Home Range Patterns

Another important factor in determining social organization in solitary primates is the extent of home range overlap with members of the same and the opposite sex (Müller and Thalmann, 2000). Field studies of aye-aye home ranges have provided insights into Daubentonia's social system and how it compares with that of other lemurs. Overviews of nocturnal primate sociality demonstrate that patterns of home range overlap vary greatly both within and between the sexes in a given species (Kappeler and van Schaik, 2002; Müller and Thalmann, 2000). Preliminary data from a 6-month study on a river island near Mananara in northeastern Madagascar show three distribution patterns in male home range size (Lhota et al., 2004). Sterling's (1993b) study of radio-collared aye-ayes on Nosy Mangabe showed male home ranges to have an area of 120-215 ha, which was three to six times the size of females' home ranges (30-40 ha ). Male home ranges often overlapped with each other and with female home ranges, whereas females seemed to maintain exclusive home ranges that did not overlap with each other at all (Figure 10). More research is needed, however, to determine whether female home ranges are always fully isolated from one another.

Male and female home range sizes differ primarily because males travel farther during nightly forays than do females. Males on Nosy Mangabe periodically went

Figure 10. Home range overlap of five Daubentonia study animals on Nosy Mangabe, 1989-1991. Females = solid line, dashed line. Males = dotted line, dot/dash line, dash/triangle line (Sterling, 1993a).

on extended forays into outlying areas, often covering between 2.2 and 4.4 km per night on successive nights, sometimes without feeding much on the longer trips. Females generally traveled less than half as far as males did. Nevertheless, female aye-ayes have much larger home ranges than diurnal lemurs of similar body size in the same habitat (Sterling, 1993b).

Several factors may be responsible, singly or jointly, for the distribution patterns of male and female aye-ayes and the differences in foraging travel distances. Resource distribution and defensibility, predation pressure, and the intensity and nature of interspecific competition all may influence dispersion patterns among mammals (Emlen and Oring, 1977; Kappeler, 1997a; Sterling, 1993b; Terborgh and Janson, 1986). These factors influence males and females differently, resulting in sex-specific social and reproductive behavior. Some researchers (CharlesDominique, 1993; Müller and Thalmann, 2000; Wrangham, 1980) argue that female behavior is influenced more directly by ecological pressures than male behavior because food availability is a major limiting factor on female fitness. Male behavior focuses more on finding mates and achieving mating success, as predicted from sexual selection theory.

The observed distribution patterns of male and female aye-ayes are consistent with the models described above. Females had ranges situated across similar elevation gradients, from 0 to 250 m, possibly in an effort to encompass a variety of both low- and high-elevation food types in their home ranges. Male aye-aye ranges may have exceeded in size and overlapped those of many females because males have greater nutritional requirements than females. However, if Daubentonia females can obtain adequate food in 30-40 ha, then males, which are of similar size, should not need 120-215 ha in which to gather food resources.

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