Scale-dependent analysis of an otter-crustacean system in Argentinean Patagonia.

CAASINI, M., FASOLA, L., CHEHÉBAR, C., MACDONALD, D.

NATURWISSENSCHAFTEN

Año: 2009 vol. 96 p. 593 - 599

0028-1042

The Southern river otter or ‘huillin’, Lontraprovocax, is an endangered species endemic of the AndeanPatagonian region of Argentina and Chile. It feeds almostexclusively on the genera of macro-crustacea: Aegla andSammastacus. The aim of this study was to analyse the roleof food availability on the huillin’s distribution using ascale-dependent analysis of crustacean and otter distribu-tions. We compared the distributions of otters and macro-crustaceans along a north–south regional gradient, betweenriver basins of northern Patagonia, in an altitudinal gradientwithin a river basin, and between habitat types within alake. We investigated the distribution of otters by signsurveys along lake shores, river banks and marine coasts,and of crustaceans using surveys in the water, undigestedremains in mink (Mustela vison) scats, presence of externalskeletons at the waterside and through interviews with localpeople. Our results show that there were heterogeneities inthe distributions of macro-crustaceans at four scales andthese were generally reflected in the distributions offreshwater otters. We conclude that the main factor limitingthe distributions of L. provocax in freshwater environmentsis the availability of macro-crustaceans. This paper showshow scale-dependent type analyses of population distribu-tion serves as a method for identifying key environmentalfactors for species for which the use of long-termdemographies is unfeasible