bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synchrony in small mammal populations of montane forest patches in southern India
Authors: Shanker Kartik , Sukumar R. 
Published: March 2003

1. Small mammal populations were studied in montane evergreen forests in the Nilgiris, southern India, using live‐trapping from January 1994 to September 1996. Two sites were selected, one with a single large forest patch and adjoining plantations, and the other with several small forest patches separated by grassland. 2. Nine species were recorded, of which eight were trapped in the forest patches, two in the grasslands and five in plantations. Rattus rattus was the most abundant species (2–36 individuals ha−1) followed by Suncus montanus (0–11 individuals ha−1). Densities of seven other species recorded were very low. 3. Synchrony in various population variables – density, biomass, mean weight, density of adults and adult females, and proportion of adults, adult females and sub‐adults – was examined for Rattus rattus populations in the forest patches and plantations. Density and biomass were studied in seven other species recorded at these sites. Spearman's rank order correlation was used as a measure of synchrony between the population variables. 4. Within‐site synchrony was higher than between‐site synchrony in population characters. Synchrony was also higher between plots within the unfragmented site than they were between plots in the fragmented site. Relatively high synchrony in proportions of adults, adult females and juveniles in the forest patches implied that breeding is probably influenced by climate and food availability, which are seasonal in this habitat. 5. Given the small patch sizes (≈1–10 ha) and low population sizes, asynchrony is likely to be an outcome of demographic and environmental stochasticity, and low dispersal rates may impede establishment of synchrony.
Behavioural interactions in stream food webs: the case of drift‐feeding fish, predatory invertebrates and grazing mayflies
Authors: Huhta Arto , Muotka Timo , Juntunen Antti , Yrjönen Mikko 
Published: March 2003

Summary 1. We examined direct and indirect behavioural responses of grazing mayfly nymphs (Baetis rhodani) to predation risk from a drift‐feeding fish (European minnow; odour manipulated), and two types of invertebrate predators, Diura bicaudata (stonefly) and Rhyacophila nubila (caddis larva). We also assessed the direct responses of the invertebrate predators to fish chemicals. 2. Based on diel gut content periodicity, D. bicaudata nymphs were strongly nocturnal foragers. R. nubila was also nocturnal, but only in a fish stream; in a stream lacking fish, their gut contents did not vary significantly on a diel basis. In the laboratory, Diura was nocturnal even in the absence of fish and almost ceased moving when fish was present. Rhyacophila shifted from aperiodic to nocturnal foraging in the presence of fish. 3. The contrasting behaviours of the two predators may be explained by their respective field distributions: D. bicaudata always co‐occurs with fish, whereas R. nubila is also found in streams without fish. Therefore, a capacity for plastic anti‐fish responses is beneficial for R. nubila, but not for D. bicaudata. 4. Drift of large Baetis nymphs was aperiodic when Rhyacophila was present, but nocturnal in all other treatments. Drift rate was highest when both Diura and fish were present and lowest in treatments with Rhyacophila. Predatory stoneflies, but not the caddis larva, induced a night‐time peak in the drift of both Baetis size‐classes. In the absence of predators, small Baetis drifted aperiodically. Interaction terms in three‐way anovas testing for the indirect effects of fish and invertebrate predators on mayfly drift periodicity and drift rate were all non‐significant, indicating that the response of Baetis to one type of predator was not modified by the other predator. 5. Our results indicate that the drift periodicity of lotic mayflies may be fine‐tuned to variations in the multi‐predator environment and that prey responses are size‐specific. We conclude that the effects of invertebrate predators on prey behaviour vary in relation to predator's foraging strategy and generalizations based on studies with only one type of predator should be avoided.
The distribution and abundance of populations limited at multiple spatial scales
Authors: Bevers Michael , Flather Curtis H. 
Published: March 2003

Summary 1. We use mathematical programming to explore long‐term equilibrium population distribution and abundance effects arising from a single‐patch reaction–diffusion model when ecological factors limit carrying capacity at two different spatial scales. Both homoogeneous and heterogeneous habitat patches are investigated under passive diffusion conditions. Capacity limits, reproduction and dispersal rates, and habitat preferences are individually varied. 2. When landscape‐scale habitat factors are strongly limiting, and reproduction and dispersal processes are less so, suitable population arrangements can be either clustered or highly fragmented. 3. Population clustering also occurs when strong habitat preferences are introduced, even though few members of the clusters may actually occupy the preferred sites. 4. As reproduction or dispersal rates become increasingly limiting in the system (i.e. as the parameters approach extinction thresholds), population clustering within a habitat patch is required to reach long‐term equilibrium population levels. 5. These results offer a potential explanation for why species–habitat association studies have been characterized by high variability.
Habitat duration, predation risk and phenotypic plasticity in common frog (Rana temporaria) tadpoles
Authors: Laurila Anssi , Kujasalo Jutta 
Published: March 2003

