Individuals of both C. alfacariensis and C. hyale were sampled for an allozyme study in France and Italy in the summer of 1992. Species determination was based on the studies of Berger and Fontaine (1947), Jarvis (1955), and Dutreix (1980). Habitat preference between C. alfacariensis and C. hyale was studied by means of field observations in the French Alps where both species occur sympatrically.
A total of 920 adult C. alfacariensis and 1155 adult C. hyale were observed from the 14th of August until the 8th of September, 1974 by HD. The location and geographical position of all sites is presented in Table 1. During the field observations the following environmental variables were noted at each locality: 1. Aspect, 2. Vegetation (cultivated – uncultivated), 3. Humidity (dry – irrigated), 4. Altitude 5. Date, 6. Weather (warm – cold), in addition to the frequency of occurrence of adults of C. alfacariensis and C. hyale.
The relative abundances of both species were regressed onto the first axis of a principal components analysis (PCA based on the environmental variables and using Statistica for Windows, version 5, StatSoft Inc.) to see if both species varied significantly (positively or negatively) in their response to this synthetic environmental gradient. The relative abundance here is the absolute abundance of species A at a given site divided by the absolute abundances of both species at the same site. We use relative abundance here because of the high variance in the absolute abundance among sites.