Peter Michael Kappeler

The diet of numerous non-volant Malagasy mammal species remains poorly documented despite increasing anthropogenic pressures on their habitats. Herein, we investigate the diet of different endemic species of Tenrecidae, Nesomyinae, and Microcebus murinus (Cheirogaleidae) in the dry deciduous forest of Kirindy (CNFEREF), central western Madagascar, with a primary focus on arthropod consumption. Sampling was conducted during two periods: the later portion of the dry season and the wet season. Arthropod consumption was assessed from fecal samples, and, where possible, with additional stomach and intestinal contents for some Tenrecidae. Dietary composition differed among taxa, with Tenrecidae and M. murinus consuming mainly Coleoptera, while Nesomyinae ingested largely Formicidae, likely associated with their consumption of fruits and seeds, which form their main food sources. Herein, we present the first observations of arthropod consumption in Nesomyinae. Arthropod consumption differed among species of this endemic subfamily, with Macrotarsomys bastardi consuming a wider variety of arthropods (six orders vs one in Eliurus spp.) and showing a significantly higher rate of arthropod consumption. Overall, this study highlights the importance of arthropods as a key trophic resource for insectivorous and non-insectivorous non-volant mammals in Malagasy dry deciduous forests, and provides baseline information for understanding their feeding ecology.

Adversities in early life compromise fitness components later in life, but the cumulative effects of multiple adversities and their timing across the lifespan remain poorly understood. To contribute comparative data from an independent primate radiation, we leverage long‐term demographic data from a wild lemur population to examine the effects of maternal loss, presence of an older sibling, maternal age, group size, temperature and rainfall on survival of 242 infants across the lifespan. We found that differently operationalized cumulative indices of early adversities predicted infant survival but did not predict survival better than single predictor models. Infant survival was reduced by maternal loss, the absence of an older sibling and large group size at death. Survival to adulthood and female longevity were positively associated with higher rainfall during infancy and negatively by larger group sizes at death; infant survival to adulthood also declined with increasing maternal age. Cumulative adversities early in life had no persistent negative long‐term effects on survival, but sample sizes decreased in the older age classes. However, rainfall as a proxy for food availability in early life had long‐term effects, with higher rainfall increasing the odds of survival to adulthood and female longevity. Hence, social and demographic adversities had stronger effects than environmental ones for early infant survival, but environmental effects in early life also appear to be important drivers of demography and life history in these critically endangered primates.

For over a century, the evolution of social system diversity has been a key focus in the fields of behavior, ecology, evolution, and the social sciences. Unlike many previous studies, which focused on the costs and benefits of evolutionary transitions to pairs or groups, the present paper explores the behavioral mechanisms that mitigate the ensuing costs. Maintaining spatial cohesion is necessary for individuals to reap the benefits of associating with conspecifics. However, this association creates unavoidable costs that promote internal strife and centrifugal forces that drive groups apart. The present review focuses on the behavioral mechanisms that mitigate this trade‐off. First, I review features of the three main categories of social systems to identify the emergence and nature of the costs of association. To further differentiate this perspective, I emphasize the importance of distinguishing between the processes that trigger and maintain the evolution of non‐solitary systems. In the subsequent section, I summarize the mechanisms by which animal pairs and groups maintain cohesion and social stability. Social order is a foundational concept in the social sciences that describes how unavoidable internal conflict among selfish individuals disrupts social stability. In the final section, I review the factors impacting social order in animals, as well as the fitness consequences of these perturbations, underscoring their evolutionary importance. I argue that behavioral homogeneity among group members serves to enhance social order and can be based on various mechanisms, including social norms. Thus, this broad comparative evaluation offers a novel perspective on the evolutionary roots of a significant component of human social behavior and identifies several novel avenues for future research on the evolution of social systems.

