Disentangling how alien species shape the seasonal dynamics of plant-pollinator communities

“Alien plants and flower visitors disrupt the seasonal dynamics of mutualistic networks” by Arroyo-Correa, Burkle & Emer has just been published in Journal of Ecology.

This study provides one of the first empirical reports of alien species shaping the seasonal dynamics of plant–flower visitor networks. Author, Blanca Arroyo-Correa, provides further insight into this research.

The presence of alien species in native communities is one of the main drivers of global change because they can drastically disrupt ecological processes, such as those involving plant-pollinator interactions. Thus, understanding how alien species affect the structure and the dynamics of communities should be a major consideration when dealing with the biodiversity crisis.

*A native bee (*Leioproctus flavescens) visiting flowers of the alien Leucanthemum vulgare (A) and Cirsium arvense (B) in invaded subalpine communities of the South Island of New Zealand. (C) A subalpine landscape invaded by alien plants and pollinators in the South Island of New Zealand. Photos: Carine Emer.

Interactions between plants and pollinators within a community comprise complex mutualistic networks, which may vary in configuration over time. However, because interaction networks are often treated as temporally static entities, we know very little about how alien species affect the temporal dynamics of pollination networks. Besides, most previous studies that account for alien species’ impacts focus on a single trophic level of the invasion, considering either alien plant or alien pollinator species. It is still an open question, whether the effects of alien species on native communities are dependent on the trophic level being analysed.

In our study, we fill these gaps by investigating how alien plants and pollinators configure temporal networks within a flowering season. Our study system is located in the South Island of New Zealand and comprehends a subalpine vegetation in which 68% of the sampled plant species, and 14% of the pollinator species that interact with them, are alien.

Using a community-level network approach we found that alien pollinator species interacted with more plant species, their interactions were more specialized, and the dependence of plant species on them was higher in comparison to native pollinators. Meanwhile, we found totally opposite patterns for alien plant species as they interacted with less pollinator species, their interactions were less specialized, and the dependence of pollinator species on them was lower compared to native plant species. Moreover, our results showed that invader complexes, in which alien species interact significantly more with each other than with native resident species, were established across the season, and this may have facilitated the spread of alien species across the study sites.

Both alien plants and pollinators increased interaction turnover through the flowering season by two distinct mechanisms: (i) promoting interaction rewiring (i.e. reassembling of pairwise animal–plant interactions when both partners occur but do not interact) in the case of alien plants, and (ii) increasing species turnover (i.e. changes in pairwise interactions as animal or plant species become present or absent over time) in the case of alien pollinators. Therefore, our results show that both alien plants and pollinators significantly influence the seasonal dynamics of mutualistic networks in which they are involved; yet its causes and consequences are dependent on the trophic level considered.

Temporal networks of plant-pollinator interactions from the South Island of New Zealand in three different communities. Each circle represents a unique pairwise interaction between a plant species and a pollinator species, and the squares represent the four time slices during the flowering season. Grey lines connect the interactions to the time slice in which they were recorded. Black circles shared among squares represent interactions persisting across time and thus connecting temporal networks.

Altogether, our findings highlight the importance of considering the consequences of aggregating interaction data with an underlying temporal structure as well as the trophic level of the invasion when it comes to assessing the impacts of alien species in the community structure. By accounting for the temporal components, we can elucidate how interactions with alien species assemble and/or disassemble over time while estimating the drivers and consequences of such seasonal dynamics.

Blanca Arroyo-Correa Estación Biológica de Doñana, CSIC, Spain

Read the full article online: Alien plants and flower visitors disrupt the seasonal dynamics of mutualistic networks | Blanca Arroyo‐Correa, Laura A. Burkle & Carine Emer

Read the Press Release here: https://www.britishecologicalsociety.org/temporal-dimension-alien-attack-plant-pollinator-communities/