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

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.

Large-scale spatial patterns of small-mammal communities in the Mediterranean region revealed by Barn owl diet

Due to mainly opportunistic hunting behaviour of Barn owl can be its diet composition used for assessing local structure of small-mammal community. We evaluated the structure of small-mammal communities in the Mediterranean region by analysing Barn owl diet using own pellets and literature data (85 localities comprising 182,343 prey individuals). Contrary to widely accepted macroecological theory, we found a latitudinal increase of small-mammal alpha diversity, a less distinct west–east increase and lower diversity on islands. The mean prey weight decreased with increasing latitude, while on islands it decreased with increasing island area. The mean prey weight on islands was further negatively affected by mean land modification by human and positively affected by its range. The diet diversity on islands was not affected either by island area or its distance from the mainland. Its composition largely conformed to the main pattern pronounced over whole the region: an unexpected homogeneity of small-mammal community structure. Despite high beta diversity and large between-sample variation in species composition, Crocidura (+ Suncus etruscus) and murids (Apodemus, Mus, Rattus, in marginal regions partly replaced by gerbillids, Meriones or Microtus) composed more than 90% of owl prey in 92% of samples. Peak abundances of these widespread species are associated with a dynamic mosaic of dense patches of sparse herb vegetation and evergreen sclerophyllous shrublands interspersing areas of human activity, the dominant habitat of the inner Mediterranean and richest food resource for foraging Barn owls. The respective small-mammal species can be looked upon as invasive elements accompanying large scale human colonization of the region since the Neolithic and replacing original island biota. Our study documented that desertification of the Mediterranean played an important role in shaping inverse latitudinal gradient in diversity of small-mammals that contradicts to widely accepted mecroecological theory.

Effects of land use, habitat characteristics, and small mammal community composition on Leptospira prevalence in northeast Madagascar

Human activities can increase or decrease risks of acquiring a zoonotic disease, notably by affecting the composition and abundance of hosts. This study investigated the links between land use and infectious disease risk in northeast Madagascar, where human subsistence activities and population growth are encroaching on native habitats and the associated biota. We collected new data on pathogenic Leptospira, which are bacteria maintained in small mammal reservoirs. Transmission can occur through close contact, but most frequently through indirect contact with water contaminated by the urine of infected hosts. The probability of infection and prevalence was compared across a gradient of natural moist evergreen forest, nearby forest fragments, flooded rice and other types of agricultural fields, and in homes in a rural village. Using these data, we tested specific hypotheses for how land use alters ecological communities and influences disease transmission. The relative abundance and proportion of exotic species was highest in the anthropogenic habitats, while the relative abundance of native species was highest in the forested habitats. Prevalence of Leptospira was significantly higher in introduced compared to endemic species. Lastly, the probability of infection with Leptospira was highest in introduced small mammal species, and lower in forest fragments compared to other habitat types. Our results highlight how human land use affects the small mammal community composition and in turn disease dynamics. Introduced species likely transmit Leptospira to native species where they co-occur, and may displace the Leptospira species naturally occurring in Madagascar. The frequent spatial overlap of people and introduced species likely also has consequences for public health.

Small terrestrial mammal distributions in Simien Mountains National Park, Ethiopia: a reassessment after 88 years

Despite the presence of mostly endemic species, the most comprehensive data set on the distribution and ecology of small mammals inhabiting Simien Mountains National Park (SMNP) dated from 1927. The study we carried out and report here provides a unique opportunity to assess the possible role of climate change over the last 88 years on the elevational distribution of mammals in the Ethiopian highlands. Between September and November 2015, three of us (EWC, WTS, YM) collected nonvolant small mammals at four sites (2,900, 3,250, 3,600, and 4,000 m a.s.l.) along the western slope of the Simien Mountains using standardized sampling. Over a 4-week period we recorded 13 species, comprising 11 species of rodents and two of shrews, all endemic to the Ethiopian Plateau. We found the greatest species richness at mid-elevations (3,250 m), consistent with a general pattern found on many other mountains worldwide, but less so in Africa. We compared our species distribution results to the 1927 data set and found upward elevational shifts in species’ ranges, highlighting the role and influence of climate change on the small mammal community. SMNP represents an exceptionally valuable core area of endemism and the best protected natural habitat in northern Ethiopia.

Low-intensity monitoring of small-mammal habitat associations and species interactions in an urban forest-preserve network

ContextAnthropogenic landscape modification and fragmentation result in loss of species and can alter ecosystem function. Assessment of the ecological value of urban reserve networks requires baseline and continued monitoring. However, depending on the desired indicators and parameters, effective monitoring can involve extensive sampling that is often financially or logistically infeasible. AimsWe employed a low-intensity, mixed-detector survey design to monitor the small-mammal community across a network of 53 fragmented forest preserves (225 sites) in a highly urbanised landscape in the Chicago metropolitan area from August to October, 2009–2012. MethodsWe used a sequential process to fit single-season occupancy and pairwise co-occurrence models for six common small mammal species to evaluate habitat associations and interspecific interactions. Key resultsShrew species and meadow voles occurred more often in open canopy-associated habitats, whereas occupancy was greater for eastern chipmunks, grey squirrels and white-footed mice in closed-canopy habitats. Habitat associations were complicated by negative pairwise interactions, resulting in reduced occurrence of meadow voles when predatory short-tailed shrews were present and lower occupancy rates of white-footed mouse when chipmunk competitors where present. White-footed mice co-occurred with short-tailed shrews, but detection of white-footed mice was lower when either eastern chipmunks or short-tailed shrews were present, suggesting that densities of these species could be inversely related. ConclusionsWe found evidence for both habitat segregation and interspecific interactions among small mammal species, by using low-intensity sampling across the reserve network. Thus, our sampling and analysis approach allowed for adequate assessment of the habitat associations and species interactions within a small-mammal community. ImplicationsOur findings demonstrated the utility of this monitoring strategy and community as bioindicators for urban-reserve networks. The approach described holds promise for efficient monitoring of reserve networks in fragmented landscapes, critical as human population densities and urbanisation increase, and we discuss how adaptive sampling methods could be incorporated to further benefit conservation efforts.