 | A pollinating insect on a Carpobrotus affine acinaciformis flowerhead. (Click image to enlarge) |
May 2008 — Using empirical tests, a pioneering study shows how plant species, such
as the prickly pear, invade Mediterranean ecosystems, and can either
rob the native plants of pollinating insects, or, surprisingly, can
attract them, thus benefiting the whole plant community, such as in the
case of balsam. The research contradicts the hypothesis of the “floral
market” whereby only the invasive flowers are seen to benefit and the
native flowers are no longer visited by pollinating insects.
Biological invasions (species transported by humans outside their
region of origin to other regions where these species become
established and expand) are one of the major causes of the loss of
biodiversity. The plants fight for nutrients, space and light, and for
pollinating insects.
An article about this subject has been published in the “Oecología”
[Oecology] journal by scientists at the Universidad Autónoma de
Barcelona (UAB), [the Autonomous University, Barcelona], the Biological
Station, Donana, CSIC [the Spanish National Research Council] and the
Instituto Mediterráneo de Estudios Avanzados (IMEDEA) [Mediterranean
Institute for Advanced Studies]. According to the research, the
existence of invasive plants in invaded sites can increase visits from
insects to the majority of native plants. In this way the “floral
market” hypothesis in which only the invasive flowers are seen to
benefit and the native flowers are no longer visited by insects is
contradicted.
Ignasi Bartomeus, a researcher at the UAB, and the main author of
the study, points out some important details to SINC: “the invasions do
not follow a single pattern: for this reason it is necessary to
understand the mechanisms and structure whereby the native species
compete”.
The two invasive plants under study, Opuntia stricata – a type of
prickly pear – and Carpobrotus affine acinaciformis – also called
Sally-my-handsome or balsam – have more eye-catching flowers and are
richer in pollen that the rest of the native plants and receive many
more insect visits that the latter.
The study reveals that the invasive plants play a central role in
the plant pollination network. This is because during the period of the
study, Opuntia stricta received 30.9% of insect visits, compared to
43.4% for Carpobrotus affine acinaciformis.
The scientists discovered that the more resources there are in the
plant community, the more pollinators will be attracted towards all of
the plants, although it is still not known whether the impact on the
seeds of the native plant is positive or not. This is the case for
Carpobrotus, which can impact upon the pollination of the native plants.
The researchers observed 23 pollinating insects for Carpobrotus and
17 for Opuntia. Compared to the native plants, the two invasive plants
have a different impact. In the first case, there was no insect that
was an exclusive pollinator, whereas in the second case, the carpenter
bee (Xylocopa violacea) was an exclusive pollinator. “The Opuntia
flowers monopolise the market, attracting all the pollinating insects
in the area to their flowers, whereas the Carpobrotus attracts more
pollinating insects to the area, but all the plants are seen to
benefit”, Bartomeus points out.
The study concludes that Carpobrotus can improve the reproduction of
the native plants whereas Opuntia reduces it. Bartomeus confirms to
SINC that “the presence of the invasive plants can alter the structure
of the plant community, and it is difficult to predict the long-term
effects of this.”
Journal reference: Bartomeus I., Vila M., Santamaría L. Contrasting effects of
invasive plants in plant-pollinator networks. Oecologia 155(4): 761-770
ABR 2008.
Source : Plataforma SINC.