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.The amount of food animals consume will affect their fitness in various ways. 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). A diet rich in lipids allows a high rate of energy intake and, in a large variety of species, the accumulation of fat reserves that cause a (seasonal) increase in body mass. 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. 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 les...

Unravelling causality from correlations: revealing the impacts of endemic ectoparasites on a protected species (tuatara)

“…Body condition is a non-destructive estimate of the energetic state of an individual (stored versus expended energy) (Schulte-Hostedde et al 2005). Thus, energy deficits (negative body condition) can reduce the resources available for direct fitness-related traits, such as reproduction, growth and survival (Robb et al 1992 ;Murray, 2002 ;Wauters et al 2007). Condition-mediated effects of parasites on host fitness have been observed in other taxa.…”

Natural infection with two genotypes of Cryptosporidium in red squirrels (Sciurus vulgaris) in Italy

“…Cryptosporidium was previously detected in red squirrels by Bertolino et al (2003) in these two localities. Squirrel densities in the study areas in the years 2000 to 2005 ranged from 0.20 to 0.42 ind./ha at Rhemes and between 0.18 FOLIA PARASITOLOGICA 55: 95-99, 2008 and 0.45 ind./ha at Cogne (Bertolino et al 2003, Wauters et al 2007). …”

“…Each trapped squirrel was placed into a zipper-tube or wire-mesh 'handling cone' to minimize stress during handling and individually marked using numbered metal ear-tags (type 1003 S, 10 by 2 mm, National Band and Tag Co. Newport, Kentucky, USA). Animals were weighed to the nearest 5 g using a Pesola spring-balance (Pesola AG, Baar, Switzerland) and the length of the right hind foot (without nail) was measured (0.5 mm) with a thin ruler (Wauters et al 2005(Wauters et al , 2007. The sex, age and reproductive condition of each subject was recorded following Dhondt (1989, 1995).…”

Testing for a predicted decrease in body size in brown bears (Ursus arctos) based on a historical shift in diet

“…With this physical and ecological flexibility, bear populations and the species have been sustained for a long period of time even in the face of drastic environmental change. Nevertheless, the historical decrease in body size has likely influenced population dynamics because body size is correlated with many population parameters, including population density, productivity, and persistence (Atkinson and Ramsay 1995;Andersson and Iwasa 1996;Post et al 1997;Laundré et al 2007;Wauters et al 2007). The major historical dietary shift in Hokkaido brown bears is likely the result of human activities, such as salmon fishing and dam construction (Matsubayashi et al 2015).…”

“…In mammals, a larger body size influences various ecological and physiological factors, including selection of available dietary resources (McNab 1971), reproductive success (Andersson and Iwasa 1996), and population growth and density (Atkinson and Ramsay 1995;Post et al 1997;Laundré et al 2007;Wauters et al 2007). However, a humaninduced shift in the diets of omnivorous bears has been reported in many regions around the world (e.g., Peirce and Van Daele 2006;Kavčič et al 2013;Hopkins et al 2014).…”