Inductive Game Theory and the Dynamics of Animal Conflict

Conflict destabilizes social interactions and impedes cooperation at multiple scales of biological organization. Of fundamental interest are the causes of turbulent periods of conflict. We analyze conflict dynamics in an monkey society model system. We develop a technique, Inductive Game Theory, to extract directly from time-series data the decision-making strategies used by individuals and groups. This technique uses Monte Carlo simulation to test alternative causal models of conflict dynamics. We find individuals base their decision to fight on memory of social factors, not on short timescale ecological resource competition. Furthermore, the social assessments on which these decisions are based are triadic (self in relation to another pair of individuals), not pairwise. We show that this triadic decision making causes long conflict cascades and that there is a high population cost of the large fights associated with these cascades. These results suggest that individual agency has been over-emphasized in the social evolution of complex aggregates, and that pair-wise formalisms are inadequate. An appreciation of the empirical foundations of the collective dynamics of conflict is a crucial step towards its effective management

Cooperative provisioning dynamics: fathers and unrelated helpers show similar responses to manipulations of begging

Cooperative provisioning dynamics between members of a pair in biparental systems has received a lot of attention, both empirically and theoretically. The dynamics of provisioning in cooperatively breeding groups, however, remains poorly understood. Such groups often include unrelated helpers that may have very different provisioning rules from related helpers and parents, since they accrue different types of fitness benefits from helping. The bell miner, 'Manorina melanophrys', provides an ideal system in which to investigate cooperative provisioning, because substantial levels of care are provided by a number of unrelated helpers per nest. We experimentally increased brood demand via targeted begging playbacks during nest visits of either breeding males or unrelated male helpers. Both types of males used similar behavioural investment rules, significantly increasing food delivery rate during playback relative to control periods. Surprisingly, all other provisioners also increased their visit rates during playbacks, although to a lesser extent. This could only have been in response to the increase in visits by the target individuals, suggesting an additional indirect mechanism by which individuals in this cooperative setting assess brood demand. The resultant overall increase in food delivery during the playback periods caused nestlings to show the expected reduction in their own begging and an increase in body mass gain. It is therefore interesting how similar the evolved provisioning responses are for all types of group member, irrespective of whether such benefits of investment in the brood are derived via kin selection (fathers) or some future direct increase in fitness (helpers)

A critical analysis of 'false-feeding' behavior in a cooperatively breeding bird: disturbance effects, satiated nestlings or deception?

'False feeding,' where helpers arrive at nests with food but fail to provision the young, has been reported in several cooperative species. This and other potentially 'deceptive' behavior has been interpreted as indicating that helping may operate as a signal within such social groups. We critically examine these phenomena in the provisioning behavior of the bell miner 'Manorina melanophrys'. Excessively close observation distances can artificially elevate the rate of false feeding in this (and other) species, but once this had been accounted for, there was little evidence for any 'deceptive' behavior by helpers or breeders. Natural and experimentally induced variation in the presence of a potential conspecific audience at the nest did not have any consistent influence upon the rate of false feeds, which was low at 7.94% of 6,880 nest visits. Instead, encountering unexpectedly low levels of brood demand provided a more parsimonious explanation for those visits where helpers failed to feed nestlings or ate the food themselves. Failure to completely transfer a load to nestlings was more likely when the load contained a high proportion of sticky lerp, indicating a simple prey-transfer problem. Finally, individuals that arrived at nests without prey were often members of neighboring breeding pairs, suggesting that these few non-feeding visits may instead involve an information-gathering function. We, therefore, suggest that future studies explicitly exclude the possibility of observer disturbance and all aspects of normal provisioning behavior before applying the terms 'false feeding' or 'deceptive' and inferring anything more than straightforward helping at the nest

Helping as a signal: does removal of potential audiences alter helper behavior in the bell miner?

Despite many studies on the evolution of cooperative breeding and helping at the nest, relatively few have explored the possibility that helping functions as a signal to gain social advantage within groups (the "pay to stay" and "social prestige" hypotheses). One of the most promising candidates for such a signaling system is the cooperatively breeding bell miner, 'Manorina melanophrys'. Large numbers of unrelated helpers attend multiple nests while giving individually identifiable vocalizations, breeding females usually remain within monitoring distance of the nest area, and females often re-pair with the hardest working male helper after the death/removal of their breeding partner. We examined the possibility that helping operates as a signal by temporarily removing the potential audience: the breeding male or the breeding female. However, there was no discernable change in provisioning behavior of helpers, relative to control periods. We also simulated the presence of the removed birds through playbacks of their individual-specific calls and again found no effect on others' visit rates, prey types, load size, and a variety of other behaviors at the nest. If either signaling hypothesis explained helping in this system, we might have expected facultative decreases in conspicuous provisioning behaviors when one or other potential audience was absent. Thus, despite possessing many of the prerequisites of a signal-based helping system, there is no evidence for such a phenomenon in bell miners. Cooperation in these groups of mixed relatedness may instead be driven by a combination of kin selection and direct benefits via group augmentation and/or pseudoreciprocity