Variation in adult sex ratios (ASR) offers important insights into evolutionary and ecological dynamics, as it reflects demographic processes and predicts sex-specific reproductive strategies. In most mammals, ASRs tend to be female-biased at older ages. Yet, Madagascar’s group-living primates and some other mammals consistently show male-biased ASRs, but the underlying mechanisms remain unclear. Wild red-fronted lemurs (Eulemur rufifrons) exhibit even birth sex ratios, no sex-specific early life mortality, higher female disappearance rates within the first 8 years of life and male-biased ASRs. Since female reproductive activity peaks between the ages of 3 and 8 years, we hypothesized that reproductive costs might be associated with higher female disappearance rates, which are indicative of likely mortality, thereby contributing to the male-biased ASRs. Event-history analyses of 27 years of demographic data revealed that reproducing younger females and older mothers who successfully raised their offspring to independence were both less likely to disappear, suggesting that short-term reproductive success is closely linked to individual condition. By contrast, females with higher cumulative lifetime reproductive effort faced an increased risk of disappearing, highlighting the long-term costs of reproduction. By linking key components of reproductive investment to sex-specific mortality, this study contributes novel insights into the demographic processes underlying ASR variation among mammals.

Social interactions are crucial for individual health and ultimately fitness, making the choice of social partners evolutionarily relevant. Previous research has shown that individuals who succeed in foraging tasks often receive increased affiliation from group members. Similarly, in a social learning context, individuals who possess valuable information become more attractive social partners. Thus, an individual’s role in a foraging context, specifically, whether it is a successful producer, can influence its social relationships. To explore this effect, we examined the interplay between social learning, producing and scrounging behavior, and social relationships in four groups of wild red-fronted lemurs (Eulemur rufifrons; N = 29). We conducted an open diffusion experiment with food boxes that required animals to learn one of two techniques to open them. 16 individuals learned to open them. Initial success was better predicted by use of individual than social information, i.e., manipulating the food boxes vs. time spent watching successful individuals or scrounging. Older males were less successful than females. Scrounging occurred in about 26% of events. The technique used, age and sex of the producer did not predict the number of scroungers. Less successful individuals and males scrounged more often. Successful individuals received more affiliative behavior during the experimental period than in the pre-experimental period, which returned to baseline levels during the post-experimental period. Thus, red-fronted lemurs recognize and reward competent foraging partners socially during periods where they can benefit from them immediately. Together, these results highlight the importance of foraging competence for social integration and partner choice.

Responses of natural populations to climate change are driven by how multiple climatic and biotic factors affect survival and reproduction, and ultimately shape population dynamics. Yet, despite substantial progress in synthesizing the sensitivity of populations to climatic variation, comparative studies still overlook such complex interactions among drivers that generate variation in population-level metrics. Here, we use a common framework to synthesize how the joint effects of climate and biotic drivers on different vital rates impact population change, using unique long-term data from 41 species, ranging from trees to primates. We show that simultaneous effects of multiple climatic drivers exacerbate population responses to climate change, especially for fast-lived species. However, accounting for density feedbacks under climate variation buffers the effects of climate change on population dynamics. In all species considered in our analyses, such interactions between climate and density had starkly different effects depending on the age, size, or life-cycle stage of individuals, regardless of the life history of species. Our work provides the first general framework to assess how covarying effects of climate and density across a wide range of population models can impact populations of plants and animals under climate change.

Infant survival is an important component of parental fitness in iteroparous species with slow life histories. From the infant's perspective, survival can be more or less directly influenced by the social environment, with group members potentially representing either a threat or a buffer against external stressors. Therefore, studying social relationship patterns during early development may provide insights into the effect of social factors on infant survival. To understand how group members interact with infants, and whether social relationships change due to the presence of infants, we conducted focal behavioral observations on four groups of wild redfronted lemurs (Eulemur rufifrons) during the birth season. Infant handling consisted mostly of grooming, while aggressive infant handling behaviors and allomaternal care occurred very rarely. Infants were groomed by individuals of all age‐sex classes at similar rates except for a trend of higher infant handling rates in juvenile females. After giving birth, mothers received more approaches and were closer in proximity to other group members than before birth, but there were no changes in grooming rates of mothers and other group members. Mothers also initiated more aggressive interactions towards other group members after giving birth. Therefore, other redfronted lemurs were clearly attracted to infants, which caused changes in affinitive relationships of mothers. At the same time, the increase in maternal aggression indicates that group members also represent some threat to infants. Our study provides a starting point for future studies, exploring how these early infant handling interactions and the mother's relationships impact an infant's subsequent survival, development and future relationships.