Urban development and stream insect communities
Are there species that are only found in streams in pristine areas?
Do some species seem to prefer developed waterways?
Do developed and undeveloped waterways differ in the number of species present?
Does the strength of any differences present vary among habitat types?
To answer some of these questions, I've collected invertebrates from six streams in the Bangor, Maine area varying in their degree of urban development.
At each stream, I took half of my samples from slow-moving pool habitats and the other half from faster-moving riffle zones. I then identified every insect in every sample to figure out what is present in each stream.
My next step is to analyze my data to assess whether there are significant differences among streams of differing levels of urban development, and between habitat types.
Aquatic insects can be sensitive to changes in their environment. As a result, a shift in community composition from more sensitive species to more tolerant species is often indicative of a larger problem of stream water quality. Also, all habitats are connected. A stream does not exist in a vacuum; rather it exists in and interacts with a forest, or a meadow. Changes in a stream community can cause changes in the communities it interacts with as well. Birds that eat aquatic insects react to changes in their food source. Plants that are eaten by terrestrial adult forms of these insects will respond to changes in their communities as well.
When we study stream communities, we often lump habitat types together. However, if different habitat types respond differently to urban development, it is possible that even where a change is happening, it could be obscured by the differential response (for example, if one habitat responds positively, and one responds negatively, the stream as a whole appears to not respond at all). Therefore, it is important to test the assumption that the apparent response at a stream-wide level accurately reflects the response of each part of the stream.