Summary 1. Common frogs (Rana temporaria) breed readily in small pools and thus expose their offspring to catastrophic mortality by desiccation. Amphibian larvae exhibit considerable phenotypic plasticity in metamorphic traits, and some species respond to environmental uncertainty by metamorphosing earlier and at smaller size. In a factorial laboratory experiment, we studied whether common frog tadpoles possess this ability. 2. We also studied the interaction between pool drying and predation risk, because in a previous study the presence of a predatory dragonfly larva delayed metamorphosis of the tadpoles. 3. We gradually removed water from half the experimental containers, while in the other half the water volume was kept constant. In the laboratory it was possible to remove the effect of increased water temperature in the decreasing volume treatment by using fluorescent lights. Tadpoles responded to decreasing volume by metamorphosing earlier and at smaller size. A greater proportion of the tadpoles metamorphosed in the decreasing volume treatment. 4. Tadpoles were less active at decreasing water level and there were significant positive correlations between activity late in the experiment and metamorphic size. This suggests that the metamorphic response to habitat drying is behaviourally mediated. 6. Early in the experiment, tadpoles developed slower in the presence of predators. At metamorphosis presence of a dragonfly larva had no effect in the whole data set, but when the constant volume treatment was analysed separately, larval period was longer in the presence of a predator. 7. Our results indicate that common frog larvae are able to respond to pond‐drying adaptively by speeding up their development, and that temperature advantage is not needed to induce this adaptive plasticity. Furthermore, pond‐drying seems to be a more important determinant of development rate than the presence of odonate predators.
Interaction between phenology and density effects on mortality from natural enemies
Authors: Hunter Alison F. , Elkinton Joseph S. 
Published: March 2003

Summary 1. The gypsy moth is one of many early spring‐feeding Lepidoptera that have outbreaks. Previous work has revealed that mortality from natural enemies varied between egg hatch dates separated by only a few weeks. However, this phenology effect was confounded with density differences caused by differential dispersal and early larval survival of the releases. 2. Five different densities of larvae were released at two different times in early spring, and monitored for the causes and amount of mortality in the field. We thus sought to separate the effects of timing and density on mortality. 3. Mortality in the larval stages due to parasitoids, disease and physiological causes was density‐dependent for both release date treatments, but the slope of the mortality vs. density line was much steeper for the early release. Total mortality over the entire generation, which included additionally mortality from predation, was density‐dependent for the early release but not for the late release. 4. The timing of egg hatch thus affects fecundity, mortality from natural enemies and the form of the relationship between density and mortality. These compounding effects may help explain why spring‐feeding insects are liable to have outbreaks.
Influence of connectivity on demography and dispersal in two contrasting habitats: an experimental approach
Authors: Boudjemadi Katia , Lecomte Jane , Clobert Jean 
Published: March 2003

Summary 1. Habitat fragmentation is involved in the present extinction crisis and is known to influence many aspects of population dynamics. The level of connectivity between populations is one of its components. In an experimental study on the common lizard (Lacerta vivipara Jacquin), we analysed in two contrasting habitats the influence of connection on dispersal patterns, on differences between dispersing and philopatric individuals, on population size, survival rates, and reproduction. 2. The experimental design consisted of eight two‐patch units. Half of them were connected by dispersal. We performed this treatment in a grassland and a wood clearance, two habitats with different resource availability (respectively called ‘rich’ and ‘poor’ habitat). 3. We expected that the loss of connection would modify juvenile dispersal patterns, have a different effect on dispersing and philopatric individuals, negatively affect survival rates and fecundity by modifying social interactions and would have different consequences in ‘rich’ habitats compared to ‘poor’ ones. 4. Connection modified dispersal patterns. Two dispersal periods occurred in unconnected units, but only one occurred in connected ones. Moreover, dispersers of the second dispersal period were morphologically similar to philopatric individuals. The loss of connection probably caused the late dispersal of individuals which would have remained philopatric in a connected context. Dispersers of the second period seemed to have lower winter survival rates than philopatric individuals, as expected if these individuals had been ‘forced’ to disperse. 5. We found that connection modified demography through juvenile winter survival rates and female reproduction depending on habitat type. Connection led to higher juvenile survival rates in ‘rich’ habitats, whereas it was not the case in ‘poor’ habitats. The loss of connection decreased female reproductive rate whatever the type of habitat. 6. This study suggests that connection can directly modify demographic parameters depending on habitat quality and involving behavioural mechanisms. It confirms that conservation management, like installation of dispersal corridors, must take into account habitat characteristics and behavioural features.
Estimating the contributions of population density and climatic fluctuations to interannual variation in survival of Soay sheep
Authors: Milner J. M. , Elston D. A. , Albon S. D. 
Published: March 2003

