Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon

Context The arctic ground squirrel (Urocitellus parryii) comprised 17% of the biomass of herbivores in the Yukon boreal forest during the summer months from 1987 to 1996 and was responsible for 23% of the energy flow at the herbivore level. By 2000, ground squirrel populations in this region collapsed to nearly zero and have remained there. Aims We summarise the population monitoring (since 1975) and recent experimental work that has been done on this key herbivore in the Kluane area of the southern Yukon to test one mechanistic hypothesis as the possible explanation for this population collapse and subsequent lack of recovery: predation. Methods Ground squirrels are the preferred summer prey of bird and mammal predators when snowshoe hare (Lepus americanus) populations are declining. We used translocations into formerly occupied habitat and radiotelemetry to determine movements and causes of death from 2009 to 2014. We surveyed 158 sites between 2008 and 2013 to measure the disappearance of colonies in alpine and forest habitats over 25 000 km2. Key results Ground squirrels from 2000 to 2013 comprised a small fraction of the herbivore biomass in the boreal forest zone, down from 17% earlier. Most forest populations (~95%) are currently extinct, whereas just over half (65%) of low-elevation meadow populations are locally extinct. One hypothesis is that ground squirrels in the forest have been driven into a predator pit from which they cannot recover. They remain abundant in alpine tundra (93% occupancy rate) and around airport runways and human habitations (97% occupancy), but there is no apparent dispersal from alpine areas down into the boreal forest. Conclusion The predator pit hypothesis is a likely explanation for the initial collapse and sustained decline in population size from 2000 to 2013. Recent attenuation of the hare cycle and milder winter climate have allowed shrubs to expand throughout the forest, thereby reducing visibility and increasing predation risk. This conclusion will be tested in further research using reintroductions to formerly occupied sites. Implication If the loss of this herbivore from the boreal forest is not reversed, predator pressure on the other major herbivores of the montane forest zone is likely to change significantly.

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Temperature and the Regulation of Enzyme Activity in the Hibernator. Isoenzymes of Liver Pyruvate Kinase from the Hibernating and Non-hibernating Arctic Ground Squirrel

Canadian Journal of Biochemistry ◽

10.1139/o74-126 ◽

1974 ◽

Vol 52 (10) ◽

pp. 894-902 ◽

Cited By ~ 14

Author(s):

Hans W. Behrisch

Keyword(s):

Molecular Weight ◽

Pyruvate Kinase ◽

Wide Temperature Range ◽

Ground Squirrel ◽

Energy Charge ◽

High Energy ◽

Ground Squirrels ◽

The Arctic ◽

Arctic Ground Squirrel ◽

Temperature Range

Liver of the hibernating (H) Arctic ground squirrel (Citellus undulatus) contains a single species of pyruvate kinase (PyK) that is distinct from the single isoenzyme of pyK observed in the non-hibernating (NH) ground squirrel, which has been previously described (Behrisch &Johnson (1974) Can. J. Biochem. 52, 547–559). The H-PyK has a pI value of 5.7 and a molecular weight of 241 000 – 243 000. Affinity of the H-PyK for the substrates phosphoenolpyruvate (PEP) and ADP is not affected by changing temperature. It is argued that this stability of the apparent Km's for substrate over a wide temperature range permits the hibernator to take advantage of the Q10 effect in maintaining a low rate of the PyK reaction. Similarly, affinity of H-PyK for the allosteric activator fructose-1,6-phosphate (FDP) and the inhibitor ATP is also conspicuously independent of temperature, suggesting a fine stoichiometry in the relative concentrations of the regulatory ligands in control of H-PyK over a wide temperature range. Further, affinity of H-PyK for the inhibitor ATP is about three- to fourfold lower than that of the NH-PyK, a condition that would favor the maintenance of a high energy charge in the hibernating liver cell. ATP apparently inhibits PyK by causing a dissociation of the enzyme molecule into two "halves" of about 110 000 molecular weight each. This dissociation is offset and reversed by FDP. Removal of the ATP by dialysis does not of itself result in a reassociation of the PyK "halves"; FDP and/or the substrates are required for the two subunits of PyK to reassociate. As the apparent Ki of H-PyK for ATP is higher than that of NH-PyK, substantially higher concentrations of ATP are required to effect the dissociation of H-PyK. Similarly, elevated concentrations of FDP are required to offset the ATP-caused dissociation of the H-PyK.Hibernating Arctic ground squirrels that are preparing to emerge finally from the hibernating state already possess substantial activities of the NH-PyK isoenzyme. This suggests that the animal "anticipates" its transition from one metabolic state from another. On the basis of these data a formal mechanism is proposed for the regulation of liver PyK in the Arctic ground squirrel in both the non-hibernating and hibernating states.

