Prospecting and philopatry to safe sites produces site-dependent population regulation

Background/Question/Methods

Density dependence in populations can be produced through a simple mechanism of heterogeneity in site (i.e., territory) quality where individuals fill up available sites in rank order of quality (site dependent regulation).  This concept implicitly assumes that individuals are perfectly informed with regard to territory quality.  The less perfect the information the more the site selection resembles random selection and density dependence vanishes.  Therefore, density dependence in populations may be an emergent feature of information use, and it follows that population dynamics, stability, and persistence will be influence by the source(s) and use of information.  However, to date, the population level consequences of private and public information use have not been rigorously examined.

Results/Conclusions

I modeled heterogeneity in territory quality created solely through variation in the risk of nest predation (or general causes of reproductive failure) for scenarios for organims with fast , slow, and intermediate life history strategies selected to represent a tradeoff in terms of annual survivorship and annual fecundity.  Individuals can use their private nest success in year t as a cue to territory quality and return (if surviving) to the same territory in year t+1 (philopatric adults).   In addition, dispersing adults (those that failed in year t) can also use conspecific nest success as a cue to territory quality that they attempt to occupy in year t+1.  Territory fidelity based on private nest success by itself can produce site-dependent regulation even though nest success is a stochastic event and hence reproductive performance is an imperfect cue.  Higher survivorship enhances the effect independent of the population’s long-term growth rate when considering random selection.  In other words, as survivorship declines experience becomes less and less useful and the settlement decisions of individuals approach randomness.  Population persistence and stability in species with lower survivorship requires prospecting on conspecific nest success and biasing settlement to sites where past success was observed.  As prospecting increase (more territories examined) population persistence and abundance increases while the coefficient of variation in abundance through time declines.  My analyses suggest that philopatry can regulate population dynamics (especially in combination with conspecific prospecting) in and of itself or creates a backdrop of biased territory settlement that contributes to these processes.  I further discuss evolutionary and ecological themes related to these analyses.