Benefits of swarming: mysids in larger swarms save energy

Mysids have previously been shown to consume oxygen at much lower rates whe n in it swarm (cohesive group in which individuals are evenly spaced but no t polarized) than when in uncohesive small groups. Thus the swarm represent s it strategy for conserving energy. In this study different swarm sizes of mysids were forced to perform escape responses by exposing them to jets of ammonium hydroxide, while measuring their oxygen uptake. Swarms of 200 ind ividuals showed no significant difference: in oxygen consumption with or wi thout the ammonium treatment. In contrast, swarms of 100 showed a significa nt increase of around 45% oxygen uptake when exposed to ammonium. In conjun ction with earlier demonstrations of increased feeding success and lower ox ygen uptake when aggregated, this work clearly confirms the energetic benef its of being in a larger social group rather than a smaller one or remainin g solitary.