Analysis of animals in groups
Analysis of animals in groups
Some species travel in groups. The detection of these species is often made of a group. It is standard practice to record the perpendicular distance to the centre of the group and the number of individuals in the group. Conventional distance sampling could then be applied to produce an estimate of the number of groups in the study area.
Converting that estimate of group abundance into an estimate of abundance of individuals creates a challenge. Simply multiplying the estimated abundance of groups by the average size of the detected groups produces biased estimates of abundance of individuals. As the following lecture describes, there is a problem of size bias. The average size of the detected groups is a positively biased estimate of the average size of groups in the population, leading to estimates of individual abundance that is too large.
The practicals in this model address this situation. You are to analyse data from a survey of Risso’s dolphins (Grampus griseus) in the eastern Atlantic Ocean. Not only will you produce estimates of group abundance, but also estimates of abundance of individuals. To prevent bias in the estimates of abundance of individuals, you will apply methods that avoid the size bias problem.
Photo by Wynand Uys on Unsplash
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