DEVELOPING A SAMPLING STRATEGY TO EXAMINE POPULATION TRENDS FOR THE ENDANGERED WINGED MAPLELEAF MUSSEL, Quadrula fragosa.
Issues when developing a sampling scheme for rare species
Federally endangered species from the St. Croix River
Past and present distribution of Quadrula fragosa.
St. Croix River Study Area
Calculating sample size to detect a difference in population size
Density at Interstate Park and Franconia
How many samples would it take to detect a change in Q. fragosa density based on quantitative sampling?
What are alternative approaches?
We have seen changes in the total population density at Interstate Park
Density at Interstate Park
PPT Slide
Q. fragosa accounts for 3.7% of the mussel community with pustules
The estimated 95% confidence limits indicate that Q. fragosa accounts for 2.5-5% of the mussels with pustules
HOW RESAMPLING WORKS - A SHORT COURSE
Our Model - To Examine how sample size influences our ability to detect a decline in the proportion of round mussels with pustules that are Q. fragosa
The production of two random samples to examine the probability of a change in the proportion of the population constituted by Q. fragosa that could be due to a chance event.
What is the probability that a 20% decline happens by chance?
Probability of detecting a certain decline in the proportion of mussels a species accounts for based on different sample sizes.
Our Proposed Sampling Regime
Sampling area at Interstate Park
How large is the impact of our sampling?
A recent (Oct. 3, 2000) sampling of 521 mussels with pustules indicated that only 1.5% were Q. fragosa. Approximately 150 mussels were collected per hour.
Some results based on these preliminary data
If these preliminary data hold true a sample size of 2500 may be insufficient to detect a 25% change with 90% confidence
We will begin our sampling next summer - 2001. We hope to continue this qualitative approach into the future coupled with continued quantitative sampling.
Email: hornbach@macalester.edu
Home Page: http://www.macalester.edu/~hornbach