NICHE-COMPLEMENTARITY OF SOUTH-AMERICAN FOXES - REANALYSIS AND TEST OF A HYPOTHESIS

The niche-complementarity hypothesis states that for coexistence to oc cur, high overlap in one dimension of the niche must be compensated by low overlap in another. Fuentes & Jaksic (1979) noted that two fox sp ecies (Pseudalopex culpaeus and P. griseus) along the western coast of South America displayed this phenomenon, compensating low habitat ove rlap (allopatry) with high dietary overlap, and high habitat overlap ( sympatry) with low dietary overlap and character displacement in body size. Fuentes & Jaksic offered scant quantitative evidence for their p roposed hypothesis of fox coexistence patterns, and the habitat scale used was rather coarse: lowlands versus highlands (Andean Ranges). Wit h the benefit of hindsight and a much better database that included on e site (Auco) where the two foxes are sympatric when they should not b e according to the Fuentes & Jaksic hypothesis, we reanalyze the sourc es used by these authors as well as reports accumulated over the subse quent years. We also report an in-depth study of resource partitioning (food, habitat, and activity time) and coexistence of sympatric foxes at Auco. At this site, the two foxes coexist by partitioning habitat at a fine-scale, maintaining interspersed non-overlapping species-spec ific home ranges in the patchy environment. Through interference, the larger P. culpaeus excludes the smaller P. griseus from high-quality ( abundant prey) habitat patches. Though sympatric they are not syntopic : the two foxes overlap little at the habitat-type scale, have interme diate food overlap and complete overlap in activity time, thus support ing the niche-complementarity hypothesis but at a finer scale. In conc lusion, the Fuentes & Jaksic hypothesis is still valid, but requires c onsideration of two factors previously ignored: the spatial scale at w hich coexistence occurs, and the availability of high-quality (large) prey.