Disentangling drivers of small mammal diversity in a highly fragmented forest system

Distribution patterns and drivers of nonendemic and endemic glires species in China

Spatial patterns and determinants of species richness in complex geographical regions are important subjects of current biogeography and biodiversity conservation research. Glires are small herbivorous mammal species with limited migratory ability that may serve as an indicator of biodiversity and ecosystems. Herein, we aimed to evaluate how multiple ecological hypotheses could explain the species richness patterns of glires in China. Initially, we constructed a mapping grid cell operating units of 80 × 80 km² which covered China's land mass and mapped the distribution ranges of the 237 glires species that had recorded. The glires taxa were separated into three response variables based on their distribution: (a) all species, (b) nonendemic species, and (c) endemic species. The species richness patterns of the response variables were evaluated using four predictor sets: (a) hydrothermal characteristics, (b) climatic seasonality, (c) habitat heterogeneity, and (d) human factors. We performed regression tree analysis, multiple linear regression analysis, and variation partitioning analyses to determine the effects of predictors on spatial species patterns. The results showed that the distribution pattern of species richness was the highest in the Hengduan Mountains and surrounding areas in southwest China. However, only a few endemic species adapted to high-latitude environments. It was found that there are differences about the determinants between nonendemic and endemic species. Habitat heterogeneity was the most influential determinant for the distribution patterns of nonendemic species richness. Climatic seasonality was the best predictor to determine the richness distribution pattern of endemic species, whereas this was least affected by human factors. Furthermore, it should be noted that hydrothermal characteristics were not strong predictors of richness patterns for all or nonendemic species, which may be due to the fact that there are also more species in some areas with less precipitation or energy. Therefore, glires are likely to persist in areas with characteristics of high habitat heterogeneity and stable climate.

Bridging macroecology and macroevolution in the radiation of sigmodontine rodents

Investigations of phenotypic disparity across geography often ignore macroevolutionary processes. As a corollary, the random null expectations to which disparity is compared and interpreted may be unrealistic. We tackle this issue by representing, in geographical space, distinct processes of phenotypic evolution underlying ecological disparity. Under divergent natural selection, assemblages in a given region should have empirical disparity higher than expected under an evolutionarily oriented null model, whereas the opposite may indicate constraints on phenotypic evolution. We gathered phylogenies, biogeographic distributions, and data on the skull morphology of sigmodontine rodents to discover which regions of the Neotropics were more influenced by divergent, neutral, or constrained phenotypic evolution. We found that regions with higher disparity than expected by the evolutionary-oriented null model, in terms of both size and shape, were concentrated in the Atlantic Forest, suggesting a larger role for divergent natural selection there. Phenotypic disparity in the rest of South America, mainly the Amazon basin, northeastern Brazil, and Southern Andes, was constrained-lower than predicted by the evolutionary model. We also demonstrated equivalence between the disparity produced by randomization-based null models and constrained-evolution null models. Therefore, including evolutionary simulations into the null modeling framework used in ecophylogenetics can strengthen inferences on the processes underlying phenotypic evolution.

Habitat Specificity Modulates the Response of Small Mammals to Habitat Fragmentation, Loss, and Quality in a Neotropical Savanna

Landscape conversion of natural environments into agriculture and pasture are driving a marked biodiversity decline in the tropics. Consequences of fragmentation might depend upon habitat amount in the landscape, while the quality of remnants can also affect some species. These factors have been poorly studied in relation to different spatial scales. Furthermore, the impacts of these human-driven alterations may go beyond species loss, possibly causing a loss of ecosystem function and services. In this study, we investigated how changes in landscape configuration (patch size and isolation), habitat loss (considering a landscape gradient of 10, 25, and 40% of remnant forest cover), and habitat quality (forest structure) affect small mammal abundance, richness, taxonomic/functional diversity, and species composition in fragmented landscapes of semideciduous forests in the Brazilian Cerrado. Analyses were performed separately for habitat generalists and forest specialists. We live-trapped small mammals and measured habitat quality descriptors four times in 36 forest patches over the years 2018 and 2019, encompassing both rainy and dry seasons, with a total capture effort of 45,120 trap-nights. Regression analyses indicated that the effect of landscape configuration was not dependent on the proportion of habitat amount in the landscape to determine small mammal assemblages. However, both patch size and habitat loss impacted different aspects of the assemblages in distinct ways. Smaller patches were mainly linked to an overall increase in small mammal abundance, while the abundance of habitat generalists was also negatively affected by habitat amount. Generalist species richness was determined by the proportion of habitat amount in the landscape. Specialist richness was influenced by patch forest quality only, suggesting that species with more demanding habitat requirements might respond to fragmentation and habitat loss at finer scales. Taxonomic or functional diversity were not influenced by landscape structure or habitat quality. However, patch size and habitat amount in the landscape were the major drivers of change in small mammal species composition in semideciduous forests in the Brazilian savanna.

