Metapopulation ecology of Notonecta in small ponds.

This thesis considers the application of metapopulation theory to a field system; two
species of Notonecta (Hemiptera: Heteroptera, Notonectidae), a freshwater invertebrate
predator, inhabiting a series of small man-made ponds known as dewponds, in the Peak
District, Derbyshire.
Surveys of pond occupancy and habitat characteristics examined the habitat preferences
and spatial population dynamics of the two species, and associations between Notonecta and
other taxa. Interspecific competition and predation between nymphs were investigated in the
laboratory and in field mesocosms to determine their potential influence on field distributions.
The two species have contrasting habitat preferences, and breed in a subset of all ponds in
the area. Choice of oviposition substrate appears to be an important mechanism of habitat
selection. The landscape scale population dynamics of Notonecta resemble those predicted by
metapopulation models, but regional persistence is determined by the availability and
distribution of suitable habitat across the landscape, rather than by a dynamic balance of
stochastic colonisation and extinction. Where the species co-occur, competition is likely and
the outcome is influenced by the amount of submerged vegetation present, which affects the
feeding efficiency of the two species. Associations between Notonecta and other taxa largely
appear to result from covariance in response to habitat factors; the distributions of Notonecta
and potential prey do not seem to be strongly linked.
Most metapopulation models assume that habitat is static, but in common with many
other field systems, metapopulation dynamics of Notonecta appear to be driven by dynamic
changes in habitat of individual patches. This suggests that in order to be of greater practical
value, future developments in metapopulation theory must incorporate effects of habitat
dynamics on regional persistence and distribution.