Chapter 1 - Núria BONADA

Regional amd local scale: convergences and divergences
speciation have acted in a different way in each region. On the other hand, several authors
have demonstrated that ecological patterns observed at higher taxonomical levels are
equivalent to the ones at genus or species (e.g. Furse et al., 1984; Ferrano & Cole, 1992; Rutt
et al., 1993; Marchant et al., 1995). However, because the high speciation present in some
families (e.g. Leptoceridae in southern hemisphere —de Moor, 1988, 1997) some divergences
observed between med-regions could be attributed to dissimilar ecological responses because
of the existence of different genus and species between regions. When detailed taxonomical
information is not available, comparisions at genus or species level are impossible. In this
case, as in our study, studies at higher taxonomic level may provide interesting insigths about
the importance of historical and ecological factors (Ricklefs, 1987).
According to the results obtained, when macroinvertebrate assemblages at family level are
studied in the 5 med-regions in the world, the historical factor seems very important in
determining macroinvertebrate community of streams in med-regions (see Figure 13 for
summary). Convergences found between med-regions in macroinvertebrate community are
unlikely related to the climate because of the short history of the mediterranean climate
(Alxelrod, 1973; Suc, 1984), and seems to be related to previous historical factors. Notable
differences are found between northern and southern hemisphere, as the early breakup
between Laurasia and Gondwanaland during the Cretaceous (70-135 myBP). As in plant
communities (Deacon, 1983), macroinvertebrates from boreal med-regions are highly
convergent, because the connections between both regions until the Eocene by Bering bridge
(Deacon, 1983), whereas macroinvertebrates in southern hemisphere are more divergent
between med-regions because the early break up of Gondwanaland in early Cretaceous. This
strong convergence observed between MedBasin and California implies lower exclusivity of
taxa in both regions at family level. On the other hand, some exclusive families in MedBasin or
California have a wider distribution than med-region it self. For instance, Prosopistomatidae or
Polymitarcidae from MedBasin are also found in African areas (Edmunds, 1972), and
Pteronarcyidae or Peltoperlidae in California have been recorded in other Neartic and Asian
regions (Zwick, 2000).
High convergences have been reported in plants between California and Chile because the
exchange of taxa through the Panama istm, 3 My ago (Naveh & Wittaker, 1979; Di Castri,
1991). Contrary to that, our study shows that Chilean macroinvertebrate community have a
weak convergence with California med-region at family level, what could be related with the
faster dispersion of plants in front of invertebrates (Cox & Moore, 1993) and the lowest
richness by the insular situation of the country between Andes, Atacama desert and Pacific
119