Advantages of social foraging in crab spiders: Groups capture more and larger prey despite the absence of a web

Abstract

Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family.

Stochastic dynamics of social patch foraging decisions

“…regarding available resource or possible threats [1, 2]. In general, the advantages of foraging in groups may include increased vigilance and protection against predators [3–5], faster estimates and minimization of variance in patchy resources or resources of uncertain quality [6, 7], and enhanced ability to capture prey [8]. Since resource distributions can be spatially heterogeneous [9–11], a common modeling assumption takes resources disbursed in patches [12–14] with little availability in between.…”

“…In general, the advantages of foraging in groups may include increased vigilance and protection against predators [3][4][5], faster estimates and minimization of variance in patchy resources or resources of uncertain quality [6,7], and enhanced ability to capture prey [8].…”

Social interactions do not drive territory aggregation in a grassland songbird

“…Insights into the drivers of territory aggregation come from nonterritorial, colonial species forming high‐density aggregations around patchily distributed food resources (e.g., Jourdain and Vongraven ) or structures required for reproduction (Wittenberger and Hunt , Sachs and Rubenstein ). Conspecifics themselves may also act as resources (Stamps ), especially in lekking species (Höglund et al ), those that cluster during locomotion (e.g., Andersson and Wallander ) or thermoregulation (Gilbert et al ), and those that hunt cooperatively (e.g., Dumke et al ) or breed cooperatively (Koenig and Dickinson ). Aggregations can also reduce predation (Hamilton , Valeix et al ).…”