The impact of an alien plant on a native plant–pollinator network: an experimental approach

Abstract

Studies of pairwise interactions have shown that an alien plant can affect the pollination of a native plant, this effect being mediated by shared pollinators. Here we use a manipulative field experiment, to investigate the impact of the alien plant Impatiens glandulifera on an entire community of coflowering native plants. Visitation and pollen transport networks were constructed to compare replicated I. glandulifera invaded and I. glandulifera removal plots. Invaded plots had significantly higher visitor species richness, visitor abundance and flower visitation. However, the pollen transport networks were dominated by alien pollen grains in the invaded plots and consequently higher visitation may not translate in facilitation for pollination. The more generalized insects were more likely to visit the alien plant, and Hymenoptera and Hemiptera were more likely to visit the alien than Coleoptera. Our data indicate that generalized native pollinators can provide a pathway of integration for alien plants into native visitation systems.

Indirect interactions between invasive and native plants via pollinators

“…This was recently supported by a study by Jakobsson et al (2008) (Schulke and Waser 2001) and, when foraging, respond to large-scale changes in habitat structure (Menzel et al 1997;Steffan-Dewenter et al 2002). However, in other studies, it has been shown that foraging behaviour of pollinators can change in response to floral abundance at small spatial scales (Kunin 1997;Goverde et al 2002;Ghazoul 2006;Lopezaraiza et al 2007). …”

“…Generalisation results in pollinators sharing floral resources, which is an assumption for indirect interactions to occur among flowering plants. Little is known about the role of indirect interactions in determining community composition of flowering plants (Levin and Anderson 1970;Waser 1978), and this question has only recently been addressed experimentally (Chittka and Schürkens 2001;Moeller 2004;Lopezaraiza et al 2007). Indirect interactions may become particularly important when exotic plant species invade native habitats and cause shifts in native pollination systems.…”

Invasive plant integration into native plant–pollinator networks across Europe

“…These studies have compared invaded networks with networks where the invader was experimentally removed and therefore the invader could have a legacy effect (Lopezaraiza-Mikel et al 2007), or along a gradient of invasion (Morales & Aizen 2002;Olesen et al 2002;Aizen et al 2008) where it is difficult to disentangle whether the main drivers of network changes are alien plants or alien pollinators and to determine which particular species are causing most of the effects. In fact, most of the evidence for the presence of alien species having disruptive effects on plant-pollination interactions (Traveset & Richardson 2006) is based on invader complexes in which supergeneralist and abundant invasive pollinators displace native pollinators and are less efficient in pollinating some native plant species.…”

Non-naturalized alien plants receive fewer flower visits than naturalized and native plants in a Swiss botanical garden

“…Likewise, the presence of an alien plant can also have a facilitative effect on flower visitation of other co occurring aliens, and therefore might promote their naturalization (Molina Montenegro et al, 2008). Nevertheless, increased flower visitation does not necessarily increase reproductive success, as there are increasing chances for heterospecific pollen transfer (Lopezaraiza Mikel et al, 2007).…”

“…On the other hand, the presence of an alien plant can in certain situations also increase flower visita tion of co occurring natives. Indeed, the aliens can act as magnet species, attracting more pollinators that spill over to natives that are in the vicinity (Lopezaraiza Mikel et al, 2007). Likewise, the presence of an alien plant can also have a facilitative effect on flower visitation of other co occurring aliens, and therefore might promote their naturalization (Molina Montenegro et al, 2008).…”