Helping as a signal and the effect of a potential audience during provisioning visits in a cooperative bird

Research on cooperative breeding has begun to focus on direct fitness benefits gained by helpers, particularly when individuals are unrelated to those they assist. There has been considerable interest in helping possibly operating as a signal, either to show off individual quality to potential mates ('social prestige') or to ensure group membership ('pay to stay'). However, empirical investigation of these phenomena remains sparse. Here we investigate the potential for signalling via provisioning behaviour in the bell miner, 'Manorina melanophrys', an obligate cooperative breeding species in which the predominantly male helpers are commonly unrelated to breeders. Aggression between birds was extremely rare, and there was little to indicate a pay to stay system. The presence versus absence of members of the breeding pair as a potential audience at the nest had little influence on helper behaviour (e.g. load size/composition, visit duration or frequency). Helpers did produce more individually distinctive vocalizations when in the presence of another helper or the breeding male, although presence of the breeding female (a likely target of male signals) surprisingly had no effect. There was also evidence that nest arrival times coincided somewhat. These results are probably best explained by the helpers and breeding males being involved in additional cooperative behaviours when away from the nest, such as mobbing. Overall, there does not appear to be any evidence that bell miner helpers use nestling provisioning to signal their quality and/or work rate to one another or to either member of the breeding pair

Do helpers really help? Provisioning biomass and prey type effects on nestling growth in the cooperative bell miner

Provisioning visits by helpers are normally assumed to confer positive fitness effects on nestlings, but few studies have actually examined the nutritional value of items helpers fed to offspring. In the cooperatively breeding bell miner, 'Manorina melanophrys', helpers deliver large proportions of 'lerp', a sugary secretion of psyllids (Hemiptera; Psyllidae). Although lerp is a major food type of adults, its nutritional value is uncertain, especially since nestlings in other nectarivorous species are usually fed only protein-rich arthropods. Helpers in this system are predominantly male and are often unrelated to broods they aid, suggesting helping might be a sexual display, with any nutritional benefits to nestlings being of secondary importance. Detailed observations revealed that the proportion of lerp delivered increased with nestling age, but that it did not differ between helpers and parents, or between related and unrelated helpers. Variation in delivered biomass (lerp+arthropods) had a positive effect on nestling condition, but variation in the proportion of prey constituted by lerp had no measurable effect on nestling mass or condition. Finally, the total amount of food, nestling body mass and condition were all positively related to the number of helpers provisioning broods. These results are consistent with helping in bell miners operating as cooperative investment in brood fitness. Given that lerp was as effective as invertebrate prey in promoting growth, these results also suggest a valid nutritional role for this easily procured food, presumably facilitated by the unusually early development of nestling digestive tracts to utilize these simple sugars

Provisioning calls of the cooperatively breeding bell miner 'Manorina melanophrys' encode sufficient information for individual discrimination

Acoustically-mediated individual discrimination has been the focus of much investigation in ornithology. For cooperatively breeding species, strong selection pressure favouring individual recognition during acts of altruism is predicted under many of the most interesting hypotheses proposed to account for helping behaviour. We investigated differences in 157 calls given by 12 different individuals as they provisioned nestlings, including both breeding and helper bell miners 'Manorina melanophrys' (Meliphagidae), a cooperatively breeding honeyeater endemic to south-eastern Australia. Individual differences were apparent in all 15 call parameters analysed, many with a high level of repeatability. Moreover, the information capacity of mew calls allows as many as 515 different signatures to exist in the system. As many parameters showed strong sex differences, separate discriminant functions were used to predict individual identity within each sex. Five parameters were used in a function that correctly identified over 90% of female calls in both a training (n=35) and test dataset (n=11) not used to generate the function. Among males, a separate function used six parameters to correctly assign individual identity in 89.3% (n=84; training) and 77.8% (n=27; test) of cases. Three original parameters, including spectral and spatial characteristics, were highly correlated with functions predicting identity in both sexes. The accuracy of functions was not influenced by a signaller's sex, breeding status, or by sampling period which was spread over as much as two breeding seasons within individuals. Significant potential therefore exists for bell miners to use these simple provisioning calls in individual discrimination. If this is the case, call information also has the potential to be used by receivers as predicted by signalling hypotheses proposed to account for cooperative helping behaviour, such as the pay-to-stay and social prestige hypotheses