Rui Cerqueira

A five-year population study of an assemblage of small mammals in Southeastern Brazil

Une etude par capture-marquage et recapture de petits mammiferes a ete realisee pendant cinq and dans une vegetation arbustive cotiere bresilienne (restinga). Cinq especes de petits mammiferes, rongeurs et marsupiaux, ont ete capturees et caracterisees par rapport a leur dynamique de population. Akodon cursor et Philander opossum ont presente les plus grandes densites de population, qui sont correlees avec le recrutement. Ils ont aussi presente un recrutement irregulier, des fluctuations de populations frequentes avec des coefficients de variation eleves, des taux de survie bas la plupart du temps et des durees de residence courtes

The parasitism of Schistosoma mansoni (Digenea–Trematoda) in a naturally infected population of water rats, Nectomys squamipes (Rodentia–Sigmodontinae) in Brazil

Schistosomiasis is a health problem in Brazil and the role of rodents in maintaining the schistosome life-cycle requires further clarification. The influence of Schistosoma mansoni on a population of Nectomys squamipes was studied by capture-recapture (1st phase, from June 1991 to November 1995) and removal (2nd phase, from April 1997 to March 1999) studies at Sumidouro, Rio de Janeiro, Brazil. During both phases coproscopic examinations were performed. At the 2nd phase the rodents were perfused and worms were counted. The population dynamics of parasites was studied. During the 1st phase, female reproductive parameters, longevity, recruitment and survivorship rates and migration patterns were studied in relation to schistosome prevalence. Water contamination (source of miracidia), abundance intermediate host and rodent migration were related to prevalence. The N. squamipes population was not obviously influenced by the infection, as shown by the high number of reproductive infected females, high longevity of infected individuals and the absence of a relationship between recruitment or survivorship rates and the intensity of schistosome infection. The data indicate that N. squamipes can increase transmission of S. mansoni in endemic areas and carry it to non-infected areas. Furthermore, this rodent can be used as an indicator of a transmission focus.

Movement patterns of five species of small mammals in a Brazilian restinga

During the course of a population study of small mammals in a Brazilian coastal shrubland we calculated the movements between successive captures, the residence time, the indices of aggregation and the kinds of movements of the five most common species of small mammal. A capture-mark-recapture study was undertaken over two years, quarterly. Philander opossum, Akodon cursor and Proechimys iheringi presented low mobility, with a high proportion of restricted movements, long residence time and larger coefficients of aggregation. Didelphis aurita and Metachirus nudicaudatus presented higher mobility and exploratory movements, short residence time and small coefficients of aggregation. The species with lower mobility had permanent popula- tions within our sampling grid, while the species with higher mobility used areas outside the grid, presenting no local populations but occupying portions of regional metapopulations.

Ecology of small mammals in a Brazilian rural area

A small mammal study was carried out in Pamparrao valley, Sumidouro, State of Rio de Janeiro, Brazil, from June 1991 to July 1996. The area was characterised by small rural properties with vegetable plantations, pasture lands and small forest fragments. Small mammals were captured in seven line transects along the valley. Eleven small mammal species were captured: the didelphid marsupials Didelphis aurita, Philander frenata and Monodelphis americana, and the rodents Nectomys squamipes, Akodon cursor, Oligoryzomys nigripes, Bolomys lasiurus, Oecomys concolor (Sigmodontinae), Rattus ratlus (Murinae), Proechimys iheringi and Euryzygo-matomys guiara (Echimyidae). The heterogeneous habitat configuration probably allowed the occurrence of marsupials and more rodent species when compared to studies in monoculture areas.

MORPHOLOGICAL DIFFERENTIATION IN THE WHITE-EARED OPOSSUM GROUP (DIDELPHIDAE: DIDELPHIS)

Abstract We analyzed phenotypic variation in white-eared Didelphis and its relevance to the current taxonomy of these opossums. On the basis of morphologic and morphometric data we show that the white-eared Didelphis can be split into 3 groups of populations referred to as albiventris, pernigra, and imperfecta. Morphologically, pernigra possesses a large, peg-like 3rd upper premolar (P3), whereas albiventris and imperfecta possess a small, non–peg-like P3. Also, albiventris has 88% of its specimens in the gray dorsal color phase, whereas the other 2 groups show similar percentages of specimens in the gray and black color phases. Morphometrically, pernigra is significantly larger (P < 0.05; analysis of variance) than the other 2 groups in most traits. Squared Mahalanobis distances among the 3 groups were found to be high, and discriminant analysis was successful in separating groups (99% of cases correctly classified). The congruence in variation of independent traits indicates genetic differentiation among populations. In addition, the sharp discontinuity observed between the parapatric albiventris and pernigra in Bolivia suggests that limited or no gene flow occurs between them. We conclude that the 3 groups analyzed here merit taxonomic recognition at the species level.

