Self-organization and spatial pattern formation is a widespread phenomenon in many ecosystems. While there is a rich body of theoretical work stemming from the insights of Alan Turing, it is often difficult to conduct detailed empirical study of the underlying mechanisms behind pattern formation. Our study system is a tropical arboreal ant whose nests form a clustered distribution in space and which, we claim exhibits self-organized criticality. The mechanism behind this pattern formation is hypothesized to be a Turing activator-inhibitor system where the activator is the budding of nests to nearby trees, and the inhibitor is a parasitic fly of the ant. Previous models have recreated the distribution of ant nests in space via density dependent mortality of nests as parameterized by field data, but none have explicitly incorporated the parasitic flies. Here we report on a number of insights regarding the dynamics of the system that stemmed from developing a model that explicitly incorporated the parasitic flies in space. We employed agent-based modeling, long-term field survey data of ant nest distributions, detailed observations of parasitic fly behavior, and developed novel statistical analysis to gain a better understanding of the dynamics that lead to self-organization of this system.
Results/Conclusions
Explicitly incorporating the parasitic fly in the model let us recreate results from previous models in addition to providing further insights. First, it predicted a pattern of higher mortality rates in younger nests, a result that was subsequently corroborated in our long-term data of ant nest distributions. To understand the driver of this particular pattern of mortality, we conducted detailed surveys that showed parasitic flies arrive sooner, in higher numbers, and attack for longer at younger ant nests than at old ones. We hypothesized that this pattern of nest mortality and attack by the parasitic fly on young nests may be a function of the demographic distribution of nests in space. We developed a statistical test to detect age-specific spatial patterns within clusters. These results suggest that the underlying biology of how nests bud creates a distinct pattern of nest ages in space. Consequently the oldest nests are located in the center of clusters and the youngest on the periphery. The long distance dispersal of the parasitic flies to clusters results in concentrated attacks on the youngest nests on the periphery the cluster, and thus younger nests act as a spatial buffer to old nests in the center of clusters.