CONICET | Buscador de Institutos y Recursos Humanos

Although ecologists and managers have beenincreasingly preoccupied with the crowding consequences of overabundantherbivores, the potential role of territorial behavior as a self-regulatoryagent among resource-defense polygyny ungulates has seldom been considered. Thecrowding mechanism underlies most regulation models in ungulate demography and relieson the assumption of an equal share of available supplies among individuals. Incontrast, in territorial systems dominant individuals monopolize resources,predicting deviations from the expected demographic outcomes under the crowdingapproach. We used empirical data on a protected guanaco (Lama guanicoe) population to test competing hypotheses aboutcrowding and territorial defense as the mechanism driving density regulation ina resource-defense polygyny ungulate. We assessed density-dependence onrecruitment at different spatial scales and density effects on preferred forageavailability. The guanaco density inside the reserve increased rapidly and thenstabilized during the last third of the study period. The absence of densityeffects on recruitment questions the existence of crowding mechanisms. Guanaconumbers stabilized below the environmental carrying capacity predicted by anequal share of available forage, supporting territorial defence as themechanism shaping population density in the area. Variability in forage cover wasindependent from changes in population density, rejecting crowding effects onfood supplies. These results are consistent with the hypothesis of aself-regulatory mechanism derived from resource defense that may preventovergrazing. Our findings suggest that other factors in addition to foodavailability may determine the demographic carrying capacity under resourcedefense systems, stressing the importance of accounting for behavioral traitswhen addressing management issues.

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