Chapter 1 - Núria BONADA

Chapter 3
Other convergences and divergences between med-regions
Convergences and divergences between med-regions have been established looking at the
communitiy structure. However, communities may display different structure in distant
regions, but present similar patterns in feeding or behavioural strategies. Because unavailable
data in some med-regions, we were not able to compare trophic relationships under similar
climatic conditions. However, some observations can be made from our study. For example, in
southern Hemisphere, where the predators Rhyacophilae lack by historical factors, they a
replaced by other macroinvertebrates with similar feeding requirements, as the Corydalidae in
South Africa. However, in some cases, some feeding strategies are not replaced because again,
local factors constrain them. That is the case of South Africa, where its oligotrophic and acidic
waters (King et al., 1979) constrain the presence of grazers in headwaters, appearing
downstream.
Concluding remarks
Historical and ecological factors have been used in our study to check for differences between
macroinvertebrate communities in med-regions. In all cases, northern hemisphere regions
have strong convergences compared with the rest of med-regions, and a closer similarity with
South Africa than SWAustralia is noticed. Scale of study and the interchange of information
between scales have been a problem for ecologists (Levin, 1992). Difficulties are found to
define and establish what are large and small scales (Peckarsky et al., 1997). We argue that
under the same climatic constrains both historical and local factors are important to
macroinvertebrate communities. Convergences or divergences in historical and ecological
factors among med-regions let us to understand convergences or divergences in
macroinvertebrate community, although other factors as the incidence of non-native
macroinvertebrates could affect similarities and differences between med-regions.
Consequently, in reference conditions, history, climate, landscape, temporality, habitat and
biotic interactions can be considered as filters acting as mechanistic factors in a hierarchical
direction, allowing the presence and enhancing the abundance of several species in front of
others (Tonn et al., 1990; Poff, 1997). Comparisons in common taxa between med-regions
suggest that historical and ecological factors could be more important than climate to
determine the abundance of several taxa in a specific habitat or flow condition. However, when
such factors let the abundance of some taxa in several regions (e.g., the high pH in California
and MedBasin enhance the presence of Mollusca), responses to habitat and temporality
between med-regions are highly convergent. From our data, more similarities have been
observed between pairs of med-regions in habitat than in flow conditions, suggesting that
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