Decreased insect visitation to a native species caused by an invasive tree in the Cape Floristic Region

Abstract

a b s t r a c tFlowering invasive plants can potentially reduce pollination rates in co-flowering native plant species by attracting shared flower visitors. We investigate the effect of a prolifically flowering invasive species, Acacia saligna (Fabaceae), on native insect-flower interactions in surrounding communities. We surveyed flower visitation to A. saligna and selected native species at invaded and uninvaded areas and assessed the extent of flower visitor overlap of A. saligna and native species across four sites in South Africa's Cape Floristic Region. Median visitation rates of bees and all insects were significantly lower to one native species (Roepera fulva) in both field seasons at the same site when A. saligna was present. This native species also had the highest flower visitor overlap with A. saligna which was driven primarily by the native honeybee, Apis mellifera subsp. capensis. Observational data showed that A. saligna inflorescences were visited most frequently by minute beetles and the native honeybee. Our findings indicate that native honeybees are important visitors to A. saligna, and that at least one native plant species experiences reduced flower visitation due to competition with A. saligna for honeybee visits. Flowering A. saligna could have widereaching effects on native plants by competing for visits from a super generalist flower visitor -the native honeybee -which may jeopardize the reproductive success of natives whose flowering time overlaps with that of A. saligna. Our study further highlights the importance of understanding the effect of a flowering invasive species on native species and the potentially important mutualism between A. saligna and honeybees.

No consistent pollinator‐mediated impacts of alien plants on natives

“…Gibson et al . ); each species pair was treated as an independent observation. For articles where results were reported using both observational and experimental approaches ( n = 4 for visitation data, n = 2 for reproductive success data) for a single species pair, each approach was treated as a separate study (e.g. Baskett et al .…”

Neighborhood‐contingent indirect interactions between native and exotic plants: multiple shared pollinators mediate reproductive success during invasions

“…Furthermore, foraging behavior in a given floral neighborhood can be contingent on pollinator identity, as pollinator groups may behave differently in the same floral environment (Stout et al 1998, Lázaro and Totland 2010a, b). Though many studies have documented inter action between native and exotic plants through pollinator services, including the effect of floral density or diversity on pollination (McKinney and Goodell 2001, Moragues and Traveset 2005, Lopezaraiza‐Mikel et al 2007, Gibson et al 2013), relatively few have examined how floral neighborhood influences multiple shared pollinators to shape the outcome of indirect native/exotic interactions (but see Lázaro and Totland 2010b).…”

Native insects and invasive plants encounters

“…For example, inflorescence of Acacia saligna is composed of multiple flowers which attract native insects due to easy access to nectar. Increased native insect visitation in A. saligna in the invaded plots of Cape Floristic Region has led to an increase in the invasiveness of the species (Gibson et al 2012(Gibson et al , 2013. The variable nature of herbivory and pollination by native insects can lead to rapid change in invasive plant range expansion dynamics (Fig.…”

“…Significant numbers of studies have emerged to understand the ecological role of invasive plants through interactions, viz. herbivory, pollination, and seed dispersal with native insect communities (Maron and Vilà 2001;Herrera et al 2002;Davies and Sheley 2007;Martins et al 2009;Vanparys et al 2008;Gibson et al 2013;Pearse and Altermatt 2013). A greater understanding of the interactions between non-native plant species and native insect communities is vital for understanding, predicting, and managing plant invasions (Vermeij 1996).…”