Microhabitat selection when detection is imperfect: the case of an endemic Atlantic forest mammal

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.

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.

Community of diurnal birds of prey in an urban area in southeastern Brazil

As urban areas expand, some species of diurnal birds of prey occupy these habitats, and many establish viable populations. The objectives of this study were to: (1) survey the species of birds of prey in the urban area located in the interior of the São Paulo state, Brazil, (2) to verify the proportion of generalist and specialist species in terms of habitat and diet, (3) determine the period that the species are more active during the time period of the point counts, and (4) to evaluate if there is a pattern of seasonality. Samples were collected monthly between October 2014 and September 2016 using the point counts method (four points; 4 hr duration each). We analyzed species richness, habitat and diet, number of contacts and frequency of occurrence, period of greatest activity, and seasonality. We recorded 19 species of birds of prey through 2555 contacts. Most of the registered species (61%) were habitat and diet generalists, and the same percentage of species classified as uncommon or rare. In relation to the period of greatest activity, falconids were more active in the first hour while accipitrids and cathartids were more active in the fourth hour. In addition, we did not observe a seasonal pattern in this community, but Gampsonyx swainsonii showed a seasonal trend. We verified that the urban area of the municipality of Pirajuí has a significant diversity of birds of prey, including specialist species of habitat and diet. This information obtained evidence the importance of urban environments for birds of prey and showed the ability of these species to use this environment. From our results, we suggest that future studies should evaluate the effects of urban areas of different sizes and degrees of urbanization on bird of prey communities.

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.

Differences in microhabitat selection patterns between a remnant and constructed landscape following management intervention

Context Achieving successful conservation outcomes in habitat creation and reintroductions requires an understanding of how species use their habitat and respond to these interventions. However, few initiatives directly compare microhabitat selection between remnant and managed habitats to measure effectiveness and evaluate outcomes. Probability of detection is also rarely included in studies on microhabitat use, which may lead to erroneous conclusions if detectability varies between variables. Methods In this study, we used the endangered green and golden bell frog (Litoria aurea) to compare differences in microhabitat-use patterns in both a remnant and a constructed habitat. A detectability study was also conducted to determine detection probabilities among microhabitats. Key results Aquatic vegetation was used more than expected in both the remnant and constructed habitats, and rock piles were utilised less than expected in the constructed habitat, despite their recommendation in most habitat templates. We found that detection probabilities altered the outcomes of abundance estimates for nearly all the measured microhabitat variables. Conclusions Future management for this species should focus on providing high proportions of aquatic vegetation. Furthermore, although rock piles have been utilised greatly in past L. aurea habitat creation, placing large rocks on a managed site is expensive and time consuming. Future management initiatives may need to focus on providing smaller proportion of rocks, which would be a more appropriate use of resources. Implications With conservation management projects increasing over the next few decades, understanding habitat use before implementing strategies should be a priority as it will provide important insights and inform decision-making for optimum habitat creation and restoration. Furthermore, accounting for detectability in microhabitat use studies is essential to avoid wrong conclusions that may negatively affect the success of ecological management strategies.