Chapter 1 - Núria BONADA

Regional amd local scale: convergences and divergences
subhumid, submediterranean or humid and subxeric or perhumid. However, from these
subclimates Di Castri (1973c) distinguished an “eumediterranean” subclimate which would be
equivalent to the semiarid and subhumid subclimates, with a precipitation range of 275-
640mm/y.
Mediterranean climate is located between the temperate and dry climate areas (see Dallman,
1998), and both regions have influenced strongly the mediterranean climate and its present
biota (di Castri, 1981; Herrera, 1995). Relationships with these adjacent climates are variable
between regions (di Castri, 1981). For example, summer precipitation is higher in South Africa
and northern Mediterranean Basin because of their proximity to tropical and temperate
regions, and lower in Chile because of Atacama Desert influences (di Castri, 1981).
Mediterranean biota and humans
Mediterranean climate originated in the Pliocene, 3.2 My ago (Alxelrod, 1973; Suc, 1984), and
therefore is a young climate in geological terms, younger than part of the biota found in these
med-regions (Raven, 1973). As a consequence, some lower vertebrate, invertebrate and plant
distributions are homogeneous, reflecting the patterns established during the Mesozoic, before
the breakup of the continents and the formation of the mediterranean climate (Deacon, 1983;
Herrera, 1995), or the later connections between regions (Nilsen, 1978; Cooke, 1972). Once the
climate was formed, similar selection forces acted in the configuration of the mediterranean
biota (Johnson, 1973), and therefore, a high similarity between regions should be expected
(Mooney, 1982). However, mediterranean areas in the world show an important variability in
ecosystems, because of geographic, microclimatic, topographic, physiographic, litologic and
historic aspects have contributed to the present faunal and floral distributions (di Castri,
1981). Several authors suggest 4 origins of the mediterranean biota (di Castri, 1991):
• Species developed in situ before the mediterranean climate formation.
• Species developed after the mediterranean climate was established.
• Species developed outside the mediterranean regions but that settled in these areas
posteriorly.
• Invasive species from human impact.
When biota is compared among med-regions, all these possible origins must be considered
and specially the historical or environmental factors (di Castri & Hadley, 1985; di Castri,
1991).
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