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All images are from the FWS Image Library unless
otherwise noted.
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Predators and Predation

• Chapter 9

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• Predators
• animals that kill other animals to survive

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Predator Behavior and Prey Survival

• Survival mechanisms
• Co-evolution
• protective shapes and coloration
• mimicry
• alertness, swiftness
• affinity for remaining in protective cover
• specialized behavioral and physical features for
  capture of prey
  
• speed, agility, claws, sharp teeth
• strength, keen smell and vision
• survivors form the next generation
• those traits for survival are passed on

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• Predator strategies
• ambush
• swift pursuit
• select weakened prey
• vulnerable prey
• individuals with oddity in color, behavior, or
  location
  
• conspicuousness
• individuals outside of normal habitat
• territoriality
• ensures adequate hunting grounds

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Predation in Natural Communities

• Relationship between predator impact on abundance
  and density of prey populations
  
• inconclusive evidence
• uncontrollable variables
• Our Vanishing Wild Life
• Hornaday 1913
• plea for protection of wild animals
• did not include carnivores
• human orientated viewpoint
• influenced attitudes against predators
• Leopold
• Thinking Like a Mountain 1949
• once had ardor for predator free environment
• understood fierce green fire dying in wolfs
  eyes
  
• understood necessity of predators

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Figure 9-1 Distributions of Gray Wolves.
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Theoretical Predator-Prey Systems

• Predator-Prey Models
• Lokka_Bolterra equations
• assume potential rate of increase for prey in
  absence of predators
  
• assume decline in predator populations in absence
  of prey
  
• assume a constant food supply for prey
• assume disease, climate, other predators constant

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Figure 9-2 Predator/Prey Oscillations
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Figure 9.3 Lynx Hare Cycles
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Laboratory Studies of Predator-Prey Systems

• Studies utilized single predator-single prey
  population
  
• Complex habitat provides advantages for prey,
  helps ensure survival of prey species
  
• mobility
• adequate food
• suitable cover
• Predators increase in numbers may be excessive,
  leading to crash, if all prey eliminated

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Figure 9-4
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Field Observations of Predator-Prey Systems

• Errington 1956
• social interactions within muskrat populations
• with the role of mink predation
• mink predation greater when muskrat numbers high
• not all muskrats equally vulnerable to predation
• due to social differences
• social outcasts almost exclusively ones killed by
  mink
  
• walking corpses
• predation before starvation
• mortality factors compensatory
• disease, starvation, predation

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Figure 9-5 a
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Figure 9-5 b
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Figure 9-5 c
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Figure 9-5 d
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• Density of prey influences feeding behavior and
  number of predators
  
• average predator consumes more prey per day if
  more prey
  
• functional response
• tendency of predators to shift diets to abundant
  prey
  
• numerical response
• numbers of predators increase with increase in
  prey density
  
• Leopolds 5 factors in predator-prey
  interactions
  
• density of prey population
• density of predator population
• characteristics of prey
• density and quality of alternate predator foods
• characteristics of predator
• means of attack, food preferences

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Isle Royale Map
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Isle Royale Predator-Prey Relationships

• Wolves, moose, beaver
• undisturbed environment
• 1900 moose introduction
• 1925 moose replaced caribou
• as dominant herbivore
• 1920 3000 moose
• 1930 overgrazed, crashed to several hundred
• 1936 fires renewed browse supply
• 1940s numbers increased, then crashed

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• 1949 wolves crossed ice
• 15 - 22 single large pack stable for ten years
• wolves primarily killed older, weak moose
• social dominance restricted breeding in wolf
  pack
  
• 1969 deep snow, moose congregated,
• depleted browse in area
• proportion of calves taken by wolves increased 25
  - 42
  
• 1980 50 wolves, 5 packs
• social strife among wolves
• severe winter, wolf numbers dropped to 30
• 1982 14 wolves, 600 moose
• 1987 15 wolves, 1400 moose
• soon moose numbers decrease as they age
• easier for wolf to attack

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• Lessons learned from Isle Royale
• ten years of study not enough to determine all
  factors
  
• unpredictable nature of weather and influence on
  wintering behavior of moose
  
• effects of moose on own food supply
• fire impact rejuvenated browse
• individual personalities of wolf packs

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Table 9.1
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Field Experiments with Predator-Prey Systems

• Experiments removing predators increased prey
  numbers
  
• indicating effective predator control can
  increase populations
  
• increased nesting success
• with fox/mallard most prey were female
• control fox, increase duck production overall
• remnants of linear cover have potential to be
  predator lanes
  