Summary1. The relative importance of density‐dependent and ‐independent factors on interannual variation in over‐winter survival was investigated in the fluctuating population of Soay sheep on St Kilda, Scotland, over the period 1985–96.2. Population density had a negative effect on survival in lambs and adult males while adult female survival showed no evidence of density dependence over the observed range of population densities.3. Climatic fluctuations associated with the winter North Atlantic oscillation index (NAO) also affected survival, which decreased in winters that were relatively warm, wet and windy. The effect was most pronounced in lambs.4. Survival was modelled using logistic regression analysis with and without year fitted as a random effect. The former incorporated stochastic year to year variation in survival. Results from the two modelling approaches were similar in terms of the regression coefficients estimated. However, the standard errors of the year‐dependent covariates, population size and NAO, were underestimated when the random year effect was ignored, leading to incorrect inferences about the relative significance of terms being made.5. Using both modelling approaches, density dependence was found to have a greater influence on survival than the effect of NAO in lambs and adult males, whereas in adult females NAO was the more important.6. Once random between‐year effects were taken into account, the individually varying terms such as body weight and faecal egg count were the most significant factors explaining differences in survival.
Breeding habitat selection in cliff swallows: the effect of conspecific reproductive success on colony choice
Authors: Brown Charles R. , Brown Mary Bomberger , Danchin Etienne 
Published: March 2003

Summary 1. One way that animals may select breeding sites is by assessing the reproductive success of conspecifics in one season and settling the next year in those habitat patches where success collectively had been greatest. This sort of habitat assessment may promote the formation of colonies at high quality sites. 2. We examined whether cliff swallows, Petrochelidon pyrrhonota, in south‐western Nebraska used conspecific breeding performance to choose colony sites. 3. Reproductive success at colony sites varied spatially within seasons and between seasons, and was autocorrelated at a site from one year to the next, but not over longer time intervals. Cliff swallows thus met the conditions for potential use of information on conspecific breeding performance. 4. Among sites re‐used in consecutive years, those with highest collective success in one season showed the greatest rates in colony growth the next season, including the greatest influx of immigrants. 5. The probability of colony‐site re‐use in successive years increased with collective reproductive success and average breeder body mass (a measure of individual condition) the previous season. 6. Cliff swallows probably use conspecific breeding performance in selecting colonies. This mechanism is one component of habitat selection that also includes attraction to conspecifics and assessment of an individual's own success.
Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens: a model for cooperatively breeding birds?
Authors: Magrath Robert D. 
Published: March 2003

Summary

Many studies of cooperatively breeding birds have found no effect of group size on reproductive success, contrary to predictions of most adaptive hypotheses. A model is proposed for variation in group‐size effects: group size has a reduced effect on success when conditions for breeding are good, such as in good environmental conditions or in groups with older breeders. This hypothesis is tested with a case study of white‐browed scrubwrens Sericornis frontalis and a review of the literature.
The scrubwren is a cooperatively breeding passerine with male helpers. Previous analyses revealed no effect of group size on reproductive success, but those analyses were restricted to groups with older females (Magrath & Yezerinac 1997). Here 7 years’ data are used to contrast the effect of group size on reproductive success for yearling and older females.
Yearling females breeding in groups had more than double the seasonal reproductive success than those breeding in pairs, even after controlling for territory quality. However, group size still had no effect on the reproductive success of older females. Yearling females tended to survive better in groups, but older females tended to survive better in pairs, emphasizing this pattern.
Yearlings breeding in pairs were more likely to be found on poor‐quality territories than those breeding in groups, exaggerating the already‐strong effect of group size on yearling success. Older females were not affected significantly by territory quality.
Group size, territory quality and female age affected different components of seasonal reproductive success. Group size increased the success of individual nesting attempts, while both territory quality and female age affected the length of the breeding season, and thus the number of breeding attempts.
A sample of the literature on cooperative breeders shows that group size has a larger effect on reproductive success in poorer conditions, caused either by younger, inexperienced breeders or poorer environmental conditions. Scrubwrens therefore illustrate a widespread pattern, which provides an explanation for much of the variation in group‐size effects among and within species. Clearly single estimates of group‐size effects for species can be inadequate to test ideas about the evolution of cooperative breeding.
The impact of weasel predation on cyclic field‐vole survival: the specialist predator hypothesis contradicted
Authors: Graham Isla M. , Lambin Xavier 
Published: March 2003

