Resumo
Estimates of local population abundances, which require carefully designed sampling procedures, can provide valuable information on population size and density. Even though small mammals are one of the most widely studied vertebrate groups, many surveys have not recorded basic information to estimate local abundances, for instance catching effort. Here we suggest a simple comparative trapping frequency index that can be used as an alternative to the relative abundance index in data sets that only contain the number of species and individuals collected, thus lacking information on sampling effort. To compare trapping frequency and relative abundances we used capture records from more than four years, from seven species of rodents and two marsupial species collected by the Brazilian Plague Service. We calculated the trapping frequency index of each species as the proportion of trapped individuals per total of all individuals caught. We found that this trapping index was significantly correlated with a relative abundance index (number of captured individuals divided by number of trap nights). Our findings suggest that the proposed index may be useful for comparisons in situations where data on catching effort is lacking. The index may also provide a simple, though approximate quantification of relative local abundances, with possible applications in comparative studies (e.g. meta-analysis). We suggest that this index is used in studies that do not focus on obtaining accurate population parameter estimates, but which nonetheless contain data that can still offer a representative measure to compare local population abundances.
Assuntos
Animais , Biodiversidade , MamíferosResumo
Estimates of local population abundances, which require carefully designed sampling procedures, can provide valuable information on population size and density. Even though small mammals are one of the most widely studied vertebrate groups, many surveys have not recorded basic information to estimate local abundances, for instance catching effort. Here we suggest a simple comparative trapping frequency index that can be used as an alternative to the relative abundance index in data sets that only contain the number of species and individuals collected, thus lacking information on sampling effort. To compare trapping frequency and relative abundances we used capture records from more than four years, from seven species of rodents and two marsupial species collected by the Brazilian Plague Service. We calculated the trapping frequency index of each species as the proportion of trapped individuals per total of all individuals caught. We found that this trapping index was significantly correlated with a relative abundance index (number of captured individuals divided by number of trap nights). Our findings suggest that the proposed index may be useful for comparisons in situations where data on catching effort is lacking. The index may also provide a simple, though approximate quantification of relative local abundances, with possible applications in comparative studies (e.g. meta-analysis). We suggest that this index is used in studies that do not focus on obtaining accurate population parameter estimates, but which nonetheless contain data that can still offer a representative measure to compare local population abundances.(AU)
Assuntos
Animais , Mamíferos , BiodiversidadeResumo
A major difficulty in the application of probabilistic models to estimations of mammal abundance is obtaining a data set that meets all of the assumptions of the model. In this paper, we evaluated the concordance correlation among three population size estimators, the minimum number alive (MNA), jackknife and the model suggested by the selection algorithm in CAPTURE (the best-fit model), using long-term data on three Brazilian small mammal species obtained from three different studies. The concordance correlation coefficients between the abundance estimates indicated that the probabilistic and enumeration estimators were highly correlated, giving concordant population estimates, except for one species in one of the studies. The results indicate the adequacy of using enumeration estimates as indexes for population size when scarce data do not allow for the use of probabilistic methods. Differences observed in the behavior of enumeration and probabilistic methods among species and studies can be related to the exclusive sampling design of each area, species-specific movement characteristics and whether a significant portion of the population could be sampled.
Resumo
A major difficulty in the application of probabilistic models to estimations of mammal abundance is obtaining a data set that meets all of the assumptions of the model. In this paper, we evaluated the concordance correlation among three population size estimators, the minimum number alive (MNA), jackknife and the model suggested by the selection algorithm in CAPTURE (the best-fit model), using long-term data on three Brazilian small mammal species obtained from three different studies. The concordance correlation coefficients between the abundance estimates indicated that the probabilistic and enumeration estimators were highly correlated, giving concordant population estimates, except for one species in one of the studies. The results indicate the adequacy of using enumeration estimates as indexes for population size when scarce data do not allow for the use of probabilistic methods. Differences observed in the behavior of enumeration and probabilistic methods among species and studies can be related to the exclusive sampling design of each area, species-specific movement characteristics and whether a significant portion of the population could be sampled.
Assuntos
Dinâmica Populacional , Roedores/classificaçãoResumo
A major difficulty in the application of probabilistic models to estimations of mammal abundance is obtaining a data set that meets all of the assumptions of the model. In this paper, we evaluated the concordance correlation among three population size estimators, the minimum number alive (MNA), jackknife and the model suggested by the selection algorithm in CAPTURE (the best-fit model), using long-term data on three Brazilian small mammal species obtained from three different studies. The concordance correlation coefficients between the abundance estimates indicated that the probabilistic and enumeration estimators were highly correlated, giving concordant population estimates, except for one species in one of the studies. The results indicate the adequacy of using enumeration estimates as indexes for population size when scarce data do not allow for the use of probabilistic methods. Differences observed in the behavior of enumeration and probabilistic methods among species and studies can be related to the exclusive sampling design of each area, species-specific movement characteristics and whether a significant portion of the population could be sampled.(AU)
Assuntos
Dinâmica Populacional , Roedores/classificaçãoResumo
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.
