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Comparison of Paleoecological Patterns in
Insular Bird Faunas: A Case Study from the Western
Mediterranean and Hawaii
Bartomeu Segui and Josep Antoni Alcover
ABSTRACT
A comparison among the Pleistocene avifaunas from the westem
Mediterranean islands (Menorca, Mallorca, and Cabrera
(Gymnesic Islands); Eivissa (=Ibiza) and Formentera (Pityusic
Islands); Corsica; Sardinia) shows great differences between those
islands with terrestrial mammals (Gymnesic Islands, Corsica, Sardinia)
and those lacking them (Pityusic Islands). A close parallel is
found between the late Pleistocene avian communities of the Pityusics
and the prehuman avifauna of the Hawaiian Islands, whereas
the communities from the remaining western Mediterranean
islands were similar ecologically to those of the eastern Mediterranean
islands. A key factor for the understanding of avian community
structure is the presence or absence of middle-sized
herbivorous mammals (Myotragus balearicus Bate on the Gymnesic
Islands and Megaceros cazioti (Deperet) on Corsica and Sardinia).
Introduction
Since the works of Darwin (1859) and Wallace (1881), the
study of islands has been a powerful tool for the advancement
of many fields of biology (Vitousek et al., 1995). The recent inclusion
of fossils in the study of insular faunas has conferred a
historical dimension to previous analyses of insular biogeography
and ecology. This new component enables us to test the
validity of faunal composition and biogeographic concepts derived
from the study of present faunas, allowing new kinds of
analyses of the components and the structure of paleocommunities
(Alcover and McMinn, 1994; James, 1995).
The study of insular fossil faunas has already changed several
paradigms of insular biogeography and ecology. Thus, the
Bartomeu Segui, Departament de Ciencies de la Terra, Universitat de
les Hies Balears, Carretera de Valldemossa, km 7.5, 07071 Ciutat de
Mallorca, Balears (Spain). Josep Antoni Alcover, Institut Mediterrani
d'Estudis Avancats, Carr et era de Valldemossa, km 7.5, 07071 Ciutat
de Mallorca, Balears (Spain).
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actual existence of ecological processes of "faunistic turnover"
for the establishment of an "insular equilibrium" (MacArthur
and Wilson, 1967) has been seriously questioned (e.g., Olson
and James, 1984; Steadman, 1986, 1995; James, 1995). Recent
findings also have questioned ecological processes, such as the
so-called "taxon cycle" (see Pregill and Olson, 1981), or postulates
to the effect that insular communities harbor species of
predators exhibiting lesser body size than those from the closest
mainland (Blondel and Frochot, 1976).
Typical insular communities are characterized by their disharmony,
by so-called "insular poverty," and by their high degree
of endemism (Wallace, 1895). These factors imply that
ecological communities assemble on islands in a peculiar way,
with an organization of ecological relationships between species
that is different from that on continents. Before human colonization,
island communities were even more peculiar than at
present (James, 1995).
The western Mediterranean islands (Figure 1) have provided
moderately rich Quaternary avifaunas (Alcover et al., 1992) as
well as prehuman faunas of mammals, reptiles, and amphibians
(see Table 1). To date, the late Pleistocene paleornithological
record consists of 55 or 56 species in Mallorca, eight in Menorca,
60 to 65 in Eivissa, two in Formentera, 74 in Corsica, and
49 in Sardinia. The fossil avifauna of Eivissa is considered to
be the best represented of prehuman bird communities of any
island in the Mediterranean region. The late Pleistocene record
of Eivissa is based on more than 150,000 fossil bird specimens,
mainly coming from a single deposit, Es Pouas (McMinn, in
prep.), as well as from another six sites of lesser importance. In
Mallorca, more than 3000 bird bones have been exhumed to
date from 14 late Pleistocene and Holocene sites (Segui, 1997).
The fossil record from Corsica and Sardinia, in spite of not being
as representative of its Quaternary avifaunas, displays several
features that allows the characterization of its prehuman
native faunas. The late Pleistocene fossil record of Menorca
and Formentera is still very limited. Because we do not consider
the fossil records of these islands to be as representative of