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Invasive Biology: The Cane Toad. By: Adriana Carpio and Juan Escobar. The Cane Toad. Spread of the Cane Toad threatens biodiversity Intraspecific competition Poisoning of native species Consumption of small native animals Combat invasion through knowledge Mode of dispersal

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Invasive biology the cane toad l.jpg

Invasive Biology:The Cane Toad

By:

Adriana Carpio and Juan Escobar


The cane toad l.jpg
The Cane Toad

  • Spread of the Cane Toad threatens biodiversity

    • Intraspecific competition

    • Poisoning of native species

    • Consumption of small native animals

  • Combat invasion through knowledge

    • Mode of dispersal

    • Rate of spread

    • Preferred habitat


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Toads on Roads

  • Hypothesis:

    • Use of roads enable toads to disperse more rapidly than densely vegetated areas


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Background

  • Previous radio tracking showed that toads prefer open areas, especially roads

  • Avoids areas with dense vegetation, except for retreat sites


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Location of Study

  • Northern Territory of Australia

  • Wet-dry Tropics

  • Varied types of habitats

    • Seasonally flooded plains

    • Small hills

    • Woodland

    • Pastures

  • Climate

    • Hot year round

    • 31-34 C maximum

    • 15-24 C minimum

    • 80% of annual precipitation in wet season



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Tracking

  • Size of location: 2800 ha

  • Duration: Feb 2005 – Feb 2006

  • 49 adults toads fitted with radio tracking device

  • Radio device placed around the waist then released

  • Exact location was recorded daily with GPS

  • Inspection of the toad locations suggested they preferentially moved along roadways and fence lines



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Orientation

  • Toads selectively disperse along roads

  • Generally they position themselves along side the road

  • NOT facing the road


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Results

  • Radio Tracking Test

    • All toads moved in the same direction, NW along the side of the road

    • Toad routes overlapped strongly

    • Toads did NOT spread out


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Tracking Results


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Locomotion

  • Toads were placed in two different settings:

    • Open areas with hard-packed gravel

    • Areas with dense pasture grass

  • Toads were capture and kept for a period of 24 hrs

  • Each toad was tested once

  • Testing took placed during the evening, when toads are most active


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Speed Test

  • Toad was placed in the center of two circles, each with different settings

  • Inner circle of each had radius of 1m

  • Outer circle had radius of 2m

  • Toads were poked on the back with stick to make them move

  • Number of hops were recorded as well as time it took to travel through each circle


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Results

  • Locomotion and Speed

    • Toads tested on hard substrate:

      • Had longer jumps on second meter than first

      • Waited less time between jumps on second meter than on first

    • Toads tested on grassy substrate:

      • Had shorter jumps on second meter than first

      • Jumped less often on second meter than first



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Proposal

  • Prior to the introduction of the Cane Toad Australia had no native toad species

  • Only frogs were native

  • Frogs and toads are genetically different

  • Recently a gene was isolated from the Cane Toad

  • This gene is responsible for triggering sexual maturity


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Proposal

  • The gene will be modified

  • It will be inserted into a virus

  • The virus will not cause disease, but will act as a vector

  • The virus will then be introduced to the environment

  • The virus will multiply, consequently multiplying the gene


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Proposal

  • The gene would insert itself into the toad gene sequence

  • This gene would then be reproduced in the toad and passed on to the offspring

  • The offspring would have the active gene

  • Not being able to reach sexual maturity



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Bibliography

  • Brown G.P., Phillips B.L., Webb J.K, Shine R. (2006) Toad on the road: Use of roads as dispersal corridors by cane toads (Bufo marinus) at an invasion front in tropical Australia. Biological Conservation 1 3 3: 8 8 –9 4.

  • http://www.fdrproject.org/


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