Louise Jodoin

Defining “high quality” food resources of herbivores: the case for meadow voles (Microtus pennsylvanicus)

SummaryFood availability, food utilization patterns and levels of some nutritional factors in plants were studied in 1984–85 in an old-field community supporting low to moderate densities of meadow voles (Microtus pennsylvanicus). Food choice and preference indices were positively related to levels of proteins, and negatively related to levels of total phenolics and ADL fibers in plants. High quality resources for voles were resources that had the highest amount of proteins, and the lowest level of total phenolics and ADL fibers among available plant species. There were only two plants species among the available ones that possessed these characteristics, Festuca rubra and Vicia cracca and they represented 25 to 50% of the available biomass during summer. Vole densities of up to 64 animals/ha were therefore not limited by the availability of high quality resources. Fecal analyses performed on 267 animals in 1984 and 269 voles in 1985 showed that all voles ate high quality resources. Meadow voles appear to choose foods with high protein content and low levels of digestion inhibitors, and not on the basis of caloric content or availability. These observations contradict predictions arising from current antiherbivore hypotheses and lead us to reconsider these models in light of this new evidence.

Is space management of female meadow voles microtus pennsylvanicus related to nutritive quality of plants

SummaryIt is thought by many (see Ims 1987 for review; Desy and Batzli 1989) that high quality food regulate population processes, territoriality and mating systems among small herbivores like meadow voles (Microtus pennsylvanicus). We thought that comparisons of nutritive components from selected plants eaten by sexually active and inactive voles, as well as between territorial and non territorial sexually active females would bring some light into these theoretical considerations. Sexually active females did have a higher diet quality over inactive ones and over active and inactive males. Nutritive components of selected species from territorial reproductive females did not vary significantly from those of the non territorial females the year of higher crowding conditions but they varied significantly the following year when population density of voles was much lower. This decline in food quality coincided with a switch in food selection. Since there were only eight plant species involved in such processes, we think that crowding condition and availability of high quality food are two factors involved concurrently in space management and territoriality among voles.

Pathology of Voles (Microtus pennsylvanicus) Fed with Plant Extracts

Several hypotheses related to antiherbivore properties of foodstuffs have recently been applied to meadow voles ( Microtus pennsylvanicus ). Most studies use simple mass parameters (body weight or internal organ weight) to detect negative or positive effects of plant preparations on weight variations. Because mass variations of internal organs are the end results of important metabolic reactions, an attempt was made to clarify relationships between standard mass variation analyses and histopathology of internal organs. Three hundred (300) voles were fed Rabbit Lab Chow coated with various dosages of plant extracts made of the most preferred plant species. After 2 and 10 weeks of treatment, the liver and kidneys were examined. Extracts of white clover ( Trifolium repens ) caused renal lesions that increased in severity with concentrations. Second growth forage at the 4–6-leaves-stage of reed phalaris grass ( Phalaris arundinacea ) and timothy ( Phleum pratense ) caused mild renal lesions, whereas that of bromegrass ( Bromus inermis ) caused vacuolar degeneration. Diets of bromegrass/timothy and bromegrass/ reed phalaris extracts caused few renal lesions. A discrepancy was found between results from histopathological exams and organ weight variation analyses. Pathological exams yielded more information on the effects of plant extracts on internal organs. Voles seemed to be affected by extracts of second growth forage, but as a whole, they appeared to be quite resistant to plant secondary metabolites.