Small mammal populations of an agroecosystem in the Atlantic Forest domain, southeastern Brazil

This study reports 2 years of the population dynamics and reproduction of a small mammal community using the removal method. The study was conducted in a rural area of the Atlantic Forest, in Sumidouro, Rio de Janeiro State, Brazil. The population sizes, age structure and reproduction were studied for the four most common species in the study area. The overall diversity was 1.67 and ranged between 0.8 to 1.67. The species richness was 13 considering the whole study. The most abundant species were the rodents Nectomys squamipes (n = 133), Akodon cursor (n = 74), Oligoryzomys nigripes (n = 25) and the marsupials Didelphis aurita (n = 58) and Philander frenatus (n = 50). Seven other rodents were captured once: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. There were higher peaks for diversity and species richness during the winter (dry) months, probably due to higher food availability. The marsupials had a seasonal reproduction with highest population sizes at the end of the rainy seasons. Nectomys squamipes reproduced mostly during rainy periods. Akodon cursor reproduced predominantly in the winter with the highest population peaks occurring during this season. The analysis of the population dynamics of the rodent species indicated that no species behaved as an agricultural pest, probably due to the heterogeneous landscape of high rotativity of vegetable cultivation. Rodent populations were more susceptible to the removal procedure than marsupial ones.

Este estudo reporta dois anos da dinâmica populacional e reprodução de uma comunidade de pequenos mamíferos através de método de remoção. O estudo foi realizado numa área rural na Mata Atlântica, em Sumidouro, Rio de Janeiro, Brasil. Os tamanhos populacionais, a estrutura etária e a reprodução foram estudados para as quatro espécies mais comuns na área de estudo. A diversidade total foi de 1,67 e variou entre 0,8 e 1,67. A riqueza de espécies foi de 13, considerando-se o estudo todo. As espécies mais abundantes foram os roedores Nectomys squamipes (n = 133), Akodon cursor (n = 74) e Oligoryzomys nigripes (n = 25) e os marsupiais Didelphis aurita (n = 58) e Philander frenatus (n = 50). Sete outras espécies de roedores foram capturadas somente uma vez: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. Houve maiores picos de diversidade e riqueza de espécies durante os meses de inverno (secos), provavelmente devido ao aumento na disponibilidade de recursos. Os marsupiais apresentaram reprodução estacional com maiores tamanhos populacionais no final das estações chuvosas. Nectomys squamipes reproduziu-se predominantemente durante períodos chuvosos. Akodon cursor reproduziu-se predominantemente no inverno, com os maiores picos populacionais ocorrendo durante esta estação. A análise da dinâmica populacional das espécies de roedores indicou que nenhuma se comportou como praga agrícola, provavelmente devido ao ambiente heterogêneo de alta rotatividade de cultivos de legumes. As populações dos roedores foram mais suscetíveis ao procedimento de remoção do que as dos marsupiais.

Genetic differentiation in geographically close populations of the water rat Nectomys squamipes (Rodentia, Sigmodontinae) from the Brazilian Atlantic Forest

We examined the genetic structure and the effects of a bottleneck in populations of the water rat Nectomys squamipes, a primary host of Schistosoma mansoni. Eight microsatellite loci were studied in 7 populations from the Sumidouro region of the Brazilian state of Rio de Janeiro. Our data, covering a four-year period during which a bottleneck occurred, revealed substantial variation (6-31 alleles per locus) and high levels of both observed (0.718-0.789) and expected (0.748-0.832) heterozygosity. Most populations were in Hardy-Weinberg equilibrium without linkage disequilibrium between loci. Overall average genetic differentiation between populations (estimated with the F ST (theta) and R ST (rho) analogues was 0.037 for theta and 0.060 for rho. There was significant allelic and genotypic differentiation between populations, especially in pairwise comparisons that included the most geographically isolated population. Direct migration estimates showed a low rate of migration, indicating that infected N. squamipes populations had a limited ability to spread S. mansoni. When the pre- and post-bottleneck populations were compared there was no detectable reduction in heterozygosity or allele number, although a significant excess of heterozygosity was detected in the post-bottleneck population.

Small non-flying mammals from conserved and altered areas of Atlantic Forest and Cerrado: comments on their potencial use for monitoring environment

Two Atlantic Forests and two Cerrado areas in Brazil were sampled for non-flying small mammal fauna. In each biome one area with altered and another with almost unaltered vegetation (national parks), were chosen to investigate these fauna. Species richness of Atlantic Forest and Cerrado was comparable in the conserved as well as in the altered areas. Data suggested that species could be divided into different ecological categories according to distribution, use of altered and/or relatively unaltered vegetation and habitat specificity. Within these ecological categories some species are appropriate indicators for monitoring environmental quality and degradation. Useful guidelines for wildlife management planning, including selecting areas for conservation units and their better boundary delimitation can ensue