Yoccoz et al. (2001) note that many monitoring programmes either
ignore or deal ineffectively with two primary sources of
variation in monitoring data: spatial variation and
detectability. Biodiversity, and trends in biodiversity, can
vary enormously between locations (reflecting differing
habitats, land uses, climates, etc.), so that monitoring
programmes should be designed to take account of this spatial
variation. This is especially critical if biodiversity is to be
monitored at a regional or global (as distinct from site) level.
Too often, monitoring programmes are conducted at
unrepresentative sites (sometimes called ‘sentinel sites’) and
conclusions generalized to the landscape as a whole. For
example, the British Butterfly Monitoring Scheme (BMS; Pollard &
Yates 1993 ) uses transects at sites chosen because they are
suitable for butterflies. Such sites are often protected
reserves, or atypical in other respects, and trends in abundance
may be unrepresentative of what is happening in the wider
countrysi