Population dynamics of two sympatric rodents in a variable environment: rainfall, resource availability, and predation

Abstract

Precipitation plays an important role in the dynamics of species found in arid and semiarid environments. However, population fluctuations generally are driven by a combination of multiple factors whose relative contribution may vary through time and among species. We monitored fluctuations of species in three trophic levels for >17 years at a semiarid community in north-central Chile. The region is strongly affected by the El Niño Southern Oscillation, resulting in high variation in rainfall that triggers dramatic changes in food resource availability, with strong effects on upper trophic levels. We focused our analyses on the role played by endogenous and exogenous (climatic) factors on the dynamics of two important rodent species in the community, Octodon degus and Phyllotis darwini. We documented population fluctuations of several orders of magnitude in response to wet and dry episodes of different strength and duration. P. darwini reached similar maximum densities, regardless of the duration of high-rainfall events, whereas O. degus showed additive effects of multiple wet years. Time series diagnostic tools revealed oscillations with a 5-year periodicity in rainfall, which may be the cause of the same periodicity and a weak second-order signal observed in the rodent dynamics. However, the dynamics of both rodent species were dominated by strong first-order processes, suggesting an important role of direct density dependence. Intraspecific competition, expressed as the ratio of rodent density/rainfall (or food resources) explained more than two-thirds of the variation in the population rate of change, whereas less than one-third was explained by lagged rainfall (or food resources). We detected no significant effects of predation. Our results contribute to a growing number of examples of dynamics governed by the combined effect of density dependence and climatic forcing. They also reveal strong bottom-up regulation that may be common in other arid environments.

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

“…nonlinear), suggesting that rainfall immediately enhances rat survival, but this effect rapidly becomes saturated. These results confirm previous studies conducted on tropical continental systems that showed a boost in rodent population dynamics, including individual survival [13], generated by an increase in primary productivity lagging behind rainfall pulses, as resource pulses move through trophic webs [45,46]. However, in the Galapagos correlations between rainfall pulses and rodent abundances were not systematic within the same Spatio-temporal modelling of rats J. C. Russell & L. Ruffino 771 island but depended mostly on habitat characteristics, such as vegetation cover or local climate [47].…”

Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa

“…By contrast to larger-bodied mammals, rodents, particularly smallsized species (i.e., <500 g), are often relatively robust to human disturbance and many species live commensally with humans (33,34). Due to their generally rapid reproductive rates and small home range sizes, populations can fluctuate dramatically over both small spatial and temporal scales, and in response to declines or removals of either rodent predators or rodent competitors, including large herbivores (35)(36)(37). Because both large predators and herbivores face a high risk of decline from human disturbances (6,10), susceptible host regulation may be a strong potential pathway by which wildlife loss can affect human disease risk.…”

Effects of Humidity Variation on the Hantavirus Infection and Hemorrhagic Fever with Renal Syndrome Occurrence in Subtropical China

“…25 Most rodent species responded directly to fluctuations in food availability, and population densities are driven by changes in food resources. 26,27 Vegetation also provides shelter and safety and keeps rodents from predators. Meanwhile, meteorological factors, especially temperature and precipitation, were also closely associated with the transmission of HFRS.…”