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
m2
captured on day 2 with marks
p =
m2/n1
N =
n1n2 / m2
Lincoln Petersen - corrected for finite population sizes
N = [(n1 + 1)(n2 + 1) / (m2 + 1)] - 1
assumptions of Lincoln Petersen
- population is closed
- marks are not lost
- all animals are equally likely to be captured
all animals are equally likely to be captured
- time
- heterogeneity among individuals
- behavioral response
violations of equal catchability
- temporal
- individual
- behavioral
violations of equal catchability: temporal
conditions change over time
violations of equal catchability: individual
each animal varies in capture probability
violations of equal catchability: behavioral
trap happy vs trap shy
additional points about L-P estimator
- animals do not have to be individually identified
- animals can be “captured” using different methods for the two sessions
physically capturing and marking animals can be:
- stressful and/or dangerous for both study species ad researchers
- logistically difficult
non-invasive “capture” and “mark” methods
- genetic methods
- photography/camera traps
non-invasive “capture” and “mark” methods: genetic methods
- collect DNA from sloughed animal cells
- individual “marks” are highly variable genetic markers across several loci that can ID at individual levels
non-invasive “capture” and “mark” methods: photography/camera traps
ID animals from natural markings
