progressive saturation of the population could be related to their formation. In this
sense, the appearance of another adult could trigger conflicts that affect reproduction among individuals from the same territory (Bertran et al. 2009). Accordingly,
after fitting territory and year into models to control for the density-dependent decay
in the productivity of the population during the study period, we found that the
formation of trios in some territories caused productivity depression in the whole
population. The decision of some individuals to enter into breeding trios as subordinates also had clear adverse consequences to population demography.
Bearded vultures entered the breeding pool by occupying poor-quality territories
(Carrete et al. 2006b) or by queuing in high-quality territories to wait until they are
available. Therefore, trio formation may be a strategy for intruders to increase their
fitness prospects by mating with a female or by increasing their likelihood of
inheriting a high-quality territory when the dominant male dies. Reproductive
success of previous owners was compromised when territories changed to trios,
suggesting that the third individual was costly. Intruders, however, are not evicted
by owners (Bertran and Margalida 2002b), perhaps because trios arise from
uncommon ecological constraints and thus the energy invested in an unusually
developed agonistic behaviour could be higher than the costs of accepting them
(Clutton-Brock and Parker 1995; Hamilton and Taborsky 2005).
Intraspecific variation in mating systems may be determined by ecological
features of the environment (Heg and van Treuren 1998) or by conflicts of interest
between individuals (Davies and Hartley 1996). The Spanish population of bearded
Fig. 15.2 Differences (mean ± s.e.) in time since territory formation (black dots) and mean
standardised productivity of territories when occupied by breeding pairs (red dots) between
traditional and new territories (modified from Carrete et al. 2006b)
352
A. Margalida
sense, the appearance of another adult could trigger conflicts that affect reproduction among individuals from the same territory (Bertran et al. 2009). Accordingly,
after fitting territory and year into models to control for the density-dependent decay
in the productivity of the population during the study period, we found that the
formation of trios in some territories caused productivity depression in the whole
population. The decision of some individuals to enter into breeding trios as subordinates also had clear adverse consequences to population demography.
Bearded vultures entered the breeding pool by occupying poor-quality territories
(Carrete et al. 2006b) or by queuing in high-quality territories to wait until they are
available. Therefore, trio formation may be a strategy for intruders to increase their
fitness prospects by mating with a female or by increasing their likelihood of
inheriting a high-quality territory when the dominant male dies. Reproductive
success of previous owners was compromised when territories changed to trios,
suggesting that the third individual was costly. Intruders, however, are not evicted
by owners (Bertran and Margalida 2002b), perhaps because trios arise from
uncommon ecological constraints and thus the energy invested in an unusually
developed agonistic behaviour could be higher than the costs of accepting them
(Clutton-Brock and Parker 1995; Hamilton and Taborsky 2005).
Intraspecific variation in mating systems may be determined by ecological
features of the environment (Heg and van Treuren 1998) or by conflicts of interest
between individuals (Davies and Hartley 1996). The Spanish population of bearded
Fig. 15.2 Differences (mean ± s.e.) in time since territory formation (black dots) and mean
standardised productivity of territories when occupied by breeding pairs (red dots) between
traditional and new territories (modified from Carrete et al. 2006b)
352
A. Margalida