CERRADO SMALL MAMMALS: abundance and distribution of marsupials, lagomorphs, and rodents in a Neotropical savanna

Climate change should drive mammal defaunation in tropical dry forests

Human-induced climate change has intensified negative impacts on socioeconomic factors, the environment, and biodiversity, including changes in rainfall patterns and an increase in global average temperatures. Drylands are particularly at risk, with projections suggesting they will become hotter, drier, and less suitable for a significant portion of their species, potentially leading to mammal defaunation. We use ecological niche modelling and community ecology biodiversity metrics to examine potential geographical range shifts of non-volant mammal species in the largest Neotropical dryland, the Caatinga, and evaluate impacts of climate change on mammal assemblages. According to projections, 85% of the mammal species will lose suitable habitats, with one quarter of species projected to completely lose suitable habitats by 2060. This will result in a decrease in species richness for more than 90% of assemblages and an increase in compositional similarity to nearby assemblages (i.e., reduction in spatial beta diversity) for 70% of the assemblages. Small-sized mammals will be the most impacted and lose most of their suitable habitats, especially in highlands. The scenario is even worse in the eastern half of Caatinga where habitat destruction already prevails, compounding the threats faced by species there. While species-specific responses can vary with respect to dispersal, behavior, and energy requirements, our findings indicate that climate change can drive mammal assemblages to biotic homogenization and species loss, with drastic changes in assemblage trophic structure. For successful long-term socioenvironmental policy and conservation planning, it is critical that findings from biodiversity forecasts are considered.

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

Small-mammal faunas of tropical savannas consist of endemic assemblages of murid rodents, small marsupials, and insectivores on four continents. Small mammals in tropical savannas are understudied compared to other tropical habitats and other taxonomic groups (e.g., Afrotropical megafauna or Neotropical rainforest mammals). Their importance as prey, ecosystem engineers, disease reservoirs, and declining members of endemic biodiversity in tropical savannas compels us to understand the factors that regulate their abundance and diversity. We reviewed field studies published in the last 35 years that examined, mostly experimentally, the effects of varying three primary endogenous disturbances in tropical savanna ecosystems—fire, large mammalian herbivory (LMH), and drought—on abundance and diversity of non-volant small mammals. These disturbances are most likely to affect habitat structure (cover or concealment), food availability, or both, for ground-dwelling small mammalian herbivores, omnivores, and insectivores. Of 63 studies (included in 55 published papers) meeting these criteria from the Afrotropics, Neotropics, and northern Australia (none was found from southern Asia), 29 studies concluded that small mammals responded (mostly negatively) to a loss of cover (mostly from LMH and fire); four found evidence of increased predation on small mammals in lower-cover treatments (e.g., grazed or burned). Eighteen studies concluded a combination of food- and cover-limitation explained small-mammal responses to endogenous disturbances. Only two studies concluded small-mammal declines in response to habitat-altering disturbance were caused by food limitation and not related to cover reduction. Evidence to date indicates that abundance and richness of small savanna mammals, in general (with important exceptions), is enhanced by vegetative cover (especially tall grass, but sometimes shrub cover) as refugia for these prey species amid a “landscape of fear,” particularly for diurnal, non-cursorial, and non-fossorial species. These species have been called “decreasers” in response to cover reduction, whereas a minority of small-mammal species have been shown to be “increasers” or disturbance-tolerant. Complex relationships between endogenous disturbances and small-mammal food resources are important secondary factors, but only six studies manipulated or measured food resources simultaneous to habitat manipulations. While more such studies are needed, designing effective ones for cryptic consumer communities of omnivorous dietary opportunists is a significant challenge.

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

The Cerrado biome is one of the global hotspots of biodiversity, and non-volant small mammals represent a significant portion of Cerrado species richness (45%) and endemism (86%). Nevertheless, we still lack a comprehensive picture of small mammal diversity patterns and drivers throughout the Cerrado. Here we surveyed small mammals across 45 sites to address species richness, abundance, and composition patterns and their drivers within and across sites, habitats, and localities at the world’s most diverse tropical savanna. As hypothesized, we found: (1) rich assemblages (12–21 species) characterized by few abundant and several intermediate-level and rare species; dominated by oryzomyine and akodontine cricetid rodents, and thylamyine and marmosine within marsupials, each tribe showing distinct habitat requirements; (2) strong habitat selectivity, with assemblages composed of forest dwellers, savanna specialists, and grassland inhabitants; and (3) similar species richness (α-diversity) but high species turnover (β-diversity) across sites, habitats, and localities, suggesting that horizontal stratification (within localities) and geographic location (across the Cerrado) are key drivers of small mammal diversity in tropical savannas. Thus, habitat heterogeneity and geographic location can be inferred as the main factors shaping species richness, abundance, and composition across the analyzed multiple spatial scales. Moreover, we found that geographical distance as well as the distance to neighbor biomes better explained species turnover, indicating landscape history and phylogenetic constraints as the major determinants of Cerrado small mammal diversity, as also evidenced for plants and other animal groups. These data highlight the need to preserve the mosaic of habitats across the different regions of the biome to conserve most of the Cerrado biodiversity.

