Should vigilance always decrease with group size?

Levels of anti-predator vigilance often decrease with group size in birds and mammals. Vigilance may also serve other purposes such as scrounging. While scrounging, individual adopt the vigilant posture to locate and eventually exploit the food discoveries of their companions. Models that combine anti-predator alertness and scrounging were developed to examine how changes in scrounger use with group size could alter the shape of the function relating vigilance to group size and whether the additional investment in vigilance while searching could be used to reduce the allocation of time to vigilance while in the food patch. Results indicate that increased allocation of time to scrounging during search can add to the overall level of vigilance and even counteract the expected decrease in vigilance with group size. However, the addition of scrounging was found to have little impact on vigilance while in the food patch. Behavioral effects that are dependent on group size, such as scrounging, may lead to changes in the shape of the vigilance function and may mitigate against any gain garnered from a reduction in individual levels of vigilance in larger groups.     

Effects of energy requirements and worker mortality on colony growth and foraging in the honey bee

Summary A model of colony growth and foraging in the honey bee (Apis mellifera L.) is presented. It is assumed that summer workers choose a foraging strategy that maximizes colony population by the end of the season subject to the constraint that enough nectar has been stored to sustain the adult population overwinter. The optimal foraging strategy is derived with respect to the number of flowers visited during one foraging trip. A forager that visits many flowers collects a substantial amount of nectar but the probability that the worker returns alive from the excursion decreases accordingly. Using dynamic modelling, I explore the effects on colony growth of colony population, colony energy requirements and mortality rate while foraging. The model shows that when the expected rate of increase in nectar reserves is low, for instance in small colonies or when mortality rate rises rapidly with foraging intensity, workers collect more nectar during each foraging trip. The increase in foraging activity is realized at the expense of colony growth. The main finding is that depending on colony status the foraging strategy that maximizes worker population implies visits to almost any number of flowers. This is in sharp contrast to predictions from traditional foraging models where foraging intensity is assumed to cluster around values that maximize net rate or efficiency. The model suggests that strategies that cluster around rate and efficiency maximization should be viewed as particular solutions to a more general problem.     

Ecological and social determinants of spacing behaviour in desert baboon groups

This paper investigates the determinants of individual spacing behaviour in a desert baboon population (Papio cynocephalus ursinus). Patterns of neighbour proximity and neighbour density were examined among adults in four groups under different ecological and social conditions (through instantaneous sampling during focal follows). Initial analysis of these data shows that (1) the use of vertical substrates (refuges such as tall trees and cliff faces) can confound patterns of spacing, and (2) individual differences in spacing can depend on the spatial scale over which it is measured. To minimise these substrate and scale effects, this analysis focuses on animals which are off refuges and examines spacing behaviour through its underlying statistical `dimensions' (identified through factor analysis). Analysis of these dimensions indicates that sex, group size, activity-habitat and female reproductive state can all have independent effects on spacing: (1) males are more dispersed than females in smaller groups, (2) male and female dispersion increases with time spent in foraging habitats, and (3) female dispersion is reduced during lactation. According to the hypotheses tested, these results indicate that feeding competition only affects spacing behaviour during foraging while predation risk plays little or no role in spacing. Most aspects of spacing behaviour are best explained by male reproductive strategies and their social repercussions. Received: 25 May 1998 / Accepted after revision: 18 July 1998     

Development of the gap model ZELIG-CFS to predict the dynamics of North American mixed forest types with complex structures

When the development of gap models began about three decades ago, they became a new category of forest productivity models. Compared with traditional growth and yield models, which aim at deriving empirical relationships that best fit data, gap models use semi-theoretical relationships to simulate biotic and abiotic processes in forest stands, including the effects of photosynthetic active radiation interception, site fertility, temperature and soil moisture on tree growth and seedling establishment. While growth and yield models are appropriate to predict short-term stemwood production, gap models may be used to predict the natural course of species replacement for several generations. Because of the poor availability of historical data and knowledge on species-specific allometric relationships, species replacement and death rate, it has seldom been possible to develop and evaluate the most representative algorithms to predict growth and mortality with a high degree of accuracy. For this reason, the developers of gap models focused more on developing simulation tools to improve the understanding of forest succession than predicting growth and yield accurately.In a previous study, the predictions of simulations in two southeastern Canadian mixed ecosystem types using the ZELIG gap model were compared with long-term historical data. This exercise highlighted model components that needed modifications to improve the predictive capacity of ZELIG. The updated version of the model, ZELIG-CFS, includes modifications in the modelling of crown interaction effects, survival rate and regeneration. Different algorithms representing crown interactive effects between crowns were evaluated and species-specific model components that compute individual-tree mortality probability rate were derived. The results of the simulations were compared using long-term remeasurement data obtained from sample plots located in La Mauricie National Park of Canada in Quebec. In the present study, three forest types were studied: (1) red spruce-balsam fir-yellow birch, (2) yellow birch-sugar maple-balsam fir, and (3) red spruce-balsam fir-white birch mixed ecosystems. Among the seven algorithms that represented individual crown interactions, two better predicted the changes in basal area and individual-tree growth: (1) the mean available light growing factor (ALGF), which is computed from the proportion of light intercepted at different levels of individual crowns adjusted by the species-specific shade tolerance index, and (2) the ratio of mean ALGF to crown width. The long-term predicted patterns of change in basal area were consistent with the life history of the different species.     

