Weather, fire, and density drive population dynamics of small mammals in the Brazilian Cerrado

Abstract

Understanding the relative importance of exogenous and endogenous factors in natural population dynamics has been a central question in ecology. However, until recently few studies used long-term data to assess factors driving small mammal abundance in Neotropical savannas. We used a 9-year data set, based on monthly captures, to understand the population dynamics of two scansorial small mammals inhabiting the Brazilian Cerrado: the semelparous gracile mouse opossum (Gracilinanus agilis), and the iteroparous long-tailed climbing mouse (Rhipidomys macrurus), the two most abundant species at Panga Ecological Station (Uberlândia/MG). We tested the impact of two fires that occurred in 2014 and 2017 on the abundance of both populations. Also, we used Royama’s framework to identify the role of the endogenous system (intraspecific competition) and exogenous factors (annual rainfall, days with minimum and maximum temperatures, annual minimum Normalized Difference Vegetation Index [NDVI], and Southern Oscillation Index) in population dynamics. Extensive and severe fires had a lasting, negative impact on the studied populations, probably by reducing the carrying capacity of the environment. Both populations were influenced by negative first-order feedback, indicating density-dependent effects. Moreover, the endogenous system and the annual minimum NDVI operated as vertical effects determining G. agilis dynamics, while the R. macrurus population was governed by the vertical effects of 1-year lagged rainfall. Our results support the contention that small mammal population fluctuations are driven by the interaction between endogenous (density-dependent) and exogenous factors, which in this study were mainly associated with habitat complexity. Despite ecological similarities shared by both species, their response and recovery time to disturbances and environmental variables varied, probably due to their contrasting life histories. Hence, we emphasize the need to consider species life histories to understand the responses of small mammals to extreme events and reinforce the importance of long-term studies that evaluate the combined effects of endogenous and exogenous variables on population dynamics.

POPULATION DYNAMICS OF THE CLIMBING MICE Rhipidomys itoan (COSTA, 2011) IN THE BRAZILIAN ATLANTIC FOREST

“…In the same study area, extreme temperatures also negatively affected small marsupials, with body mass of less than one kilogram (Ferreira et al 2016b). Rhipidomys mastacalis was also affected by temperature in the savanna region, but in an opposite way; a decrease in population growth rate was related to the number of very cold days in the previous year (Rossi & Leiner 2022).…”

“…Small mammals, in general, have their dynamics dominated by a first-order mechanism, as is the case of rodents in dry and temperate regions (Berryman 2001, Merritt et al 2001, Lima et al 2006) and rodent and marsupials from tropical forests (Kajin et al 2008, Zangrandi 2011, Ferreira et al 2016a, Santos 2019). The only study that evaluated the feedback structure of a Rhipidomys population was conducted with Rhipidomys mastacalis for nine years in a tropical savanna ecoregion of Brazil (Rossi & Leiner 2022). Population growth rate was strongly determined by population density in the previous year, also indicating the occurrence of a first-order negative feedback, as in R. itoan.…”

“…Other studies in Brazil have pointed out contrasting results. Direct positive effects of La Niña events were observed in population abundance of Akodon cursor and Necromys lasiurus in the coastal Atlantic Forest (Restinga; Pacheco 2009) and in the Amazonian savanna (Magnusson et al 2010), respectively, while no effect was recorded for R. mastacalis in a Cerrado savanna (Rossi & Leiner 2022).…”

Remotely sensed environmental measurements detect decoupled processes driving population dynamics at contrasting scales

“…Its data products have contributed to a rapid expansion of interdisciplinary research that relies on ecological knowledge and remote sensing data to describe a variety of patterns, including tracking loss of wetland habitat, detecting shifts in forest canopy composition, and monitoring shifts in phenological cycles (Vogelmann et al, 2016 ). Much of this work is forward‐looking, seeking to describe how natural systems evolve as climate change progresses and to construct relevant projections, but historical remote sensing data can also be used to add new dimensions to datasets lacking contemporaneous environmental measurements (e.g., Boult et al, 2018 ; Ndegwa Mundia & Murayama, 2009 ; Rossi & Leiner, 2022 ). Herein, we combine remote sensing and weather modeling data with previously collected demographic data to describe environmental factors influencing various components of population dynamics.…”

Ecology of Tropical Forest Small Mammal Populations: Patterns and Process Revealed by the Longest Long-Term Monitoring Study in Brazil

“…These studies have identified both trophic interactions (food and/or predation) and seasonality as the main drivers of population dynamics of small mammals at higher-latitude temperate forests (Yoccoz et al 2001), deserts (Lima et al 2001), and grasslands (Aars & Ims 2002). Aside from these well-known studies, most studies evaluating small mammal population dynamics in tropical environments to date have been shortterm, which undermine the understanding of population patterns and processes (Cerqueira et al 1993, Barros et al 2015, but see da Rosa et al 2021, Rossi & Leiner 2022.…”