3.4 Endemism
Neo- and palaeoendemism
A fair number of island endemics belong to groups
that formerly had a more extensive, continental dis-
tribution. Since colonizing their island(s) in the
remote past (over either land or sea), they have
failed to persist in their original form in their main-
land range (Box 3.3). The implication is that not allislands and mainland area, and in this sense both
dispersal and vicariance reasoning has relevance to
the region’s biogeography.
●Because of the complexity of the colonization sce-
narios within Macaronesia, assigning these islands
to a particular phyto- or zoo-geographic region, or
mainland source area, is inevitably going to be
problematic; nevertheless, there is clearly a strong
Mediterranean flavour to the biota.
ENDEMISM 63Box 3.3 Palaeoendemism of the Macaronesian laurel forest
We illustrate the idea of palaeoendemism with an
example drawn, once again, from the islands of
Macaronesia. The laurel forests of the Azores,
Madeira and the Canaries are examples of the
evergreen broadleaved subtropical biome that can
be found between 25 and 35 latitude in both
hemispheres (i.e. Texas, Florida, Atlantic islands,
Chile, Argentina, South Africa, South East Asia,
Japan, South Australia, and New Zealand)
growing, at least in Macaronesia, under the
influence of orographic cloud layers (Santos-
Guerra 1990). The Macaronesian laurel forests are
considered to be the only surviving remnants of a
once rather richer forest flora, which was
distributed in central Europe (fossils found in
Austria and Hungary) and southern Europe (fossils
found in France, Italy, and Spain) during the
Oligocene–Miocene (Axelrod 1975; Sunding
1979). Today we know that the laurel forest has
been present on the Atlantic islands at least from
the late Pliocene (a minimum of 2 Ma) (Sziemer
2000) and, very likely, much longer.
The failure of these forests to persist in Europe
has been attributed to a range of dramatic
geological and climatic events that took place in
Europe following the transition of the Tethys
ocean seaway into the largely enclosed
Mediterranean basin during the Tertiary. In
particular, around the end of the Tertiary, the
connection between the Mediterranean and
Atlantic closed between c.5.6 and 5.3 Ma, leading
to the Mediterranean drying out almost
completely, with associated drought and
salinization. This spectacular event was followed
by the glacial cycles of the last 2–3 million years
and the desertification of the Saharan region,which began 5–6 Ma (Blondel and Aronson
1999). With the closure of the Panama strait,
and the associated shifts in global ocean
currents, the present-day Mediterranean climate
developed some 3 Ma and with it emerged the
Mediterranean sclerophyllous forest, which was
better adapted to the new prevailing climatic
conditions of hot, dry summers and cool, wet
winters.
The explanation for the survival of this ‘relict’
forest flora on the Atlantic islands, albeit in rather
species-poor form, has been attributed to three
factors.
●The islands may have been buffered from the
climatic extremes of mainland southern and
central Europe and the Mediterranean by their
mid-Atlantic location.
●The topographic amplitude of the islands has
enabled vertical migrations of several hundred
metres in response to such changes in climate as
the islands have experienced.
●The existence in the higher islands of a
stable orographic cloud layer has counteracted
the aridity of the generally Mediterranean cli-
mate, especially so in the northern hemisphere
summer.
As a result, the laurel forests of the Atlantic
islands possess a number of plant species that are
considered to be palaeoendemics. These include
the following Madeiran/Canarian species known
from Tertiary deposits in Europe (5.3 Ma in South
France):Persea indica,Laurus azorica,Ilex
canariensis,Picconia excelsa. However, this is not
to say that they are absolutely identical to the
ancestral forms (see table), and as Carlquist (1995)