Behavioral Ecology and Sociobiology

Minimizing observer bias in behavioral research: blinded methods reporting requirements for Behavioral Ecology and Sociobiology

Exploitative competition alters bee foraging and flower choice Abstract In this field experiment, we test and support the hypothesis that exploitative competition between bees can influence several aspects of their foraging behaviour. Three treatments of lavender patches were set out: bumble bees excluded, honey bees excluded, control. Bumble bees are known to handle lavender flowers more rapidly than honey bees, partly due to their longer tongues. As predicted, excluding these superior competitors consistently (n = 4 trials) and greatly increased honey bee numbers per patch (14-fold increase; P < 0.001). The exclusion of bumble bee also caused multiple changes to honey bee foraging behaviour: time spent on a patch (+857 %; P < 0.001), flower handling time (+16 %, P = 0.040), interval between probed flowers (−27 %, P = 0.012), proportion of interflower flights (−26 %, P < 0.001) and flowers rejected (−12 %, P < 0.001). Conversely, and also as predicted, excluding honey bees had no effect on bumble bee numbers or foraging behaviour. A key consequence of bumble bee exclusion was to increase the mean flower nectar content from 0.007 to 0.019 μl (+171 %). By constructing an energy budget, we find that this leads to honey bees making a substantial, rather than a marginal, energetic profit per flower visited. Our results show the foraging behaviour of individual bees is extremely flexible and greatly influenced by the effects of interspecific competition on nectar rewards. Collectively, these individual decisions can have rapid and important consequences at the community level, including competitive exclusion.

A trade-off between pre- and post-copulatory sexual selection in a bean beetle Abstract It is now generally recognized that it is necessary to examine how sexual selection operates across the lifespan of a male, in order to understand the total sexual selection in action. However, less attention has been paid to the fact that selection pressures can change in response to varying environmental conditions. Here, we examine male allocation to trait subject to pre- and post-copulatory sexual selection in Callosobruchus chinensis. We find evidence of a trade-off between dispersal ability and testes size and sperm transfer, across geographical strains. In addition, male mating success of strains with larger testes and better dispersal ability, respectively, changed in response to environmental conditions. Males with better dispersal ability had greater success in securing mates, compared to males with larger testes, under conditions where it was harder to find females. There was no difference in male ability to secure mates when it was easy for them to find females. However, we suggest that males with larger testes are likely to have an advantage in sperm competition under conditions where it is easier to find females, and when females are thus likely to mate multiply. Our results indicate that environmental fluctuations and trade-offs can work in conjunction to maintain alternative male behavioral reproductive strategies.

No longer naïve? Generalized responses of rabbits to marsupial predators in Australia Abstract Predation is an important selective force on prey species, but avoiding predators can be costly. Efficient decisions on who to avoid (predator recognition) and when (situations with different predation risk) will determine the chances of prey survival. In coevolved predator-prey systems, detection of predator odours generally induces a response in potential prey to reduce predation risk. However, prey may not necessarily respond to odours of predators with which they have no previous experience, as predicted by the prey naïveté hypothesis. In turn, perceived predation risk may also modulate predator recognition and the intensity of antipredator responses. In this study, we investigate the responses of an introduced prey species, the European rabbit (Oryctolagus cuniculus), to odours from coevolved and non-coevolved, sympatric and allopatric predators in situations of high and low numbers of predators in Australia. We used pellet counts to quantify rabbits’ use of space on experimental plots treated with predator odours. Rabbit avoidance of plots scented with coevolved predator odours was strongest, but they also responded to non-coevolved, marsupial predators. Predator abundance did not affect predator recognition in rabbits, although responses were more intense in situations where perceived predation risk was low and the intensity of responses decreased over time. Our results suggest that rabbits may have learned to recognize novel marsupial predators after 150 years of exposure in their introduced range.

Hierarchical analysis of avian re-nesting behavior: mean, across-individual, and intra-individual responses Abstract Anti-predator behavior is a key aspect of life history evolution, usually studied at the population (mean), or across-individual levels. However individuals can also differ in their intra-individual (residual) variation, but to our knowledge, this has only been studied once before in free-living animals. Here we studied the distances moved and changes in nest height and concealment between successive nesting attempts of marked pairs of grey fantails (Rhipidura albiscapa) in relation to nest fate, across the breeding season. We predicted that females (gender that decides where the nest is placed) should on average show adaptive behavioral responses to the experience of prior predation risk such that after an unsuccessful nesting attempt, replacement nests should be further away, higher from the ground, and more concealed compared with replacement nests after successful nesting attempts. We found that, on average, females moved greater distances to re-nest after unsuccessful nesting attempts (abandoned or depredated) in contrast to after a successful attempt, suggesting that re-nesting decisions are sensitive to risk. We found no consistent across-individual differences in distances moved, heights, or concealment. However, females differed by 53-fold (or more) in their intra-individual variability (i.e., predictability) with respect to distances moved and changes in nest height between nesting attempts, indicating that either some systematic variation went unexplained and/or females have inherently different predictability. Ignoring these individual differences in residual variance in our models obscured the effect of nest fate on re-nesting decisions that were evident at the mean level.

Territoriality in a snake Abstract Territorial behaviour, whereby dominant animals gain priority access to critical resources, is widespread in some animal lineages, but rare in others. Theory suggests that territoriality will evolve only when animals can economically defend sites that contain critical resources (typically mates, sometimes food). In striking contrast to their close relatives the lizards, male defence of territories for access to mates has not been reported in snakes. In south-eastern Australia, receptive female small-eyed snakes thermoregulate under “hot rocks”, concentrating mating opportunities and thus, potentially allowing males to enhance their fitness by defending these rocks from rivals. We videotaped staged contests between resident and intruder males and analysed data on cohabitation patterns from a long-term (21 years) mark-recapture study. In staged contests, males actively defended hot rocks from intruder males; and thus, larger males actively displaced their smaller rivals. In the wild, larger males were found under rocks with more or larger females. These results suggest that the thermally driven concentration of female small-eyed snakes has rendered hot rocks economically defensible, and thus favoured the evolution of territoriality in a snake.

