Wood Mouse Apodemus Sylvaticus Winter Food Supply: Density, Condition, Breeding, and Parasites

Abstract

We determined the individual and population responses to food availability of wood mice Apodemus sylvaticus wintering in small forest woodlots by means of a food addition experiment. The allocation of the extra provided energy to the maintenance of body condition and reproduction was expected to vary between sexes due to their different energy investment in reproduction and to the different indirect costs of reproduction associated with different hormone-mediated susceptibilities to parasite infections.There were no effects of food supplementation on the density of adult males or on the overall density of mice. However, adult females were marginally more abundant and the sex ratio was more balanced in supplemented woodlots. Body condition (as estimated by body mass, body mass relative to body size, and amount of fat reserves), did not differ among treatments for either adult males or females. The prevalence and intensity of endoparasites of short life cycle (oxyurid nematodes) were lower in food-supplemented woodlots than in controls and lower in females than in males. No differences were found for endoparasites with long life cycles (telacid nematodes and cestodes). Males with intermediate parasite loads were in better body condition than either nonparasitized or highly parasitized individuals, and the body condition of each group of males was better in foodsupplemented woodlots than in controls. This nonlinear relationship between parasite loads and body condition was apparently due to indirect costs of reproduction in control woodlots, where there was a direct relationship between male reproductive effort (relative testis size) and parasite loads. This relationship was not found in supplemented woodlots.Most individuals were breeding actively at the end of winter. Males had larger testicles, and females showed an advanced breeding, and probably enhanced survival and larger litter sizes, in supplemented woodlots. Individual mice wintering in Mediterranean fragmented forests are thus food limited, and directed most of the extra provided food resources to reproduction without losing body condition or antiparasite abilities. This enhanced reproduction, rather than improved body condition, may translate into larger population densities and recruitment.

Preliminary effects of fire and mechanical fuel treatments on the abundance of small mammals in the mixed-conifer forest of the Sierra Nevada

“…Increased precipitation and cone crop events may have increased the availability of seeds and vegetation across the landscape. Small mammals are known respond positively to food supplementation experiments, and annual increases may have been a result of increased survival, reproduction, reduced territory size, or increased predator vigilance (Koskela et al, 1998;Arenz and Leger, 2000;Dobson and Oli, 2001;Yunger, 2002;Diaz and Alonso, 2003;Huitu et al, 2003;Unangst and Wunder, 2004). Finally, gray fox (Urocyon cinereoargenteus) occurrence declined from 53% to 37% to 10% from 2001 to 2003 (Amacher, unpublished camera trap data).…”

Effects of spatio-temporal variation in food supply on red squirrel Sciurus vulgaris body size and body mass and its consequences for some fitness components

“…At VAL, males reached higher autumn mass in 2002 than in2003 and 2004 (DLSM, pB0.05, Fig. At VAL, males reached higher autumn mass in 2002 than in2003 and 2004 (DLSM, pB0.05, Fig.…”

“…Food assimilation produces energy necessary for body growth and/or maintenance of body condition and for reproductive investment, as well as essential nutrients such as proteins, carbohydrates, minerals, and vitamins (Robbins 1993, Cuthill andHouston 1997). Moreover, heavier animals often are more likely to reproduce successfully, particularly in female mammals, and tend to be better competitors (social dominance) than conspecifics of smaller size or lesser body mass (Wauters and Dhondt 1989a, Robbins 1993, Law 1995, Cuthill and Houston 1997, Lin and Batzli 2001, Diaz and Alonso 2003. In many vertebrates, a relatively high body mass in relation to body size is an indication of good condition: such individuals are more likely to survive critical periods of food shortage or extreme weather conditions (Blem 1990, Millar and Hickling 1990, Schulte-Hostedde et al 2001.…”

Effects of forest fragmentation on the oak–rodent mutualism

“…Forest fragmentation may have major effects on these factors. Regarding intraspecific competition for acorns, small oak woodlots house denser wood mouse populations than continuous forest (García et al , Díaz and Alonso ). Besides, acorn production is expected to be larger in small oak woodlots due to relaxed intraspecific competition among trees at forest edges since acorn production is strongly dependent on local tree density (Koenig et al ).…”