Biogeographic and fragmentation-related research biases on antbirds and non-flying small mammals in Brazil

Major biogeographic and taxonomic biases are recurrent in biological surveys, including fragmentation studies. Detecting biases and subsequent gaps is crucial to steer future research and suitable conservation policies. We evaluated biogeographic and fragmentation-related biases on antbirds and non-flying small mammals in Brazil, two oversampled and vulnerable taxonomic groups, by surveying papers in the Scielo and the Web of Science. We found 566 articles published from 1945 to 2018, including 55 and 43 fragmentation studies for antbirds and small mammals, respectively. Considering the species richness for each group across the Brazilian biomes, the number of publications for small mammals tended to disproportionately increase while increasing richness. The Atlantic Forest, the most degraded and densely populated biome, contained the highest number of publications. However, the Amazon included a disproportionately high number of papers considering its low population density. Conversely, non-forest biomes such as the Caatinga, Pampa and Pantanal were mostly overlooked. Our results show that research effort for small mammals and antbirds in Brazil is biogeographically biased. We call future research to consider more studies across non-forest biomes and vast unexplored areas within forest biomes to overcome major knowledge gaps on diversity, distribution and ecology of antbirds and small mammals in Brazil.

Niche partitioning in small mammals: interspecific and biome-level analyses using stable isotopes

Small mammal assemblages from South America provide a unique opportunity to measure coexistence and niche partitioning between marsupials and placentals. We tested how these two major clades partition environmental resources by comparing stable isotopic ratios of similar sized Didelphidae and Sigmodontinae in four Brazilian biomes: Pampas grassland, Pantanal wetland, Cerrado woodland savanna, and Atlantic Forest. Generally, didelphid isotopic niche follows a scaling law, because we found an association between δ15N enrichment and body mass. Sigmodontines that primarily partition the environment via forest strata showed a greater intake of C4 or/and crassulacean acid metabolism (CAM) plants than didelphids, as reflected by their wider trophic niche. Values of δ13C were highest in savannas and grasslands (Cerrado and Pampas biomes), and values of δ15N were highest in the Atlantic Forest (in sigmodontines) and Pampas (in didelphids). While assessing patterns between the two major Brazilian biomes (Atlantic Forest and Cerrado), we found evidence of a broader trophic niche for both clades in the Cerrado. In the Atlantic Forest, niche occupation by Didelphidae was completely enclosed within the Sigmodontinae trophic niche. Both clades showed less overlap in the Cerrado, a less productive environment. Our results highlight the importance of a comparative framework and the use of stable isotopes for testing ecological questions related to how small mammalian communities partition their niche.

Association between predator species richness and human hantavirus infection emergence in Brazil

Hantavirus infection is a rodent-borne disease (RBD) transmitted by urine or feces (as the natural reservoirs) with an annual estimated worldwide incidence of ~150,000 cases. Previous ecological studies suggested that higher species richness of rodents could decrease the risk of RBDs in humans, because the regulatory pressure of predators could reduce contact among rodents, and between humans and rodents. Using surveillance data, we investigated the association of predator species richness with hantavirus infection emergence in 5562 Brazilian inland municipalities between 2007 and 2017. Multivariable logistic regression models were used for the analyses. Diurnal and non-diurnal predator species were independent explanatory variables in the models. Rodent species richness and demographic, socioeconomic, and environmental factors were used as covariates. During the study period, 1084 cases were reported in 429 municipalities. The results showed a reverse-U-shaped association between diurnal predator species richness and hantavirus infection emergence (odds ratio [OR] 0.463, 0.688, and 0.553 for the first [lowest], third, and fourth [highest] quartiles, respectively, using the second quartile as a reference), while higher non-diurnal predator species richness tended to be associated with higher emergence risk (OR 0.134, 1.065, and 2.708 for the first, third, and fourth quartiles, respectively). The difference in these associations illustrates the complexity of the effects of predator species richness on human RBDs, which require further investigation in follow-up studies. The results showed a close link between environmental factors and public health, emphasizing that the One Health concept should be employed to understand the dynamics of RBDs.

