Variation in nest relocation of harvester ants is affected by population density and food abundance

Movement patterns of animals throughout their habitat depend on the associated costs and benefits, which vary among species and potentially among populations. Here, we compare the nest relocation patterns of seed-harvesting ant colonies between 2 populations in northern and southern California, and over time. Understanding the causes and consequences of nest relocation by harvester ants is particularly important because these ants shape the ecological communities in which they reside. We show that nest relocation is both variable between the 2 populations and consistent within a population over more than a decade. Relocation frequency and distance was greater at the site with lower population density, shorter period of vegetation growth, and slightly higher humidity. Thus, when the benefits associated with finding new resources through nest relocation are high and the costs of desiccation or encountering other colonies during relocation are low, nest relocation becomes a preferable behavioral strategy. These findings suggest that populations adjust their movement patterns based on the ecological conditions they face. Consequently, our findings may explain site-specific ecological dynamics that emerge from the behavioral rules of an ecosystem engineer.