Justin D. Yeakel

Introduction Quantifying the flux of individuals into and out of populations is a central challenge that lies at the intersection of ecology and evolutionary biology. In a real sense, a population's true density, and how it changes over time, will be known only in small or artificial environments, with the remaining task to grasp the uncertainties in both the data available and the models used to infer population trends (Oppel et al. 2014).

eLife Assessment This is a valuable study that tests the functional role of food-washing behavior in removing tooth-damaging sand and grit in long-tailed macaques and whether dominance rank predicts level of investment in the behavior. The evidence that food-washing is deliberate is compelling and the evidence that individual investment in the behavior varies is solid. Overall, the article should be of interest to researchers interested in foraging behavior, cognition, and primate evolution.

Abstract Bacterial cooperation involves the exchange of metabolites, which can range from costless byproducts of metabolism to intentionally produced and costly molecules. These interactions occur across spatial scales, from direct cell contact to the diffusion of metabolites in the environment. Due in part to this variety of interaction modes, the impacts of mutualism on bacterial community dynamics remain unclear.