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Competition

•• CompetitionCompetition–– Two species use the same limited Two species use the same limited

resource resource oror harm one another while harm one another while seeking a resourceseeking a resource

–– Resource CompetitionResource Competition–– Interference CompetitionInterference Competition

Competition• Resource Competition

– Organisms use common resources that are in short supply

Competition• Interference Competition

– Organisms seeking a resource harm one another in the process, even if resource is not in short supply

Competition• Long history in ecology

• Competitive exclusion principle: Complete competitors cannot coexist– Leads to specialization

Competition• N. American ungulates tend to be

generalists…

• flexible in habitat use and feeding?

• Why?– Pleistocene extinction 12,000 – 15,000

years ago most large mammals went extinct…..

Competition

• Page 66, Bailey 1984

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Competition

• Page 66 from Bailey 1984

Competition

• Would you expect competition among these species?

• Which ones and under what conditions?

Competition

• Even though species occupy different niches, enough overlap for competition– Contemporary examples?– How would you know if competition is

occurring?

• Examine diet overlap– Study of ungulates in the Texas Hill

Country

Competition

• Tables 1 and 2 from Henke et al. JWM 52:595-598

Competition

• Another way is to look at several niche dimensions. If a lot of overlap, then competition is possible….

Isle and Hellgren 1995 J. Mammalogy 76:784-799

Competition

• Bedding sites also different– Pigs bedded on edge of mottes with better visibility– Peccaries bedded in thick vegetation with low visibility

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Competition• On Chaparral WMA (JWM 65:99-110)

– Pigs used more open areas; less selective in placement of HR because HR was large

– Peccaries favored dense woody vegetation and were more selective in HR placement

– Pigs used open areas, peccaries used thick vegetation with more cactus

– Temporal – day vs. night habitat use

Competition• Competition understood best through

manipulative experiments

• Expensive to conduct, will see data later

Competition• Livestock – Wildlife Competition??

Competition• Livestock – Wildlife Competition

– Important because both wildlife and livestock have value that people wish to capture

• Different from wildlife--wildlife – Livestock densities above sustainable– Not subject to density dependent controls– Artificial feed, water and removed if range

conditions become bad

Competition• Impacts of livestock on wildlife• Direct – resource and interference

competition that we have discussed• Indirect (esp. if grazing pressure is high)

– Reduction in plant vigor– Lower reproduction by plants– Changes in vegetation cover types– Changes in plant species composition– Change habitat use & movements of wildlife

Competition• Operational impacts

– Species of livestock– Grazing regime (timing and duration)– Fencing– Water development– Range alteration (e.g. brush control)– Predator-prey relations altered– Disturbance from management activity – Disease

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Competition• White-tailed deer in general

– Least likely to compete with cattle– Compete with sheep for forbs– Compete with goats for browse

• Wet years – deer preferred– cattle > goats > sheep

• Dry years – deer preferred– cattle > sheep > goats

• Avoided pastures w/ livestock• Survival and natality lower w/ livestock

Competition• Study of cattle-deer competition in western

Colorado (Ecological Applications 6:200-227)

– Elk winter ground, cattle summer grazing

• Positive effects of elk– Removed dead grass, cattle diets better quality

• Negative effects of elk– Forage biomass was reduced

Competition

• Higher diet quality was not enough to make up for reduced intake rate

– Lower calf production in pastures grazed by elk– Dead grass was important as a buffer in this

arid system– Elk grazing reduced this buffer

Competition

• Lessons for wildlife management:– Well managed grazing may serve as a tool in

deer management by removing grass and promoting growth of forbs

– In Great Basin, livestock grazing reduced fires and promoted shrub growth. Benefited mule deer whose populations increased through the mid 1900s

Intraspecies competition?

• Males and females live in different habitats or use habitats differently…. Why??

• Predators?• Avoid competition?• Different food quality requirements?

Sexual Segregation

• Larger-bodied males eat abundant, high-fiber forage– Rumen capacity = prolongs

retention time– Able to use fiber for energy

• Females smaller-bodied, but requirements change– Better post-rumen digestion

and nutrient absorption– Digestive tract changes

Barboza and Bowyer 2000

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Predation

• Views of predators have changed

• Considered competitors & dangerous– Early form of game management– Military shot predators in YNP soon after it was

established

• 1930s – different view emerges– Leopold watches wolf die– Errington proposes “doomed surplus”

Predators in South Texas• Original predators:­ Wolves­ Lions­ Jaguars­ Bears­ Coyotes­ Bobcat ­ And people!

• Now….

