Influência de fatores endógenos e exógenos na dinâmica populacional de dois pequenos mamíferos em uma área de cerrado denso na Estação Ecológica do Panga (Uberlândia/MG, Brasil)

Abstract

Due to the increasing anthropogenic impacts that cause climate change and alter the frequency and intensity of extreme climatic events, it is crucial to understand the factors that drive natural populations. Population fluctuations are a result of growth rate parameters such as survival and recruitment. Environmental disturbances, such as fires, affect populations through direct and/or indirect effects. In addition to these exogenous variables, endogenous factors such as population density can also affect the regulation of populations. We used a 9-year time series to evaluate the effects of endogenous and exogenous factors on the population dynamics of two small mammals (Gracilinanus agilis and Rhipidomys mastacalis) in a cerrado denso area in Uberlândia/MG. Using the Royama framework, we identify the role of the endogenous system (density) and exogenous factors (rainfall, cold days, warm days, NDVI, and SOI) on the population annual growth rate, checking whether these factors exert vertical (acting on survival and/or reproduction), lateral (modifying environmental carrying capacity) or non-linear (changing the strength of density dependence) effects. We also evaluated the delayed effects of density and exogenous factors (rainfall, habitat quality, cold days, and fire) on species survival and recruitment rates. Two severe and extensive fires that occurred during the studied period allowed us to analyze the impact of these disturbances on the demographic parameters of the populations. The fires indirectly affected the populations through a reduction in carrying capacity, where none of them returned to pre-fire abundance patterns. We detected negative effects of density (endogenous factor) on population growth rates, mainly affecting recruitment of G. agilis males and R. mastacalis males and females, due to the negative effects of increased intraspecific competition at high densities. The demographic parameters of the marsupial G. agilis were primarily affected by its semelparous life-history, however, we found that rainfall also affected this species through vertical effects on habitat cover/quality (measured via NDVI) and increased resource availability, which affected survival and recruitment. In R. mastacalis cold days in the previous year exhibited vertical effects on the growth rate, while habitat quality in the previous year exhibited positive effects on survival and negative effects on recruitment. Severe and extensive fires had strong indirect effects on populations. Despite ecological similarities (habit, diet), the timing of response and acting factors was variable among species, due to distinct life-histories. Thus, we emphasize the importance of considering life-history and endogenous and exogenous factors in the population regulation of small mammals, since the results found here can be found in other species in the Cerrado.