sents 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. KEY WORDS. Diffusion; fractal dimension; oriented search; random walk; search behaviour.

Effects of density dependence on animal movements have received much attention in ecology, but it is still debated to what extent dispersal and movements in general are density dependent, and their potential contribution to population regulation processes. Here, we determine the occurrence and nature of density dependence in the movements of a Neotropical marsupial, the black‐eared opossum Didelphis aurita Wied‐Neuwied 1826. Using spool‐and‐line tracking devices, we estimated the tortuosity of fine‐scale movements of 149 individuals by their fractal dimension D. We evaluated the relative importance of population size, reproductive or climatic seasons and reproductive maturity of individuals as determinants of movement tortuosity, using a model selection approach. Population size was the most important determinant of movement tortuosity, with season (climatic seasons for females, reproductive seasons for males) and reproductive maturity as secondary but also important variables. We detected a positive density‐dependent effect on movement tortuosity, resulting in more intensive use of areas by individuals during periods of high population size. This positive association between movement tortuosity and population size is more likely to result from intraspecific competition, which forces individuals to explore their environment more intensively during high‐density periods. Therefore, despite being density dependent, movements in D. aurita apparently do not contribute to population regulation mechanisms.

Body size and extinction risk in Brazilian carnivores. Biota Neotrop., 9(2): http://www.biotaneotropica.org.br/v9n2/en/ abstract?article+bn00509022009.Abstract: Because extinctions are not random across taxa, it is important for conservation biologists to identify the traits that make some species more vulnerable. Factors associated with vulnerability include small geographical ranges, low densities, high trophic level, "slow" life histories, body size, and tolerance to altered habitats. In this study we examined the relationship of body size, reproductive output, longevity, and extinction risk for carnivores occurring in Brazil. We used generalized linear models analyses on phylogenetically independent contrasts to test the effect of body size alone, and the combined effect of body size, litter size and longevity on extinction risk. Body size appeared in the two best models according to the selection criteria (AIC), and it was the most plausible bionomic variable associated with extinction risk. Litter size and longevity, bionomic traits previously associated with threat risk of Brazilian carnivores, were implausible. The higher extinction risk for larger species could result from body size influencing vulnerability to different human activities, such as killing, habitat destruction and fragmentation, and the small size of natural reserves. Keywords: carnivores, independent contrasts, longevity, reproductive output, South America, vulnerability to extinction.FORERO-MEDINA, G., VIEIRA, M.V., GRELLE, C.E.V. & ALMEIDA, P.J. Tamaño corporal como factor de amenaza en carnívoros brasileros. Biota Neotrop., 9(2): http://www.biotaneotropica.org.br/v9n2/es/ abstract?article+bn00509022009.Resumen: Debido a que las extinciones no son aleatorias a través de los diferentes taxa, es importante para los biólogos de la conservación identificar las características que hacen a algunas especies más vulnerables. Los factores asociados con la vulnerabilidad incluyen distribuciones geográficas pequeñas, densidades poblacionales bajas, niveles tróficos altos, historias de vida "lentas", tamaño del cuerpo, y tolerancia a habitats alterados. En este estudio examinamos la relación del tamaño corporal, el potencial reproductivo y la longevidad con el riesgo de extinción para los carnívoros brasileros. Realizamos análisis de modelos lineares generalizados con contrastes filogenéticamente independientes para probar el efecto del tamaño corporal solo, y el efecto combinado del tamaño corporal, el tamaño de la camada y la longevidad sobre el riesgo de extinción. El tamaño del cuerpo apareció en los dos mejores modelos de acuerdo con el criterio de selección (AIC) y es la variable bionómica más plausible afectando el riesgo de extinción. El tamaño de la prole y longevidad, otras variables bionómicas que han presentado tal efecto en otros estudios, fueron implausibles. La mayor probabilidad de amenaza para las especies grandes puede deberse a que el tamaño del cuerpo afecta la vulnerabilidad a diferentes actividades humanas como la caza, la de...

We study the population size time series of a Neotropical small mammal with the intent of detecting and modelling population regulation processes generated by density-dependent factors and their possible delayed effects. The application of analysis tools based on principles of statistical generality are nowadays a common practice for describing these phenomena, but, in general, they are more capable of generating clear diagnosis rather than granting valuable modelling. For this reason, in our approach, we detect the principal temporal structures on the bases of different correlation measures, and from these results we build an ad-hoc minimalist autoregressive model that incorporates the main drivers of the dynamics. Surprisingly our model is capable of reproducing very well the time patterns of the empirical series and, for the first time, clearly outlines the importance of the time of attaining sexual maturity as a central temporal scale for the dynamics of this species. In fact, an important advantage of this analysis scheme is that all the model parameters are directly biologically interpretable and potentially measurable, allowing a consistency check between model outputs and independent measurements.

Population projection models have received much attention in ecology and made important theoretical advances in the last 50 years. They represent vital tools for improving conservation strategies and management actions. Here we attempt to join some of theoretical advances made in the field of population projection modelling, briefly revise the history and present some applications derived from population matrix models in ecological and evolutionary studies.

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Evolutionary theory predicts that viable wild populations confront environmental variation by maintaining the variance of the most important vital rates low, a phenomenon also known as demographic buffering. However, patterns diverging from the demographic buffering hypothesis have also been reported.Here we used Population Matrix Models to test the hypothesis of buffering in the early survival of an Atlantic Forest marsupial. We used sensitivity analyses, which allow quantifying the effects that perturbations in specific vital rates could have on the population's growth rate. We obtained the sensitivities, elasticities, and second-order derivatives of the discrete population growth rate with respect to different vital rates for a population of the black-eared opossum (Didelphis aurita, Marsupialia, Didelphidae) in a preserved Atlantic Forest, the state of Rio de Janeiro, Brazil. The second-order derivatives offer an insight into the selection forces occurring during the life cycle, clarifying the processes behind the common pattern of early-survival importance. We found evidence of buffering in early survival, however, in one of the cohorts, early survival displayed evidence of opposed behavior to the expected under demographic buffering, thus revealing that established life-history patterns can be quickly modified by a small change in one vital rate.

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