Social foraging and dominance relationships: the effects of socially mediated interference

In socially foraging animals, it is widely acknowledged that the position of an individual within the dominance hierarchy of the group has a large effect upon its foraging behaviour and energetic intake, where the intake of subordinates can be reduced through socially mediated interference. In this paper, we explore the effects of interference upon group dynamics and individual behaviour, using a spatially explicit individual-based model. Each individual follows a simple behavioural rule based upon its energetic reserves and the actions of its neighbours (where the rule is derived from game theory models). We show that dominant individuals should have larger energetic reserves than their subordinates, and the size of this difference increases when either food is scarce, the intensity of interference suffered by the subordinates increases, or the distance over which dominant individuals affect subordinates increases. Unlike previous models, the results presented in this paper about differences in reserves are not based upon prior assumptions of the effects of social hierarchy and energetic reserves upon predation risk, and emerge through nothing more than a reduction in energetic intake by the subordinates when dominants are present. Furthermore, we show that increasing interference intensity, food availability or the distance over which dominants have an effect also causes the difference in movement between ranks to increase (where subordinates move more than dominants), and the distance over which dominants have an effect changes the size of the groups that the different ranks are found in. These results are discussed in relation to previous studies of intra- and interspecific dominance hierarchies.     

农药对熊蜂的生态毒理研究进展

熊蜂(Bombus spp.)因其独特形态特征及生物学特性成为农业生产中重要传粉昆虫,在维持自然及农业生态系统平衡发挥重要作用。近年来,熊蜂多样性呈减少趋势,农药不合理施用为重要因素之一。本文基于农药对熊蜂的毒理学研究现状,系统整理了熊蜂急性致死和慢性亚致死毒理研究方法,围绕农药对熊蜂的急性毒性,亚致死剂量农药对熊蜂精子活性及体温调节等生理发育,颜色分辨及学习记忆行为、肠道微生物结构及解毒因子等方面影响展开综述,对研究中存在的问题和未来研究方向进行了思考和展望,旨在为农药的科学使用、生物环境安全评估及熊蜂多样性保护提供参考。     

A novel survey of raptor collections in Europe and their potential to provide samples for pan-European contaminant monitoring

Environmental Science and Pollution Research - This paper provides a novel survey of current collections of frozen raptor carcasses and tissue samples in natural history museums (NHMs),...     

Detection and quantification of chlordecone in contaminated soils from the French West Indies by GC-MS using the 13C10-chlordecone stable isotope as a tracer

Chlordecone is an organochlorine insecticide that has been widely used to control banana weevil in the French West Indies. As a result of this intense use, up to 20,000 ha are contaminated by this insecticide in the French West Indies, and this causes environmental damage and health problems. A scenario of exposure was drawn by French authorities, based on land usage records. Many efforts have been made to monitor the occurrence of chlordecone and its main metabolites using different analytical methods, including GC, GC/MS, LC/MS, and NIRS. Although these different methods allow for the detection and quantification of chlordecone from soils, none of them estimate the bottleneck caused by extraction of this organochlorine from soils with high adsorption ability. In this study, we used ¹³C₁₀-chlordecone as a tracer to estimate chlordecone extraction yield and to quantify chlordecone in soil extracts based on the ¹³C/¹²C isotope dilution. We report the optimization of ¹³C₁₀-chlordecone extraction from an Andosol. The method was found to be linear from 0.118 to 43 mg kg^?1 in the Andosol, with an instrumental detection limit estimated at 8.84 μg kg^?1. This method showed that chlordecone ranged from 35.4 down to 0.18 mg kg^?1 in Andosol, Nitisol, Ferralsol, and Fluvisol soil types. Traces of the metabolite β-monohydrochlordecone were detected in the Andosol, Nitisol, and Ferralsol soil samples. This last result indicates that this method could be useful to monitor the fate of chlordecone in soils of the French West Indies.