Line transect lecture

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Line transect lecture
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Vegetation transects (Offwell, UK)
High seas salmon off BCs Coast
Duck transects along roads (N. Dakota)
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Example 1 UK Butterfly monitoring scheme

                                                
            
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Example 2 Raptor Census - Kyle Elliott (2002)
and the Vancouver Natural History Society
Bald eagles
Short-eared owls
Red-tailed hawks
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Q1. Why transects, not always quadrats? Q2. What
are potential biases in method?
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Animals (in particular) detection bias
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Animals (in particular) detection bias
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Example VNHS Raptor census (Elliott, 2002)
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• Two general methods (see Krebs)
• Distance from random point to organism.
• 2. Distance from randomly selected organism to
  neighbouring organism.

2
1
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• Two general methods (see Krebs)
• Distance from random point to organism.

nearest
Area of circle (p r 2) contains one individual
Inverse of Density individuals per unit area
r
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• Two general methods (see Krebs)
• Distance from random point to organism.

All methods calculate area per individual for
each circle, calculate mean area per indiv.,
invert
n p sum (r2)
r
byth-ripley
r
r
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• Two general methods (see Krebs)
• Distance from random point to organism.

If look at third closest organism, we are
calculating area per three organisms, or if
divide by three, mean area per organism (n 3).
3n - 1 p sum (r2)
r
ordered distance
r
r
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• Two general methods (see Krebs)
• Distance from random point to organism.
• 2. Distance from randomly selected organism to
  neighbouring organism.

2
1
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• Two general methods (see Krebs)
• 2. Distance from randomly selected organism to
  neighbouring organism.

Area per two individuals, but two circles
cancels out to same p r 2 formula as before
r
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• Two general methods (see Krebs)
• 2. Distance from randomly selected organism to
  neighbouring organism.

Area per two individuals, but two circles
cancels out to same p r 2 formula as before
r
n p sum (r2)
byth-ripley
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• Two general methods (see Krebs)
• 2. Distance from randomly selected organism to
  neighbouring organism.

Problem how to randomly select first
individual? Nearest organism to a random point
BIASED
Never selected
Frequently selected
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• WAYS TO RESOLVE PROBLEM
• Mark all organisms with a number, and then
  randomly select a few.

BUT if we could count all organisms, we wouldnt
need a census!
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• WAYS TO RESOLVE PROBLEM
• Mark all organisms with a number, and then
  randomly select a few.
• Use a random subset of the area (mark organisms
  in random quadrats).

Byth and Ripley
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• WAYS TO RESOLVE PROBLEM
• Mark all organisms with a number, and then
  randomly select a few.
• Use a random subset of the area (mark organisms
  in random quadrats).
• Use a random point to locate organisms, but then
  ignore area between it and organism (biased to
  emptiness).

T-square
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The 2 snipers
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Spatial pattern
More uniform
More aggregated
Random
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