ORIGINS OF ALTRUISM DIVERSITY I: THE DIVERSE ECOLOGICAL ROLES OF ALTRUISTIC STRATEGIES AND THEIR EVOLUTIONARY RESPONSES TO LOCAL COMPETITION
Article first published online: 16 APR 2012
© 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.
Volume 66, Issue 8, pages 2484–2497, August 2012
How to Cite
Van Dyken, J. D. and Wade, M. J. (2012), ORIGINS OF ALTRUISM DIVERSITY I: THE DIVERSE ECOLOGICAL ROLES OF ALTRUISTIC STRATEGIES AND THEIR EVOLUTIONARY RESPONSES TO LOCAL COMPETITION. Evolution, 66: 2484–2497. doi: 10.1111/j.1558-5646.2012.01630.x
- Issue published online: 26 JUL 2012
- Article first published online: 16 APR 2012
- Accepted manuscript online: 21 MAR 2012 09:26PM EST
- Received September 15, 2011 , Accepted February 13, 2012
- Cooperation, local competition, r-selection, K-selection, sunk cost, public goods, provisioning, nest defense
Nature abounds with a rich variety of altruistic strategies, including public resource enhancement, resource provisioning, communal foraging, alarm calling, and nest defense. Yet, despite their vastly different ecological roles, current theory typically treats diverse altruistic traits as being favored under the same general conditions. Here, we introduce greater ecological realism into social evolution theory and find evidence of at least four distinct modes of altruism. Contrary to existing theory, we find that altruistic traits contributing to “resource-enhancement” (e.g., siderophore production, provisioning, agriculture) and “resource-efficiency” (e.g., pack hunting, communication) are most strongly favored when there is strong local competition. These resource-based modes of helping are “K-strategies” that increase a social group's growth yield, and should characterize species with scarce resources and/or high local crowding caused by low mortality, high fecundity, and/or mortality occurring late in the process of resource-acquisition. The opposite conditions, namely weak local competition (abundant resource, low crowding), favor survival (e.g., nest defense) and fecundity (e.g., nurse workers) altruism, which are “r-strategies” that increase a social group's growth rate. We find that survival altruism is uniquely favored by a novel evolutionary force that we call “sunk cost selection.” Sunk cost selection favors helping that prevents resources from being wasted on individuals destined to die before reproduction. Our results contribute to explaining the observed natural diversity of altruistic strategies, reveal the necessary connection between the evolution and the ecology of sociality, and correct the widespread but inaccurate view that local competition uniformly impedes the evolution of altruism.