Distribution and Abundance of Small Mammals along an Elevational Transect in Temperate Rainforests of Chile

Abstract

Assemblages of small mammals in temperate Andean rainforests of southern South America are diverse but poorly known. Herein, we describe an elevational transect through temperate rainforests in Valle de La Picada, Chile, during February and March, 1984. The transect consisted of standardized removal trapping (165 traps set in lines at ca. 7-m intervals and operated for 6 consecutive days) at each of seven elevations: 425 m, 505 m, 620 m, 715 m, 820 m, 920 m, and 1,135 m. A total of 514 small mammals representing two species of marsupials and seven species of sigmodontine rodents was collected. Trap success averaged 7.4% across traps, days, and elevations. Number of captures by individual traps during the sample period was indistinguishable from a Poisson distribution, both throughout the transect and at individual levels, suggesting independence of captures among traps. Captures were biased significantly by trap type, with museum specials securing significantly more Dromiciops australis and all forms of Akodon than Sherman live traps; the same biases were suggested by captures of Irenomys tarsalis and Auliscomys micropus . As expected, total number of individuals taken at each elevation declined throughout the sampling period while the cumulative number of species rose. Number of species, number of individuals, and species diversity varied inversely with elevation. Number of species and species diversity taken each day reached a maximum after 2–4 days of sampling. Captures of Rhyncholestes raphanurus, Akodon sanborni , putative hybrids of A. sanborni and Akodon longipilis , and I. tarsalis were correlated inversely with elevation. Conversely, D. australis, A. longipilis , and A. micropus were taken more commonly at higher elevations, whereas captures of Oryzomys longicaudatus, Akodon olivaceus , and Geoxus valdivianus appeared unrelated to elevation. Systematic sampling procedures are viewed as essential for describing fundamental patterns of abundance and distribution that can be compared with other studies.