As our planet’s climate becomes increasingly erratic, scientists are racing to uncover how these changes ripple through the fabric of animal societies. A groundbreaking study, spanning more than three decades, has illuminated how natural climate fluctuations influence the complex interplay of social dynamics and competition within and between groups of white-faced capuchin monkeys in Costa Rica. The findings reveal that environmental extremes can profoundly reshape the balance of costs and benefits in group living, altering how animals strategize space use, resource competition, and social cohesion.
Group living is often hailed as a survival strategy that confers significant advantages—enhanced defense capacity, cooperative vigilance, and collective strength against rivals. Yet, it is also burdened by internal competition for limited resources. The study, led by Professor Susan Perry and her collaborators at the Max Planck Institute of Animal Behavior (MPI-AB) and the University of Konstanz, shows how this delicate trade-off between the benefits of strength in numbers and the costs of sharing finite food supplies dynamically shifts in response to climatic cycles.
For over 33 years, Perry’s team meticulously observed 12 adjacent groups of capuchin monkeys inhabiting the dwindling patches of tropical dry forest in Costa Rica, collecting detailed behavioral data on 335 individuals. Satellite-derived environmental imagery complemented these observations, offering precise measurements of forest greenness and canopy coverage. This interdisciplinary approach unveiled how seasons and multi-year climate phenomena like El Niño and La Niña modulate resource distribution and consequently influence group interactions and territorial behavior.
Under typical environmental conditions, capuchin groups demonstrated a distinct pattern: individuals in larger parties consumed fruit at reduced rates due to intensified intragroup competition. This slower intake rate was, however, mitigated by the ability of larger groups to expand their ranges, often encroaching upon and displacing neighboring smaller groups. By monopolizing higher-quality foraging zones, these bigger coalitions effectively internalized the cost of feeding more mouths, thereby balancing the competitive disadvantages of size.
The tropical dry forest environment serves as the perfect natural laboratory for such studies. Unlike rainforests with relatively constant resources, this biome experiences stark seasonal fluctuations, particularly a pronounced dry season beginning around January. During this arid period, essential resources—water, fruit, and shade—become sparse and clumped along river corridors, intensifying competition as groups are forced into closer proximity. Intriguingly, during the dry season, capuchin territories showed reduced overlap, yet encounters between groups became more frequent and aggressive, signifying heightened territorial defense.
Crucially, the study documented how the influence of group size on space use and competition becomes destabilized when extreme climatic events disrupt usual seasonal patterns. El Niño-induced droughts and La Niña-related heavy rains both heightened foraging costs and undermined the dominance advantages larger groups typically enjoy. In extreme conditions, the spatial buffer that allowed large groups to secure better resources disappears, eroding the benefits of living in a sizeable coalition.
As Dr. Brendan Barrett, co-senior author and research leader at MPI-AB, explains, “While large groups usually benefit by outcompeting smaller neighbors for prime foraging grounds, these benefits reach a threshold under climatic extremes. Prolonged environmental stress may push individuals to leave or even cause entire groups to fragment, fundamentally reshaping the social landscape.” Such fragmentation could have cascading effects on population structure, social interactions, and ultimately species survival.
These findings question long-standing ecological assumptions about the stability and scalability of group living in primates and other social animals. The prevailing model suggested that bigger groups reliably compensate for their increased resource demands by simply enlarging their home ranges. Yet, the new research highlights a more nuanced reality: the efficacy of this strategy is contingent on the consistency of environmental conditions, making social structures vulnerable to intensified climate variability projected under global warming scenarios.
The study underscores the value of long-term data collections in teasing apart the complexities of ecological and social phenomena. Founded in 1990, the Lomas Barbudal Monkey Project led by Perry is among the longest-running field primate studies worldwide. Its unique combination of behavioral monitoring and satellite environmental data enabled unprecedented insights into how habitat quality fluctuates seasonally and across broader climate cycles, affecting the monkeys’ social and spatial strategies.
From a methodological standpoint, this work exemplifies the power of combining fine-scale behavioral ecology with remote sensing technology. Behavioral observations quantified energetic intake rates through fruit consumption metrics, while satellite imagery tracked vegetation health and resource distribution. This integrative approach allowed researchers to model the interactive effects of group size, neighborhood dynamics, and environmental variation on competition and territory use.
Still, the study measured energetic costs rather than directly linking these changes to survival or reproductive success—parameters that will be critical in predicting long-term population trajectories under shifting climates. Dr. Odd Jacobson, lead author, emphasizes the next frontier: “To forecast how climate change could destabilize social living, we must connect the dots from resource competition and space use to birth and death rates. Understanding this chain will reveal whether erratic environmental pressures permanently alter animal societies.”
In a broader context, this research reveals how climatic volatility, an aspect intensifying with anthropogenic climate change, might not only challenge individual species’ survival but also fundamentally transform the social infrastructures upon which many species rely. For social primates, whose evolutionary success intertwines with group living, such changes may alter mating systems, cooperative behaviors, and even genetic exchange over time.
As natural climate oscillations like El Niño and La Niña increase in frequency and severity in the twenty-first century, the primates of Costa Rica’s tropical dry forests serve as a poignant sentinel. Their adaptive responses and vulnerabilities offer crucial foresight about how entire ecosystems might restructure. The study leaves an open question: how will primate societies adapt if climatic extremes become the new normal, and what conservation strategies can support these complex social networks amid inevitable environmental upheaval?
Subject of Research: Animals
Article Title: Environmental fluctuations alter the competitive trade-offs of group size in a social primate
News Publication Date: 6-May-2026
Web References:
https://lbmp.anthro.ucla.edu/
DOI: 10.1038/s41559-026-03048-8
Image Credits: Susan Perry / University of California Los Angeles
Keywords: Ecology, Ethology, Climate Change, Social Primate, Group Dynamics, Tropical Dry Forest, Foraging Competition, El Niño, La Niña, Animal Behavior, Conservation
