The Effects of Habitat Geometry on Territorial Defense Costs: Intruder Pressure in Bounded Habitats

Computer simulation models were used to explore the effect ofhabitat geometry on intruder pressure for territories in differentlocations within a patch of uniformly high quality habitat,for territories in patches of different shapes and sizes, andfor patches surrounded by different types of suboptimal habitats. In models in which the edges of the habitat patch are impermeable(hard-edged), intruders do not leave the central territorialhabitat, H, and intruder pressure is lower for territories onthe edge of H than for more centrally located territories. Averageintruder pressure for any given loop of territories (, for loop = i) is positively relatedto both the proportion of territories on the edge of the patch(ESR) and the average distance moved by intruders. In models in which the edges of H are permeable (soft-edged),intruders are able to move between H and the surrounding habitats,which were of two types: sinks (no intruders generated there)and reserves (a source of intruders). The presence of sinksdramatically reduces both and average intruder pressure over H () as compared to hard-edged habitats, and both and are negatively related to the proportion of territories on theedge of the patch (ESR). Conversely, and are positively related to ESR when the surrounding habitat acts as an intruder-reserve. Data from empirical studies of territorial species agree withmany of the direct and indirect qualitative predictions of thesemodels. The effects of habitat geometry on defense costs maybe important in many territorial species, and should be takeninto account in future studies.     

The Lek System in Uganda Kob Antelope

The tradition with which both male and female Uganda kob returnto permanently located territorial breeding grounds (TG's orleks), along with the dispersion of individuals in relationshipto a home TG and morphological variation between individualsassociated with different TG's, indicates that the total populationof kob in the Toro Game Reserve and its vicinity is subdividedinto relatively closed breeding units. Mathematical analysesof linear body measurements show significant differences inmorphological features between three demes, not only in averagesbut also in the inter-relatedness of body characteristics, suggestingan underlying genetic integrity within demes. Interdemic geneflow through individuals appears to be inconsequential, butthere may be significant gene flow through the formation oftemporary TG's. Altruistic behavior among territorial males may contribute tokinship selection, and the individual kob behavior in responseto predation suggests that altruism may have a bearing on theregulation of predation. The lek system of social organizationmay be significant in maintaining genetic heterogeneity in thekob antelope, which lives in geographically isolated populationsthroughout its range.