Microhabitat of small mammals at ground and understorey levels in a deciduous, southern Atlantic forest

Is resource partitioning between two sympatric species of Gracilinanus (Didelphimorphia: Didelphidae) related to trophic and spatial niches?

Small mammal species may occur in sympatry, and it is relevant to investigate the mechanisms that lead to coexistence of the closely related species. Despite this, studies evaluating the coexistence of closely related Neotropical marsupials are insipient. The aim of this study was to analyse the mechanisms of resource partitioning between the sympatric species of mouse opossums Gracilinanus agilis and G. microtarsus (Didelphidae), evaluating their trophic and spatial niche. We hypothesized that G. agilis and G. microtarsus differ in at least one niche dimension (space use or food preferences) as a mechanism of coexistence. In the study we analysed trophic niche by evaluating the frequency of occurrence of food items present in Gracilinanus faeces. Also, we analysed spatial niche by comparing the vegetal stratum where the individuals were captured and its relationship with the environmental complexity. Both species presented a high trophic niche overlap, with differences in the frequencies of occurrence of the consumed items. Although the most frequent items in the faeces were Hymenoptera, Isoptera and Coleoptera, their proportion differed significantly between the two species. The variety of food items also differed, with flowers being more frequent in G. agilis diet, whereas fruits were more recorded for G. microtarsus. The spatial niche was very similar, with both species being more captured in the forest understory. However, habitat complexity influenced the abundance of both species, especially litter depth and its biomass of leaves. The results indicated that the coexistence of the two species is associated with the trophic and spatial niche, and that this niche segregation could be allowing closely related species of Gracilinanus to coexist.

The Presence of Mycobacterium leprae in Wild Rodents

Leprosy is a chronic infection caused by Mycobacterium leprae. There is a lack of data regarding environmental reservoirs, which may represent a serious public health problem in Brazil, especially in the state of Pará, which occupies the fourth position in incidence of cases in the country. Previous studies report evidence of infection occurring among armadillos, mangabei monkeys, and chimpanzees. In the present study, wild animals were captured and tested for the presence of anti-PGL-1 antibodies and M. leprae DNA. Fieldwork was carried out from October to November of 2016 in the cities of Curionópolis and Canaã dos Carajás, southeast of Pará state. Small and medium-sized wild animals were captured using appropriate traps. A total of 15 animals were captured. Sera and viscera fragments were collected and tested by ELISA and PCR methods. The presence of M. leprae DNA was confirmed by sequencing of specific gyrase gene in three animals of two different species, including one Necromys lasiurus (liver sample) and two Proechimys roberti (kidney and liver samples). This unprecedented finding suggests that species other than those previously reported are responsible for maintaining M. leprae in nature.

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.

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.

Marsupial versus placental: assessing the evolutionary changes in the scapula of didelphids and sigmodontines

It is not a new concept that marsupials and placentals are distant and distinct clades among mammals. In South America, these animals coexist, occupy similar niches and, in some cases, are similar in appearance. This is especially true with respect to the locomotor categories of smaller rodents belonging to the family Cricetidae or, more specifically, the subfamily Sigmodontinae, compared with the marsupials of the Didelphidae family. In this study, we have investigated both the similarities and the differences between the two clades by examining locomotion-dependent adaptation, a crucial survival mechanism that has affected the morphology of both clades. We applied geometric morphometrics to quantify the shape of the scapula, which is a very adaptable structure. We found similar morphological adaptations between the clades, especially with respect to adaptation to life in trees. Moreover, Didelphidae are influenced by phylogenetic history to a greater extent than Sigmodontinae with regard to variation of scapula shape and allometry. These differences can be explained by the greater degree of body size variation that exists within the Didelphidae. Didelphidae have an ancient evolutionary history in South America compared with the Sigmodontinae, which have undergone a very successful and rapid diversification more recently.

Sympatry and habitat associations of sigmodontine rodents in a neotropical forest-savanna interface

Small mammal communities in the Neotropics are composed largely of sigmodontine rodents. However, many questions regarding these communities remain unanswered, especially those pertaining to fine-scale sympatry and habitat selection. To address this, we examined sigmodontine community structure and vegetation in the western margin of the Upper Paraná Atlantic Forest and the southwestern-most extent of the Cerrado (CE) (an extensive South American savanna ecoregion) of Paraguay. Vegetation classifications were derived from satellite imagery combined with maps based on extensive ground-based surveys. The three most abundant species (Akodon montensis, Hylaeamys megacephalus, and Oligoryzomys nigripes) were found most often in microsympatry with conspecifics, and were negatively associated with other species. Akodon montensis was associated with high forest (HF), and H. megacephalus with bamboo understory (BU), whereas O. nigripes did not exhibit a habitat preference. The first two species' distributions within the landscape were found to be driven primarily by habitat selection, and O. nigripes by a behavioral response (avoidance) to the presence of the other two species. Moreover, habitat influences whether or not a particular species associates with, or avoids, conspecifics or other species.

