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

2000 ◽  
Vol 78 (8) ◽  
pp. 1309-1319 ◽  
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.

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

2015 ◽  
Vol 42 (2) ◽  
pp. 176 ◽  
Author(s):  
Jeffery R. Werner ◽  
Charles J. Krebs ◽  
Scott A. Donker ◽  
Rudy Boonstra ◽  
Michael J. Sheriff
Keyword(s):  
Boreal Forest ◽  
Ground Squirrel ◽  
Boreal Forests ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Forest Zone ◽  
Winter Climate ◽  
Population Collapse ◽  
Predator Pit

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.

scholarly journals Arctic ground squirrel predation on collared lemmings

1990 ◽  
Vol 68 (4) ◽  
pp. 757-760 ◽  
Author(s):  
Rudy Boonstra ◽  
Charles J. Krebs ◽  
Michelle Kanter
Keyword(s):  
Northwest Territories ◽  
Ground Squirrel ◽  
Ground Squirrels ◽  
Intensive Study ◽  
Arctic Ground Squirrel ◽  
Spermophilus Parryii ◽  
Arctic Ground Squirrels

We document the first recorded evidence of predation of collared lemmings (Dicrostonyx kilangmiutak) by arctic ground squirrels (Spermophilus parryii). During an intensive study of lemming populations at Pearce Point, Northwest Territories, using livetrapping and radiotelemetry, we found one and six lemmings predated by arctic ground squirrels in 1987 and 1988, respectively. Predation involved some or all of the following: digging lemmings out of burrows, carrying them to temporary ground squirrel burrows, and partial or complete consumption. The best evidence was obtained during 1988, when a minimum of 4.5% (6/132) of radiotagged lemmings were killed by squirrels.

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

2015 ◽  
Vol 97 (1) ◽  
pp. 135-144 ◽  
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.

scholarly journals How apparent competition and predator responses led to the decline of Arctic ground squirrels in the boreal forests of the southwest Yukon

2016 ◽  
Author(s):  
Jeffery R Werner ◽  
Elizabeth A Gillis ◽  
Rudy Boonstra ◽  
Charles J Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition and indirect mutualism via prey switching are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers and changes in the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. Arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators when few individuals are left in a colony.

Ketone bodies: a source of energy during hibernation

1981 ◽  
Vol 59 (5) ◽  
pp. 754-760 ◽  
Author(s):  
Josefine C. Rauch ◽  
Hans W. Behrisch
Keyword(s):  
Ground Squirrel ◽  
Ketone Body ◽  
Ketone Bodies ◽  
Ground Squirrels ◽  
Brown Fat ◽  
Arctic Ground Squirrel ◽  
Tissue Concentrations ◽  
Brown Adipose ◽  
Spermophilus Undulatus ◽  
Arctic Ground Squirrels

Tissue concentrations of acetoacetate and β-hydroxybutyrate (ketone bodies) were determined for the blood, liver, caecum, heart, and axillary brown fat, from nonhibernating and hibernating arctic ground squirrels, Spermophilus undulatus, in late spring and during winter, respectively. AcetylCoA and acetoacetylCoA concentrations were measured in the liver, heart, and brown adipose tissue.Except that the concentration of acetylCoA remained unchanged in the liver, all tissues investigated showed elevated concentrations of acetylCoA, acetoacetylCoA, and ketone bodies during the hibernating state. From the increased concentrations of acetoacetate and β-hydroxybutyrate it was deduced that active ketone body metabolism occurs in the hibernating arctic ground squirrel, and that during hibernation, ketone bodies are probably an important source of energy.

scholarly journals Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs

2014 ◽  
Vol 10 (11) ◽  
pp. 20140734 ◽  
Author(s):  
Rudy Boonstra ◽  
Kaiguo Mo ◽  
Douglas Ashley Monks
Keyword(s):  
Ground Squirrel ◽  
Anabolic Steroids ◽  
Muscle Growth ◽  
Ground Squirrels ◽  
Arctic Ground Squirrel ◽  
Androgen Action ◽  
Trade Offs ◽  
Arctic Ground Squirrels ◽  
Columbian Ground Squirrels ◽  
Southern Species

