Productivity, individual-level and colony-level flexibility, and organization of work as consequences of colony size

Abstract

In social insects, colony-level complexity may emerge from simple individual-level behaviors and interactions. Emergent global properties such as colony size, which can be viewed as a consequence of life history traits, may inf luence individual-level behaviors themselves. The effects of colony size on productivity, body size, behavioral f lexibility, and colony organization are examined here by considering colony size as an independent variable. Large colony size commonly corresponds with complex colony-level performance, small body size, and lower per capita productivity. Analyzing the construction behavior of various wasp societies reveals that complexity of individual behavior is inversely related to colony size. Parallel processing by specialists in large colonies provides f lexible and efficient colony-level functioning. On the other hand, individual behavioral f lexibility of jack-of-all trades workers ensures success of the small and early societies.Evolutionary biology recently has developed new interest in explanations of how autonomous units can cooperate to form more complex systems (1). Parallel-processing systems poised at the boundary between chaos and order are well able to adapt and evolve (2). Parallel processing requires the existence of several agents or units, plus mechanisms that ensure the specialization and organization of these units into a complex efficient system. An intriguing and simple system organized in this way can be found in social insects, where the colony conducts all of its operations concurrently instead of sequentially. Reliability theory posits that redundancy at the subunit level is more efficient than redundancy at the system level (3). In relation to insect colonies, a system of redundant components (labor is divided by task, the separate tasks are concatenated to form a complete sequence) is preferred to several separate systems (wherein each individual performs the entire sequence independently of other individuals

Survival and productivity benefits to social nesting in the sweat bee Megalopta genalis (Hymenoptera: Halictidae)

“…This result is contrary to the trend first noted by Michener (1964) (see discussion in Karsai and Wenzel 1998) that per capita productivity decreases as group size increases (but see Bouwma et al 2005Bouwma et al , 2006. However, some other facultatively social species show no per capita productivity decrease when moving from solitary to social nesting.…”

“…Nest defense and other benefits that increase with group size have often been considered insufficient to favor eusociality because per capita productivity decreases with increasing colony size across many species of social insects (Michener 1964;Wenzel and Pickering 1991;Karsai and Wenzel 1998). However, many facultatively and/or primitively social species show an increase in per capita productivity when moving from solitary to social groups (Schwarz 1994;Tierney et al 1997Tierney et al , 2000Tierney et al , 2002Schwarz et al 1998;Field et al 1999Field et al , 2000Hogendoorn and Zammit 2001;Coelho 2002;Joyce and Schwarz 2006;Thompson and Schwarz 2006), and even in larger-colony species, the negative relationship may not be universal (Bouwma et al 2005(Bouwma et al , 2006.…”

Task Partitioning in a Ponerine Ant

“…A similar phenomenon was observed in the eusocial wasp species Polybia occidentalis (Jeanne, 1991) and Mischocyttarus mastigophorus (O'Donnell, 1998). This points to the role of colony size as an important evolutionary parameter (Karsai & Wenzel, 1998;Bourke, 1999;, the impact of which could be better understood with a threshold model.…”

Why do not all workers work? Colony size and workload during emigrations in the ant Temnothorax albipennis

“…Colony size is often thought to be a major factor in achieving complex collective behaviour (Oster and Wilson 1978;Pacala et al 1996;Karsai and Wenzel 1998;Bourke 1999;Anderson and McShea 2001;Buhl et al 2004;O'Donnell and Bulova 2007). For example, larger colony size is thought to be associated with greater individual specialisation (Karsai and Wenzel 1998;Gautrais et al 2002;Thomas and Elgar 2003), higher rates of information flow and more frequent interactions (Burkhardt 1998;Karsai and Wenzel 1998;Gordon and Mehdiabadi 1999) and higher efficiency at collective behaviours such as task partitioning (Anderson 1999) or exploration (Dornhaus and Franks 2006). These effects may influence individual activity levels, with workers in smaller colonies having to be more flexible (Burkhardt 1998;Karsai and Wenzel 1998) or risk averse (Herbers 1981) than those in larger colonies.…”