Experimental manipulation of ecological and cognitive conditions produces the entire conformity–diversity spectrum in a single species

Identifying the factors that drive individuals in a population to conform to the same behavior or to exhibit behavioral diversity is crucial for understanding collective decision-making, information transmission, and culture, yet remains challenging. Here, we propose and test a conceptual model predicting a population's position along a conformity-diversity (CD) spectrum based on two key axes shaping the CD landscape: an ecological axis, representing competition over depleted resources, which favors diversity over conformity (since resources are depleted sooner if all individuals conform to the same resource type), and a cognitive axis reflecting the relative ease of learning a behavior socially versus individually. Our experiments show that manipulating these two primary factors is sufficient to produce the full CD spectrum within a single species. Specifically, studying socially foraging house sparrows, we manipulated competition using depleted or nondepleted feeding wells and manipulated the relative ease of learning a task individually by manipulating levels of experience and task difficulty. As predicted by the model, sparrows exhibited strong conformity under the combination of "no food depletion" and "difficult individual learning" conditions, strong diversity under the combination of "food depletion" and "easy individual learning" conditions, and intermediate levels of conformity under mixed conditions. The results show that a population's position along the CD spectrum is highly flexible and sensitive to ecological and task-related conditions. Accordingly, the demonstrated CD surface may be viewed as an evolving reaction norm, and hence as a baseline over which additional factors shaping social conformity and differentiation can be tested.