干旱区生态环境知识资源中心

Little is known about the biology and ecology of the myrmecophagic species Leprolochus birabeni Mello-Leitao, 1942 (Zodariidae), the only representative of this genus in Argentina. This species is typical of arid environments of the north of Argentina, and their study in the Chaco Seco is relevant, because is a highly disturbed ecoregion and one of the few with dry subtropical forests in the World. The aim of this work is to study the demography of this species, considering its seasonal variation in native environments, and if the livestock grazing and the agriculture, two of the most common anthropogenic activities of the Chaco Seco ecoregion, produce changes in their populations in the province of Salta (Argentina). We consider three type of environments: native (NA); affected by cattle and goats (NP); and affected by agriculture (NC). The latter corresponds to patches of native vegetation in an agricultural matrix. Three sampling sites were selected on each type of environment, where seasonal samplings using pitfall traps were performed during autumn, winter and spring (2006) and summer (2007). We collected 549 spiders of L. birabeni, with the juveniles reaching until the 64.12% of total abundance, followed by males (26.41%) and females (9.47%). At landscape level, spring season showed the highest number of individuals, reaching 44.99% of the total abundance, while autumn reported the lowest percentage (7.83%). The juveniles increase observed during the winter would indicate an adaptation to environmental conditions. The same pattern was observed in NA and NC environments, but not in NP ones. The later environments showed a decrease in the adult abundances across the seasons, while the NC populations showed an increase of male abundances during spring season with a sharp reduction of females and juveniles throughout the year. The abundance of L. birabeni in NA environments was higher (41.06% of total abundance) and the least value was reported in NC environments (24.67%). The two most common anthropogenic activities affecting the Chaco Seco of the province of Salta modify both the seasonal changes as the representation of the different developmental stages and sexes of the native populations of L. birabeni, being the most damaging factor the modification of the native environments by the agriculture.