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Resource availability plays a key role in driving variation in somatic growth and body condition, and the factors determining access to resources vary considerably across life stages. Parents and carers may exert important influences in early life, when individuals are nutritionally dependent, with abiotic environmental effects having stronger influences later in development as individuals forage independently. Most studies have measured specific factors influencing growth across development or have compared relative influences of different factors within specific life stages. Such studies may not capture whether early-life factors continue to have delayed effects at later stages, or whether social factors change when individuals become nutritionally independent and adults become competitors for, rather than providers of, food. Here, we examined variation in the influence of the abiotic, social and maternal environment on growth across life stages in a wild population of cooperatively breeding meerkats. Cooperatively breeding vertebrates are ideal for investigating environmental influences on growth. In addition to experiencing highly variable abiotic conditions, cooperative breeders are typified by heterogeneity both among breeders, with mothers varying in age and social status, and in the number of carers present. Recent rainfall had a consistently marked effect on growth across life stages, yet other seasonal terms only influenced growth during stages when individuals were growing fastest. Group size and maternal dominance status had positive effects on growth during the period of nutritional dependence on carers, but did not influence mass at emergence (at 1 month) or growth at independent stages (>4 months). Pups born to older mothers were lighter at 1 month of age and subsequently grew faster as subadults. Males grew faster than females during the juvenile and subadult stage only. Our findings demonstrate the complex ways in which the external environment influences development in a cooperative mammal. Individuals are most sensitive to social and maternal factors during the period of nutritional dependence on carers, whereas direct environmental effects are relatively more important later in development. Understanding the way in which environmental sensitivity varies across life stages is likely to be an important consideration in predicting trait responses to environmental change.

Candidate model sets for all analyses in Mares et al. Breeding decisions in sociable weavers

In group living animals where natal dispersal is delayed, prospecting allows individuals to asses their future dispersal and breeding opportunities and, in males of some species, may minimize the costs of delaying dispersal by enabling extra-group breeding while still resident in the natal group. While evidence of prospecting is widespread, comparatively little is known about the development of this behaviour and few studies have investigated the factors that may affect investment in prospecting, as it is typically difficult to monitor such mobile individuals. Prospectors typically encounter neighbouring groups during extraterritorial forays and resident individuals in these groups respond aggressively to approaches by extra- group males, given the potential loss in direct and indirect fitness that prospectors may inflict. As with prospecting behaviour, few studies have investigated the causes of individual differences in investment in repelling prospectors and measured the costs of such territory defence. In this dissertation, I exploit our ability to closely monitor prospecting males in meerkats, to investigate the causes of individual variation in extraterritorial prospecting effort and aggressive responses to prospector intrusions. In Chapter 3, I show that, as adults, heavier males invest more in prospecting than lighter ones, and that males time their forays in order to maximize their chances of dispersal, while minimizing the associated costs by prospecting when neighbouring groups are in close proximity to their own. In Chapter 4, I demonstrate that males that are heavier in early life start prospecting at a younger age and contribute less to helping later in life, than lighter males. In Chapter 5, I show that the threats posed by prospectors towards residents are associated with high investment by resident males in repelling intruders, which has measurable costs in terms of weight gain and cooperative contributions to offspring care. Finally, in Chapter 6, the experimental presentation of scent cues reveals that meerkats discriminate between resident and extra-group male scent cues, and that resident dominant males exhibit stronger responses to indirect evidence of prospectors than other group members., This work was supported by the Secretaría Nacional de Ciencia, Tecnología e Innovación (SENACYT) and the Instituto para la Formación y Aprovechamiento de Recursos Humanos (IFARHU) [grant number 270-2007-339]