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What if it gets crowded? Density‐dependent tortuosity in individual movements of a Neotropical mammal

A. L. Almeida, Paulo José, Vieira, Marcus Vinícius, Prevedello, Jayme Augusto, Kajin, Maja, Forero‐Medina, German, Cerqueira, Rui
Austral ecology 2015 v.40 no.7 pp. 758-764
Didelphis, females, forces, fractal dimensions, intraspecific competition, males, opossums, population size, seasons, sexual maturity, tropics
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.