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Hibernation strategies and patterns in sympatric arctic species, the Alaska marmot and the arctic ground squirrel

Journal of Mammalogy ◽

10.1093/jmammal/gyv163 ◽

2015 ◽

Vol 97 (1) ◽

pp. 135-144 ◽

Cited By ~ 7

Author(s):

Trixie N. Lee ◽

Franziska Kohl ◽

C. Loren Buck ◽

Brian M. Barnes

Keyword(s):

Ground Squirrel ◽

Core Body Temperature ◽

Ground Squirrels ◽

The Arctic ◽

Arctic Ground Squirrel ◽

Slow Cooling ◽

Ambient Temperatures ◽

The Difference ◽

Arctic Ground Squirrels ◽

Core Body

Abstract We compared patterns of core body temperature ( Tb ) change, including inter-individual synchrony, in 2 free-living arctic hibernators that differ in size and sociality, the Alaska marmot ( Marmota broweri ) and the arctic ground squirrel ( Urocitellus parryii ). We report overwinter Tb changes from 3 to 4 marmots from the same hibernaculum in each of 3 years and from 7 ground squirrels that hibernated at 2 nearby burrow sites in 1 year. Very close synchrony in the timing of torpor and arousal cycles in Alaska marmots indicates social hibernation and thermoregulation, while lack of synchrony in arctic ground squirrels further confirms solitary hibernation. The mean duration between the first and last marmot measured within the group to initiate an arousal was 3.7±2.5h and to recool to 30°C during torpor entrance was 5.7±3.7h. The minimum Tb recorded in marmots was 0.6°C and in ground squirrels was −2.0°C. Marmots entering torpor displayed an interrupted pattern of Tb change defined by 2 distinct rates of cooling, early and late during entry, that differed by 21-fold. Ground squirrels cooled in a continuous pattern, initially 3-fold slower than marmots during rapid cooling but 4-fold faster during slow cooling. Both species must minimize energy expenditure to survive long arctic winters; our results suggest that Alaska marmots do this through social thermoregulation, while arctic ground squirrels decrease Tb below freezing to minimize the difference between body and ambient temperatures.

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A note comparing the primary structure of hemoglobin β chains of the arctic ground squirrel and the yellow-bellied marmot

Canadian Journal of Zoology ◽

10.1139/z87-480 ◽

1987 ◽

Vol 65 (12) ◽

pp. 3197-3200

Author(s):

Lawrence K. Duffy ◽

Margaret M. Ehrhardt ◽

Michael Romero ◽

Gregory L. Florant

Keyword(s):

Amino Acid ◽

Ground Squirrel ◽

Ground Squirrels ◽

The Arctic ◽

Sequence Difference ◽

Arctic Ground Squirrel ◽

Marmota Flaviventris ◽

Amino Terminal ◽

Recent Origin ◽

Β Chain

Hemoglobin β chains were isolated from both the arctic ground squirrel (Citellus parryii undulatus) and the yellow-bellied marmot (Marmota flaviventris). After various enzymatic and chemical cleavages, the primary structures of these β chains were determined. Only one sequence difference was found between the yellow-bellied marmot β chain and that of the European marmot (Marmota marmota). Ground squirrels (C. p. undulatus, Citellus townsendii, and Citellus citellus) showed more species-related differences than the marmots, with the β chain of the arctic ground squirrel differing from that of the townsend ground squirrel by four amino acid substitutions. In the amino terminal region of the β chain, a partial sequence analysis showed that Citellus tridecemlineatus was more similar to C. p. undulatus than to C. townsendii. These biochemical differences could reflect either an increased evolutionary rate of speciation in ground squirrels over that in the genus Marmota or a more recent origin of the species in the genus Marmota. The amino acid differences between these hemoglobins do not appear to be functionally significant in these ecologically similar animals.

