Variable interspecific competition under megadrought conditions: rodent population dynamics in semiarid Chile

Abstract

Deciphering how climatic variability modulates the interspecific interactions in natural systems is one of the most interesting and least studied ecological processes. Rodent outbreaks or irruptions in semiarid Chile are associated with rainfall pulses driven by the El Niño Southern Oscillation (ENSO). During the last decade, north‐central Chile has experienced an almost uninterrupted sequence of > 10 dry years, the so‐called megadrought, which had led to a new ecological benchmark in this region. We employ a diagnostic approach to analyze abundance data regarding two rodent species, Phyllotis darwini and Abrothrix olivacea, using a 33 year time series spanning from 1987 to 2019. Our population dynamic models provide evidence of competitive interactions within and between both species. This result is novel because we show that rainfall variability influences the degree of interspecific competition and that it is asymmetric. The diagnostic approach used here offers a way to develop simple population models that are useful for understanding the causes of population fluctuations and for predicting population changes under a climate change scenario.

Seasonal Hair Glucocorticoid Fluctuations in Wild Mice (Phyllotis darwini) within a Semi-Arid Landscape in North-Central Chile

“…This pattern may not have been noticeable in samples from the spring of 2022 (September and October) because HCC reflects cumulative concentrations in the period leading up to sampling [37,74], and the impact of rainfall on resources might not have been as pronounced during that time. During water scarcity periods, rodents likely faced challenges related to limited trophic resources and increased competition, both intraand interspecific [2,49]. Given the favorable conditions following the rainy season [71], corticosterone concentrations could decrease.…”

“…Arid and semi-arid environments present environmental challenges for mammals, which have been exacerbated under the scenario of climate change [1]. These challenges include intense solar radiation, high temperatures, and scarce precipitation, which constrain primary production, thereby affecting the trophic chain and potentially intensifying competition for resources [1][2][3]. Under adverse environmental conditions, such as those mentioned, animals experience an increase in energy demand [4], regulated by the hypothalamic-pituitary-adrenal (HPA) axis, resulting in elevated blood levels of glucocorticoids (GC) [4,5].…”