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Line transect lecture

Line transect lecture. Vegetation transects (Offwell, UK). High seas salmon off BC’s Coast. Duck transects along roads (N. Dakota). Example 1: UK Butterfly monitoring scheme. Example 2: Raptor Census - Kyle Elliott (2002) and the Vancouver Natural History Society. Bald eagles.

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Line transect lecture

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  1. Line transect lecture

  2. Vegetation transects (Offwell, UK) High seas salmon off BC’s Coast Duck transects along roads (N. Dakota)

  3. Example 1: UK Butterfly monitoring scheme

  4. Example 2: Raptor Census - Kyle Elliott (2002) and the Vancouver Natural History Society Bald eagles Short-eared owls Red-tailed hawks

  5. Q1. Why transects, not always quadrats? Q2. What are potential biases in method?

  6. Animals (in particular): detection bias

  7. Animals (in particular): detection bias

  8. Example: VNHS Raptor census (Elliott, 2002)

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

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

  11. 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 π sum (r2) r byth-ripley r r

  12. 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 π sum (r2) r ordered distance r r

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

  14. 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 π r 2 formula as before r

  15. 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 π r 2 formula as before r = n π sum (r2) byth-ripley

  16. 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

  17. WAYS TO RESOLVE PROBLEM: • Mark all organisms with a number, and then randomly select a few. BUT if we could count all organisms, we wouldn’t need a census!

  18. 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

  19. 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

  20. The 2 snipers Excellent aim, crooked sights Cross-eyed cat, Straight sights

  21. Spatial pattern More uniform More aggregated Random

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