Chapter 1 - Núria BONADA

Chapter 7
(e.g., Ormerod & Edwards, 1987; Graça et al., 1989) revealing the strong relationships
between aquatic biota and environmental variables. Commonly, a large set of variables has
been used to assess species autoecology and to understand distribution patterns. However,
although factors determining distributions may be numerous and complex, are also
intercorrelated (Prenda & Gallardo, 1992) and, in practice, few variables may allow us to
define assemblages of species occurring in similar ecological conditions (e.g., Carter et al.,
1996; Wiberg-Larsen et al., 2000). Multivariate analyses are very useful to demonstrate the
hierarchical effect of variables in determining organism’s distribution (Wiberg-Larsen et al.,
2000). The strong relationship between macroinvertebrates and environmental variables has
been used all around to predict biological communities given a set of measured variables (e.g.,
Wright et al., 1984; Smith et al., 1989).
Mediterranean climate is characterized by a high seasonality with cold and wet winters and
hot and dry summers (Köppen, 1923; Paskoff, 1973). The Mediterranean basin rivers
subjected to these climatic patters have an annual and interannual variability in discharge
regimes, with floods and droughts frequent and predictable (Gasith & Resh, 1999; Bonada et
al., Chapter 3). Mediterranean fauna is well known to have a high diversity, level of endemicity
and complexity as the result of the interaction of complex historical and ecological factors,
making the area unique from a biogeographical point of view (Balletto & Casale, 1989). In the
Iberian Mediterranean area, numerous studies in taxonomy and ecology of macroinvertebrates
have been done since the eighties (see Alba-Tercedor et al., 1992), but although several
taxonomical lists for specific macroinvertebrates cover all Iberian Peninsula, most of the
ecological studies have been performed at a very small scale (e.g. one or few basins).
Nowadays, studies at larger scales are increasing, and some of them are focused in looking at
the environmental factors implied in the differential distribution of taxa (Mellado et al., 2002;
Vivas et al., in press).
Trichoptera is a well-represented group in the Iberian Peninsula (with 331 species, Vieira-
Lanero, 2000 with two new species from González & Ruiz, 2001 and Zamora-Muñoz et al.,
2002 —see Bonada et al., Chapter 7) and highly endemic (González et al., 1987). Although in
this area Trichoptera has been studied since the middle of nineteen century, most of these
studies have been focused in taxonomical rather than ecological aspects (but see for example,
García de Jalón, 1986). Moreover, an unequal knowledge between caddisfly fauna in north and
south areas of Iberian Peninsula is still noticed, with more studies performed around where
specialists are (González et al., 1987). Recent faunistic studies in southern areas of Spain
noticed also a high endemicity (e.g., Ruiz et al., 2001). Most of these studies are based on
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