Resumo
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.
Resumo
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.
Resumo
Climate, altitude and vegetation are usually considered as limiting factors in plant and animal distribution. Among vertebrates, climate and vegetation have consistently been considered as major determinants of geographical distributions. Here we analyzed the role of climate and the vegetation in limiting the geographical range of Atlantic Forest species of Drymophila Swainson, 1824 and assessed the performance of discriminant analysis to model the distribution of sympatric taxa. From each empirical point (locality) we recorded the values for nine climatic variables and the type of vegetation. The climatic data were obtained from a climate database elaborated by the Laboratório de Vertebrados and vegetation data from the ecoregions digital map of Latin America. The overlap of the climatic distribution map with the ecoregion map suggested that both factors are important in limiting the geographical range of Drymophila species. The discriminant approach, as applied here, was not satisfactory when compared with similar analysis carried out on parapatric species.
Resumo
Climate, altitude and vegetation are usually considered as limiting factors in plant and animal distribution. Among vertebrates, climate and vegetation have consistently been considered as major determinants of geographical distributions. Here we analyzed the role of climate and the vegetation in limiting the geographical range of Atlantic Forest species of Drymophila Swainson, 1824 and assessed the performance of discriminant analysis to model the distribution of sympatric taxa. From each empirical point (locality) we recorded the values for nine climatic variables and the type of vegetation. The climatic data were obtained from a climate database elaborated by the Laboratório de Vertebrados and vegetation data from the ecoregions digital map of Latin America. The overlap of the climatic distribution map with the ecoregion map suggested that both factors are important in limiting the geographical range of Drymophila species. The discriminant approach, as applied here, was not satisfactory when compared with similar analysis carried out on parapatric species.
Resumo
Climate, altitude and vegetation are usually considered as limiting factors in plant and animal distribution. Among vertebrates, climate and vegetation have consistently been considered as major determinants of geographical distributions. Here we analyzed the role of climate and the vegetation in limiting the geographical range of Atlantic Forest species of Drymophila Swainson, 1824 and assessed the performance of discriminant analysis to model the distribution of sympatric taxa. From each empirical point (locality) we recorded the values for nine climatic variables and the type of vegetation. The climatic data were obtained from a climate database elaborated by the Laboratório de Vertebrados and vegetation data from the ecoregions digital map of Latin America. The overlap of the climatic distribution map with the ecoregion map suggested that both factors are important in limiting the geographical range of Drymophila species. The discriminant approach, as applied here, was not satisfactory when compared with similar analysis carried out on parapatric species.
Resumo
A fundamental step in the emerging Movement Theory is the description of movement paths, and the identification of its proximate and ultimate drivers. The most common characteristic used to describe and analyze movement paths is its tortuosity, and a variety of tortuosity indices have been proposed in different theoretical or empirical contexts. Here we review conceptual differences between five movement indices and their bias due to locations errors, sample sizes and scale-dependency: Intensity of Habitat use (IU), Fractal D, MSD (Mean Squared Distance), Straightness (ST), and Sinuosity (SI). Intensity of Habitat use and ST are straightforward to compute, but ST is actually an unbiased estimator of oriented search and ballistic movements. Fractal D is less straightforward to compute and represents an index of propensity to cover the plane, whereas IU is the only completely empirical of the three. These three indices could be used to identify different phases of path, and their path tortuosity is a dimensionless feature of the path, depending mostly on path shape, not on the unit of measurement. This concept of tortuosity differs from a concept implied in the sinuosity of BENHAMOU (2004), where a specific random walk movement model is assumed, and diffusion distance is a function of path length and turning angles, requiring their inclusion in a measure of sinuosity. MSD should be used as a diagnostic tool of random walk paths rather than an index of tortuosity. Bias due to location errors, sample size and scale, differs between the indices, as well as the concept of tortuosity implied. These differences must be considered when choosing the most appropriate index.
Resumo
A fundamental step in the emerging Movement Theory is the description of movement paths, and the identification of its proximate and ultimate drivers. The most common characteristic used to describe and analyze movement paths is its tortuosity, and a variety of tortuosity indices have been proposed in different theoretical or empirical contexts. Here we review conceptual differences between five movement indices and their bias due to locations errors, sample sizes and scale-dependency: Intensity of Habitat use (IU), Fractal D, MSD (Mean Squared Distance), Straightness (ST), and Sinuosity (SI). Intensity of Habitat use and ST are straightforward to compute, but ST is actually an unbiased estimator of oriented search and ballistic movements. Fractal D is less straightforward to compute and represents an index of propensity to cover the plane, whereas IU is the only completely empirical of the three. These three indices could be used to identify different phases of path, and their path tortuosity is a dimensionless feature of the path, depending mostly on path shape, not on the unit of measurement. This concept of tortuosity differs from a concept implied in the sinuosity of BENHAMOU (2004), where a specific random walk movement model is assumed, and diffusion distance is a function of path length and turning angles, requiring their inclusion in a measure of sinuosity. MSD should be used as a diagnostic tool of random walk paths rather than an index of tortuosity. Bias due to location errors, sample size and scale, differs between the indices, as well as the concept of tortuosity implied. These differences must be considered when choosing the most appropriate index.