Identifying structural connectivity priorities in eastern Paraguay's fragmented Atlantic Forest

The Atlantic Forest of eastern Paraguay has experienced extensive recent deforestation. Less than one-third of the region is forested, and the remaining forest largely consists of isolated remnants with potentially disrupted connectivity for forest fauna. We used a graph theory approach to identify those forest remnants that are important in maintaining landscape structural connectivity for mammals in this fragmented forest. We quantified structural connectivity for forest remnants over the period 2000-2019 at three levels: the entire network of Atlantic Forest remnants in eastern Paraguay; at 10 smaller, nested spatial scales (40-10,000 m) encompassing a range of potential mammalian dispersal abilities; and at the level of individual remnants. We used 10 graph theory metrics to assess aspects of network complexity, dispersal-route efficiency, and individual remnant importance in supporting structural connectivity. We identified forest remnants that serve as important structural connectivity roles as stepping stones, hubs, or articulation points and that should be prioritized for connectivity conservation. Structural connectivity was constrained for organisms incapable of travelling at least 9-12 km (farthest distances between nearest-neighboring forest remnants depending on whether smaller remnants were included or not) and was particularly limited for area-sensitive forest-specialist mammals. With the increased forest loss and fragmentation that is occurring, the connectivity of this system will likely be further compromised, but most of the remnants that we identified as playing important roles for structural connectivity were outside of the country's proposed "green corridor," indicating additional areas where conservation action can be directed.

Long-term changes in a small mammal community in a temperate zone meadow subject to seasonal floods and habitat transformation

We tested small mammal (SM) community response to the influence of seasonal floods and habitat transformation in a temporal zone meadow (west Lithuania). The habitat transitioned from a natural flooded meadow in 2008-2012 to a mowed and pastured area in 2020. SM were trapped in late summer to autumn using lines of 25 traps (145 in total), the number of trapping sessions being one or several per year. We tested the hypotheses that: (1) any reaction to the multiple disturbances is species-specific, that is, the relative abundance of SM species and their proportion in the community differs with respect to the flood magnitude and habitat transformation, and (2) at the guild level, disturbances favor habitat generalists, thereby changing the characteristics of SM community. The average relative density of SM was 20.25 individuals per 100 trap nights (range 7.56-40.67), with 4-year-long cyclical changes of density observed. In separate years, we recorded from 4 to 9 species; Shannon's diversity index varied from 0.46 to 2.19, with expressed change of the dominant species. Habitat generalist species were favored, while habitat specialists were disadvantaged. As the meadow transformation progressed, unfavored states in the SM community prevailed, with excessive numbers of granivore and herbivore species present. Our study suggests that multiple disturbances may lead to an increase in relative abundance, species richness, and diversity within the SM assemblages.

Small mammal glucocorticoid concentrations vary with forest fragment size, trap type, and mammal taxa in the Interior Atlantic Forest

Species that live in degraded habitats often show signs of physiological stress. Glucocorticoid hormones (e.g., corticosterone and cortisol) are often assessed as a proxy of the extent of physiological stress an animal has experienced. Our goal was to quantify glucocorticoids in free-ranging small mammals in fragments of Interior Atlantic Forest. We extracted glucocorticoids from fur samples of 106 small mammals (rodent genera Akodon and Oligoryzomys, and marsupial genera Gracilinanus and Marmosa) from six forest fragments (2–1200 ha) in the Reserva Natural Tapytá, Caazapá Department, Paraguay. To our knowledge, this is the first publication of corticosterone and cortisol levels for three of the four sampled genera (Akodon, Oligoryzomys, and Marmosa) in this forest system. We discovered three notable results. First, as predicted, glucocorticoid levels were higher in individuals living withing small forest fragments. Second, animals captured live using restraint trapping methods (Sherman traps) had higher glucocorticoid levels than those animals captured using kill traps (Victor traps), suggesting that hair glucocorticoid measures can reflect acute stress levels in addition to long-term glucocorticoid incorporation. These acute levels are likely due to urinary steroids diffusing into the hair shaft. This finding raises a concern about the use of certain trapping techniques in association with fur hormone analysis. Finally, as expected, we also detected genus-specific differences in glucocorticoid levels, as well as cortisol/corticosterone ratios.