More than meets the eye: importance of recognizing life history and population structure in monitoring populations

摘要

Most studies investigating demographics focus on the breeding portion of the population for multiple reasons. Recruitment must follow reproduction, and hence, the breeding component of populations is the obvious place to start when assessing population status. Second, it is fairly easy to monitor individuals during their reproductive cycle, particularly those that initiate, maintain and defend territories and/or nests, or are conspicuous for other reasons, for example, mate attraction. However, by focusing attention only on the breeding population, researchers may neglect an important demographic component influencing species or population trajectory (Penteriani, Ferrer & Delgado, 2011). In species where individuals are long-lived and either require multiple years to achieve reproductive maturity or breeding territories and nest sites are limited, sub-adults or nonterritorial ‘floaters’ may reside elsewhere geographically, away from breeding individuals and therefore, undocumented during census work. For example, to reproduce and defend territories is costly (e.g. Hanssen et al., 2005; Harshman & Zera, 2007). Therefore, it may benefit individuals who are not defending territories or maintaining a pair bond to focus on meeting life-history requirements elsewhere or possess movement patterns that may elude researchers when conducting field counts.