Predicting polygynous settlement while incorporating varying female competitive strength

The rationale behind the polygyny threshold model is that thebreeding situation quality (BSQ) males have to offer femalesvaries, and that differences in BSQ offset females' costs ofsharing with other females, thus favoring polygynous settling.It predicts that the first chosen territories become polygynousfirst, and that breeding success of secondary and contemporarymonogamous females is similar. This is not generally found.Testing of the polygyny threshold model (PTM) assumes that femalesare equal competitors and distribute ideally free around availablebreeding resources, a condition probably not often met. If sharinga male is costly, and competitors differ in quality, weakerindividuals should experience degrees of competitive exclusion.Setting female competitive abilities proportional to arrivalorder, we use an individual-based interference-competition modelto examine settlement patterns. Shifts in the ratio of variancein interfemale competitiveness to interterritorial differencesin BSQ result in various settlement patterns, with differentpredictions concerning settlement order and fitness returns.We find support for the novel predictions from data on northernlapwing (Vanellus vanellus), starling (Sturnus vulgaris), piedflycatcher (Ficedula hypoleuca), and blue tit (Parus caeruleus).We suggest that before testing polygyny predictions, an evaluationof the settlement sequence should be made, which may help togenerate more accurate predictions. We argue that violationof the "equal female" assumption may explain much of the discrepancybetween predictions and empirical findings in previous testsof the PTM, and that secondary females in general have lowersuccess than do monogamous breeders because they are of lowerquality.