Timing of fawn deaths

Vreeland (2002) – 218 fawns

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18

14

728%

12.0%4.3%

59.2%23.3%

18.0%

47.9%54.0%

12.7%

20.4%24.7%

27.6%

1.9%19.4%

27.0%10.3%

73.0%

What kind of coyote predationrates have been reported?

Predation

• Predation effects are complex• Predators limit prey in some situations

• How can we determine predator effects?­ Mortality sources­ Manipulated systems­ Manipulative studies

Predation

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• Figs. 1 and 2 from JWM 38:857

Predation Predation

• Welder Refuge:

­ coyotes & bobcats

­ 361 ha enclosure for 7 years

Predation Predation

• Lions­ S Texas: 49% (37 of 75) lion kills = deer­ 58 bucks marked near Freer in late ’80’s

• 15 deaths• 2 killed by lions

• Bobcats­ Scats at Welder

• Deer hair May-Aug, peaks in June• Adult deer rarely taken

Predation

• Coyotes­ 81 fawns collared in 60’s

• 58 died, 29 = coyote

­ Freer study, 58 adult bucks• 3 deaths where coyote was probable

­ Heffelfinger study, 3 yrs, 97 bucks• 8 deaths, 3 where blood, signs of struggle

Predation

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Predation Predation

• Vulnerability of prey­ Habitat quality

­ Animal quality• Poor quality animals more susceptible to predation

­ Buffer species

­ Predator evasion strategy• Not effective against all predators

Role of predators not appreciated until recently

Consider Aldo Leopold’s changing views on wolves and predators in general……

Predators are part of the system So what’s the bottom line…

In productive deer herds, coyote predation may not be a significant factor

You must consider coyote predation in the context of your deer herd conditions!

So what’s the bottom line…

In low-productivity herds, coyote predation may limit the number of does that can be harvested.

Either must increase productivity, or reduce mortality (control?).

How to limit coyote

predation?

Consider the habitat…

Cover!

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South Texas is a place of contrastsSouth Texas is a place of contrasts South Texas is a place of contrastsSouth Texas is a place of contrasts

Grazing management = cover management

Grazing management = cover managementRain: the great equalizer

Abundant forage for lactating doesPlenty of cover for fawns

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Drought: the real fawn-killer

Poor forage for lactating doesPoor forage for lactating does

Little cover for fawnsLittle cover for fawns

Fewer buffer speciesFewer buffer species

Supplemental Feeding:the Other Equalizer

•• Help even out drought effectsHelp even out drought effects­­ Increase deer visibilityIncrease deer visibility

­­ Increase individual productivityIncrease individual productivity•• Fawns/doeFawns/doe•• Body or antler sizeBody or antler size

­­ Increase density (more deer)Increase density (more deer)…… not always a not always a good thing! good thing!

­­ Expensive, but effective in arid regionExpensive, but effective in arid region

Flexibility:adjust grazing

for drought

Predation• Wolves and bears controlled in Alaska and

Yukon to benefit moose populations– Use this manipulation to study predation effects

• Bears and wolves near carrying capacity– Moose densities avg=148/1000km2 (range 45-

417)

• Bears and wolves below carrying capacity– Moose densities avg=663/1000km2 (range 169-

1447)

Predation

• 4 factors influence effect on prey– Ratio of predators to prey

– Vulnerability of prey

– Changes in predator behavior

– Density independent factors

Predation

• Ratio of predators to prey–Higher ratio predators likely to limit

prey species

–1 wolf:200 caribou is stable

–1 wolf:20 moose is stable

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• Fig. 31-7 from text book

Predation• Ratio of predators to prey

–Numerical response of predators • More deer = more food more

coyotes (or wolves, etc.)??–Prey diversity–Alternative prey could remove numerical

response. –Many small mammals may allow coyote

populations to remain high, even if deer decrease

Predation

• Ratio of predators to prey– R values, longevity of prey and predators

• Predators lower reproductive rates and higher survival rates than prey

– Predator swamping• When prey is vulnerable, have many

individuals to limit predator impact• Caribou calves

Predation

• Fig.1 JWM 65:19-24

Predation

• Ratio of predators to prey–Geographic concentrations of

predators• Garbage dumps and bears

–Intrinsic regulation of predators• Territoriality could limit predator

numerical response

Predation• Predator behavior

– Concentration of predation• Success causes predators to focus effort

– Predator learning• Experience more effective techniques

– Predator group facilitation• Groups of predators more successful than

single predator (e.g. wolf packs)

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Predation

• Predator behavior– Concentration of predator effort (e.g. lynx

eat fewer caribou calves when hares are abundant)

• Density independent processes– Weather or habitat changes can influence

all these factors, but not related to prey density