the Ecology of Urban Green Space:Decreasing Habitat Quality and
to common perception, cities in the UK contain substantial areas
of “green space” which therefore has conservation potential,
but the factors affecting the ecology of these urban spaces needs
to be understood.
involves changes in habitat
quality, but also habitat
isolation. The habitat quality
of urban green space is affected by, for example, increasing
pollution; intensive management and recreational use; soil
disturbance and the presence of non-native plants. These factors
influence the suitability of habitat patches for given
invertebrate species. Planners will ask, what are the most
important things to do to improve habitat quality?
also increases the isolation of habitat patches through (a)
habitat fragmentation and (b) encapsulation in an ‘urban
matrix’. If we find that populations are limited by isolation, the ecology of urban
green spaces needs to be understood in terms of models of island
biogeography. Planners will then need to ask, does this
site have low conservation potential because it is isolated? Will
building here significantly increase the isolation of nearby
patches? Will “wildlife corridors” enhance biodiversity by
aim of this project is to investigate whether isolation can be
shown to have a significant effect on urban invertebrate
assemblages. Three initial hypotheses are tested here:
H1: Increasing patch
isolation affects habitat specialists more than habitat
generalists should be less affected as they survive more readily
in the matrix between patches)
H2: Increasing isolation
will affect poor dispersers more than good dispersers
dispersers should be more affected because they find it harder to
move between patches).
Corridors of similar habitat act significantly to reduce isolation
in an urban environment.
Sixty-five sites were selected:
derelict sites across the conurbation in areas of low &
wetland sites located either on or off a river corridor that
flows through the conurbation;
woodland sites located on four rural-urban gradients.
Beetles and spiders were sampled at each site between April and
assemblages are then characterised in terms of:
richness, diversity, dominance, rarity, & ‘urbanity’;
traits, sex-ratio, habitat fidelity, morphology, wing morph,
& dispersal ability.
addition, allozyme analysis is used for a limited number of
Measures of “habitat quality” were taken:
samples were tested for moisture, pH, and OM content;
penetrability, cover of litter, bare ground, moss; and degree
of shading were quantified;
type, structure and density were recorded
“Landscape metrics” describing the area surrounding each patch
A GIS is
used to analyse the structure and nature (including
‘permeability’) of the urban matrix surrounding each site.
preliminary results are as follows:
appears linked to a decline in the species richness of
carabids at wetland sites (particularly habitat specialists).
Further analysis is required to establish the cause (H1
R. Cole “wildlife corridor” does not appear to enhance the
number of wetland specialist species but it may act to
increase and stabilise the number of habitat generalists (H4);
assemblages of derelict sites appear unaffected by isolation
(as measured by the amount of similar habitat in the
vicinity). This is perhaps due to the high mobility of the
habitat specialist species (H2 and H3).