older nestlings (14-15 days) received more artificial food and aphids. (6) The diet of nestling great tits also varied with age: young nestlings (3-9 days) being fed greater than expected numbers of spiders, earwigs (Dermaptera), and Diptera. (7) In both species, nestling diet was not independent of time of day. Blue tits brought fewer Lepidopteran larvae than expected from 07.00 to 16.00 h, and more aphids. Great tits brought more spiders than expected from 08.00 to 13.00 h, and more Diptera from

Effects of dispersal date on winter flock establishment and social dominance in marsh tits Parus palustris

Abstract: (1) We studied the effect of sex, size, age and prior occupancy on social dominance winter flock establishment in a population of marsh tits Parus palustris L. (2) When sex was accounted for, time of establishment in the winter flock-prior occupancy, was critical for the outcome of later aggressive interactions juveniles within flocks. Residents won all interactions with intruders irrespective controlling for sex. (3) Success in, and timing of, establishment were closely linked with hatching lower proportion of late-hatched than early-hatched juveniles became established winter flocks; they also became established later. Even small differences in hatching greatly influenced dominance and the probability of becoming established flock. (4) Since early establishment depends on early hatching, dominance and survival juveniles are determined by how early their parents start breeding. Furthermore, will be strong selection for quick establishment after (Less)

Life history of the land snail arianta arbustorum along an altitudinal gradient

Abstract: SUMMARY (1) The life history of the polymorphic land snail Arianta arbustorum was investigated in five natural populations along an altitudinal gradient from 1220 to 2600 m in the Swiss Alps. In order to assess the environmentally-induced variation of reproductive characters snails were transplanted to the lowlands. (2) Adult size decreased from 19-9 to 16-0 mm (mean shell breadth) with increasing altitude, age at maturity increased from 1-9 to 5-0 years, but median adult longevity and adult survival rates were approximately the same at all altitudes. (3) Clutch number, clutch size, egg size and reproductive investment per year decreased with increasing altitude in resident snails, whereas reproductive investment per egg increased. Within populations, clutch number, number of eggs produced per year and egg size scaled allometrically with shell size indicating a size-specific fecundity. (4) Transplanted snails laid 1-3-11-5 times more clutches than did resident snails. However, no differences in clutch size, egg dry weight and hatching success were found between transplanted and resident snails, except in one population, in which transplanted snails laid smaller clutches with larger eggs and scored a lower hatching success. (5) Transplanted snails were less variable in reproductive characters than resident ones, except for hatching success. (6) In general, life-history characters did not appear to be correlated with shell or body colour. (7) Although proximate factors like temperature explain most of the variation in life history, evidence was obtained also for genetic divergence among populations. The results match the predictions of the adversity selection model well, rather than those of bet

Survival rate in the great tit parus major in relation to sex, age, and immigration status

Abstract: SUMMARY (1) Survival rates of Great Tits were studied using data collected in Wytham Wood, Oxfordshire. The breeding population was split into four groups by sex and status (born in nestboxes = residents, not known to be born in nestboxes = immigrants). Survival rates were only measured for breeding adults, the large majority of which were 1 year old when first found breeding. (2) Survival rates were estimated using a recent modification of Cormack's (1964) method. Relationships between these estimates and several environmental variables were investigated. (3) The comparison of two different estimates of capture rate showed that some birds seem to miss 1 year of breeding in nestboxes more often than others; these are more likely to be immigrants. (4) Age, sex, and immigration status of the birds have a strong influence on the survival rate. (5) Male survival rate is negatively related to the density of blue tits, while that of females is not. We suggested that this may be related to the cost of defending a territory. (6) Female survival rate is negatively related to the beech crop production of the previous year (BCC). BCC is probably an indirect measure of the number of resident males, so that the relationship reflects competition between males and females. (7) Survival rates of immigrant males and resident females are affected by different variables from those affecting resident males and immigrant females. Although it is difficult to explain these differences satisfactorily, they may be related to sex differences in dispersal behaviour. (8) The survival rates of the four groups seem to differ irrespective of the age of the birds. In any year females may survive better or worse than males and independently immigrants may survive better or worse than residents. These differences in survival between the four groups are not consistent in direction, although sometimes strongly significant.

