Morphological traits explain the individual position within resource-consumer networks of a Neotropical marsupial

Knowledge regarding the influence of individual traits on interaction patterns in nature can help understand the topological role of individuals within a network of intrapopulation interactions.We tested hypotheses on the relationships between individuals'positions within networks(specialization and centrality)of 4 populations of the mouse opossum Gracilinanus agilis and their traits(i.e.,body length,body condition,tail length relative to body length,sex,reproductive condition,and botfly parasitism)and also seasonal effects in the Brazilian savanna.Individuals with lower body length,better body condition,and relatively shorter tail were more specialized(i.e.,less connected within the network).Individuals were also more specialized and less connected during the warm-wet season.The relationship between individuals'position in the network and body traits,however,was independent of season.We propose that specialization may arise not only as a result of preferred feed-ing strategies by more capable individuals(i.e.,those with better body condition and potentially prone to defend and access high-quality food resources)but alsobecause of morphological constraints.Smaller/younger individuals(consequently with less experience in foraging)and short-tailed individuals(less skilled to explore the vertical strata of the vegetation)would feed only on a subset of the available food resources and consequently become more specialized.Moreover,individuals are more specialized during the warm-wet season because of high competition(population-dense period)and higher ecological opportunities(resource-rich period).Therefore,our study reveals the relevance of individual traits inshaping interactionpatternsandspecialization inpopulations.

Temporal niche overlap among insectivorous small mammals

Being active in the same environment at different times exposes animals to the effects of very different environmental factors,both biotic and abiotic.In the present study,we used live traps equipped with timing devices to evaluate the potential role of biotic factors(competition and food abundance)on overall overlap in the temporal niche axis of 4 insectivorous small mammals in high-elevation grassland fields(‘campos de altitude’)of southern Brazil.Based on resources availability(invertebrates),data on animal captures were pooled in 2 seasons:‘scarcity’(June 2001−September 2001)and‘abundance’(November 2001-May 2002)seasons.We tested for non-random structure in temporal niche overlap among the species in each season.These species were the rodents Oxymycterus nasutus(Waterhouse,1837),Deltamys sp.,Akodon azarae(Fischer,1829),and the marsupial Monodelphis brevicaudis Olfers,1818.The studied community was mainly diurnal with crepuscular peaks.Simulations using the Pianka index of niche overlap indicated that the empirical assemblage-wide overlap was not significantly different from randomly generated patterns in the abundance season but significantly greater than expected by chance alone in the scarcity season.All the species showed an increase in temporal niche breadth during the abundance season,which appears to be related to longer daylength and high nocturnal temperatures.Patterns on both temporal niche overlap and temporal niche breadth were the opposite to those that we were expecting in the case of diel activity patterns determined by competition for dietary resources.Therefore,we conclude that competition did not seem to be preponderant for determining patterns of temporal niche overlap by the studied community.