Longer-term responses of a floodplain-dwelling marsupial to experimental manipulation of fallen timber loads

Abstract

Fallen timber is an important component of many aquatic and terrestrial ecosystems around much of the world. Its distribution and abundance has been extensively altered, especially over the past 200 years. While correlative evidence suggests that many species require fallen timber for them to occupy locations, there are few precisely controlled field experiments that show conclusively how species respond to variation in loads. We manipulated wood loads (ranging from 0 to 80 Mg ha−1) and monitored the response over 6 years of a species of marsupial, the yellow-footed antechinus Antechinus flavipes. The antechinus appeared to prefer locations having fallen-timber loads ⩾20 Mg ha−1. Antechinuses avoided bare areas (i.e. 0 Mg ha−1) and areas having finer forms of woody material. Changes in densities of the antechinus in excess of those occurring in the control plots were clear after 2 years following manipulation of loads, and were even more pronounced after almost 6 years. Therefore, we are confident that higher loads are favoured by the antechinuses. There was no evidence of breeding success by females in sites with ⩽20 Mg ha−1, and that the highest, consistent breeding activity was achieved at sites with the greatest fallen-timber loads (80 Mg ha−1). Our results, which experimentally were designed to address responses to fallen-timber loads, were complicated by perturbations caused by managed flooding episodes of the experimental area. Flooding appears to lead to population booms of the antechinus, most probably related to irruptions of prey species such as carabid beetles and wolf spiders, which are large-bodied and are prey for the antechinus. Nevertheless, we show that there are differences in densities in different wood-load treatments even against a background of boom-and-bust dynamics associated with flooding.