Résumé
Animals may anticipate and try to avoid, at some costs, physical
encounters with other competitors. This may ultimately impact their
foraging distribution and intake rates. Such cryptic interference
competition is difficult to measure in the field, and extremely little is
known at the interspecific level. We tested the hypothesis that smaller
species avoid larger ones because of potential costs of interference
competition and hence expected them to segregate from larger competitors
at the scale of a resource patch. We assessed fine-scale spatial
segregation patterns between three African herbivore species (zebra Equus
quagga, kudu Tragelaphus strepsiceros and giraffe Giraffa camelopardalis)
and a megaherbivore, the African elephant Loxodonta africana, at the scale
of water resource patches in the semi-arid ecosystem of Hwange National
Park, Zimbabwe. Nine waterholes were monitored every two weeks during the
dry season of a drought year, and observational scans of the spatial
distribution of all herbivores were performed every 15 min. We developed a
methodological approach to analyse such fine-scale spatial data. Elephants
increasingly used waterholes as the dry season progressed, as did the
probability of co-occurrence and agonistic interaction with elephants for
the three study species. All three species segregated from elephants at
the beginning of the dry season, suggesting a spatial avoidance of
elephants and the existence of costs of being close to them. However,
contrarily to our expectations, herbivores did not segregate from
elephants the rest of the dry season but tended to increasingly aggregate
with elephants as the dry season progressed. We discuss these surprising
results and the existence of a trade-off between avoidance of
interspecific interference competition and other potential factors such as
access to quality water, which may have relative associated costs that
change with the time of the year.