The Lynx and the Snowshoe Hare

Which factors cause the cyclical oscillations in the population?

Presented by Megan McCarthyWinter Ecology – Spring 2005

Mountain Research Station – University of Colorado, Boulder

A Closer Look: Lynx and Hare Dynamics

• Predator Prey Relationships and The Phase-Shift Model: A General Description

• The Canadian Lynx and The Snowshoe Hare: Animal Characteristics and Behavioral Traits

• The Cyclic Predator–Prey Relationship between the Lynx and the Hare

• Different Philosophies about and Possible Causes of the Cyclic Predator-Prey Patterns

• Other Possible Causes and Effects• Conclusion and Review

Predator-Prey RelationshipsThe Balance of Nature…• Bottom Up Dynamic (Prey Controls Predator)

– Structure depends on prey availability and nutrient content from low trophic levels

• Top Down Dynamics (Predator Controls Prey)– Wolf and Moose Relationship– Structure of lower trophic levels depends on effect of consumers at high trophic levels

(Hassel, 1998)

The Predator: Lynx Canadensis;The Canadian Lynx

• Snowshoe-like paws• Long haired, beautiful

coat• Eyesight better then

other senses• 10 – 14 kg. when

mature• Prey on Hare mainly –

also Ptarmigan, Vole, Red Squirrels and other flesh

One of Sixteen Lynx Kittens born in Colorado Summer 2004

(Marty, 1995)

The Prey: Lepus AmericanusThe Snowshoe Hare

• Snowshoe-like hind Legs

• Nocturnal• 3m bounds at 45mph• 2 kg when mature• Diet consists of

foliage from plant and trees

(Marty, 1995)

Predator – Prey Relationships: A Description

•

The predator’s abundance curve almost always lags behind that of the prey

(Madler, 1998)

Range of Lynx and Snowshoe Hare

Current Lynx Distribution

(Launchbaugh, 2004)

Description of the Dynamics

• Cycle First seen by Hudson Fur Traders 100 years ago

• 10 year population cycles• Went from 7-9 hares per hectare in ’90 to

0-1 per hectare in ’91• Winter after crash dropped from 30 – 3

lynx per 100 km2• Continue to die off 2 years after the hare

crash(Marty, 1995)

Causes of Phase Shift Dynamic• Hare Populations increase and eat vegetation • Vegetation produces secondary defense

compounds in response – less palatable and nutritious

• Triggers hare pop. crash – hares cannibalize – end up dying in great numbers

• Lynx continue to feed on hares, but run out of prey eventually

• Plant growth slowly recovers and rejuvenate hare population

(Ecological Model, 2002)

Oscillations of the Two Populations Over Time

(Ecological Model, 2002)

Top Down???• Is the Canadian Lynx the main factor in the decline

in Hare population?

• NO! The Lynx continue to breed and reproduce until the run out of prey

• If lynx predation main cause, the flux should not occur when there are hardly any lynx, but it does

• Other factors must be at work• Then what causes the original decline???

Bottom Up????• Does the hares supply of vegetation control the population

of the Lynx? YES!!! Diet of hares decrease – hares die off and

Lynx have to turn to other prey

So…What Happens???

• The lynx are picky and many starve to death• Lack of predators, the vegetation grows back • Lack of predators and more vegetation, the Snowshoe

Hare rejuvenates• With more prey and available nutrition, the Lynx population

grows and the cycle begins!

(Poole, 1994)

Counter – Philosophies

Vegetation:Hares also adapt to the vegetation defenses and chemical counter-defenses over time, therefore cycle is not mainly affected by lack of nutritious vegetation.

Trapping: Trapping of the Lynx is a huge reason why the hare population sky rocketsThis idea comes from the top down theory

(MacLean, 1980)

VEGETATION• Hares are efficient winter

browsers• They can forage in harsh

winter environments• Hares avoid chemicals

found in plants due to increasing population

• Hares dilute any chemical ingested by eating a wide variety of other plants

Snowshoe Hare Eating (Marty, 1995)

of the Canadian Lynx • What effect does

trapping have on the cyclical flux of the populations?

• Just as many of the trapped lynx would’ve died anyway because of bottom up… or not?

• How can this question be tested?

(Krebs)

Evidence for Trapping Effecting Populations

• In 1982 lynx population crashed then in 1987 lynx fur was a high value and demand

• There was another crash in 1992 after trapping had become sky high

• Fat, Healthy lynx can still be found in time of pop drop from eating other prey

(Marty, 1995)

Testing the Trapping Hypothesis

• Mature Lynx most important to population growth

• Create refuges against trapping for these lynx

• Untrapped refuges will:– Prevent local extinctions– Increase lynx population – Maximize trapping harvest in the long term

(Hassel, 1998)

Summary and Review of Ideas:

• The Lynx – SS Hare cyclic dynamic is a classic example of the traditional predator – prey relationship.

• The cycle is most likely a combination of a top down, bottom up domination.

• Many environmental and external factors such as the food web, vegetation adaptations, trapping and prey preference effect the population flux, rather then just a sole proprietor.

What Can We Conclude??? The balance of natural processes is extremely

delicate. They are affected by any force placed upon them and reflect the concentric circles and chains of energy of the natural environment that are their foundation.

ReferencesEcological Modeling. Volume 152, Issue 1, June 15 2002. Pages 89-

102.Hassel, M.P. www.pnas.org. Vol. 95, Issue 18, 10661-10664,

September 1, 1998.Krebs, Charles J. www.esajournals.org. Ecology. Vol 79, no.4. Pp.

1193-1208.Launchbaugh. www.cnr.uidaho.edu. U of Idaho, Foraging Ecology.

2004.MacLean, Stephen. www.gi.alaska.edu. June 9, 1980.Madler, Sylvia. www.sci.sdsu.edu. Biology 5th Edition. 1998.Marty, Sid. lynx.uio.no/jon/lynx/cglynx1b.htm. Canadian Geographic

Magazine, Sept./Oct. 1995.Poole, Kim G. lynx.uio.no/lynx/nancy/news/cn20_04.htm. Cat News.

Issue 20. Spring 1994.