Movement and use of environmental structures, climbing supports and shelters by Akodon montensis (Sigmodontinae, Rodentia) in the Atlantic Forest of southern Brazil

Movements under environmental structures and on supports, and the use of shelters by Akodon montensis were assessed using the spool-and-line technique. Movements of a few individuals of Thaptomys nigrita, Brucepattersonius iheringi and Oligoryzomys nigripes were also assessed and briefly described. Akodon montensis often used fallen logs, lianas and ferns as climbing supports for movements. The species moved under different environmental structures with differing frequencies, with greater use of dense litter followed by lianas and fallen branches. The studied sigmodontine species used shelters of different compositions and structures, and differed in displacement behavior. This study is the first to contribute to understanding the movement and use of environmental structures, shelters and climbing supports by A. montensis.

Helminth metacommunity structure of wild rodents in a preserved area of the Atlantic Forest, Southeast Brazil

Abstract The helminth fauna and metacommunity structure of eight sympatric sigmodontine rodents were investigated at the Serra dos Órgãos National Park, an Atlantic Forest reserve located in the State of Rio de Janeiro, southeast Brazil. Rodents of the species Abrawayaomys ruschii, Akodon montensis, Blarinomys breviceps , Delomys dorsalis, Oligoryzomys flavescens, Oligoryzomys nigripes, Oxymycterus quaestor and Thaptomys nigrita were found infected with helminths. Akodon montensis presented the highest total helminth species richness, with six different species of helminths. The nematode Stilestrongylus lanfrediae was the most abundant and prevalent helminth species observed. The host-parasite network analysis showed little interactions among host species. Akodon montensis seems to act as a keystone-species in the rodent community. This species shared the nematodes Stilestrongylus aculeata with A. ruschii and Protospirura numidica criceticola with T. nigrita, and the cestode Rodentolepis akodontis with D. dorsalis. The congeners host species O. flavescens and O. nigripes shared the nematodes Guerrerostrongylus zetta and S. lanfrediae. The rodents B. breviceps and O. quaestor did not share any helminths with other hosts. The helminth metacommunity showed a random pattern on both infracommunity and component community levels, indicating different responses by each helminth species to the environmental gradient.

Microhabitat structure and food availability modelling a small mammal assemblage in restored riparian forest remnants

Small mammal populations respond to environmental changes in secondary riparian forest remnants in different ways, depending on the influences of biotic and abiotic variables. The present study evaluated how habitat/microhabitat structure and food availability influence small mammal assemblages in restored riparian forest remnants. Pitfall traps disposed in three linear transects were used to collect small mammals during 9 months of field work. General linear models were built to test the hypothesis that microhabitat structure (litter biomass and type – leaves and branches) and food availability (richness of zoochoric tree species and arthropods) influence species richness and abundance of small mammals. Three hundred and eighty-two individuals belonging to 14 species were captured. Biomass and type of litter (leaves or branches) provided greater structural to microhabitats, allowing the coexistence of morphologically similar species. Besides, food availability influenced foraging strategies of marsupials, forcing them to use the forest floor when zoochoric plants were rare. Thus, litter structure and food availability, allowing spatial segregation of the small mammal species using the forest fragments. We concluded that the maintenance of small mammals and their ecosystem services in restored riparian forests are dependent on habitat structure and food availability, thus, litter and zoochoric plants should be conserved in riparian forest fragments, especially those reforested.

Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil

The Atlantic Forest is one of the most disturbed Brazilian biomes, with 183 out of 298 species of mammals occurring in the state of Rio de Janeiro. In this study, we aimed to characterize the diversity, community structure, and habitat use of small mammals in the FIOCRUZ Atlantic Forest Campus (CFMA), including areas of Pedra Branca State Park (PBSP, subunit Pau da Fome), state of Rio de Janeiro. We also compared species diversity and composition between two moments 15 years apart (2001 and 2012–2015) and analyzed the population dynamics of the marsupial Didelphisaurita (Wied-Neuwied, 1826). Small mammal captures were made in different habitats: sylvatic-urban interface areas near human dwellings, disturbed forest, and preserved forest areas. Five marsupial species and four rodent species were captured in both periods. There was a reduction in species richness and β diversity between the two periods, indicating that disturbances in the environment over the years may have affected the small mammal community structure. The most altered environment showed the greatest species richness and abundance, while the forest areas showed the smallest values, which may be explained by the loss of mammal species, mainly specialist species in forested areas. We identified three groups of species according to habitat preferences: one related to environments with a higher density of vegetation in upper strata – Marmosaparaguayana (Tate, 1931) and Monodelphisamericana (Müller, 1776), another related to a higher density in lower forest strata – Akodoncursor (Winge, 1887), and another with no association with the investigated habitat variables – D.aurita and Oligoryzomysnigripes (Olfers, 1818). The small mammal community structure showed a low level of nestedness in both sampling periods. This study is the first report to evaluate the community structure of small mammals in the sylvatic-urban interface area of Pedra Branca State Park, the largest forest reserve within an urban area in Brazil. The surveys indicate that the small mammal diversity was low in both sampling periods and in both areas, and a species loss in the Pau da Fome locality was observed, despite it is a conservation unit. The greater species abundance and richness in the most disturbed areas suggest an increase of factors favoring the occurrence of synanthropic and opportunistic species.

Habitat quality versus spatial variables as determinants of small mammal assemblages in Atlantic Forest fragments

Fragment size, isolation, and matrix properties have received considerable attention as predictors of species richness, abundance, and composition in habitat patches. However, measurements of habitat attributes or habitat quality are more directly related to the proximate effects of habitat fragmentation and may be more determinant of assemblages than traditional explanatory variables at local scales. We determine how habitat structure in fragments—a measure of habitat quality—compares to fragment size, isolation, and matrix properties as determinants of richness, abundance, and composition of non-volant small mammals in a fragmented landscape of Atlantic Forest. Small mammals were surveyed once in 25 fragments in the Macacu River watershed, Rio de Janeiro, Brazil, from 1999 to 2001 and 2005 to 2009. A total of 83 candidate models were formulated and compared by Akaike Information Criteria. Habitat structure was one of the main determinants of small mammal assemblages in fragments, as important as fragment isolation for species composition and climatic season for species richness. Rodents were more abundant in fragments with increased overstory and understory vegetation density and more fallen logs. The contrary pattern was found for overall species richness and for species of terrestrial habit, which were more abundant in fragments with more open forest: decreased overstory and understory vegetation density and less fallen logs. Habitat quality in fragments may be a more important determinant of assemblages of small mammals and other vertebrates than previously considered in landscape and land use studies.

O tamanho e isolamento dos fragmentos e as propriedades da matriz têm recebido considerável atenção como preditores da riqueza, abundância e composição de espécies em manchas de habitat. Entretanto, medidas dos atributos do habitat ou da qualidade do habitat são mais diretamente relacionadas aos efeitos imediatos da fragmentação de habitat, e seriam mais determinantes das comunidades do que as variáveis explicativas tradicionais. Determinamos como a estrutura do habitat nos fragmentos—uma medida da qualidade do habitat—se compara ao tamanho e isolamento dos fragmentos, e às propriedades da matriz como determinantes da riqueza, abundância e composição de espécies de pequenos mamíferos não-voadores em uma paisagem fragmentada de Mata Atlântica. Os pequenos mamíferos foram amostrados uma vez em 25 fragmentos na Bacia do Rio Macacu, Rio de Janeiro, Brasil, de 1999 a 2001 e de 2005 a 2009. Um total de 83 modelos foram formulados e comparados utilizando o Critério de Informação de Akaike. A estrutura do habitat foi um dos principais determinantes das comunidades de pequenos mamíferos nos fragmentos de mata, tão importante quanto o isolamento entre fragmentos para a composição de espécies e os efeitos das estações climáticas sobre a riqueza de espécies. Os roedores foram mais abundantes nos fragmentos com estratificação vertical e sub-bosque mais densos e com maior presença de troncos caídos. O padrão contrário foi encontrado para a riqueza total de espécies e para espécies de hábito terrestre, que foram mais abundantes em fragmentos com estratificação vertical e sub-bosque menos densos e menor presença de troncos caídos. A qualidade do habitat em fragmentos pode ser determinante das comunidades de pequenos mamíferos e outros vertebrados, mais importante do que considerado previamente em estudos de paisagens e uso da terra.