Print PageGlobal climate change is influencing the frequency and intensity of rainfall events in many regions. At a semiarid site in north-central Chile we have monitored small mammal populations since 1989 with a large-scale live-trapping grid complex. Though initially designed to assess the relative roles of competition and predation in community function, selective exclusions of vertebrate predators and/or putative small mammal competitors have yielded relatively small and/or mostly transitory effects on small mammal population dynamics and plant community composition. Instead, the overwhelming influence of abiotic influences at this site (most notably rainfall) has shown shifts in the relative importance of biotic vs. abiotic drivers.
Results/Conclusions
Our study has now spanned 5 El Niño/high rainfall episodes lasting 1-3 years. Typically, resident (“core”) small mammals such as Abrothrix olivaceus, Phyllotis darwini, and Octodon degus experience dramatic fluctuations during and following rainfall pulses. On the other hand, temporary residents (“opportunistic”) such as Oligoryzomys longicaudatus and A. longipilis disappear from the thorn scrub for varying periods of time. All species persist in more mesic nearby habitats near dry stream courses (“aguadas”). Since a 3-year high rainfall event in 2000-2002, mean annual rainfall has increased in this region, mainly due to a lack of prolonged droughts. This appears to reflect fundamental changes in the frequency and intensity of abiotic influences, which may reflect consequences of global climate change. We apply a qualitative model initially developed for ephemeral plants in arid regions, which suggests that long-lived, slow-reproducing small mammal species should increase in relative abundance as rainfall pulses occur in closer temporal proximity. Changes in the small mammal assemblage at our site are consistent with these predictions. O degus, a caviomorph rodent with a slow and delayed reproductive potential, now comprises a more constant proportion of the small mammal biomass in the thorn scrub, there has been reduced variation in species diversity. Thus, increased rainfall, a predicted consequence of global climate change in this region, may be leading to changes in small mammal assemblage structure and composition. Ultimately, this will result in a more stable, less oscillatory assemblage in the thorn scrub. Long-term consequences of changes in rainfall patterns due to El Niño Southern Oscillations (ENSO) with important teleconnections to global-scale phenomena will lead to diverse changes at the community level here.
