Synergistic effects of temperature, diet and colony size on the competitive ability of two ant species

Multiple biotic and abiotic factors influence species coexistence and co-occurrence patterns. In a competitive environment, for example, temperature and diet variation may modify both foraging behaviour and aggression, thereby changing competitive interactions and species co-occurrence patterns. In New Zealand, two endemic ant species (Prolasius advenus and Monomorium antarcticum) often form allopatric distributions; though also periodically do co-occur in the same habitat. Here, we performed a long-term laboratory experiment in an attempt to understand how diet, colony size and environmental conditions may influence these co-occurrence patterns. The consequences of temperature and diet variation differed between P. advenus and M. antarcticum. Colonies of P. advenus exhibited increased aggression and foraging activities at higher temperatures. In addition, P. advenus colonies augmented their foraging activities when deprived of a carbohydrate-rich food source. Conversely, small M. antarcticum colonies exhibited higher aggression than when in large colonies, and increased their foraging activities at lower temperatures. The modulation of aggression and foraging behaviour may influence the likelihood of small P. advenus and M. antarcticum colonies persisting in the long term. Our results are compatible with the hypothesis that the environment is likely to be a strong filter for the negative co-occurrence patterns we observe between P. advenus and M. antarcticum in New Zealand. Furthermore, this study provides a mechanistic explanation for potential impacts of climate warming on community structure. Environmental modification of aggression and foraging behaviour could potentially alter competitive interactions and influence community assembly.