Abstract: In many mammalian species, female success in raising offspring improves as they age. The residual reproductive value hypothesis predicts that each individual offspring will be more valuable to the mother as she ages because there is less conflict between the current and potential future offspring. Therefore, as mothers age, their investment into individual offspring should increase. Empirical evidence for an influence of declining residual reproductive value on maternal investment is unconvincing. Older mothers may not invest more, but may be more successful due to greater experience, allowing them to target their investment more appropriately (targeted reproductive effort hypothesis). Most studies do not preclude either hypothesis. Mare age significantly influenced maternal investment in feral horses living on the North Island of New Zealand. Older mares, that were more successful at raising foals, were more protective for the first 20 days of life, but less diligent thereafter. Total maternal input by older mothers did not seem to be any greater, but was better targeted at the most critical period for foal survival and a similar pattern was observed in mares that had lost a foal in the previous year. In addition, older mothers were more likely to foal in consecutive years, supporting the hypothesis that they are investing less than younger mares in individual offspring. Therefore, older mothers seem to become more successful by targeting their investment better due to experience, not by investing more in their offspring.

Abstract: In two experiments, hungry rats, Rattus norvegicus, were present in one side of an operant chamber while a conspecific demonstrator in the adjacent compartment moved a single lever either up or down for a food reward. During a subsequent test session, in which these rats were allowed access to the lever for the first time, all responses were rewarded regardless of their direction. In experiment 1, rats that were prevented from observing the direction of lever movement by means of a screen showed a reliable demonstrator-consistent response bias, while rats that had observed the direction of lever movement and in addition had access to any odour cues deposited on the lever did not. In experiment 2, each rat observed another rat (the `viewed' demonstrator) moving a lever either up or down. They were then transferred into the test compartment of a different operant chamber in which another rat (the `box' demonstrator) had moved the lever in the same direction as the viewed demonstrator or in the opposite direction. These observer rats showed a reliable preference for their box demonstrator's direction, but responded in the opposite direction to their viewed demonstrator. Taken together, the results of these experiments suggest that directional responding by rats in a vertical movement two-action test is influenced by demonstrator-deposited odour cues in addition to visual experience of a demonstrator's behaviour. Furthermore, while odour-mediated local enhancement gave rise to demonstrator-consistent responding, visual observation of a conspecific appeared to have the reverse effect. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Abstract: In many cooperatively breeding species, group members form a dominance hierarchy or queue to inherit the position of breeder. Models aimed at understanding individual variation in helping behavior, however, rarely take into account the effect of dominance rank on expected future reproductive success and thus the potential direct fitness costs of helping. Here we develop a kin-selection model of helping behavior in multimember groups in which only the highest ranking individual breeds. Each group member can invest in the dominant's offspring at a cost to its own survivorship. The model predicts that lower ranked subordinates, who have a smaller probability of inheriting the group, should work harder than higher ranked subordinates. This prediction holds regardless of whether the intrinsic mortality rate of subordinates increases or decreases with rank. The prediction does not necessarily hold, however, where the costs of helping are higher for lower ranked individuals: a situation that may be common in vertebrates. The model makes two further testable predictions: that the helping effort of an individual of given rank should be lower in larger groups, and the reproductive success of dominants should be greater where group members are more closely related. Empirical evidence for these predictions is discussed. We argue that the effects of rank on stable helping effort may explain why attempts to correlate individual helping effort with relatedness in cooperatively breeding species have met with limited success.

Abstract: We used comparative data to test functional hypotheses for 17 antipredator behaviour patterns in artiodactyls. We examined the literature for hypotheses about auditory and visual signals, defensive behaviour and group-related antipredator behaviour in this taxon and derived a series of predictions for each hypothesis. Next, we documented occurrences of these behaviour patterns and morphological, ecological and behavioural variables for 200 species and coded them in binary format. We then pitted presence of an antipredator behaviour against presence of an independent variable for cervids, bovids and all artiodactyls together using nonparametric tests. Finally, we reanalysed the data using Maddison's (1990, Evolution, 44, 539-557) concentrated-changes tests and a consensus molecular and taxonomic phylogeny. We found evidence that snorting is both a warning signal to conspecifics and a pursuit-deterrent signal, lack of evidence that whistling alerts conspecifics and indications that foot stamping is a visual signal to warn group members. Evidence suggested that tail flagging was a signal to both conspecifics and predators, that bounding, leaping and stotting were used both as a signal and to clear obstacles and that prancing functioned similarly to foot stamping. Analyses of tail flicking, zigzagging and tacking were equivocal. We confirmed that inspection occurs in large groups, freezing enhances crypticity, and species seeking refuge in cliffs tend to be small. Entering water and attacks on predators had few correlates. Finally, group living, a putative antipredator adaptation, was associated with large body size and species living in open habitats, confirming Jarman's (1974, Behaviour, 48, 215-267) classic hypothesis. Bunching and group attack apparently deter predators. Despite limitations, comparative and systematic analyses can bolster adaptive hypotheses and raise new functional explanations for antipredator behaviour patterns in general.

Abstract: Self-directed behaviour (SDB) can be used as a behavioural indicator of stress and anxiety in nonhuman primates (Maestripieri et al. 1992, Animal Behaviour, 44, 967-979). We investigated the effect of nearest neighbours' relative dominance status on the SDB of sexually mature female olive baboons, Papio anubis. When the animal nearest to (within 5 m of) a female was a dominant individual, SDB rates (a combined measure of self-scratching, self-grooming, self-touching, body shaking and yawning) increased by ca. 40% over those observed when the nearest neighbour was a subordinate. The results indicate that (1) SDB can be used as a measure of uncertainty during the social interactions of cercopithecine primates and (2) as there was considerable variation in SDB response according to the nature of the dominant individual, SDB can be used to assess relationship security (i.e. the perceived predictability of a relationship for one partner). Finally, in combination with measures of affiliation rate, SDB may provide insight into relationship value.