Ecological predictors of spider sociality in the Americas

• Published in: Global ecology and biogeography 2015-10, Vol.24 (10), p.1181-1191
• Main Authors: Guevara, Jennifer, Avilés, Leticia
• Format: Article
• Language: English
• Subjects: Anelosimus; Araneae; biogeographical patterns; distribution modelling; elevational gradient; environmental factors; females; Hypotheses; insect size; insects; latitudinal gradient; linear models; phylogeny; Predation; primary productivity; progeny; Rain; rain forests; rain intensity; risk; seasonality; social behavior; Temperature; tropics; variance; webs
• ISSN: 1466-822X; 1466-8238
• DOI: 10.1111/geb.12342

AIM: To evaluate the relative importance of environmental factors relevant to specific hypotheses that have been proposed to explain the distribution of social and subsocial Anelosimus spiders in the American continent and Ecuador. For social species, we test the seasonality and prey size hypotheses, which posit that species forming long‐lived multifemale colonies require aseasonal conditions and warm and productive environments in which large insects can develop. For subsocial species, we test the rain intensity and predation risk hypotheses, which posit that species whose colonies contain a single female and her offspring cannot occupy areas where strong rains cause frequent damage to their webs and where warm temperatures and high productivity promote greater predation. LOCATION: America, Ecuador. METHODS: Using generalized linear models, hierarchical variance partitioning, Maxent distribution modelling and phylogenetically controlled regressions, we analysed the relative importance of environmental variables that either directly or indirectly relate to these non‐exclusive hypotheses – temperature and precipitation seasonality (seasonality hypothesis), annual temperature and net primary productivity (insect size and predation hypotheses) and rain intensity (rain intensity hypothesis). RESULTS: Temperature seasonality, followed by annual temperature and rain intensity, were the most important predictors of the distribution of spider sociality across America, whereas temperature and rain intensity predominated in the largely aseasonal Ecuador. In general, social species were associated with lower temperature seasonality, warmer temperatures and higher rain intensity than subsocial species. MAIN CONCLUSION: The association of social Anelosimus with warm and wet areas in the tropics is consistent with both the seasonality and prey size hypotheses, i.e. both aseasonal conditions and warm temperatures, which allow large insects to develop, are needed for large social colonies to form. That subsocial Anelosimus drop‐out from tropical areas with warm temperatures and high rain intensity is consistent with the hypotheses that high predation risk and disturbance by strong rains exclude subsocial Anelosimus from the lowland rain forest.