An Alternative Explanation for Leopolds Kaibab Deer Herd Irruption - - PowerPoint PPT Presentation

An Alternative Explanation for Leopold’s Kaibab Deer Herd Irruption of the 1920’s

The Kaibab Plateau: “Mountain lying down”/Buckskin Mountain

• The Kaibab is a natural

laboratory with specific geographic boundaries

• It is a block plateau 45 miles

wide x 60 miles north to south

• To the South is GCNP
• To the West is Kanab Canyon
• To the East is desert and cliffs
• To the North is open sagebrush

flats to the canyons of Utah

The story begins:

• Paiute Indians lived here for

countless generations depending on deer for hides used as trade goods.

• It can be postulated that some sort
• f dynamic equilibrium existed

between the various animals and plants and the Native peoples who moved through them as hunter- gatherers.

• Unprecedented change came to the

Kaibab with settlers who began to run herds of cattle and sheep beginning in the late 1880’s.

• No controls meant overgrazing and

extensive damage and change to vegetation.

A Reserve is Established

• Pres. Benjamin Harrison

established Grand Canyon Forest Reserve, North in 1893.

• Theodore Roosevelt set aside these

lands for protection of game animals in 1906. Paiute hunting was ended.

• In 1908, the area was renamed the

Kaibab National Forest

• In 1919, Grand Canyon National

Park was created from 320,000 acres of the KNF.

Livestock and Predators

• Along with cattle came the

perceived need to control predators.

• Predators present: Coyotes,

Bobcats, Wolves, Mountain Lions

• Predator hunting was done by

stockmen until a concerted government program to eliminate all predators began in 1913.

• Estimated predator kills 1907-

1923: Coyotes 3,000 Bobcats 120 Wolves 11 Mountain Lions 674 (Russo 1964)

Livestock Records

• Earliest recorded use dates to 1885:

2,000 cattle.

• 1887-1889: 20,000 cattle

200,000 sheep “in the surrounding desert country and on the Kaibab Mountain” (Mann

and Locke 1931)

• Records 1889-1906 not available.
• 1906: 9,000 cattle

20,000 sheep

• 1916: 15,000 cattle

5,000 sheep

• Controls on livestock before 1934

were token gestures.

The Deer Problem Emerges

• Deer may never have been
• numerous. Rasmussen (1941)

estimates 4,000 in 1906.

• For unknown reasons, deer

began to multiply in the early 1900’s.

• Range deterioration was noticed

in 1918.

• By 1924, estimates of deer

numbers ranged from 50,000 - 100,000.

• Mass starvation from 1925-1930

was accompanied by severe range deterioration.

The Kaibab Deer Population 1860 - 1940

Leopold’s Early Thoughts on Deer Population Dynamics

• He was in the vanguard of a new

scientific awareness of interactions in natural systems.

• Deer populations were stable over

time and could be easily managed by the manipulation of any limiting factor: food, water, cover,

• predation. Deer were influenced

by their environment, but were not an influence upon it.

• Predators could only harm deer.
• Hunter demand was so high that

there could never be too many deer.

Flader 1974

Leopold Changes his Thinking

• In 1936 on a visit to the Chihuahua

sierra in Mexico, he observed for the first time deer and predator coexisting in an environment without human manipulation (Flader

1974).

• Wolves, mountain lions and deer

were existing in equilibrium.

• A pivotal experience.
• Deer are not isolated items of

management but are part of an interdependent biotic community.

• The community has balance or

natural health.

Leopold Changes his Thinking, cont.

• Deer were beginning to
• verpopulate many areas of the

country at this time (Leopold et al.

1947).

• Predators were no longer the

enemy but “precision instruments of control” (Flader

1974) and needed to be included

in management plans.

• This change in thinking is

passionately expressed in his essay “Thinking like a mountain” (1949).

San Francisco Peaks

Leopold and the Kaibab

• Leopold, Aldo. 1943. Deer
• irruptions. Transactions of the

Wisconsin Academy of Sciences, Arts and Letters 35:351-369.

• The Kaibab was a finely balanced

natural system

• Deer were at the carrying capacity
• f the habitat.
• Predation kept them from
• verpopulation and habitat

destruction.

• Removal of predators caused

uncontrolled growth of the deer herd, an irruption.

• A great story is born.

Irruption, cont.

• No irruptions are recorded in North

America or in Germany before predator removal.

• There are only two irruptions

known from Canada.

• Disturbance of the system by

human intervention, the removal of predators, paved the way for irruption.

• By his own admission, the evidence

is circumstantial.

• It is an irresistible, easy to

understand, intuitive explanation.

• The Kaibab deer herd became a

textbook example of the balance of nature.

Problems with the Paradigm

• Challenges came first from an article

by Graeme Caughley (1970) who characterized Leopold’s use of 100,000 deer as arbitrary.

• Caughley stated that ungulate irruptions

have usually been attributed to a change in food supply that allowed high rates of growth.

• Leopold was an exception to all other

known cases.

• The Kaibab story quickly disappeared

from ecology texts.

• Colinvaux (1973) called his story a

“fiction” and an exercise in “imaginations and artistry”.

What Do We Know?

• Not much about deer, predator or

livestock numbers before 1906.

• Horses, dairy cattle and unlawful

livestock were common.

• Deer exceeded the carrying

capacity of the Plateau and crashed in the late 1920’s.

• The Kaibab deer herd is a story

about human perceptions of the natural world and of how nature responds to human intervention, timely concepts indeed.