Habitat diversity or area per se? species richness of woody plants, carabid beetles and land snails on Islands

Abstract: SUMMARY (1) We examine patterns of species richness of woody plants, carabid beetles and land snails, respectively, on seventeen undisturbed forested islands (area range: 0-6-75 ha) in Lake Malaren, Sweden, in relation to area, isolation, vegetation structure, habitat diversity, habitat heterogeneity, and other factors. (2) The slopes of the species-area relations (z-values in the power model) are 0 10 for woody plants, 0-16 for land snails, 0-36 for carabid beetles, and 0-62 for forest birds. The z-values differ significantly from zero and also differ between all organism groups except woody plants and land snails on one hand, and land snails and carabid beetles on the other. (3) Island area is the best single predictor of species richness in the organism groups examined. Since habitat variables and island area are uncorrelated on the studied islands, we can reject the habitat diversity hypothesis as an explanation for the species-area relations found. (4) Total densities of woody plants and land snails were not correlated with island area, while the total density of carabid beetles was positively correlated with island area. (5) Islands with a high proportion of wet forests have relatively higher species richness of carabid beetles, and the number of land snail species relates positively to the proportion of deciduous forest. The patterns found are discussed in relation to general species richness theories.

Population biology of snowshoe hares. II. Interactions with winter food plants

Abstract: SUMMARY . i (1) We investigated interactions between snowshoe hares (Lepus americanus) and their food plants in winter during a cyclic fluctuation in numbers at Kluane, Yukon, between 1977 and 1985. • (2) The winter diet of hares at Kluane was dominated by four species of shrubs and trees. Betula glandulosa, the most preferred species, was common on only four of nine study plots. Salix glauca was eaten most often in mid-winter, when Betula was covered by snow. Where Betula was absent, Salix was eaten at or above the level expected from its relative abundance. Picea glauca was generally not preferred, but was eaten, especially where Betula was absent. Shepherdia canadensis was eaten fourth most often. (3) By the peak of the cycle in the winter of 1981-82, hares had removed much of the biomass of small twigs of Betula glandulosa and Salix glauca from three study plots. Hares had little effect on the biomass of Pice a glauca twigs. The biomass of these three species on two control plots at the end of the 1981-82 winter was, however, still sufficient to support the hares residing there. A larger population of hares on a third plot with added food depleted their supply of natural foods more severely. ( 4) An analysis of the fates of tagged twigs showed that hares browsed an average of 63% of Betula glandulosa twigs, 26% of Salix glauca twigs, 20% of Shepherdia twigs, and 14% of Picea glauca twigs in the winter during the 3 years of peak density. At the peak in hare numbers in 1981-82, over 80% of Betula twigs were eaten. Twigs within 50 em of the ground were browsed most often. (5) Heavily-browsed Betula glandulosa bushes grew new twigs rapidly after hare numbers had declined. Salix glauca showed less terminal regrowth, but produced stump sprouts, which we did not measure. Picea glauca and Shepherdia were not heavily browsed, nor did they grow faster after browsing by hares. (6) Adult hares became heavier in spring as numbers rose, and then lighter as their numbers declined. The latter effect was absent on plots with added food. Growth rates of juvenile hares in summer and autumn declined as hare numbers rose, but did so more slowly on two plots where food was added. Juveniles lost mass in winters of peak density, but did not do so on two plots with added food. The growth rates of juvenile hares recovered within 2 years of the decline. (7) Our results suggest that snowshoe hares at Kluane did not experience an absolute food shortage in winter at peak densities. Also, radio telemetry studies at Kluane showed that most hares died of predation, not starvation. We suggest that a relative food shortage

