Winners and Losers: How Woody Encroachment Is Changing the Small Mammal Community Structure in a Neotropical Savanna

Abstract

Years of fire suppression, decreases in herbivores, and global climate change have led to shifts in savannas worldwide. Natural open vegetation such as grasslands and shrublands is increasing in wood density, but the effects for small mammals are not well understood. While most of the mammal studies from the Brazilian Cerrado are concentrated in the core area of this large Neotropical savanna, its southern portions are suffering from biome shifting through woody encroachment. Herein, we surveyed a small mammal community from the southeastern boundary of Cerrado (Santa Bárbara Ecological Station) and evaluated the micro and macro environmental variables shaping community structure in order to investigate how the woody encroachment in the last 15 years may have influenced this assemblage. We recorded 17 species of marsupials and rodents along five distinct habitats in a gradient from grasslands to woodlands. Although richness was not affected by microhabitat variables, total and relative abundance varied according to habitat type and in relation to herbaceous, shrub, and tree density. Rodents such as Calomys tener and Clyomys laticeps were positively affected by increasing herb cover, Cerradomys scotti and Oligoryzomys nigripes by shrub cover, while the marsupial Didelphis albiventris had higher association with increasing tree cover. We detected an increase of 27.4% in vegetation density (EVI) between 2003 and 2018 in our study site, and this woody encroachment negatively affected the abundance of some small mammals. The open-area specialists Cryptonanus chacoensis and C. scotti had a decrease in abundance, while D. albiventris and O. nigripes were favored by woody encroachment. Our data suggest that woody encroachment is shifting community composition: small mammals often associated with grasslands and open savannas are likely to be negatively affected by woody encroachment; while species that rely on tree-covered habitats are likely to benefit from an increasing woody landscape. Therefore, forest-dwellers are gradually replacing open-vegetation inhabitants. Active management of open formations (e.g., with prescribed burning) may be needed to maintain Cerrado biodiversity, especially considering the open-area endemics.

Habitat Heterogeneity and Geographic Location as Major Drivers of Cerrado Small Mammal Diversity Across Multiple Spatial Scales

“…Although less studied, fine-scale habitat variables (e.g., grass cover, canopy cover, number of termite mounds, and soil type) might also be related with Cerrado small mammal richness and abundance patterns at local scale Furtado et al, 2021). Vegetation structure was shown to influence savanna vertebrate diversity, especially by altering the availability of food resources, refuge sites, presence of competitors, and/or predators, as well as their dispersal capacity (Kutt and Woinarski, 2007;Price et al, 2010;Sirami and Monadjem, 2012;Ribeiro et al, 2019).…”

Tropical savanna small mammals respond to loss of cover following disturbance: A global review of field studies

“…Similarly, 118 species of small mammals occur across the Cerrado savanna region of Brazil, with local richness as high as 26, yet N. lasiurus represented >20% of individuals captured in the aggregate of 96 field studies (Mendonça et al, 2018); this, and only a handful of other small-mammal species are the focus of habitat-related studies we found for the current review, meaning that responses to habitat perturbations by most native Cerrado small-mammal species are unknown. Importantly, Furtado et al (2021) fills some of this knowledge gap for seven species of small mammals of the Cerrado. Finally, as we mentioned earlier, we found no studies of habitat effects on small mammals from South Asian TSE at all.…”

“…While not directly examining fire, Furtado et al (2021) found that shrub encroachment resulting from years of fire suppression in the southeastern Cerrado is changing the small-mammal community composition from open-country or grassland specialists (e.g., Necromys lasiurus and Cryptonanus spp.) to closed-canopy forest specialists (e.g., Didelphis albiventris and Oligoryzomys nigripes).…”

Mammals in São Paulo State: diversity, distribution, ecology, and conservation

“…In the absence of controlled fires and herbivory, many open savannas are becoming dominated by trees (transitioning into cerradão), a phenomenon known as the "wood encroachment" (Stevens et al 2017). Specialists in open savannas such as the Pampas Deer, Marsh Deer, and the rodents Clyomys laticeps, Cerradomys scotti, and marsupials such as Cryptonanus chacoensis are negatively affected by increasing wood encroachment (Furtado et al 2021).…”