An Alternate Explanation for the Irruption

• Livestock grazing, in particular
• vergrazing, caused a change in the

composition and structure of the vegetation on the Kaibab that favored the deer herd and made irruption possible.

• The roles of predators, fire and

logging were were contributing factors but probably minimal.

Top of Nankoweap Trail

Components of the Kaibab Irruption

• 1. Forage
• 3. Deer
• 2. Predator

• 1. The Forage Complex
• Russo (1964): the only real change on the

Plateau in the last 100 years that has any direct bearing on deer is vegetative and caused by livestock grazing.

• At low density, cattle and deer do not

compete, but they do at higher densities.

• Deer do not compete with cattle for

grass, but cattle compete with deer for forage.

• Livestock do compete with deer for

space

Summer Range

• The Kaibab deer were most

probably limited by summer range

(Russo 1964, Mann 1941, Mackie et al. 1998).

• Tender green forage is needed for

lactation and fawn growth.

• High elevation supports grassy

parklands not frequented by deer until after cattle arrived.

• Livestock stripped native grasses.

An invasion of forbs, annuals and shrubs followed.

• “A weedy park in poor condition

for cattle is better for deer than a grassy park in good condition for cattle” (Kimball and Watkins 1951).

Coleman Lake

Summer Range, cont.

• Grazing by one animal can increase

species favorable to another.

• Increases can accumulate over time

altering botanical composition and structure (Vallentine 2001).

• Effects are more pronounced when food

preferences do not overlap.

• Sinclair (1979) wrote at length of how

different ungulates on the Serengeti facilitated each others food supply by differential grazing.

• In general, across the West, heavy

livestock pressure converted grasslands to shrub lands which favored increased deer

• productivity. This led to the widespread

increases in deer populations of the 1920’s and 1930’s (Austin et al. 1986).

• Did cattle facilitate deer on the Kaibab?

Little Springs

• 2. The Predator

Felis concolor

• The dominant carnivore.
• 4,000 deer might be able to support 50

predators.

• Hornocker (1970) reported a ratio of

1:114 and 14-20 kills/predator/year.

• Can predation limit deer numbers in

such a way as to regulate the population?

• Regulation: equilibrium that depends
• n density dependent factors that

reduce reproductive rates.

• Do mountain lions have a direct

numerical and functional response to increasing prey numbers?

The Predator, cont.

Constraints

• Territoriality: enforced boundaries and

social avoidance behavior (Hornocker 1969

and Seidensticker et al. 1973).

• Cougar density is probably determined

by habitat quality (Logan et al. 1996).

• Vegetation structure and physiography of

habitat: broken country for hiding and stalking and for caching prey.

• Nursery areas: security and water supply

for raising kittens.

• Other constraints:

Prey distribution Prey defenses and behavior Prey quality

The Predator, cont.

• The vegetation-topographic/predator

numbers-prey vulnerability complex

(Seidensticker et al. 1973).

• Inter- and intraspecific relationships
• f both predator and prey species,

combined with the influences of climate, topography and the distribution of vegetation form dynamic interactions at many spatial scales.

The Predator, cont

Other Considerations

• Livestock could have served as

alternate prey to keep predator numbers high.

• Hunters may have exaggerated their

prowess to impress employers.

• As cougars are killed populations

become destabilized. Their territories become available allowing for influx of

• thers producing a real or apparent

increase (Katnik 2002).

• Predation is often compensatory.
• Long-term stochastic variations in the

environment are more likely responsible for large scale population cycles in ungulates than is predation pressure (Wielgus 2003).

• 3. The Deer
• Mule deer populations have long term

cycles possibly driven by weather phenomena (Marshall et al. 2002).

• Deer reproductive rates are related to

changing nutritional conditions that vary

• ver time independent of predation rates

(Connolly 1978).

• Deer growth rates are not density

dependent until excessive densities have been reached. (Ballard et al. 2001).

• Prey abundance above a certain

threshold can swamp the predator

(VanBallenbergh 1989, Mech 1970).

• Several researchers have stated that

range conditions and food supply are the limiting factors for ungulates (Cowan 1950,

Wallmo and Regelin 1981).

The Deer, cont.

Effects of Predation

• It distributes deer across the landscape.
• Areas of unused forage were observed
• n the Kaibab during the irruption.
• Reduction of herd size might increase

available nutrition and increase the birth rate through lower interspecific competition or some other behavioral response (Errington 1956).

• Predators may in some way favor their
• wn food supply in the same way that

management for hunting attempts to keep a population at maximum productivity.

The Deer, cont.

• Abundant prey makes the abundant

predator possible.

• Natural selection processes

resulting from predation may cause a prey to populate their habitat nearer to K yet below density induced stress levels (Howard 1965).

• It is hard to suppress deer in good

habitat (Leopold, S. 1959).

Coming Full Circle

• The Kaibab story of Leopold

centered around the predator.

• My thesis moved considerations
• f deer irruption onto the

vegetation and deer dynamics.

• The predator is still important,

but is seen in a different light.

• Among all other considerations,

forage is still the center of concern because it is the basis

• f deer nutrition and

productivity.

• I conclude that the Kaibab deer

herd was most likely forage driven and not predator limited.

Modeling the Kaibab Deer Herd with Stella

• An excellent model of the Kaibab

as a predator limited system is found in Ford (1999).

• This model was modified and

expanded to limit the number of predators.

• Growth of new vegetation was

made variable to allow simulation

• f changes from grazing that may

have driven the irruption.

• A category of damaged biomass

was added track destruction of habitat caused by the irruption.

Kanab Canyon