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Spatial modeling of feral swine to determine effective population

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									  Spatial modeling of feral swine to
    compare population control
            techniques
J. Burton, M. Drigo, Y. Li, A. Peralta, J. Salzer, K. Varala




                                      http://tncweeds.ucdavis.edu
Background


        Feral swine (Sus scrofa)
   Invasive species
      – Destructive rooting
        behavior
      – Very high
        reproductive rates
      – Generalist feeding                      http://mediaarchive.ksc.nasa.gov/detail.cfm



        habits
      – Intelligent



                              httpwww-hogstoppers-comwildpigsigns-html
We created a spatially explicit model to test
 specific methods for feral swine population
 control at Fort Benning, Georgia




                                USDA APHIS
Background


         Site - Fort Benning, GA
   • U.S. Military Installation
   • Home to threatened and
     endangered species (Red-
     Cockaded Woodpecker,
     Relict Trillium)
   • Feral swine prey on and
     destroy habitat of TES
   • Currently implementing
     swine bounty program
Species background


                              Diet
   • Anything!
   • Benning data
      – Summer: grass, roots,
        tubers and invertebrates   www.sciencedaily.com   http://www.abc.net.au/reslib


      – Winter: mast (tree nut)
        crop - acorns, palmetto
        berries, grapes and
        hickory nuts
   • Small vertebrates, row
     crops, carrion, garbage

                                                           www.vetmed.ucdavis.edu
Species background


                     Groups
   • Sounders
      – Typically 1-3 sows with piglets
      – Can be much larger when food
        is scarce
   • Mature boars solitary except
                                          http://thelinkery.com




     during breeding season
   • Sows solo +/- 1 month from
     farrowing (birthing)
Species background


                         Mortality
   • Lifespan at least 15
     years
   • Few predators
      – Primary: humans
                                     http://www.peopleandwildlife.org



      – Other (neonates):
        coyotes, bobcats,
        mountain lions, large
        raptors and feral dogs
   • Hunting decreases
     population growth rate
     (Hanson, 2006)
                                              www.hogstoppers.com
Species background


        Reproductive Parameters
  • Sex ratio: about 1:1
  • Age
     – Females (sows) 5-10 months
        • Depends on nutrition, boar
          exposure                                        www.treesforlife.org.uk

     – Males (boars) 5-8 months
        • Fertility increases to ~ 18 months
     – No reproductive senescence noted
  • Litter size
     – 3-13 (varies with age of sow)
                                               http://www.wildlifeextra.com/images
     – High piglet mortality
Species background


        Reproductive Parameters
  • Breeding Interval
    6 - 7 months
     – Piglets weaned at 2-3
       months, sow estrus 1
       week later
     – Gestation nearly 4
       months
     – 2 litters/year observed
       under favorable           http://www.ipm.ucdavis.edu
       conditions
Species background


        Reproductive Parameters
   • Timing
      – Density dependent
         • Sometimes, but not observed at Ft. Benning
      – Reproduction: year-round, bimodal (Nov, Feb)
      – Fertility decreases with food shortage, heat stress
         • Mast crop
         • Surface water
   • Populations recover quickly when conditions
     improve
Species background


           Range and Movement
   • Range data varies widely: 304 – 6175 acres

   • Boar ranges larger, typically double that of sounders
      – Boars move to sounders for breeding

   • Resource driven
      – Summer: marshes
      – Winter: wooded areas

   • Daily movement
      – 0.4 to 0.7 mile
      – Varies with food, water availability
              Central questions
• How would a contraceptive program affect the density and
  spatial distribution of the Fort Benning feral swine population
  over time?

• Could a contraceptive program replace lethal control for this
  population?

• What is the most effective method for contraceptive delivery?

• How would the combination of sterilization and lethal control
  programs affect the density and spatial distribution of the
  feral pig population?
Model construction


                     Code Skeleton
Map information


                  Pig
                  Access
                                   Human
                                   Access



   Mast
                           Water
Control methods


                                    Sterilize or Kill?
Aerial/                                                                                                                              Bait
Ground bait                                                                                                                          station




              http://www.bios ecurity.govt.nz/files /publicati ons/             www.pgc.state.pa.us/ pgc/lib/pgc/press /2007/



*Hunting                                                                                                                             Trap




                http://blog.mlive.com/flintjournal/news now/2007/11/PIG   http://www.nrm.gov.au/proj ects/nsw/hnep/images/2006-07a
Model construction


                     Bait
                        Put baits in a square of patches at
                        specified rate

                        if pigs move to a patch carrying
                        bait and if pig is a female

                        change female pig to sterile at
                        specified rate
           Movement:
  Patch Attractiveness Function
• Calculated at each timestep
• Considers
  – Residency (whose home range is this?)
  – Food (mast)
  – Surface water availability
  – Random “attractiveness” factor
Model – User Interface
Model – Code Sample
Model – Code Sample
Viewing Sounder Ranges
    Management implications
• Initial findings:
  – Individual control
    methods not
    feasible
  – Combination may
    better achieve
    control objectives
        Acknowledgements
• Stephen Ditchkoff Lab - Auburn University
• Mike Mitchell and Bill Sparklin -
  Montana State University
• Mark Thornton - Fort Benning
• Jim Westervelt and Bruce Hannon
• Bruce MacAllister
• Spatial Ecosystem Modeling class 2008

								
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