From: George Wuerthner gwuerthner@gmail.com
Sent: Wed Jul 18 12:12:19 2012
Subject: Elk/Wolf Dissertation Defense
This video cast link below is a very detailed presentation by Authur Middleton of his research on elk and wolves in the Sunlight Basin area of Wyoming. if you haven't heard of his research previously, he basically concludes that a reduction of elk forage quality in summer due to rising temperatures, combined with higher grizzly predation pressure (41% of calves killed by grizzlies) is responsible for a reduction in migratory elk herds in this area. The study is worth listening to even though it is an hour as a nice example of some ecological research. It will apparently only be on line for a week so watch it now if you can. Below are his key points. In particular, there has been an astounding 8 degree rise in July temp. in Y'stone in the past few decades. Sent: Wed Jul 18 12:12:19 2012
Subject: Elk/Wolf Dissertation Defense
http://wyocast.uwyo.edu/WyoCast/Play/c063214dfcec4b3bba2bd6cdac991a8f1d
Arthur Middleton research
Background:
* The motivation behind the research was to consider the cause of the observed population decline of the Clarks Fork migratory elk herd. The herd has been declining since the mid-1990s, i.e., since wolves were reintroduced to Yellowstone.
* Hypothesis: Does the presence of wolves in the Greater Yellowstone area lead to "non-consumptive effects" (i.e., stress/fear effects) on the Clarks Fork herd sufficient to reduce the elk population? More specifically, do female elk respond to the presence of wolves in such a manner (e.g., moving to areas of high cover/low forage value) that their fat stores are depleted, and thus their pregnancy rates go down?
Findings:
* Elk do not respond to the presence of wolves until the wolves are within 1 km (i.e., in the immediate area).
* There is no difference in habitat usage or foraging behavior of an elk before/after a wolf encounter.
* Interactions (of the <1 km variety) between a wolf and any individual elk from the migratory herd were relatively infrequent, occurring once every 9 days.
* Predation risk was not an influencing factor on elk body fat percentage. In fact, looking across a number of herds, late winter body fat percentages were higher in elk herds whose range overlapped with wolves.
* Body fat percentage in March was an important predictor of pregnancy probability. Thus, summer factors affecting probability of conception (e.g., drought) seem more important than winter factors affecting fetal mortality rates.
Conservation/Management Implications:
* Wolves appear to affect elk numbers largely or entirely through direct killing and consumption. Thus, managers probably don't need to account for nonconsumptive effects of wolves on elk populations. Wolf control on winter ranges is not likely to be useful.
* Elk are pretty good at dealing with wolves; any changes in range distribution are probably unrelated to wolf presence.
* The findings of this study throw into some doubt the findings of the studies showing that wolves are driving down elk populations, thus benefiting riparian vegetation.
* What might be happening to the elk? Two likely causes of decline include drought effects and grizzly bear predation. Specifically:
(1) Over the past 20 years, Yellowstone has experienced an increase in July temperatures of 8 degrees F. This has led to an earlier and shorter green-up of grasses, an important food source for elk. If a nursing female is unable to obtain sufficient nutrition to both sustain her calf and put on fat stores, she is unlikely to calve the next year. Indeed, a low pregnancy rate among lactating females has been observed.
(2) Grizzly bears are the #1 predator of elk calves in Yellowstone (accounting for 41% of elk calf predation). This effect may be strengthening as bears continue to lose key forage items (e.g., whitebark pine nut and cutthroat trout).
wolves and elk in yellowstone
* The motivation behind the research was to consider the cause of the observed population decline of the Clarks Fork migratory elk herd. The herd has been declining since the mid-1990s, i.e., since wolves were reintroduced to Yellowstone.
* Hypothesis: Does the presence of wolves in the Greater Yellowstone area lead to "non-consumptive effects" (i.e., stress/fear effects) on the Clarks Fork herd sufficient to reduce the elk population? More specifically, do female elk respond to the presence of wolves in such a manner (e.g., moving to areas of high cover/low forage value) that their fat stores are depleted, and thus their pregnancy rates go down?
Findings:
* Elk do not respond to the presence of wolves until the wolves are within 1 km (i.e., in the immediate area).
* There is no difference in habitat usage or foraging behavior of an elk before/after a wolf encounter.
* Interactions (of the <1 km variety) between a wolf and any individual elk from the migratory herd were relatively infrequent, occurring once every 9 days.
* Predation risk was not an influencing factor on elk body fat percentage. In fact, looking across a number of herds, late winter body fat percentages were higher in elk herds whose range overlapped with wolves.
* Body fat percentage in March was an important predictor of pregnancy probability. Thus, summer factors affecting probability of conception (e.g., drought) seem more important than winter factors affecting fetal mortality rates.
Conservation/Management Implications:
* Wolves appear to affect elk numbers largely or entirely through direct killing and consumption. Thus, managers probably don't need to account for nonconsumptive effects of wolves on elk populations. Wolf control on winter ranges is not likely to be useful.
* Elk are pretty good at dealing with wolves; any changes in range distribution are probably unrelated to wolf presence.
* The findings of this study throw into some doubt the findings of the studies showing that wolves are driving down elk populations, thus benefiting riparian vegetation.
* What might be happening to the elk? Two likely causes of decline include drought effects and grizzly bear predation. Specifically:
(1) Over the past 20 years, Yellowstone has experienced an increase in July temperatures of 8 degrees F. This has led to an earlier and shorter green-up of grasses, an important food source for elk. If a nursing female is unable to obtain sufficient nutrition to both sustain her calf and put on fat stores, she is unlikely to calve the next year. Indeed, a low pregnancy rate among lactating females has been observed.
(2) Grizzly bears are the #1 predator of elk calves in Yellowstone (accounting for 41% of elk calf predation). This effect may be strengthening as bears continue to lose key forage items (e.g., whitebark pine nut and cutthroat trout).
wolves and elk in yellowstone
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