We highlight two features. First, because of the
impoverishment in species, island pollination and
dispersal networks tend to feature endemic super-
generalist species, both among the animals and
plants (Olesen et al. 2002). Secondly, pollination
and/or dispersal relationships can appear bizarre
in relation to those found on continents, because
the functions are carried out, in the absence of more
common continental pollinators or dispersers, by
groups of animals not frequently involved in such
functions (Traveset 2001).
The emergence of endemic super-generalists
Traditionally, pollination studies focused on single
plant species or, at most, on guilds of related plant
species and the insects pollinating them (Traveset
and Santamaría 2004). This reflects formerly domi-
nant ideas that pollination mutualisms were the
result of highly co-evolved interspecific relation-
ships. More recent community-level work has
shown that pollination processes are typically more
generalized in nature than previously thought,
with many insect and plant species interacting, and
thus yielding weak pairwise relationships.
However, the connectance level (the percentage of
all possible animal–plant interactions within a net-
work that are actually established) has been found
to diminish in species-rich communities (Olesen
and Jordano 2002). On islands, where species-poor
communities prevail, the existence of pollination
networks with a high degree of connectance is thus
to be expected. Studies within the Azores, the
Canaries, and Mauritius show connectance levels
varying between 20 and 30% (Olesen et al. 2002).
The exception to this range was provided by the
Macaronesian laurel forests, a community domi-
nated by palaeoendemic tree species, where the
value obtained was 9%, indicating a higher level of
specialization.
Recent work suggests that island networks often
involve a few super-generalized animal pollinators
serving many plant species, and a few super-
generalized plant species that are visited by many
pollinators (Olesen and Jordano 2002). Bombus
canariensis, the endemic Canarian white-tailed
bumblebee, provides us with one such example. It
occurs from the coast up to 2000 m and is known to
pollinate 88 plant species (Hohmann et al. 1993). In
a laurel forest studied on La Gomera, Bombus
canariensiswas found to visit 48% of the plant
species participating in the network. Similarly,
the endemic Canarian bee Anthophora allouardiivis-
its at least 46% of the plant species of a subdesert
scrub community on Tenerife (Olesen et al. 2002).
An even greater degree of generalism is displayed
by an endemic Halictusbee in Flores (Azores)
(60%), by the endemic day gecko Phelsuma ornata
from Ile aux Aigrettes (Mauritius) (71%), and by the
endemic bee Xylocopa darwinifrom the Galápagos
(77%).
Among plants, the Macaronesian islands again
provide examples of endemic plant species with
generalized pollinator relationships. These
includeAeonium holochrysum, a member of the
coastal subdesert scrub, visited by 80% of the
known community of pollinators, and Azorina
vidalii, an Azorean endemic shrub, visited by
75% of the pollinator community. Conversely,
Lavandula buchii, an endemic plant restricted to
the old Teno and Anaga massifs of Tenerife, is
pollinated by only 10 insect species (Delgado
2000), in comparison with its continental congener
Lavandula latifoliafrom Southern Spain, which is
pollinated by 80 species (Herrera 1989). This illus-
trates that a more comprehensive comparative
analysis is needed to establish if the apparent
tendency towards generalist species is a general
feature of remote islands.
It has been suggested that one reason for the
success of many introduced species on islands is
the formation of ‘invader complexes’, whereby
introduced species preferentially establish interac-
tions with other introduced species (D’Antonio
and Dudley 1993). However, Olesen et al. (2002)
find little support for the invader complex concept
in pollination networks analysed on the Azores
and Mauritius. Rather, endemic supergeneralist
species tend to include newcomers in their net-
works, either in the form of endemic insects polli-
nating exotic plants, or by endemic plants being
pollinated by exotic insects. In these cases, the
endemic super-generalists may be pivotal to the
successful establishment of alien species that180 ARRIVAL AND CHANGE