LB 35-291 - Differential response of small mammal species to interannual variability of vegetation biomass in a semiarid ecosystem of Chile

Climate change is becoming a severe threat to biodiversity conservation worldwide, particularly in areas expected to experience relevant changes in precipitation patterns. In arid and semiarid ecosystems, precipitation patterns play a crucial role as the amount and seasonal length of the rainfall period will drive the availability of vegetation biomass during the dry period. Thus, interannual variation in precipitation patterns may generate dramatic changes in yearly available vegetation biomass, which may translate into major shifts of primary consumer populations (PCPs), generating bottom-up control of the trophic web. While some PCPs may show immediate responses to biomass changes, others may have lagged responses, helping to reduce fluctuations in PCPs and, therefore, on the trophic web. We analyzed the relationship between interannual changes in vegetation biomass and the yearly shifts in small mammal populations over 31 years (1989-2019), in a semiarid ecosystem within the Bosque Fray Jorge National Park, Chile. We used the median annual values of NDVI (Landsat satellite images 30m/pixel) as a proxy of yearly patterns of vegetation biomass within the park, and linear models (root-transformed) to test for significant relationships with the yearly data of abundance of seven small mammal species sampled in monthly live-trapping surveys. The analyses were made assuming no time lag, as well as with one- and two-year lags in demographic responses to changes in vegetation biomass. All model residuals were checked for normality and temporal autocorrelation. Our results show a positive relationship (r2=0.236, p=0.006) between changes in same-year vegetation biomass and the total abundance of small mammals within the park. We did not find a lagged response for total small mammal abundance. We also found significant positive same-year responses to vegetation biomass for three species (Abrothrix longipilis [r2=0.127, p=0.049], Abrothrix olivaceus [r2=0.330, p=0.001], Phyllotis darwinii [r2=0.155, p=0.028]). Three species (Thylamys elegans, Octodon degus, and Octodon lunatus) did not show significant relationships with vegetation biomass patterns. Interestingly, A. longipilis also shows a significant positive one-year lagged response to biomass changes (r2=0.138, p=0.043), and Abrocoma bennettii shows a positive response (r2=0.222, p=0.043) only for the one-year lag analysis. These results highlight the differential response that different small mammal species may have to fluctuations in available yearly resources. Furthermore, the one-year lagged response of A. bennettii and A. longipilis may fundamentally stabilize the trophic web by reducing the fluctuation in PCP biomass between wet and dry years.