The effects of island area, isolation and source population size on the presence of the grayling butterfly Hipparchia semele (L.) (Lepidoptera : Satyrinae) on British and Irish offshore islands
Rlh. Dennis, The effects of island area, isolation and source population size on the presence of the grayling butterfly Hipparchia semele (L.) (Lepidoptera : Satyrinae) on British and Irish offshore islands, BIODIVERS C, 7(6), 1998, pp. 765-776
Records of Hipparchia semele on British and Irish islands have been modelle
d against island area, isolation (sea and land distance) and the size of th
e nearest potential source populations. All three variables have been found
to contribute significantly to the presence or absence of H. semele on the
islands. Isolation is a more significant predictor than island area. This
result differs from the multiple species case where area was found to be a
more important influence than isolation. Records on islands are also shown
to depend on the size of populations at the nearest sources; this underpins
the relationships identified for the multiple species case, first, between
the number of species on islands and at nearest sources and, second, betwe
en the incidence of species on islands and at nearest sources. There are cl
ear indications that smaller islands may become increasingly marginalized f
or H. semele; with ongoing habitat loss, because isolation increases and so
urce populations become sparser, the probability of H. semele recolonizing
islands also decreases.