Cooperative capture of large prey solves scaling challenge faced by spider societies

Abstract

A decrease in the surface area per unit volume is a well known constraint setting limits to the size of organisms at both the cellular and whole-organismal levels. Similar constraints may apply to social groups as they grow in size. The communal three-dimensional webs that social spiders build function ecologically as single units that intercept prey through their surface and should thus be subject to this constraint. Accordingly, we show that web prey capture area per spider, and thus number of insects captured per capita, decreases with colony size in a neotropical social spider. Prey biomass intake per capita, however, peaks at intermediate colony sizes because the spiders forage cooperatively and larger colonies capture increasingly large insects. A peaked prey biomass intake function would explain not only why these spiders live in groups and cooperate but also why they disperse only at large colony sizes, thus addressing both sociality and colony size range in this social spider. These findings may also explain the conspicuous absence of social spiders from higher latitudes and higher elevations, areas that we have previously shown to harbor considerably fewer insects of the largest size classes than the lowland tropical rainforests where social spiders thrive. Our findings thus illustrate the relevance of scaling laws to the size and functioning of levels of organization above the individual.Anelosimus ͉ cooperation ͉ group foraging ͉ sociality ͉ allometry

Caught in the web: Spider web architecture affects prey specialization and spider–prey stoichiometric relationships

“…Future work should include these (e.g., web architecture, size, orientation, location/elevation above ground, and silk properties) and other spider specific traits (e.g., venom properties and metabolic rates) that could affect the degree of specialization of spider–prey interactions. Similarly, social lifestyle and the construction of communal three‐dimensional webs by social spiders influence the insects captured with both sociality and colony size playing an important role in spider–prey interactions (Yip, Powers, & Avilés, 2008). In this study, half of the sheet‐tangle spiders had a social lifestyle while the other half were solitary spiders, and this could have increased variation in the prey types captured by spiders in this group.…”

Differences in group size and the extent of individual participation in group hunting may contribute to differential prey-size use among social spiders

“…We also found that the two more social species, A. jabaquara and A. dubiosus, do not passively filter aerial prey, but instead exhibit increased colony member participation for particular sizes of prey, perhaps to better exploit the most appropriate resources for their colony sizes. Yip et al [7] found that growing spider colonies face a scaling predicament as the threedimensional volume of the refuge area increases more quickly than the two-dimensional surface of the prey-capture web, resulting in less capture area per individual. The spiders make up for the fewer insects caught per capita by capturing increasingly large ones as colony size increases [7].…”

“…Yip et al [7] found that growing spider colonies face a scaling predicament as the threedimensional volume of the refuge area increases more quickly than the two-dimensional surface of the prey-capture web, resulting in less capture area per individual. The spiders make up for the fewer insects caught per capita by capturing increasingly large ones as colony size increases [7]. Thus, species that form large colonies are only found in lowland tropical and subtropical areas, where there is a much greater abundance of large insects than at higher elevations or latitudes [8,9].…”

Evolution of optimal Hill coefficients in nonlinear public goods games

“…It is interesting that sigmoid inputoutput functions are not limited to interactions between cells and molecules [e.g. : Chuang et al 2010, Cornforth et al 2012, Karey & Sirbasku 1988Jourdan et al 1995, Archetti et al 2015], but have been described for behavioural interactions in animal societies, where the benefit of social interactions in a group are often non-linear (in some cases sigmoid) functions of the number of cooperative members [Rabenold 1984, Bednarz 1988, Packer et al 1990, Stander 1991, Creel 1997, Yip et al 2008]. While our argument was essentially about enzyme kinetics, and therefore we have assume that the individual players are individual cells and the population is a population !…”