Introduction to distance sampling

David L Miller

Overview

  • Line transects
  • Simple estimates of abundance
  • Why is detectability important?
  • What is a detection function?
  • First look at fitting models in R

How many animals are there? (500!)

plot of chunk plot

General strategy

  • Take a sample in some fixed areas
  • Find density/abundance in covered area
  • Multiply up to get abundance

General strategy (What did we assume?)

  • Take a sample in some fixed areas
    • Sample is representative
  • Find density/abundance in covered area
    • Estimator is “good”
  • Multiply up to get abundance
    • Sample is representative

Plot sampling

plot of chunk plotsampling

  • Surveyed 10 quadrats (each \( 0.1^2 \) units)
    • Total covered area \( a=10 * 0.1^2 = \) 0.1
  • Saw \( n= \) 59 animals
  • Estimated density \( \hat{D}=n/a= \) 590
  • Total area \( A=1 \)
  • Estimated abundance \( \hat{N}=\hat{D}A= \) 590

Strip transect