Androgens have benefits, such as promoting muscle growth, but also significant costs, including suppression of immune function. In many species, these trade-offs in androgen action are reflected in regulated androgen production, which is typically highest only in reproductive males. However, all non-reproductive Arctic ground squirrels, irrespective of age and sex, have high levels of androgens prior to hibernating at sub-zero temperatures. Androgens appear to be required to make muscle in summer, which, together with lipid, is then catabolized during overwinter. By contrast, most hibernating mammals catabolize only lipid. We tested the hypothesis that androgen action is selectively enhanced in Arctic ground squirrel muscle because of an upregulation of androgen receptors (ARs). Using Western blot analysis, we found that Arctic ground squirrels have AR in skeletal muscle more than four times that of Columbian ground squirrels, a related southern species that overwinters at approximately 0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph nodes was equivalent in both species. Brain AR was also modestly but significantly increased in Arctic ground squirrel relative to Columbian ground squirrel. These results are consistent with the hypothesis that tissue-specific AR regulation prior to hibernation provides a mechanism whereby Arctic ground squirrels obtain the life-history benefits and mitigate the costs associated with high androgen production.

scholarly journals You can hide but you can’t run: apparent competition, predator responses and the decline of Arctic ground squirrels in boreal forests of the southwest Yukon

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2303 ◽  
Author(s):  
Jeffery R. Werner ◽  
Elizabeth A. Gillis ◽  
Rudy Boonstra ◽  
Charles J. Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition via prey switching followed by positive indirect effects are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers, and the changes to the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. When few individuals are left in a colony, arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators.

Patterns of hibernation in the arctic ground squirrel

1975 ◽  
Vol 53 (9) ◽  
pp. 1345-1355 ◽  
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.

scholarly journals How apparent competition and predator responses led to the decline of Arctic ground squirrels in the boreal forests of the southwest Yukon

2016 ◽  
Author(s):  
Jeffery R Werner ◽  
Elizabeth A Gillis ◽  
Rudy Boonstra ◽  
Charles J Krebs
Keyword(s):  
Ground Squirrel ◽  
Boreal Forests ◽  
Apparent Competition ◽  
Ground Squirrels ◽  
Critical Threshold ◽  
Snowshoe Hare ◽  
Sympatric Populations ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Arctic Ground Squirrels

Throughout much of North America’s boreal forest, the cyclical fluctuations of snowshoe hare populations (Lepus americanus) may cause other herbivores to become entrained in similar cycles. Alternating apparent competition and indirect mutualism via prey switching are the mechanisms behind this interaction. Our purpose is to document a change in the role of indirect interactions between sympatric populations of hares and arctic ground squirrels (Urocitellus parryii plesius), and to emphasize the influence of predation for controlling ground squirrel numbers. We used mark-recapture to estimate the population densities of both species over a 25-year period that covered two snowshoe hare cycles. We analysed the strength of association between snowshoe hare and ground squirrel numbers and changes in the seasonal and annual population growth rates of ground squirrels over time. A hyperbolic curve best describes the per capita rate of increase of ground squirrels relative to their population size, with a single stable equilibrium and a lower critical threshold below which populations drift to extinction. The crossing of this unstable boundary resulted in the subsequent uncoupling of ground squirrel and hare populations following the decline phase of their cycles in 1998. The implications are that this sustained Type II predator response led to the local extinction of ground squirrels. Arctic ground squirrels may also have exhibited an Allee effect caused by the disruption of social signalling of approaching predators when few individuals are left in a colony.

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

1974 ◽  
Vol 52 (10) ◽  
pp. 894-902 ◽  
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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