Intermediate Disturbance Hypothesis, Urbanisation & Campus Natural Areas
Urbanization can sometimes result in an increase in species richness, especially at intermediate levels of development. An increase in diversity at moderate levels of urbanization has been thought to be related to the intermediate disturbance hypothesis.
For instance, a study that examined urban:rural distribution of bird diversity found that diversity of bird species was highest in areas of intermediate disturbance.
However not all animals or plants respond in the same way to the same stresses. For instance, in one study that examined the diversity of butterflies near Peterborough Ontario, the authors hypothesised that intermediate levels of disturbance explained the high diversity of butterflies; while in another case, intermediate disturbance levels were hypothesised to facilitate the establishment of non-native species of ants that would otherwise be displaced by native species (King and Green 1995).
Clearly, the relationship between forests, disturbance and urbanisation is not a simple one - nor one that is likely to affect all species in the same fashion.
However, as you have already seen, there is a growing literature of evidence of the domination of urban natural areas by exotic (non-native, invasive) species. In this case, an invasion may increase total species richness but actually decrease the diversity of native species. This has been called biotic homogenisation (the replacement of local biotas with non-native species that can co-exist with humans). In fact, one common observation for many taxa is that the number of nonnative species increases with urbanization, while the number of native species decreases.
Urbanization can sometimes result in an increase in species richness, especially at intermediate levels of development. An increase in diversity at moderate levels of urbanization has been thought to be related to the intermediate disturbance hypothesis.
For instance, a study that examined urban:rural distribution of bird diversity found that diversity of bird species was highest in areas of intermediate disturbance.
However not all animals or plants respond in the same way to the same stresses. For instance, in one study that examined the diversity of butterflies near Peterborough Ontario, the authors hypothesised that intermediate levels of disturbance explained the high diversity of butterflies; while in another case, intermediate disturbance levels were hypothesised to facilitate the establishment of non-native species of ants that would otherwise be displaced by native species (King and Green 1995).
Clearly, the relationship between forests, disturbance and urbanisation is not a simple one - nor one that is likely to affect all species in the same fashion.
However, as you have already seen, there is a growing literature of evidence of the domination of urban natural areas by exotic (non-native, invasive) species. In this case, an invasion may increase total species richness but actually decrease the diversity of native species. This has been called biotic homogenisation (the replacement of local biotas with non-native species that can co-exist with humans). In fact, one common observation for many taxa is that the number of nonnative species increases with urbanization, while the number of native species decreases.
How do these principles relate to the campus woodlots and natural areas?
Remember - we learned from Dr. Larson, that the "field" beside the Dairy Bush is actually already full of small trees.
Remember - we learned from Dr. Larson, that the "field" beside the Dairy Bush is actually already full of small trees.
We learned from Master student Gwyn Govers that the effects of Garlic Mustard within the Dairy Bush are most pronounced near access trails.
Can the "field" beside the Dairy Bush be developed in the manner detailed below from the Campus Master Plan without deleterious effects to the Dairy Bush (such as increasing pressure of invasive species such Garlic Mustard or the further isolation of provincially significant species such as the Blue Ash)?
Put another way, can the management of the Dairy Bush and the Dairy Bush field be better adaptively managed separately or together?
As new and active members of the University community - your opinion about this matters!
Put another way, can the management of the Dairy Bush and the Dairy Bush field be better adaptively managed separately or together?
As new and active members of the University community - your opinion about this matters!