Geoscience Reference
In-Depth Information
3
Adaptive Sa
mpling Methods
Jennifer Brown
3.1 Introduction
Environmental managers' need for accurate information about ecologi-
cal populations is increasing as the demand for cost-effective management
expands. The ability to detect the current status of a population is essen-
tial for managers to be able to decide when to take appropriate manage-
ment action and for assessing the success—or otherwise—of alternative
management interventions. Information is needed about population status
for scientists to assess and evaluate alternative population models and for
understanding population dynamics. In the previous chapter, the idea of
sampling and selecting a portion of the population compared with assessing
and measuring every individual in the population was introduced. Here, we
introduce a range of sampling designs that are particularly relevant to eco-
logical sampling and in fact have been designed mostly with these situations
in mind (Thompson, 2003). To be more precise, these designs were developed
for surveying populations that are rare and clustered.
Ecologists' interest in rare and clustered populations is because these
populations often represent the extremes of biological processes, such as the
early incursion of invasive species or the near extinction of endangered spe-
cies. They can also be the most challenging to survey because without some
targeted field effort, most of the sample units, by definition, will not contain
the rare species of interest. Survey designs that assist in targeting field effort
to where the species of interest is should improve the quality and quantity of
information from the survey.
There is no one definition for rare and clustered populations that all stat-
isticians and ecologists agree on, but generally, these are populations that
are difficult to detect (in fact, they may not be rare but sightings of them
are rare) or populations that are sparse in some sense. Sparseness can come
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