Habitat classification: General considerations

[First paragraph(s)...]
There appear to be two approaches to the subject of this symposium; the environment may be broken down into a number of categories to which the habitat of any organism may be referred, or the habitats of particular organisms may be defined and classified in relation to one another.
If the first alternative is used, ecologists are confronted with a continuous portion of space in which organisms live. Are there in fact any units to classify apart from those imposed by the classification chosen? It is evident that the environment is not homogeneous and that very different communities occur in different parts of it. This lack of uniformity can be expressed by positive and negative correlations between the distribution of species and it should be possible to delineate any communities that may exist, without subjective bias. However, because the environment is continuously varying, there will generally be transitions between communities, and although it may be comparatively easy to impose boundaries they are unlikely to be absolute.