Sociality BIOL 3100

Why be social? What are the benefits?

1. Improved Foraging Cooperative hunting may be favored by selection if individuals average at least as much food as they would get by hunting alone. Because food is shared by groups, success must greatly increase.

1. Improved Foraging Harris’s Hawk hunt in family groups – larger group sizes are more successful at killing cottontails and jackrabbits and average energy intake for groups of 5-6 is higher on average than in smaller groups.

1I. Decreasing predation risk Alarm calling Dilution Effect Mobbing

III. Conserving heat and water

Metabolic rates of emperor penguins in small groups are reduced by 39% compared to isolated birds and those in larger groups are reduced by another 21% (Gilbert et al. 2008).

IV. Conserving energy by moving together Heart beats and wing beat intensity for pelicans flying solo are much higher than for those flying in formation.

IV. Conserving energy by moving together

Costs to living in groups

I. Increased Competition -Dendropoma maxima, a vermetid snail that lives in coral reefs, secretes a sticky mucous net to trap plankton, then draws the net back in, eating the mucous and the palnkton. - When snails are grouped together, mucous nets overlap and stick together, so end up eating the nets of their neighbors. Thus, in areas of high density, snails must adjust for the presence of neighbors by retracting nets more quickly.

II. Increased risk of disease and parasites

Some strategies to reduce parasite establishment 1)Some primates use toxic secretions from millipedes to clean their fur 2)Bees and ants collect and apply antimicrobial products to their nest material 3)Termites fumigate their nest with volatile antiseptic chemicals and enrich walls with antimicrobial feces 4)In bees, efficiency of antimicrobial defenses increase with degree of sociality 5)Bees, ants and termites remove corpses and create “graveyards” – sometimes exposing corpses to UV sunlight to kill fungal spores

III. Interference with reproduction Extrapair copulations, egg dumping