Holarctic Marmots as a factor of Biodiversity.
Rumiantsev V.Yu;, Nikol'skii A.A. & Brandler O.V. eds.,
Abstracts of the
Conference on Marmots (Cheboksary, Russia, 25-30 August 1997), Moscow ABF 1997, 216p.
BODY-MASS DIVERSITY IN MARMOTS
K.B. Armitage, D.T. Blumstein
Department of Systematics and Ecology, The University of Kansas
Marmots are the largest mammals known to be true hibernators. A major advantage of large body size is that fat storage scales directly with mass (M1) and that the use of fat during hibernation at low environmental temperatures scales with M0.5. Maximal mass occurs at immergence into hibernation and minimal mass occurs at emergence or during the early part of the active season. Mass loss is the difference between maximal and minimal masses. Immergence mass and emergence mass are highly correlated. There is a 2-fold difference in body-mass in the 13 species considered in this analysis. We explore differences in body-mass and mass loss, which is the difference between immergence mass and emergence mass.
Total mass loss is correlated with immergence mass (IM). The rate of mass loss (g/d), specific mass loss (m/g IM/d), total mass loss, and percentage of IM lost are significantly correlated with each other (r varied from 0.72 to 0.94). These relationships suggest that big species are big because they require the use of considerable mass during hibernation. However, no measure of mass loss is significantly correlated with the length of hibernation, which suggests that factors other than energy use during torpor are important.
Emergence mass, the length of the active season, and age of first reproduction are interrelated. The smaller species first breed at age two; if large, they have a longer active season. The larger species, with a short to moderately long active season, breed at age three, except M. monax, with the longest active season, breeds at age one.
Environmental harshness may provide a unifying theme that integrates all life-history traits. Five features of marmot biology provide evidence of environmental harshness. First, reproductive females accumulate less fat than barren females and embryos may be reabsorbed in bad years. Second, many species lose mass following emergence.Third, home range areas vary from 0.13 ha to 13.8 ha; this variation may reflect resource availability. Fourth, many species mate before emergence or initiate development before emergence. Fifth, the females of many species skip reproduction for one or more years.
Social thermoregulation, in which adults or subadults warm juveniles, is a source of mass loss. Mass loss patterns are related to four types of social systems that we define based on summer and winter social groups. M. monax females live solitarily in a diffuse harem polygyny where the home range of one male may overlap the home ranges of several females; solitary hibernation occurs and daily mass loss is relatively high. In M. flaviventris females form social groups with an adult male to form a concentrated harem polygyny. Hibernation typically is solitary except for juveniles.Concentrated harem polygyny also occurs in M. olympus and M. caligata where females
live somewhat independently during the summer and all hibernate as a group.
Mass loss is high. The remaining species live in integrated family groups with joint hibernation and lose a high percentage of mass.
We conclude that heavy energy demands are met by a large body size. The mass cycle of marmots can be fully understood when we can partition out the various sources of loss that are associated with environmental harshness.