Chapter 1 - Núria BONADA

Chapter 3
CALIFORNIA 70.8% MEDBASIN
80%
80%
64.3%
SOUTH AFRICA 70% SW AUSTRALIA
Figure 12. Percentages of similarity between med-regions considering common abundant and
representative (IV-value) taxa in riffles and pools habitats.
DISCUSSION
Traditionally, convergence in ecology has had a deterministic framework, where communities
developed under similar conditions would have a common structure (Cody & Mooney, 1978).
However, several approaches argue that historical factors and intrinsic indeterminism can
imply divergence even under similar environments (Samuels & Drake, 1997). The scale of
study is important to check for global convergences and divergences between regions, as some
scales of observation can obscure others (Samuels & Drake, op. cit.). Overall, our study has
focused at two levels with the mediterranean climate as a common denominator: regional and
local.
Regional scale: historical factors
Appropriate taxonomical sufficiency in aquatic studies has been highly discussed in stream
ecology, and especially in bioassessment (Resh & Unzicker, 1975; Cranston, 1990; Marchant
et al., 1995; Bowman & Bailey, 1997). Although the use of a low taxonomical resolution
implies a gain in precision and information in the responses (Furse et al., 1984; Resh et al.,
1995), at large scale, when different regions in the world are compared in taxonomical
composition and ecological responses, higher taxonomical levels can be more useful as
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70%