The role of alien species on plant-floral visitor network structure in invaded communities

Abstract

The interactions between pairs of native and alien plants via shared use of pollinators have been widely studied. Community level studies however, are necessary in order to fully understand the factors and mechanisms that facilitate successful plant invasion, but these are still scarce. Specifically, few community level studies have considered how differences in invasion level (alien flower abundance), and degree of floral trait similarity between native and invasive species, mediate effects on native plant-pollinator communities. Here, we evaluated the role of alien species on overall plant-floral visitor network structure, and on species-level network parameters, across nine invaded coastal communities distributed along 205 km in Yucatán, México that vary in alien species richness and flower abundance. We further assessed the potential the role of alien plant species on plant-floral visitor network structure and robustness via computational simulation of native and invasive plant extinction scenarios. We did not find significant differences between native and alien species in their functional floral phenotypes or in their visitation rate and pollinator community composition in these invaded sites. Variation in the proportion of alien plant species and flower abundance across sites did not influence plant-pollinator network structure. Species-level network parameters (i.e., normalized degree and nestedness contribution) did not differ between native and alien species. Furthermore, our simulation analyses revealed that alien species are functionally equivalent to native species and contribute equally to network structure and robustness. Overall, our results suggest that high levels of floral trait similarity and pollinator use overlap may help facilitate the integration of alien species into native plant-pollinator networks. As a result, alien species may also play a similar role than that of natives in the structure and stability of native plant and pollinator communities in the studied coastal sand dune ecosystem.

Integrating floral trait and flowering time distribution patterns help reveal a more dynamic nature of co‐flowering community assembly processes

“…), we do not expect environmental constraints to strongly influence plant species overlap in flowering time within a season. Pollinator community at the study area is composed by multiple functional groups but is strongly dominated by bee flies, butterflies, flies, social and solitary bees (Albor et al., 2019; Campos‐Navarrete et al., 2013; Parra‐Tabla et al., 2019).…”

“…Although this type of densitydependent relationship has been shown for pairs of interacting plant species (Brown, Mitchell, & Graham, 2002;Jakobsson, Lázaro, & Totland, 2009;Rathcke, 1983Rathcke, , 1988Seifan, Hoch, Hanoteaux, & Tielbörger, 2014), knowledge of density-dependent effects in structuring species interactions at the community level is limited (but see Bergamo, Streher, Traveset, Wolowski, & Sazima, 2020). As a result, along the entire study area, the density and diversity of co-flowering species can be up to 10 and 2 times higher in the rainy season compared to the dry season, respectively (Albor et al, 2019;Parra-Tabla et al, 2019). This seasonal dynamic occurs as a result of drastic changes in the environment (temperature, precipitation) that occur predictably during certain months of the year.…”

Pollen transfer networks reveal alien species as main heterospecific pollen donors with fitness consequences for natives

“…Alien species represent around 30% of total plant richness (Parra‐Tab la et al., 2018) and a high percentage of all the flowers available to pollinators in these communities (76% ± 30, M ± SD ), but with high variability among sites (12%–99%; Table 1). Alien plant species also share a high proportion of the primary insect pollinators with native plant species (Albor et al., 2019; Suárez‐Mariño et al, 2019; Parra‐Tab la et al., 2019). Following Parra‐Tab la et al.…”

“…The study of plant–pollinator networks based on flower visitation has further suggested that co‐flowering communities are robust to species invasion (e.g. Parra‐Tab la et al., 2019; Vilà et al., 2009 but see Albrecht et al., 2014). However, if the arrival of alien plant species exacerbates HP transfer, it could affect the robustness of co‐flowering communities and their long‐term stability independently of changes in pollinator visitation (see Fang & Huang, 2016).…”

“…This study examines HP transfer networks in nine coastal co‐flowering communities that have experienced recent invasion (<30 years) of alien plant species, but with varying degrees of invasion intensity across sites (Parra‐Tab la et al., 2018). Plant–pollinator networks in these communities have revealed that alien plants are well integrated, and that their presence does not seem to compromise network structure and robustness (Parra‐Tab la et al., 2019). However, the effects of plant species invasion on HP transfer networks and its potential post‐pollination consequences are unknown.…”