Climatic variability and body size variation in the muskrats (Ondatra zibethicus) of North America

Abstract

Patterns of geographic variation in nine morphological characters of adult muskrats (Ondatra zibethicus) are investigated by multiple regression and canonical correlation analysis. Three variables describing the annual precipitation regimen account for 16 to 33% of the variance in each of the skeletal measurements. Highly variable precipitation patterns result in low rates of germination and survivorship for preferred aquatic food plants which in turn reduces average total food availability for muskrats. In large individuals nutritive demands may exceed supply, thus selection favors smaller body size in areas of low food availability.After removing the variation attributable to three precipitation variables, the residual variation in the morphological variables is exposed to canonical correlation analysis with a set of 10 environmental and geographic variables. A canonical variate loaded for climatic seasonality accounts for 60% of the variance in a canonical variate of the morphological residuals which load as a general body size variate. It is argued that seasonality is a major factor selecting for large body size in muskrats and other organisms. During seasonal periods of resource abundance natural selection favors individuals with rapid growth to a large size, while concurrently enhancing survivorship through oncoming periods of resource shortage.

Palaeoenvironmental analysis of the Aragonian (middle Miocene) mammalian faunas from the Madrid Basin based on body-size structure

“…These rules have been almost equally accepted (Mayr, 1956(Mayr, , 1963Ashton et al, 2000;Ashton, 2001;Meiri and Dayan, 2003) and rejected (Scholander, 1954;McNab, 1971;Fuentes and Jaksić, 1979;Meiri et al, 2007). Although the original ideas expressed by Bergmann and Allen are not exactly supported, a relationship between climatic proxies and mammal body size can be established (Boyce, 1978;Wigginton and Dobson, 1999;YomTov and Geffen, 2006) and confirms the value of this feature in climate inference.…”

Clinal variation in body size and sexual dimorphism in an Indian fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae)

“…In contrast to explanations based on surface/volume ratios, the fasting endurance hypothesis is based on a relationship between starvation time and body mass that is derived from total units, and therefore can be interpreted with respect to both total and mass-specific rates of metabolism (McNab, 1999). This hypothesis has received correlative support from studies of intraspecific variation in temperate zone rodents (Boyce, 1978;Owen, 1989), marsupials (Quin et al, 1996), and passerine birds (Murphy, 1985). The fasting-endurance hypothesis deserves serious attention in nonmigratory tropical frugivores and nectarivores that rely on the sequential overlap of fruiting and flowering peaks in different plant species throughout the annual cycle.…”

Patterns of landscape and assemblage structure along a latitudinal gradient in ocean climate

“…Most species vary in their ecology across latitude in response to large-scale environmental variability (Brown 1984); these responses include changes in demography (Boyce 1978, 2011a). Describing such large-scale patterns, and elucidating the processes that create them, can make an important contribution to ecology, evolutionary biology, and conservation (Briggs 1974, Lüning 1990, Roy et al 1998.…”