A new species of Akodon Meyen, 1833 (Rodentia: Cricetidae: Sigmodontinae) endemic from the Brazilian Cerrado

Akodon is the second most diverse genus of sigmodontine rodents, comprising 40 extant species. Widely distributed through different environments of South America, the genus ranges from forested to open-vegetation areas, from semiarid to mesic regions, and from Andean altitudes to the lowlands of eastern Brazil. In Brazil, most species are from the Atlantic Forest, inhabiting lowland and montane habitats, with a few taxa also present in areas transitional with the Cerrado and Pantanal. Based on an integrative approach of genetics (cytogenetic and molecular data) and morphology (qualitative and quantitative external and craniodental data), we present in this contribution the hypothesis of a new species of Akodon based on specimens collected in the southwestern limit of the Cerrado domain, in the seasonally dry forests of the Serra da Bodoquena, Mato Grosso do Sul, Brazil. The new species was recovered as a distinct lineage sister to Akodon philipmyersi, a poorly known species from the Northern Campos grasslands of Misiones Province, Argentina, and can be distinguished from its congeners by its karyotype (2n = 40, FN = 40), morphology (morphometric, pelage, and skull characters), as well as by its degree of genetic divergence (above 7.5% in Cytb sequences). This new species is endemic to the Cerrado, one of the world’s biodiversity hotspots, and to Serra da Bodoquena, one of the top priority areas for conservation in Brazil. Moreover, the new species increases the number of lineages of Akodon in Brazil, emphasizing the richness and endemism currently found in the Cerrado domain, and the importance of the open formations to the diversification of Neotropical taxa.

Partitioning beta diversity to unravel mechanisms underlying the distributions of nonvolant small mammls in Brazil’s Cerrado

Species distributions and the mechanisms that produce patterns in the occupation space are recurrent themes in community ecology. Here, we examine beta diversity among assemblages of small mammals in the Cerrado domain of Brazil to partition the effects of turnover and nestedness on species distributions. Our objective was to evaluate whether balanced spatial variation in abundance (β bal) and abundance gradients (β gra) are congruent within and among habitats and localities of the Brazilian Cerrado. In addition, we wanted to understand whether ecological mechanisms, such as dispersal limitation, habitat filtering, and species sorting, drive the distribution patterns of the Cerrado small mammals. We analyzed the occurrence and abundances of small mammals from 16 localities widely distributed across the Cerrado biome, and grouped our data with respect to two distinct spatial scales. Baselga’s Bray–Curtis index of dissimilarity and its respective partitions, i.e., balanced variation in abundance (β bal) and abundance gradients (β gra), were estimated between sampling units at the two spatial scales. Thus, we used exponential models to search for distance decay in species similarity between pairs of localities and between similar habitats. Our results show that differences between small mammal assemblages in the Cerrado are driven mainly by species replacement rather than independent gain or loss of species, both at small and large scales. The spatial turnover patterns of small mammals in the Cerrado biome are determined by a combination of large scale (biogeographic, spatial) and local mechanisms (low dispersal and habitat specificity). However, processes occurring at small scales seem to be more important in species sorting than processes occurring at large scales. The spatial configuration of the landscape and the extent and quality of habitats strongly influence the rate of species turnover in Cerrado. Thus, protecting the different types of habitats should be of prime importance to conserving the diversity of Cerrado small mammals.

Spatiotemporal Dynamics of Hantavirus Cardiopulmonary Syndrome Transmission Risk in Brazil

BACKGROUND

Hantavirus disease in humans is rare but frequently lethal in the Neotropics. Several abundant and widely distributed Sigmodontinae rodents are the primary hosts of Orthohantavirus and, in combination with other factors, these rodents can shape hantavirus disease. Here, we assessed the influence of host diversity, climate, social vulnerability and land use change on the risk of hantavirus disease in Brazil over 24 years.

METHODS

Landscape variables (native forest, forestry, sugarcane, maize and pasture), climate (temperature and precipitation), and host biodiversity (derived through niche models) were used in spatiotemporal models, using the 5570 Brazilian municipalities as units of analysis.

RESULTS

Amounts of native forest and sugarcane, combined with temperature, were the most important factors influencing the increase of disease risk. Population at risk (rural workers) and rodent host diversity also had a positive effect on disease risk.

CONCLUSIONS

Land use change-especially the conversion of native areas to sugarcane fields-can have a significant impact on hantavirus disease risk, likely by promoting the interaction between the people and the infected rodents. Our results demonstrate the importance of understanding the interactions between landscape change, rodent diversity, and hantavirus disease incidence, and suggest that land use policy should consider disease risk. Meanwhile, our risk map can be used to help allocate preventive measures to avoid disease.