The ecology of spider sociality – A spatial model

The emergence of animal societies offers unsolved problems for both evolutionary and ecological studies. Social spiders are specially well suited to address this problem given their multiple independent origins and distinct geographical distribution. Based on long term research on the spider genus Anelosimus, we developed a spatial model that recreates observed macroecological patterns in the distribution of social and subsocial spiders. We show that parallel gradients of increasing insect size and disturbance (rain, predation) with proximity to the lowland tropical rainforest would explain why social species are concentrated in the lowland wet tropics, but absent from higher elevations and latitudes. The model further shows that disturbance, which disproportionately affects small colonies, not only creates conditions that require group living, but also tempers the dynamics of large social groups. Similarly simple underlying processes, albeit with different players on a somewhat different stage, may explain the diversity of other social systems.

Methods
This dataset was created by a spatial computer model written in python. The dataset contains the main results, further results can be re-generated by the python code, or its minor variants, available as a supplement of our publication.

The modelled grid incorporates parallel gradients of insect size and disturbance in a square lattice grid, one end of which represents a high elevation tropical cloudforest, the other, a lowland tropical rainforest. As we move from the cloudforest to the rainforest, insects get larger and disturbances more severe. Each node can be inhabited by a single colony of either a subsocial or a social spider species, as inspired by those in the genus Anelosimus.