Urban Ecology: An Introduction by Ian Douglas & Philip James

Author:Ian Douglas & Philip James [Douglas, Ian]
Language: eng
Format: azw3
ISBN: 9781136266959
Publisher: Taylor and Francis
Published: 2014-10-30T04:00:00+00:00

SPATIAL PATTERNS IN ANIMAL DISTRIBUTION

In ecological terms, varying degrees of urbanization correspond to different levels of frequency and intensities of disturbance. The relationship between the distribution of animals and the degree of urbanization is inconsistent across different animal taxa. For some taxa, a peak occurs in suburbia, supporting the intermediate disturbance hypothesis, while for others population density declines as urbanization increases. The intermediate disturbance hypothesis proposed by Connell (1978) seeks to account for patterns of diversity in tropical rainforest and coral reefs. The hypothesis predicts that species richness should be highest at intermediate levels of disturbance. It is based on the argument that disturbances continually disrupt the process of succession towards climax species in biological communities. The perturbations create space for colonization by less competitive individuals and species than those that form the climax. Thus there is a tradeoff between a species’ colonizing ability and its competitive ability which leads to the habitat becoming patchy and dynamic (Wilson 1994). Patches that are frequently and/or intensely disturbed are expected to exhibit low species richness because few species are able to colonize during the brief periods between disturbances or tolerate the high intensities of their impact. On the other hand, patches that experience infrequent and/or low intensity disturbances also are expected to be poor in species, because they become dominated by competitively superior taxa (i.e. K-selected species). Hence, richness should be highest at intermediate levels of disturbance because both rapid colonizers (r-selected species) and more competitive species (K-selected species) co-occur (Townsend et al. 1997). In urban areas, it is the suburbs that exhibit disturbance that is neither too frequent or intense nor too infrequent or slight.

Both age-specific mortality and density-dependent selection (the key element of the r/K paradigm) are important in an organism’s life history. It has been recognized that body size plays a crucial role in determining the timescale of mammalian life histories: almost all life-history parameters correlate with body size, with small mammals having short lives and large ones living longer. This pattern underlies the hypothesis that body size, or another strongly correlated variable such as brain size or metabolic rate, is a key factor in whether or not a member of a species survives changing environmental conditions.

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