Changes in host behaviour caused by immature larvae of the eye fluke: evidence supporting the predation suppression hypothesis Abstract The manipulation of host behaviour by the not-fully-developed, immature larvae of trophically transmitted parasites is attracting growing interest. A theoretical model predicts that while facilitation of host predation risk is advantageous for fully developed parasite larvae, the immature ones should make hosts less vulnerable to the predators (predation suppression hypothesis). However, there is still little evidence of such manipulation by non-infective parasite stages. We tested whether immature trematode larvae of the eye fluke, Diplostomum pseudospathaceum, a common parasite of many freshwater fishes, enhance the anti-predatory responses of their host (Oncorhynchus mykiss). To test the predation suppression hypothesis, we experimentally infected young-of-the-year (YOY) rainbow trout and studied the influence of pre-infective metacercariae of the eye fluke on the anti-predator behaviour of the fish. Fish activity, depth preference and the ability to avoid simulated predation were evaluated in the experiments. Infected fish—harbouring a moderate number of immature metacercariae—were significantly less vulnerable to simulated predation (dip-net catch) and less active (horizontal move), but their swimming depth (vertical position) was not changed when compared with the control fish harbouring no larvae. Our findings suggest that immature larvae of D. pseudospathaceum induce changes in host behaviour that can protect them from predation, thereby supporting the predation suppression hypothesis and indicating that manipulations caused by immature parasites may play an important role in modulating predator–prey interactions.

Social networks in changing environments Abstract Social network analysis (SNA) has become a widespread tool for the study of animal social organisation. However despite this broad applicability, SNA is currently limited by both an overly strong focus on pattern analysis as well as a lack of dynamic interaction models. Here, we use a dynamic modelling approach that can capture the responses of social networks to changing environments. Using the guppy, Poecilia reticulata, we identified the general properties of the social dynamics underlying fish social networks and found that they are highly robust to differences in population density and habitat changes. Movement simulations showed that this robustness could buffer changes in transmission processes over a surprisingly large density range. These simulation results suggest that the ability of social systems to self-stabilise could have important implications for the spread of infectious diseases and information. In contrast to habitat manipulations, social manipulations (e.g. change of sex ratios) produced strong, but short-lived, changes in network dynamics. Lastly, we discuss how the evolution of the observed social dynamics might be linked to predator attack strategies. We argue that guppy social networks are an emergent property of social dynamics resulting from predator–prey co-evolution. Our study highlights the need to develop dynamic models of social networks in connection with an evolutionary framework.

Male rhesus macaques use vocalizations to distinguish female maternal, but not paternal, kin from non-kin Abstract Recognizing close kin and adjusting one’s behavior accordingly (i.e., favor kin in social interactions, but avoid mating with them) would be an important skill that can increase an animals’ inclusive fitness. Previous studies showed that philopatric female rhesus macaques (Macaca mulatta) bias their social behavior toward maternal and paternal kin. Benefits gained from selecting kin should, however, not only apply to the philopatric sex, for which the enduring spatial proximity facilitates kin discrimination. Given that dispersal is costly, the dispersing sex may benefit from migrating together with their kin or into groups containing kin. In male rhesus macaques, natal migrants bias their spatial proximity toward familiar male kin rather than familiar non-kin. Here, we set up playback experiments to test if males use the acoustic modality to discriminate familiar female kin from non-kin in a non-sexual context. Males responded differently to the presentation of “coo” calls of related and unrelated females, with their reaction depending on the interaction between kin-line (maternal vs paternal kin) and degree of relatedness (r = 0.5, 0.25). Specifically, males were more likely to respond to close kin compared to more distant kin or unrelated females, with this effect being significant in the maternal, but not paternal kin-line. The present study adds to our knowledge of kin recognition abilities of the dispersing sex, suggesting that male rhesus macaques are also able to identify kin using the acoustic modality. We discuss that the probability of response might be affected by the potential benefit of the social partner.

Variability in individual rates of aggression in wild gray seals: fine-scale analysis reveals importance of social and spatial stability Abstract Aggressive interactions are costly for individuals in time, energy, or physical damage, and in polygynous mating systems, there is high variability in the rates and intensity of aggression across individuals and within breeding seasons. However, examinations into the drivers of this variability are often conducted in isolation, in non-wild systems, or the predictor variables in question, for example, dominance, are averaged across large spatial, social, or temporal scales. The aim of this study was to adopt a fine spatial and temporal scale approach to investigate the factors associated with inter-individual variation in aggression in wild, breeding male gray seals within three consecutive breeding seasons. To do this, we fit models examining if the daily frequency of aggression and probability of escalated aggression for males was best explained by factors such as dominance score, proximity to competitors or females, local social stability, and the occurrence of stochastic environmental events. Stability of neighbor identities was the strongest correlate of reduced male aggression. Dominance status did not correlate with aggression at the daily scale, with the exception of one period after a natural disturbance to the breeding colony where dominant males had relatively reduced rates of aggression. These findings emphasize the importance of local social stability in explaining inter-individual variation in aggression in a wild population and suggest that factors associated with aggression are context dependent in relation to the natural environment. Furthermore, we highlight the utility of a fine temporal scale and incorporating spatial parameters when investigating variability in aggression in wild systems.