Biology Reference
In-Depth Information
proved to be highly competitive in various communities and most adaptable
in colonizing new habitats far from the places of their origin. Considering
that the colonized areas may be limited in nectar resources, these bees can
constitute a threat to the local pollinator fauna, especially to small solitary
bees in the cases where their foraging host breadths
overlap. This applies
particularly to the almost omnipresent
Apis mellifera
, which has been ob-
served frequenting the majority of plant species within any one geographic
region, visiting nearly 40,000 different plant species (Crane, 1990). The
situation is also alarming within the Mediterranean, where honeybees are
extensively managed for honey production not only in agricultural lands, but
also in marginal lands, woodland and scrubland, as well as in protected ar-
eas. As an example, within the 30-ha
phrygana
community in Athens,
A. mellifera
was recorded visiting 103 out of the 133 available plant species
(Petanidou & Potts, 2006). In such cases, honeybees could also be displacing
native bees by just reducing their resource base (Petanidou & Ellis, 1996;
Forup & Memmott, 2005).
Bumblebees (
Bombus
spp.), whose natural range is largely confined to
the temperate northern hemisphere, have recently been introduced to various
countries to enhance crop pollination. In the Mediterranean region, espe-
cially in typical Mediterranean habitats where bumblebees are relatively
uncommon (Petanidou & Ellis, 1993), this fashion started in the 1980s and
continues to date on an enormous scale, mainly in order to assist pollination
in greenhouses. Following escapes from commercial colonies, such introduc-
tions lead to unwanted invasions, which may spread over large areas (Dafni
& Shmida, 1996; Dafni, 1998).
It has been argued that depletion of nectar on a daily basis before native
bees begin to forage, may result in a significant asymmetry in competition in
favour of these introduced species (Goulson, 2003). On Mt Carmel in Israel,
Dafni and Shmida (1996) reported declines in abundance of medium- and
large-sized native bees (and also of honeybees) following the arrival of
Bombus terrestris
in 1978. Hingston and McQuillan (1999) recorded displace-
ment of two species of
Chalicodoma
(Megachilidae) in Tasmania by introduced
B. terrestris
, which the authors consider a threat to Australian ecosystems
(Hingston & McQuillan, 1998). Based on measurements of the high com-
petitiveness of
B. terrestris
to native bees, it has been suggested that
unregulated movements of non-native populations of the species within
Europe should be banned without a full risk assessment (Ings et al., 2005).
The impacts of
A. mellifera
introductions are similar: Goulson et al. (2002)
found higher abundances of native bees in honeybee-free sites in Tasmania;
Forup and Memmott (2005) observed some changes in floral host breadth of