• ease of predators to find prey when concentrated
  in small area
  
• some studies show predators do not control prey
  populations
  
• Public perception of predators vary widely

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Figure 9-7
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Alaska Wolf Control

• Justification in some areas to enhance recovery
  of moose and caribou populations
  
• prey populations increased
• wolf predation was primary cause of moose
  mortality
  
• hunting also contributing factor in moose
  decline
  
• recommended reducing hunting
• severe weather a factor in moose decline
• low moose numbers caused slower decreases in wolf
  numbers
  
• moose populations would eventually recover
  without human intervention
  

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• 1985 Alaska Policy
• determination of desired level of wolf and prey
  population in each management area
  
• permission for air hunts only if Board of Game
  determines prey population severely depressed and
  game harvest below long-term averages
  
• scientific evidence indicates the cause of low
  prey populations is wolf predation
  
• alternate management methods are not likely to
  bring about recovery of prey
  
• must act in public interest
• consumptive and non-consumptive uses of wildlife
• hold public hearings

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Predation on Domestic Animals

• Natural selection of wild
• herbivores
• alertness
• agility
• speed
• stealth
• Domestic animals
• products of artificial selection for food
  products
  
• 1960s concern for wildlife and ecology
• role of predators as selective agents on prey
• inhumanity of some predator control methods

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• Extent of Predator Problem
• coyote damage to sheep in western states
• 20 lambs on 10 ranches
• 14 million loss of lambs/year
• 5 million loss of ewes
• 19 million total loss of sheep per year to
  coyote predation
  
• Control Methods
• trapping
• den hunting
• shooting
• poisoning

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• Leopold Report 1964
• all native animals are resources of inherent
  interest and value, and responsibility of
  government
  
• local control of wildlife populations is an
  essential part of management policy where crops,
  livestock, human health and safety are damaged or
  jeopardized
• Cain Report 1971
• Nixon prohibited poisons for predator control on
  federal land
  

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• Effectiveness of Control Methods on Coyote
  Numbers
  
• 1931 Animal Damage Control moved to Department
  of Ag from dept. of wildlife
  
• concerns aligned with ranchers/farmers
• kills 70,000 - 85,000 coyotes /yearly in 13
  states
  
• 18 - 29 coyote population killed
• increased reproduction and pup survival
  compensate for losses
  
• produce larger litter 7 pups vs. 3.6 with no
  control states
  
• Effects of Coyote Control on Other Animals
• other animals killed in course of coyote control
• 25 bobcats killed
• other animals killed by poison Compound 1080
• secondary poisoning, when animals scavenge on
  killed coyotes an issue also

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Table 9-6
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• Public Policy and Predator Control
• public acceptance important in determination of
  acceptable methods for managing wildlife
  
• non-lethal methods preferred over lethal
• guard dogs
• repellent chemicals
• birth control
• of the lethal methods, most acceptable
• shooting from ground
• fast acting poisoning
• pay for losses next preferred, but after above
  methods
  
• most unacceptable
• aerial gunning
• denning
• pay ranchers not to raise sheet
• traps
• slow poisons

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Figure 9-10
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• Federal policies in US (Cain 1972)
• animal damage control designed to ensure
  maintenance of native wildlife and habitats
  
• selective depredations
• control goals
• human health and safety from wildlife borne
  disease
  
• economic losses in residential and industrial
  situations
  
• forests, range, ag crops, livestock protected
  from direct damage and wildlife borne diseases if
  offset all costs of control
  
• animal-control program conducted when/where
  demonstrated need as determined by US
  Fish/Wildlife Service
  
• Annual work plan developed fro animal control in
  each state
  

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• Wildlife Society Policy
• support only those animal control programs
  justified biologically, socially, economically
  
• encourage continuing research designed to improve
  methods of
  
• accurately assessing wildlife damage
• measuring effectiveness of damage control
  programs
  
• recommend that efforts of control be minimum
  required to bring damage within tolerable limits
  
• recommend efforts of control be the minimum
  required to bring damage within tolerance limits
  
• support use of only the most efficient, safe,
  economical, humane control methods for
  depredating animals, advocate lethal control only
  when all other methods unsatisfactory
• urge all control programs closely regulated by
  state/federal laws

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Summary

• Predator-prey systems
• effects of predators dependent on community
  complexity
  
• effects of severe weather and hunting additive
• Controversy surrounding predator control
• Compound 1080