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

Abstract

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat-related differences in body size and variability of seedcrops, suggesting differential selection for smaller squirrels in spruce-larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed-crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.

Interspecific competition affects the expression of personality-traits in natural populations

“…Also, keeping grey squirrel densities low by removal could decrease the intensity of interspecific competition resulting in reduced selective pressure on local adaptations of personality. Finally, other phenotypic characteristics may have more pronounced effects on fitness than personality traits; in fact we found strong positive effects of a squirrel’s body mass on reproduction, in agreement with earlier studies 16,32,34 .…”

Stress in biological invasions: Introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels

“…Each trapped squirrel was individually marked using numbered metal ear-tags (type 1003 S, National Band and Tag, Newport, KY, USA). We weighed squirrels to the nearest 5 g using a spring-balance (Pesola AG, Baar, Switzerland) and measured the length of the right hind foot (without nail, 0.5 mm) with a ruler (Wauters et al, 2007). A female's reproductive status was defined as nonbreeding (anoestrous, vulva small, no longitudinal opening, not lactating), postoestrous and pregnant (vulva partly or strongly swollen with longitudinal opening, enlarged belly during late pregnancy), or lactating (nipples large, milk excretion can be stimulated).…”

Invading parasites: spillover of an alien nematode reduces survival in a native species

“…The dependent variable local survival (model ii) from time t0 to time t12 was scored 1 if an individual was still present in the study area 12 months after the initial capture (time t0 ), it was scored 0 when it was no longer present at time t12 . (see also Wauters et al 2007 andSanticchia et al 2018b). Juvenile squirrels (\ 260 g) were excluded from the analyses.…”

“…Since seasonal fluctuations in body mass as well as effects of reproductive condition on body mass differ between male and female red squirrels (Wauters and Dhondt 1989;Wauters et al 2007) and reproductive success was determined only for females, we analysed the effects of parasite infection for each sex separately.…”

“…At first capture, each squirrel was marked with a numbered ear-tag (Monel 1005 1L1 ear-tag, National Band & Tag Co. Newport, KY, USA) and sexed. At every trapping occasion, squirrels were weighed to the nearest g using a spring balance, their right hind foot measured to the nearest 0.5 mm (nails excluded) with a thin wing ruler (Wauters et al 2007;Mazzamuto et al 2017b), and their reproductive condition recorded as described in (Dantzer et al 2016). We considered a female as reproductively active when it was in post-oestrus, pregnant or lactating (Wauters and Lens 1995;Santicchia et al 2018b).…”