MARK RECAPTURE

Lab 10 Fall 2011

Why?

We have 4 goals as managers of wildlife Increase a population Decrease a population Maintain a population Monitor a population

Achieving our 4 goals

What tools do we have thus far to do this? Map species distributions

Where are they? Where could they be put? Population growth

How fast are they reproducing? Population viability

How long can they last? How many are there?

Distance sampling Mark - recapture Dave the wildlife manager

How many are there?

Mark and recapture is a method commonly used to estimate population size.

fails to detect all individuals present within a population of interest every time

Abundance and density estimation

Open vs. Closed

Closed population –no recruitment (birth or immigration) or losses (death or emigration) Geographic Demographic

Open population – a population that changes in size and composition from births, deaths, and movements.

Capture-recapture models

Closed-population models two samples – Lincoln-Petersen model  several samples (k>2) – Schnabel

(Schumacher-Eschmeyer) model and models in program CAPTURE.

Open-population models (note: geographic closure is still a critical assumption)  Cormack-Jolly-Seber models (based on k>2)

in Program MARK. Combination of open and closed models

(Pollock's Robust Design) in Program MARK.

Lincoln-Petersen

A sample of C1 animals is Caught, marked, and released (M2). Later a sample of C2 animals is Captured, of which R2 animals are Recaptures that were previously Marked.

If capture probability (p) is independent of marking status, then the proportion of marked animals in the second sample should be equivalent to the proportion of marked animals in the total population (N) so that

R/C = M/N

Assumptions

CLEARRrrr

Population is Closed

Marks are not Lost between sample

Animals are Equallylikely to be captured

Marking does not Affect catchability

Each sample is Random

Recorded correctly and Reported on Recovery

Sources of variation

capture probability ( p) = probability of an animal being caught in any trap.

Variation in p comes from??  heterogeneity behavior time

Schnabel estimator

Extending the Lincoln-Peterson method Treating multiple samples as a series of

Lincoln-Peterson (L-P) samples and obtained a population estimate as a weighted average of the L-P estimates

Assumptions

Same as L-P but assumptions apply to all sampling periods. same capture probability for a given

sampling occasion but capture probabilities can vary among sampling periods.

BONUS!! Test for violations of assumptions

Program CAPTURE

 2CAPTURE, which provides a user-interface to CAPTURE Need to create the input before you can

analyze it CAPTURE performs abundance and

density estimation from information provided by user

Notation in output from CAPTURE

t - number of trapping occasions. n(j) - number of animals captured in the jth sample, j=1,...,t.

This is the total number of captures in the experiment. u(j) - number of new (unmarked) animals captured in the jth

sample, j=1,...,t. f(j) - the capture frequencies. The number of individuals

captured exactly j times in t days of trapping j=1,...,t. M(j) - the number of marked animals in the population at time of

the jth sample, j=2,...,t. Note that M(1) equals zero. M(t+1) - the number of distinct individuals caught during the

experiment. N^ - the estimated population. p^ - estimated probability of capture. p^(j) - the estimated probability of capture by occasion. p-bar - average probability of capture for the generalized

removal model. c^ - estimated probability of recapture.