Resumo
A fundamental step in the emerging Movement Theory is the description of movement paths, and the identification of its proximate and ultimate drivers. The most common characteristic used to describe and analyze movement paths is its tortuosity, and a variety of tortuosity indices have been proposed in different theoretical or empirical contexts. Here we review conceptual differences between five movement indices and their bias due to locations errors, sample sizes and scale-dependency: Intensity of Habitat use (IU), Fractal D, MSD (Mean Squared Distance), Straightness (ST), and Sinuosity (SI). Intensity of Habitat use and ST are straightforward to compute, but ST is actually an unbiased estimator of oriented search and ballistic movements. Fractal D is less straightforward to compute and represents an index of propensity to cover the plane, whereas IU is the only completely empirical of the three. These three indices could be used to identify different phases of path, and their path tortuosity is a dimensionless feature of the path, depending mostly on path shape, not on the unit of measurement. This concept of tortuosity differs from a concept implied in the sinuosity of BENHAMOU (2004), where a specific random walk movement model is assumed, and diffusion distance is a function of path length and turning angles, requiring their inclusion in a measure of sinuosity. MSD should be used as a diagnostic tool of random walk paths rather than an index of tortuosity. Bias due to location errors, sample size and scale, differs between the indices, as well as the concept of tortuosity implied. These differences must be considered when choosing the most appropriate index.
Resumo
Abrawayaomys ruschii is considered as a rare species due the scarcity of samples in scientific collections and in published lists, being difficult to assign it to any proposed suprageneric classification among the Sigmodontinae. We report here a new record of A. ruschii, the first for this species in the Rio de Janeiro state (Aldeia Sapucai - Terra Indígena do Bracuí, Angra dos Reis). Because of the small sample size it is not possible to define a precise geographic range, but the known localities in Brazil are in different ecoregions of the Atlantic forest. The present specimen was captured in a secondary forest habitat, near a mature forest. The karyotype revealed a diploid number of 58 chromosomes, with 25 pairs of acrocentric chromosomes, and four biarmed (metacentric and submetacentric) pairs of chromosomes.
Abrawayaomys ruschii é considerada como espécie rara devido à escassez de amostras em coleções científicas e em listas de faunas publicadas, dificultando qualquer proposta de classificação supragenérica entre os Sigmodontinae. Aqui apresentamos um novo registro de A. ruschii, sendo o primeiro para o estado do Rio de Janeiro (Aldeia Sapucai - Terra Indígena do Bracuí, Angra dos Reis). Por causa do pequeno número de exemplares existente não é possível definir uma distribuição geográfica precisa, entretanto, todas as localidades conhecidas estão em diferentes ecorregiões da Mata Atlântica. O espécime aqui reportado foi capturado em clareira com bambús na borda de uma floresta contínua aparentemente madura. O cariótipo de A. ruschii revelou um número diplóide igual de 58 cromossomos, com 25 pares de cromossomos acrocêntricos e quatro pares de cromossomos com dois braços (metacêntricos e submetacêntricos).
Resumo
Abrawayaomys ruschii is considered as a rare species due the scarcity of samples in scientific collections and in published lists, being difficult to assign it to any proposed suprageneric classification among the Sigmodontinae. We report here a new record of A. ruschii, the first for this species in the Rio de Janeiro state (Aldeia Sapucai - Terra Indígena do Bracuí, Angra dos Reis). Because of the small sample size it is not possible to define a precise geographic range, but the known localities in Brazil are in different ecoregions of the Atlantic forest. The present specimen was captured in a secondary forest habitat, near a mature forest. The karyotype revealed a diploid number of 58 chromosomes, with 25 pairs of acrocentric chromosomes, and four biarmed (metacentric and submetacentric) pairs of chromosomes.
Abrawayaomys ruschii é considerada como espécie rara devido à escassez de amostras em coleções científicas e em listas de faunas publicadas, dificultando qualquer proposta de classificação supragenérica entre os Sigmodontinae. Aqui apresentamos um novo registro de A. ruschii, sendo o primeiro para o estado do Rio de Janeiro (Aldeia Sapucai - Terra Indígena do Bracuí, Angra dos Reis). Por causa do pequeno número de exemplares existente não é possível definir uma distribuição geográfica precisa, entretanto, todas as localidades conhecidas estão em diferentes ecorregiões da Mata Atlântica. O espécime aqui reportado foi capturado em clareira com bambús na borda de uma floresta contínua aparentemente madura. O cariótipo de A. ruschii revelou um número diplóide igual de 58 cromossomos, com 25 pares de cromossomos acrocêntricos e quatro pares de cromossomos com dois braços (metacêntricos e submetacêntricos).