A device and standard variables to describe microhabitat structure of small mammals based on plant cover

Studies quantifying habitat structure generally use several instruments. This paper aims to propose a new and efficient device to characterize microhabitat structure of small mammals. Seven measurements were taken: plant cover, litter cover, rock cover, canopy cover, and vegetative obstruction at three heights. The device is a 0.25 m2 square wooden frame (0.50 m x 0.50 m) divided in to 100 open squares by wire mesh. Average time spent to measure each trapping station was six minutes. This new device is efficient, i.e., quick, practical, simple, and reliable. It can be used in any kind of forest. We propose this method as a standard method to describe habitat structure.

The chromosomes of Nectomys (Rodentia, Cricetidae) with 2n = 52, 2n = 56, and interspecific hybrids (2n = 54)

Karyologic comparisons of Nectomys with 2n = 52 and 2n = 56, captured in different regions of Brazil, revealed the existence of two presumptive tandem fusions. These differences proved to represent drastic reproductive barriers between these two karyologic groups, based on an analysis of spermatogenesis in captive-bred hybrids (2n = 54). In these hybrid specimens, cytologic and histologic analyses indicated severe meiotic arrest and the presence of two trivalents in the first meiotic division, in which 26 elements were frequently observed. These findings and the sterility of crosses between F1 males and females as well as backcrosses indicated that Nectomys populations with 2n = 52 and 2n = 56 should be considered different species and that the present taxonomic arrangement of this genus must be reviewed.

Population dynamics of four marsupials and its relation to resource production in the Atlantic forest in southeastern Brazil

Variations in mammal population sizes can be related to the availability and abundance of their resources. This study reports the population dynamics of four didelphid marsupials (Didelphis aurita, Philander frenatus, Marmosops incanus and Metachirus nudicaudatus) and its relation to litter fall, used as a measure of resource production. A capture-mark-recapture study (CMR) was carried out in a disturbed area of the Atlantic forest in Rio de Janeiro State, Brazil, in three grids in the locality of Garrafão from April 1997 to February 1999, every other month. Litter was collected every month using 15 squared litter traps of 0.25 m2 in the grids (5 in each grid). Leaves, twigs, reproductive structures and total litter fall rates were calculated as tons ha–1month–1. Population densities, survivorship and recruitment rates were estimated. For D. aurita and P. frenata, population densities were correlated positively only with litter production. For M. incanus, population density was correlated positively with survivorship, litter production and negatively with rainfall. M. nudicaudatus population density was correlated only with recruitment and twigs abundance. The availability of fruits and arthropods had a large influence in the proximal causes on the variation of small mammal populations. In forests where there is an adequate rate of decomposition of the litter, we may understand how resources influence population variation, and litter becomes the base of resources for such marsupials in the Atlantic forest.

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.

Comparative gross morphology of the digestive tract in ten Didelphidae marsupial species

Natural diets of Didelphidae species vary in the amounts of invertebrates, fruits and small vertebrates eaten. We investigated the digestive morphology of ten species of didelphid marsupials varying in food habits. The purpose was to describe and to compare the shape and relative size of the digestive tract portions among species studied and relate them to food habits. The form of the gastrointestinal tract in this family is simple, with a unilocular stomach, small intestine, large intestine and caecum. Caluromys philander was the species with highest association between digestive tract measurements and its frugivorous habits. However, although its caecum is morphologically distinct from the other species, the relative length is small when compared to the more faunivorous Metachirus nudicaudatus. Stomach length of Philander frenata is related to a more carnivorous diet, while large intestine length of Didelphis aurita is related to its omnivore diet. The digestive tract measurements of the other species appear to be related with a variable degree of morphological differentiation from a generalized form related to omnivory toward a more carnivorous diet. Great caecum relative size distinguished Metachirus nudicaudatus from the most other species and its relationship with diet is not well understood.