Biology Reference
In-Depth Information
(e.g., reduced fruit or seed yield in agricultural systems) and nature conser-
vation (e.g., local extinction of species).
Copiously offered nectar is often the most effective fee for an introduced
alien species to establish and become invasive. Especially in the Mediterra-
nean, where nectar is not abundant, efficient invasive plants are expected to
be those offering high nectar or pollen yields. Such high nectar yields may
also be available at the population level in situations of extremely high num-
ber of flowers that some plants or populations may have. This is the case for
Bunias orientalis
, an extremely successful invasive plant species in central
Europe, which is a food source for bumblebees and honeybees, but has nega-
tive impacts on the fitness of native plant species (Schurkens & Chittka,
2001). Examples like this must raise the attention of managers and decision
makers before any site management is implemented. In this respect, the de-
liberate introduction of the American species
Phacelia tanacetifolia
as a
nectar source plant in central Europe and the Mediterranean is astounding,
especially when considering the cost of irrigation in an area suffering from
extreme drought (Petanidou, 2003).
6.2
Invasive bees: beekeeping, bumblebee management,
and wild bee conservation
The diet of all bee species consists exclusively of pollen and nectar collected
from flowers, although it may occasionally be supplemented by other sub-
stances, such as honeydew, plant sap, waxes, resins, and water (Michener,
1974). As a consequence, pollen and nectar are the most sought-after foods
within a community, and the source of competition among bees and other
flower-visiting insects, at least in periods when these resources are limited.
Among all bees, honeybees and bumblebees are notorious for exploiting
floral rewards, and a bulky literature has accumulated on their competitive
efficiency against solitary bees (see Goulson, 2003, for a review).
Both honeybees and bumblebees possess undoubted foraging abilities.
Apart from having relatively long tongues, these large and hairy animals
thermoregulate in flight and retain heat within their large nests, therefore
being able to exploit all sources of nectar in the community by foraging ear-
lier in the morning than many native, solitary bee species or under
unfavourable weather conditions, thus reducing the food base of other bees
(Corbet et al., 1993; Dafni & Shmida, 1996; Willmer & Stone, 2004). In ad-
dition, they are generalists with large and long-lived colonies and so are able
to adapt to a succession of different flower sources as they become available.
Having such assets, it is no wonder that honeybees and bumblebees have
