Available online 30 April 2024

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The adaptive benefits of cooperation among humans have been widely studied. However, is being cooperative always adaptive across various combinations of ecological conditions? Existing work has focused on cultural, inter-, and intra-individual predictors of cooperation yet there is a lack of research on how an individual's ecology may come into play. In this work, we focus on the interaction of two ecological factors—population density and resource scarcity—on cooperation. Population density is often accompanied by social competition for limited resources. We hypothesise that in response to cues of high (versus low) population density, people facing resource-scarcity would adaptively lower their cooperativeness, more so than those with resource abundance. Results from two studies support our hypothesis—population density lowers cooperation, but only for people who perceive lower resources or social status. Our findings provide insights that cooperation varies adaptively as a function of interacting ecological factors.

Section snippetsPopulation density and cooperation

Human populations have experienced fluctuations in population sizes throughout ancestral history (Hu et al., 2023; Schiffels & Durbin, 2014). It is plausible that organisms evolved to display behavioral plasticity to respond adaptively to ecological changes. For instance, animals of the same species from urban (versus nonurban) ecologies display large differences in habitation preferences, personality differences and social behavior (Caspi et al., 2022). Likewise, humans also experience more

The interaction of resource availability and population density

While there is a negative influence of population density on cooperation, the heightened competition for resources accompanying higher density may only pose a severe threat or stressor to people with fewer resources who already face challenges due to their state of scarcity. Resource scarcity has always posed a severe threat to mortality. For the majority of mankind's evolutionary history, humans have relied on acquiring resources from their environment for survival (Orians & Heerwagen, 1992).

Research overview

Across two studies, we test our hypotheses. In Study 1, we measured perceptions of population density and examined whether it negatively influences cooperation in an economic game among those with low (but not high) resource availability. In Study 2, we retain the same approach while experimentally manipulating population density.

In this work, we operationalize cooperation in the form of choosing to prioritise others' benefit over oneself. Other work has also used this economic paradigm to

Study 1

In Study 1, as an initial test of our hypotheses, we measured perceptions of population density and use several measures of perceived resource availability. We operationalized resource scarcity using three measures: (1) childhood resource availability, (2) current resource availability, and (3) subjective SES on the MacArthur ladder (Adler et al., 2000). All these measures reflect subjective perceptions of having sufficient resources to meet one's livelihood needs, or general socio-economic

Participants and procedure

Participants are recruited from undergraduate courses in a major Singapore university.4 After eliminating incomplete responses (N = 23 had <55% of the study completed), the final sample size collected was N = 148 (28 male, 120 female), with a mean age of M = 23.89, SD = 1.77. A post-hoc power analysis based on the averaged f2 of three population density x resource availability interaction terms revealed that our sample yielded a statistical power of 85.29%.

After acknowledging the informed

Results

There were no significant effects of gender and age on the amount given to the recipient in the dictator game (ps > 0.30). The descriptive statistics are reported in Table 1. We note that our three resource availability measures are correlated and thus, for hypothesis testing, we also created a composite measure by averaging the standardised versions of these scales.

Discussion

The results of Study 1 support both our hypotheses. Across three measures of resource availability and the composite resource scale, people who perceived resource scarcity were less cooperative when they perceived higher (versus lower) population density (supporting H1). In contrast, the cooperation rate of people who perceived resource abundance was unaffected by perceptions of population density (supporting the attenuated effects we expected; H2), with the exception of one measure of resource

Study 2

A key limitation of Study 1 was that population density was measured, disallowing us from drawing causal inferences. Hence in Study 2, we experimentally manipulated population density and expect that cues of high (versus low) population density will negatively influence cooperation rates for those with low resource availability (H1), but to a smaller extent for those with high resource availability (H2). We retained the same measures of resource availability and cooperation as in Study 1.

Participants and procedure

Using the results from Study 1 to determine effect size of the interaction effects, we calculated the average f2 from the three population density x resource availability interaction terms. We yielded an average f2 of 0.062, which reflects a small-moderate effect size (Cohen, 2013).

We then conducted a power analysis on G*Power. To achieve 80% power with an effect size of 0.062; a sample of 129 participants is needed. Study 2 had a sample size of N = 228 undergraduate students (46 male, 182

Results

Similar to Study 1, there were no significant effects of gender and age on cooperation in the dictator game (ps > 0.70). The descriptive statistic of each variable is shown in Table 3.

Discussion

In Study 2, we manipulated population density using a pre-tested manipulation and replicated the findings from Study 1. Supporting H1, the cooperation rate of people who reported lower current resource availability was negatively influenced by cues of high population density. Supporting H2, the cooperation rate of people with higher current resources was not influenced by either high or low population density cues. Notably, the unexpected positive resource-cooperation slope for those with high

General discussion

While existing literature has identified many cultural, intra-, and inter-individual differences that may explain cooperative tendencies (e.g., Keltner et al., 2014; Piff, Kraus, Cheng, & Keltner, 2010; Piff, Kraus, Côté, et al., 2010), there is a shortage of research investigating how broader ecological factors may simultaneously interact to influence the cooperation (for a review on key ecological dimensions, refer to Sng et al., 2018). The adaptive value of cooperation varies across

Conclusion

The current literature has rarely considered the simultaneous influence of ecological factors when examining predictors of cooperation. Our work bridges this gap by investigating how two such factors—perceived resource scarcity and population density—interact to influence cooperative behaviors. While high population density negatively influences the cooperation levels of people who perceive resource scarcity, those with perceived abundance in resources remain relatively unaffected by population

CRediT authorship contribution statement

Lynn K.L. Tan: Writing – review & editing, Writing – original draft, Visualization, Validation, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Norman P. Li: Writing – review & editing, Writing – original draft, Supervision, Methodology, Conceptualization. Kenneth Tan: Writing – review & editing, Writing – original draft, Supervision, Methodology, Conceptualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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