Foraging effort and life span of workers in a social insect

Abstract: SUMMARY (1) An inverse relationship between the effort an animal invests into current activities and its expected future life duration is important for life-history traits and, in particular, would provide a connection between foraging strategy and life-time fitness. Energetically low-cost foraging strategies such as those practised by nectar-collecting workers of the honeybee (Apis mellifera) are considered to be adaptive if foraging effort reduces life span (Schmid-Hempel et al. 1985). We here tested whether there is an inverse relationship between foraging activity and life span. (2) Workers of a colony were individually marked, placed at random into one of five treatment groups and their activities and life span observed. Treatments differed in the length of time individual bees were allowed to leave the hive to forage within an 8-h period each day (with schedules systematically altered from day to day). During the treatment period, individuals of the 0-h group could never leave the hive, those in other groups were allowed to exit the hive for 2, 4, 6 or 8 h (i.e. always). Sliding doors at the hive entrance were operated by an observer to ensure that only the appropriate individuals were kept back while others could forage freely. (3) There were no differences among groups in average adult life span (eclosion to last observation) (for individuals in the 0-h group: 41 6 + 2-0 S.E. days, N= 49; 2 h: 41-3 + 1.9, N=59; 4 h: 41.9+1 8, N=57; 6 h: 45.1 +22, N=46; 8-h: 39.0+2.3, N=49), despite differences in the number of foraging trips per individual/treatment period, and despite a threefold increase across treatment groups in the total number and duration of trips over the entire life span. In pairwise comparisons, average life span of workers in the 8 h group was shorter than those of workers in the 6 h group. (4) Within groups, however, there was a significant negative correlation between life span and number of trips per period, or time out of the hive per period, respectively. This relationship was largely due to hard-working individuals. We also found a significant positive correlation between the average amount of time a bee spent inactive in the hive, rather than being active, and its life span. We conclude that a reduction in the average work load below what bees accept under natural conditions (such as tested here) would not significantly lengthen life span of workers, but that life span might be reduced if bees increased their work load.

Foraging abilities and niche breadths of two percids, Perca fluviatilis and Gymnocephalus cernua, under different environmental conditions

Abstract: Foraging abilities and niche breadths of two percids, Perca fluviatilis and Gymnocephalus cernua, under different environmental conditions

Factors Affecting Breeding Success of Peregrines in South Scotland

Abstract: SUMMARY (1) During 1974-82, peregrines in south Scotland produced an annual average of 1 15 young per territorial pair, between 0-60 and 1.45 in different years. Heavy rain in May lowered productivity, by reducing hunting success and by soaking exposed nests. Early clutches, begun before mid-April, were larger and more successful than later ones. (2) All pairs nested on cliffs; the few large cliffs were preferred, so that, as the population grew, more pairs used small cliffs. Cliff height and accessibility to human climbers greatly influenced nesting success, as did exposure. Those nests in recesses were most successful. (3) Performance improved as females aged; laying became progressively earlier and clutches progressively larger, from 1 to 5+ years. (4) Despite some slight eggshell thinning (attributed to DDE), organochlorine residues had at most a small impact on productivity in the years concerned (in contrast to earlier years). (5) The overall density of breeding peregrines more than doubled during the 9-year study, and also varied between different parts of the study area. But over the range of densities observed, no density-dependent depression of breeding success occurred.

