NEW METHODS FOR THE STUDY OF VERTICAL STRATIFICATION OF NEOTROPICAL OPOSSUMS.

Novos métodos vêm sendo desenvolvidos para o estudo da estratificação vertical dos pequenos mamíferos neotropicais, como alternativas aos métodos convencionais que usam armadilhas de captura de animais vivos. Nesta revisão descrevemos três métodos alternativos para estudar a estratificação vertical dos marsupiais didelfídeos nas florestas tropicais: testes de desempenho em uma abordagem ecomorfológica, carretel de rastreamento e ninhos artificiais. O histórico de uso de cada um é revisto, discutindo suas vantagens e desvantagens, e apresentando exemplos de resultados inéditos obtidos através de seu uso. Testes de hipóteses mais acurados sobre estruturação de comunidades locais e questões relacionadas à demografia de populações podem ser obtidos com a combinação destes novos métodos com métodos convencionais, que se complementem, minimizando suas deficiências.New methods have been developed for the study of vertical stratification on small neotropical mammals, alternative to traditional methods using live traps. We reviewed three such alternative methods to study vertical stratification of didelphid marsupials in tropical forests: performance tests in an ecomorphological approach, spool-and-line, and artificial nests. The history of each method was reviewed, discussing their advantages and pitfalls, and presenting examples of the unique results reac,hed. More accurate tests of hypothesis about assemblage structure and population demography can be obtained by combination of traditional and alternative methods, which complement each other, minimizing their limitations

USO DO ESPAÇO VERTICAL POR PEQUENOS MAMÍFEROS NO PARQUE NACIONAL SERRA DOS ÓRGÃOS, RJ: UM ESTUDO DE 10 ANOS UTILIZANDO TRÊS MÉTODOS DE AMOSTRAGEM

In this study we analyze the use of forest strata by species of small mammals using three sampling methods: livetraps, artificial nests, and spool-and-line devices. With livetraps and a total effort of 69,525 trap-nights (17,550 in the canopy) there were 2,759 captures of 1,172 individuals of 15 species, eight marsupials and seven rodents. In the nests, the effort was 6,018 nest verifications, with 71 individuals of six species registered. With the spool-and-line devices, 53,000 m of line were tracked in 403 paths of 272 individuals of four species of marsupials. Sampling the canopy was essential to properly characterize the structure of the community, particularly regarding relative abundance of species. The results of the different sampling methods were complementary, each one with its own advantages and limitations to study the vertical use of the forest by small mammals. The combination of the three methods revealed that the small mammal community in Garrafão is clearly stratified, but the vertical use of the forest by small mammals is more complex and sophisticated than a simple classification by dominant strata used. Some species use predominantly the ground, others the canopy, but only these extremes are detected by livetraps. This method alone does not allow a detailed analysis of use of the understory and even the canopy by predominantly terrestrial or scansorial species.O estudo avaliou o uso dos estratos da floresta pelas espécies de pequenos mamíferos através de três métodos de amostragem: armadilhas de captura viva, ninhos artificiais e carretel de rastreamento. Nas armadilhas e com esforço total de 69.525 armadilhas-noites (17.550 no dossel), houve 2.759 capturas de 1.172 indivíduos de 15 espécies, sendo oito espécies de marsupiais e sete de roedores. Nos ninhos, com esforço total de 6.018 verificações, foram registrados 71 indivíduos pertencentes a seis espécies. Foram mapeados com carretel de rastreamento aproximadamente 53.000 m de linha em 403 caminhos de 272 indivíduos, de quatro espécies de marsupiais. A amostragem do dossel foi imprescindível para a caracterização adequada da estrutura da comunidade, principalmente quanto às abundâncias relativas das espécies. Os diferentes métodos de amostragem foram complementares em seus resultados, cada um com vantagens e limitações para o estudo da estratificação vertical de pequenos mamíferos. A análise conjunta dos dados revelou que a comunidade de pequenos mamíferos do Garrafão apresenta marcada estratificação vertical, mas o uso dos estratos da floresta por pequenos mamíferos é mais complexo e sofisticado que a simples classificação por estrato utilizado. Algumas espécies usam predominantemente o solo ou dossel, mas apenas estes extremos são detectados pelas armadilhas. Este método por si só não é capaz de detalhar o uso do sub-bosque e mesmo do dossel por espécies predominantemente terrestres ou semiterrestres

Artificial nests as an alternative to studies of arboreal small mammal populations: a five-year study in the Atlantic Forest, Brazil

Despite the great diversity of Brazilian Atlantic forest small mammals, natural history of most species is unknown due to their cryptic and nocturnal habits, but also due to the inadequacy of methods to capture some species, especially those of arboreal habits. A new technique, based on the use of artificial nests (AN) to record arboreal marsupials, is presented. Artificial nests were combined with traditional live traps to study the population ecology of four didelphid marsupial species. After 62 months of monitoring, 119 individuals were recorded 243 times (total success = 5.2%). Only 26 individuals (22%) were recorded by both AN and live trap methods, and two of the four species were never captured by live traps, only by AN. Live traps alone would have provided biased data of the structure of small mammal assemblages, creating artificial tendencies in population dynamics of many species. Detectability estimates based on mark-recapture data could correct bias resulting from the use only live traps, but these estimates require that at least some individuals of each age class or stage are captured. Only the combination of AN and live traps can produce more accurate data on population dynamics and assemblage structure. This study demonstrates that artificial nests represent a new method that should be combined with live traps in studies of small mammal assemblages and populations

Comparing the effectiveness of tracking methods for medium to large-sized mammals of Pantanal

Most Neotropical mammals are not easily observed in their habitats, and few studies have been conducted to compare the performance of methods designed to register their tracks. We compared the effectiveness of track registry between sand plots and two tracking methods that use artificial materials to record tracks: the sooted paper, and the plastic board methods. The latter is described here for the first time. From 2002 to 2005, we conducted two experiments in three study sites in the Pantanal region of Brazil. We compared the artificial methods with the sand plot by registering track presence/absence, the number of identifiable tracks, and the total number of tracks (identifiable and unrecognizable) in each tracking plot. Individuals avoided artificial tracking plots either by not stepping on them or by doing it fewer times than on the sand plots. The use of artificial materials to register mammal tracks resulted in underestimates that are especially relevant to short-term ecological studies. We recommend the use of the traditional sand plot method whenever possible and the development of detailed studies on the efficiency of artificial methods under a variety of environmental conditions and time lengths. Despite their relatively lower efficiency, we believe that artificial methods are useful under specific conditions and may be more efficient if used in more comprehensive sampling efforts