Power analysis for a Mark Power analysis for a Mark recapture projectrecapture project

Dan BachenDan BachenDepartment of EcologyDepartment of Ecology

Montana State UniversityMontana State University

Project overview

• Data collection– Blacktail WMA – 24 plots– 4 weeks

Mark Recapture

• Data collection Methods – Trap grids 8x8– Sherman live traps– 5 nights per plot– Unique marks

• 4 species– Deer mouse dominant

> 90% of captures

Data example

SiteCapture Location

N1Capture Location

N2

Capture Location N3

Capture Location N4

Capture Location N5

SC1 0 4G 0 0 0

SC1 0 4E 0 0 0

SC1 0 6F 4G 0 0

Power analysis

• Goals – Optimize sample size

• Treatment effect -.1 to -1• 20 sites used (10 treatment, 10 control)• 40 sites used (20 treatment, 20 control)

– Effect of -.84 recorded by Ostoja 2009

• Assumptions– Abundance estimates normal– Capture probability

• .2 un-captured individuals• .9 captured individuals

Power analysis

• Methods– Generate abundances using likelihood

analysis (Rcapture)– Quantify statistics– Use statistics to set parameters– Iterate experiment– Score success

Results

Mean: 7.44

SE: 5.84

0

20

40

LC1LC2LC4LC6LT1 LT2LT3 LT4LT5 LT6SC1SC2SC3SC4SC5SC6ST1ST2ST3ST4ST5ST6Sites

Ab

un

da

nce

1

1

Abundance by Plot

Results

0 20 40 60 80 100

0.0

00

.05

0.1

00

.15

0.2

00

.25

Proportion successful at -10% TE

Index

succ

ess

.sa

mp

le.s

ize

0 20 40 60 80 100

0.0

0.2

0.4

0.6

0.8

1.0

Proportion successful at -80% TE

Index

succ

ess

.sa

mp

le.s

ize

Results

TE 10 20-0.6 0.63 0.92-0.7 0.77 0.98-0.8 0.86 0.995-0.9 0.92 0.99-1 0.97 0.99

Discussion

• Experiment might have worked

• Did I use the right tools?– No– Aggregation of samples

• Example:– Abundance= 158.2 – SE= 2.3

Future Work

• Re-run power analysis aggregating samples– New tools– RMark

• Compare results to other techniques