Summary

The delayed density‐dependent predation of specialists such as weasels (Mustela nivalis L.) may result in cycles in the abundance of their prey. We estimated the demographic impact of weasel predation on field‐vole (Microtus agrestis L.) survival using capture–recapture data from a large‐scale, replicated predator‐manipulation experiment conducted in six unfenced populations in Kielder Forest, northern England. The density of weasels was experimentally reduced through continuous live‐trapping in the three removal populations. Field‐vole survival was compared between paired removal and control populations during the increase, peak and decline phases of a vole population cycle. Apparent survival and recapture probabilities were estimated using open population Cormack‐Jolly Seber models.
Field‐vole survival varied extensively both spatially between populations and temporally, being highest in the late autumn and over winter and lowest each year in spring and early summer. Patterns of variation in male and female survival were similar between populations over time, but there was independent spatial and temporal variation between adults and juveniles. Variation in weasel abundance explained 18% of this independent spatial and temporal variation between adult and juvenile field‐vole survival.
The average increase in annual vole survival resulting from weasel removal over the 2‐year period was 27% and 25% for adult male and female field voles, respectively. Decreased weasel abundance increased adult field‐vole survival. Adult‐vole survival in the absence of weasels was predicted to be approximately 8% higher than in the presence of one weasel per 4–5 ha. Surprisingly, weasel removal resulted in lowered juvenile field‐vole survival, possibly reflecting increased emigration or mortality due to infanticide. A simple two age‐class demographic model indicated that the decrease in juvenile survival in response to reduced weasel predation pressure did not fully compensate for the increase in adult survival.
As weasel numbers fluctuated seasonally, with highest weasel densities occurring in late summer and autumn and little spring to spring variation, the impact of weasel removal on field‐vole survival was greatest during the breeding season. However, vole population‐growth rates were unrelated to adult survival at that time and correspondingly no divergence was observed between the trajectories of control and removal vole populations even when weasel numbers were greatest in control sites. In contrast, vole population‐growth rates were closely correlated with survival during the non‐breeding season. Nevertheless all control and removal populations experienced a cyclic decline in winter 1999–2000 in spite of the increased adult survival in experimental treatments.
We conclude that the impact of weasel predation on field‐vole survival was neither sufficient nor necessary to initiate and drive the cyclic decline of field‐vole populations in Kielder Forest.
Landscape complementation and food limitation of large herbivores: habitat‐related constraints on the foraging efficiency of wild pigs
Authors: Choquenot David , Ruscoe Wendy A. 
Published: March 2003

Summary

The effect that the proximity of habitats containing essential resources has on animal abundance at large spatial scales is called landscape complementation. Landscape complementation can influence interaction between large herbivores and their food resources where the proximity of habitats containing essential resources constrains their foraging or demographic efficiency.
We tested the effect that the proximity of a thermal refuge (riverine woodlands) had on interaction between wild pigs and their food resources (pasture). The numerical response of pigs (Sus scrofa L.) (estimated as r quarter−1) to pasture biomass was contrasted between four sites that were progressively more isolated from a major floodplain containing extensive areas of riverine woodland. To test whether proximity to riverine woodlands affected the numerical response of pigs through a constraint on foraging efficiency, we contrasted the numerical response of pigs between the four areas as pasture biomass declined. To test whether pigs exploited riverine woodlands primarily as a thermal refuge, we contrasted the numerical response of pigs between the four areas in different seasons.
We found that although pasture biomass was similar in the four areas, r was lower than expected for given pasture biomass on the two areas further away from riverine woodlands. We also found that while the effect that proximity to riverine woodlands had on the numerical response of pigs became more pronounced when pasture biomass was low, it was not significantly affected by season.
These results suggest that the need to access riverine woodlands compromises the foraging efficiency of wild pigs when the distance to this habitat is relatively high, but that the need to access this habitat may not be purely related to thermoregulation.
We developed a simple mechanistic model that allows the effects of landscape complementation on herbivore foraging and demographic efficiency to be estimated, and used the model to predict the effect that proximity to riverine woodlands would have on variation in pig density. The model suggests that wild pigs cannot persist in areas more then 10 km from extensive riverine woodlands, unless those areas are periodically re‐colonized. This suggests that at the margin of their range around inland river systems, given locations that can be occupied by wild pigs will vary temporally between being sources, pseudosinks and sinks.