| Summary: | Several biotic and abiotic stressors can influence community assembly. The negative co-occurrence patterns observed within many communities, for example, may derive either from behavioural similarities (e.g. species displaying high aggression levels towards each other) or habitat preference. I evaluated the role of several stressors that may shape New Zealand’s ant communities. First, I investigated (in chapter 2) the co-occurrence patterns of two native ant communities located within transitional grassland-forest habitats. I also monitored the temperature variation in these habitats over a one-year period. I found that grasslands are exposed to higher temperature variation than forest habitats. I also found that some ants are mostly associated with forest habitats and others with grasslands. Using null models to examine these communities, I found evidence that two ant species (Monomorium antarcticum and Prolasius advenus) exhibit negative co-occurrence patterns. In the reminder of my thesis I developed a series of laboratory-based experiments to examine the processes that could explain the co-occurrence patterns that I observed in these ant communities. In chapter 3, I subjected heterospecific groups of ants to interactions in controlled conditions. I asked if interspecific aggression predict the survival probability and co-occurrence patterns described in chapter 2. My results demonstrated that aggression predicted the survival probability of interacting ant species and their co-occurrence patterns. I argued that aggressive behaviour might reflect the risks imposed by competitors. Differences in aggression may thus be a key factor influencing sympatric and allopatric co-occurrence patterns of these ant communities. In chapter 4, I tested the hypotheses that arrival sequence and diet influence the strength of interactions between colonies of two species that exhibited negative co-occurrence patterns (P. advenus and M. antarcticum). When arriving first, P. advenus displayed increased aggression and M. ...
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