Reproductive allocation decisions in a risky environment: a cross-species comparison — ASN Events

Reproductive allocation decisions in a risky environment: a cross-species comparison (#519)

Gretchen F Wagner 1 , Emeline Mourocq 1 , Michael Griesser 1
  1. University of Zürich, Zürich, Switzerland

Nest predation is an important force in the evolution of reproductive strategies in birds. Yet, it remains unclear to what extent species vary in their response to changes in nest predation risk for a given reproductive event.  Life-history theory proposes that the pace of life, fecundity and parental care strategies are key factors influencing reproductive decisions. We experimentally increased the perceived risk of nest predation prior to egg-laying in eight bird species that comprise a range of life-history and ecological characteristics, allowing us to test which factors play a role in the expression of risk-dependent reproductive flexibility. The perceived increase in the risk of nest predation had little effect on clutch size, egg size and clutch volume across species. However, species with an extended association between parents and offspring substantially increased their within-clutch variation in egg volume. These findings indicate that risk-induced changes in reproductive allocation differ among species. Furthermore, within-clutch variation in egg size is a previously unconsidered response to an increase in nest predation risk. Birds decrease their provisioning rate with an increased risk of nest predation, but predation risk may change rapidly within a breeding event. Thus, species may adopt a brood reduction strategy over uniformly altering their reproductive investment when the risk is high at the time of laying. This response is most evident in species with a prolonged parental investment, as they are afforded more opportunity to even out the condition of their offspring if they successfully evade nest predation.