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Patterns of hibernation in the arctic ground squirrel

Canadian Journal of Zoology ◽

10.1139/z75-160 ◽

1975 ◽

Vol 53 (9) ◽

pp. 1345-1355 ◽

Cited By ~ 22

Author(s):

Peter Morrison ◽

William Galster

Keyword(s):

Annual Cycle ◽

Ground Squirrel ◽

Ground Squirrels ◽

The Arctic ◽

Light Cycle ◽

Arctic Ground Squirrel ◽

Active Season ◽

Cyclic Patterns ◽

Arctic Ground Squirrels ◽

Normal Light

Cyclic patterns were defined in subspecies of arctic ground squirrels (Citellus undulatus) from the Brooks and Alaskan Ranges. In the annual cycle a heterothermal (hibernation) season with entry, maintenance, and emergence stages was distinguished from a homeothermal (active) season with reproductive, recovery/growth, maintenance, and fattening stages. The heterothermal season consisted of a series of short hibernation cycles in which heterothermal (hibernation) periods with reentry, refractory, and irritable phases were distinguished from homeothermal (active) periods with arousal, maintenance, and preparation phases. Squirrels in which exposure to darkness at 5 °C was delayed (Nov. vs. Sept.) showed a lesser response but emerged synchronously with the normal group. Entry was attenuated with a normal light cycle at 5 °C (8 vs. 3 weeks). Juveniles showed a 2- to 4-week delay in entry as compared to adults.

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Experimental manipulation of predation and food supply of arctic ground squirrels in the boreal forest

Canadian Journal of Zoology ◽

10.1139/z00-055 ◽

2000 ◽

Vol 78 (8) ◽

pp. 1309-1319 ◽

Cited By ~ 25

Author(s):

Andrea E Byrom ◽

Tim J Karels ◽

Charles J Krebs ◽

Rudy Boonstra

Keyword(s):

Boreal Forest ◽

Ground Squirrel ◽

Population Change ◽

Ground Squirrels ◽

Adult Survival ◽

Food Supplementation ◽

Snowshoe Hare ◽

Arctic Ground Squirrel ◽

Predator Removal ◽

Arctic Ground Squirrels

We examined whether arctic ground squirrel (Spermophilus parryii plesius) populations in northern boreal forest in the Yukon Territory, Canada, were limited by food, predators, or a combination of both, during the decline and low phases of a snowshoe hare cycle. From 1990 to 1995, populations were monitored in large-scale (1 km2) experimental manipulations. Squirrels were studied on eight 9-ha grids: four unmanipulated control grids, two food-supplemented grids, a predator-exclosure grid, and a predator-exclosure + food-supplemented grid. Population density was measured on all grids by livetrapping and active-season survival was measured using radiotelemetry. Population densities were lowest in 1992 and 1993 (2 years after the snowshoe hare population decline). Rates of population change were negative from 1991 to 1993, when predation pressure was most intense after the snowshoe hare decline, and positive from 1993 to 1995, when hares and predators were at low densities. Predation accounted for 125 of 130 mortalities (96%) of radio-collared squirrels. Adult survival was significantly lower in 1992 and 1993 than in 1994 and 1995, and was a strong predictor of annual rates of population change in arctic ground squirrels. Treatments were ranked as follows in their effect on adult survival: predator exclosure + food-supplemented > food-supplemented > predator exclosure > controls. Juvenile survival was lowest in 1992, and food addition and predator removal separately increased juvenile survival. On average, predator exclusion increased population densities twofold, food supplementation increased densities fourfold, and food supplementation and predator removal together increased densities 10-fold. We conclude that food and predation interact to limit arctic ground squirrel populations in the boreal forest during the decline and low phases of the snowshoe hare cycle. The snowshoe hare cycle may indirectly create a lagged secondary fluctuation in arctic ground squirrel populations through shared cyclic predators.

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