New version page

UI WLF 448 - Estimating Population Size

Pages: 7
Documents in this Course

9 pages

5 pages

5 pages

5 pages

2 pages

7 pages

5 pages

6 pages

6 pages

4 pages

11 pages

5 pages

49 pages

3 pages

76 pages

21 pages

13 pages

7 pages

4 pages

7 pages

4 pages

5 pages

2 pages

9 pages

5 pages

Load more
Upgrade to remove ads
Upgrade to remove ads
Unformatted text preview:

10/21/2011 1 Estimating Population Size using Mark-Recapture techniques Why use capture methods? • Allows for estimation of density •Allows for estimation of birth and mortality rates •More practical method for small, fast, hard to spot species10/21/2011 2 There are variety of models for mark-recapture studies that attempt to account for different assumptions of the base model. These deal with: • Capture rates • Individual variation • Post-trap response • Time General Mark-Recapture methods: • Population sampled 2 or more times • Captured individuals marked and released in first session • Additional session(s) to follow, in some cases new unmarked individuals marked • Capture can be physically trapped, photographs, DNA samples, etc10/21/2011 3 Lincoln-Petersen method: • Population sampled 2 times (1 recapture event) • Captured individuals marked and released in first session • Closed population • Probability of catching individuals equal in both session • Marks not lost, gained, or overlooked • Marks needn’t be unique to individuals Lincoln-Petersen method: n1 = # captured and marked in 1st session n2 = Total # captures in 2nd session m2 = # of marked animals captured in 2nd session Remember our general model for abundance estimates: Estimate of abundance = Count / estimated probability of detection N-hat = n1 / (m2 / n2) or N-hat = n1 * n2 / m210/21/2011 4 Lincoln-Petersen method: n1 = # captured and marked in 1st session n2 = Total # captures in 2nd session m2 = # of marked animals captured in 2nd session Chapman modified this original formula to account for bias due to small samples: N-hat = (n1 +1)/ (m2 +1) / (n2 +1) or N-hat = (n1 +1) * (n2 +1) / (m2 +1) Session 1 Session 2 Lincoln-Petersen method: = marked individual = unmarked individual10/21/2011 5 Marks can be unique patterns on individuals capture in images. An example of this is Calambokidis & Barlows study of Humpback Whales Closed models w/ >1 recapture periods: • Population sampled 2 times (1 recapture event) • Captured individuals marked and released in first session • Closed population • Probability of catching individuals equal within a sampling period but can vary between sampling periods • Marks not lost, gained, or overlooked • For some models/purposes Marks need must be unique to individuals, unique encounter histories created • Calculation intensive, use programs such as CAPTURE or Program MARK for analyses10/21/2011 6 Different models address different sources of variation in capture probabilities: • M0 = Equal Catchability Model (null model) -- Assumes every animal in the population has the same p-hat for each sampling period in the study. • Mh = The Heterogeneity Model -- Assumes that each animal has a unique p-hat that remains constant over all trapping occasions. Furthermore, capture probabilities are assumed to be a random sample of all individuals in the population. • Mb = The Trap Response Model -- Adjusts for a change in capture probabilities caused by a response to trapping. An assumption of the Mb model is that the initial p-hat for all animals is the same (equal catchability). Different models address different sources of variation in capture probabilities: • Mbh = The Heterogeneity and Trap Response Model-- Based on the assumption that each animal has its own unique pair of potential capture probabilities, pj and cj (j = 1, ..., N animals in the population), where pj is the initial capture probability and cj is the recapture probability. • Mt = The Time Variation (Schnabel) Model -- Based on the assumption that every individual in the population has the same p-hat for a given sampling occasion, but capture probabilities can vary at each sampling time. • Other Time-Dependent Models: Mth, Mtb, and Mtbh (various combinations of the above models).10/21/2011 7 Open Models: •Cormack-Jolly-Seber models (based on k>2) in Program MARK. •Combination of open and closed models (Pollock's Robust Design) in Program

View Full Document
Download Estimating Population Size
Our administrator received your request to download this document. We will send you the file to your email shortly.
Unlocking...
Sign Up

Join to view Estimating Population Size 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?