Question

Design a mark recapture study for an endangered species of butterfly, Bremner’s fritillary Speyeria zerene bremnerii . There is presumed to be a relatively small (somewhere between 100s to a few thousand) population that is restricted to Gary Oak woodland habitats on Southern Vancouver Island, an area that is fairly accessible to researchers. You only have a field crew of two to work with though. Additionally, capturing these insects comes with risks to the insects, but you desire a high degree of accuracy and precision in your estimates of the true population size. How many butterflies do you mark? How much effort do you invest in recapturing them? How many times do you perform recaptures? What trade-offs must be considered in the design of this sampling program? Justify your answers in terms of the trade-offs you are making.

Answer 1

• 76 butterflies (38 male and 38 female) are marked.
• These low number of recaptures creates problem when statistical analysis are used in case of population estimation program and separates the probability of a precise population. However, one assumption has been considered that the changes daily population levels are fairly consistent and calculations are done using a range of Scott's average phi values (The range of phi values are indicated from 0.2-0.6).
• 19 times recaptures are performed.
• Jolly-Seber population estimation programs must be considered in the design of this sampling program.