The quantification of habitat architecture for explanations of arthropod assemblage patterns: a comparison of two methods

摘要

A drop disc, originally conceived as a quick and easy method of measuring vegetation height, was compared to the more labour-intensive point quadrat pins in terms of usefulness in quantifying the vertical architecture of field-layer vegetation at a number of broadleaved woodland sites in Buckinghamshire, UK. The drop disc produced measures of height which correlated strongly with those of the point quadrat, as well as a potentially useful value corresponding to 'volume of vegetation', and it is suggested that this technique was relatively more efficient at producing useful data. A number of measures of architectural complexity showed considerable variation in how they ranked sites based upon both real and contrived data. One of these, Fisher's (or Williams') alpha, is shown to be unsuitable for this application. Based upon the weak and non-significant correlations of derived statistics, the practical difficulties in measuring architecture and unfounded assumptions that regard all arthropod speciesen masse, it is reasoned that explanations of community patterns with respect to architecture must be treated with caution.