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Forage preferences in two species of prairie dog (Cynomys parvidens and Cynomus ludovicianus): implications for hibernation and facultative heterothermy


Erin M. Lehmer, Department of Biology, University of Utah, Salt Lake City, UT, USA


Several laboratory studies have shown that the ingestion of dietary linoleic (18:2 ω6) acid before winter can promote deep and continuous torpor, whereas excess consumption of α-linolenic acid (18:3 ω3) can interfere with an animal's ability to reach and maintain low body temperatures during torpor. As mammalian heterotherms obtain linoleic and α-linolenic acid strictly from the diet, diet selection has been proposed as a mechanism that allows hibernators to ingest levels of linoleic and α-linolenic acid that promote favorable torpor patterns. Here diet, dietary nutrient content and patterns of forage preference of a representative hibernator, the Utah prairie dog Cynomys parvidens, and a facultative heterotherm, the black-tailed prairie dog Cynomys ludovicianus, were examined under natural field conditions. Diets of black-tailed (BTPD) and Utah prairie dogs (UTPD) differed across seasons (BTPD F26,108=9.59, P<0.01; UTPD F38,80=3.25, P<0.01) and elevations (BTPD F26,108=20.15, P<0.01; UTPD F38,80=20.51, P<0.01), and forage preference indices indicate that neither species randomly selected plant species relative to their abundance on colonies in any season. Black-tailed prairie dogs did not consume or avoid consumption of plant species based on levels of total lipids, linoleic acid, α-linolenic acid or nitrogen. Considering only the plants consumed, black-tailed prairie dogs appeared to prefer plants with low levels of α-linolenic acid (F1,19=5.81, P=0.03), but there were no detectable relationships between preference and other nutrients. Utah prairie dogs consumed plants higher in α-linolenic acid (t=1.98, P=0.05) and avoided plants high in linoleic acid (t=−2.02, P=0.04), but consumption-avoidance decisions did not appear to be related to nitrogen or total lipids. Of the plants consumed, Utah prairie dogs again preferred plants high in α-linolenic acid (F1,17=4.62, P=0.05). Levels of linoleic and α-linolenic acid were positively correlated in plants consumed by prairie dogs (BTPD Pearson r=0.66, P<0.01; UTPD Pearson r=0.79, P<0.01), reducing the opportunity for independent selection of either lipid.