Metapopulation dynamics of the bog fritillary butterfly: demographic processes in a patchy population

Metapopulation models predicting the persistence of species on the verge of extinction in fragmented landscapes have to include local population dynamics. In this paper, we report on a 9-yr study in which a patchy population of the bog fritillary was monitored each year, with special focus on quantifying demographic parameters. We parameterised various constrained linear models (CLM) with capture-mark-recapture (CMR) data collected in the field each year and we tested the effects of several variables on demographic parameters. Selecting the best CLM, we estimated the mean and the variance of (1) individual parameters (survival and catchability) and (2) population features (population size, sex-ratio and recruitment). Survival was not related to the age of the individual but decreased continuously during the flight period, which means that lifetime expectancy is conversely related to the delay between the moment of the emergence of a given individual as compared to the emergence of the first adult in the population. Survival was lower in males than in females, as a consequence of male mate-locating behaviour. Daily population size fits a parabolic distribution in both sexes, males appearing, reaching their abundance peak and dying before females. Yearly variation in the sex-ratio is the consequence of the between-sex difference in the recruitment curve. Total adult population size shows large variations between years. Analysis of the relation between growth rate and abundance indicates density dependence, probably related to parasitism of the larval stages. Density at the equilibrium is about 200 adults/ha

Can demographic parameters be estimated from capture-recapture data on small grids? A test with forest rodents

This preliminary study proposes small trapping grids as an alternative to traditional large grids for the simultaneous monitoring of several rodent populations by capture-recapture. Monthly trapping sessions of wood mouse Apodemus sylvaticus (Linnaeus, 1758) and bank vole Clethrionomys glareolus (Schreber, 1780) were carried on over a small area (0.015 ha, 21 traps). The coherence of demographic parameter estimates on such small grids with those obtained on classical large grids was checked by performing two trapping sessions on a larger grid (0.9 ha, 110 traps, 10 m mesh) surrounding the small grid. We compared the two grid designs on the basis of sex ratio upon first capture, trap saturation rate, minimum number alive (MNA), monthly survival, and trappability. These demographic parameters proved to be non-biased by the trapped area, even though the precision was lower on the small grid. Small grids seem therefore to give the same picture of population dynamics as classical large grids except for parameters sensitive to an edge effect (eg density). By decreasing significantly the trapping effort, small grids will be of particular interest whenever the simultaneous operation of several trapping grids is needed (eg to compare different environmental conditions)

Differential foraging in presence of predator and conspecific odors in bank voles: A field enclosure study

Bank voles detect and discriminate other organisms, e. g., predators versus conspecifics, based on olfactory clues like urine, feces, or scent marks. The present field enclosure experiment was set up to determine whether scented food is sufficient for inducing such differentiated reactions in bank voles. Fourteen different odors were tested, divided into four categories: (1) terrestrial predators, (2) avian predators, (3) conspecifics, and (4) neutral origin (human, dog, solvent-treated, and unscented). The odors were extracted with methanol from pellets or feces, or were an artificial substitute. To test the influence of odors on the foraging behavior of voles, artificial food patches containing scented feeders were used. The feeders were cleaned and refilled daily with a calibrated amount of food sprayed with 1 ml of a different odor randomly chosen. The patches were also equipped with monochromatic cameras to monitor the occurrences of voles around the feeders. Both the visits at scented feeders and food consumption were analyzed for each odor. The results show that relative to their foraging activity on unscented food, bank voles significantly reduce it on food scented with odors of terrestrial predators, and increase it in the presence of conspecific odors. Their foraging activity was not affected by neutral scent, nor by scents from avian predators. These results prove that bank voles react to scented food in a way that varies according to the source of odor, even in the semi-natural conditions of an outdoor enclosure. © 2010 The Ecological Society of Japan