Reproductive costs in two sex-role reversed pipefish species (Syngnathidae)

Abstract: (1) In two species of pipefish (Syngnathidae) the reproductive costs of the two sexes were compared to see how they might influence patterns of sex-role reversal. (2) In Syngnathus typhle, males brood their offspring in a brood pouch, providing them with nutrients and oxygen. Sexes are monomorphic. Males faced reproductive costs in terms of a lower food intake compared with females. Also, males grew more slowly than females, which yields a cost to future reproduction, as larger males could brood more offspring. No sexual difference in predation risk was found. The over-winter survival of males was probably lowered because intestinal fat deposition was delayed as a result of their reproductive efforts. (3) In Nerophis ophidion, males brood their offspring attached to their ventral body side, and provide them with nutrients and oxygen. Sexes are dimorphic, females being larger and brighter in colour. Males suffered an increased predation risk when brooding. No indications of energetic costs were found, e.g. through a lowered food intake or a slower growth rate. (4) Reproductive costs differed in the two species, probably reflecting differences in brood care. However, in both species the limiting sex, males, faced higher reproductive costs than females, as would be expected in sex-role reversed animals.

Population biology of snowshoe hares. III: Nutrition, plant secondary compounds and food limitation

Abstract: Etude de la dynamique d'une population de Lepus americanus de la region du Lac Kluane (Yukon) de 1977 a 1986.Les auteurs verifient 2 hypotheses concernant les cycles de population : la limitation alimentaire et la composition chimique des plantes consommees.Les proteines fecales sont utilisees comme indice de la qualite de la nourriture principale.Les auteurs suggerent que la predation est la cause necessaire du cycle des lievres et qu'elle est meme dans certaines circonstances la seule

Seasonal food shortage, weight loss, and the timing of births in saddle-back tamarins (saguinus fuscicollis)

Abstract: SUMMARY (1) Annual birth peaks in the breeding of several primate species are thought to correlate with seasonal changes in food availability, yet no study published to date has both correlated birth seasonality with food availability, and shown that the physical conditions of individuals decline during annual periods of food scarcity. (2) We document the following observations in a population of saddle-back tamarins (Saguinusfuscicollis Spix; Callitrichidae) at the Cocha Cashu Biological Station in Peru's Manu National Park. (3) The availability of both fruits and insects was substantially lower during the annual 4-month dry season (May-September) than at other times of the year. (4) Individual tamarins lost an average of 5% of their weight over this period. (5) Three-quarters of twenty-two S. fuscicollis births at this site occurred between November and February, and none occurred between mid-March and mid-August. (6) We suggest that tamarin births at Cocha Cashu are timed such that lactation and weaning occur when food is abundant, because during the period of low food availability, there would be insufficient food to meet the demands of lactation and to serve as easily obtainable weaning foods. In this sort of seasonal environment, tamarins appear to be constrained, by the seasonality of their food supply, from breeding as frequently as they do in captivity.

Time Allocation in the Kestrel (Falco tinnunculus), and the Principle of Energy Minimization

Abstract: (1) Time allocation of the kestrel in the Netherlands was established by dawn to dusk observation of focal birds. Time budgets were analysed with respect to time of year, phase of the breeding cycle, sex and weather conditions. (2) The common vole, Microtus arvalis L., was the major food source (92% of food items caught) with minor additions, especially in summer, of common shrews, Sorex araneus L., songbirds and juvenile waders. (3) Flight-hunting and perching were the two main foraging modes. Flight-hunting yielded, on average, 2.2 small mammals h-1 in winter and 4.7 in summer. Perching yield dropped from 0.3 mammals h-1 in winter to below 0.1 in summer. Flight-hunting yield reflected seasonal variations in food availability, perching yield did not. (4) There was no stage in the annual cycle where available daylight limited the daily flight-hunting time. There were no weather conditions where daily flight-hunting exceeded an average of 3.6 h or 20% of the active day. Stringent periods, in the sense that all buffer time is used for foraging, were found neither in winter, when food was scarce, nor in summer when food demand was highest. (5) Experimentally increased hunger of the brood led to increased male parental effort in terms of time spent flight-hunting plus flying, with a recorded maximum of 60% of the active day. Flight-hunting yield did not increase. (6) In winter, kestrels minimized energy expenditure, not foraging time, by using the low-cost low-profit technique of perch-hunting. In summer they maximized daily energy gain within limits probably set by their rate of food assimilation.