Chapter 4: Abundance Flashcards
population
a collection of individuals of a species in a defined area, for which it is meaningful to refer to abundances, birth and death rates, sex ratios, and age structure
BIDE equation
Nt+1 = Nt + Bt + It - Dt - Et
density
if abundance is scaled per unit area
incomplete detection
since we cannot count them all, we have to deal with it
estimate of abundance variable
N
estimate of abundance formula
N = count / p
census
complete count
the value of p is often
< 1
indices
- not sampling actual animals
- cannot estimate p
indices: to rely on for abundance
known relationship between index and abundance
indices: to rely on for trend
constant relationship between index and abundance
transect methods
count animals along a line
types of transect methods
- distance sampling
- replicated counts
- viewshed methods
distance sampling
- p decreases with distance
- detection function can be estimated
key assumptions of distance sampling
- all animals directly on the line are seen
- animals are counted only once and do not move before being sighted
- perpendicular distances are measured exactly
example of sightings from a line, from a center of a circle
point counts of birds
CMR
capture-mark-recapture
two types of CMR models
- closed population models
- open population models
closed population models
no change in the population during sampling period (no births, deaths, immigration or emigration)
open population models
birth, death, immigration, and/or emigration may occur and be estimated
mark-recapture concept
- sample animals from a population and mark them
- let the population mix
- resample the population
- count marked and unmarked animals
Lincoln-Petersen: Foundational method
2 sessions
- 1 session to mark animals
- 1 session to estimate p
n1
captured on 1st day
n2
captured on 2nd day
