Alien plants and flower visitors disrupt the seasonal dynamics of mutualistic networks

Abstract

Alien species can drastically disrupt ecological processes such as those involving plant–pollinator interactions, performing central roles that may affect the structure of native pollination networks. However, most studies to date have focused on a single trophic level of alien species, evaluating either the impacts of an alien pollinator or an alien plant species, and have neglected their joint effects on the seasonal dynamics of mutualistic networks. Here, we aim to fill this gap by investigating how alien plant and flower visitor (here used as a proxy for pollinator) species structure temporal networks, and how these species affect the beta‐diversity of interactions across a flowering season. Our study system is located in the South Island of New Zealand, where 68% of the sampled plant species and 14% of the flower visitor species that interact with them are alien. Alien flower visitor species exhibited higher interaction degree, specialization and strength than their native counterparts, while alien plant species showed the opposite pattern. We found that invader complexes (in which alien species interact significantly more with each other than with native species) were established across the season, and interactions involving alien plant species were the main connectors of the temporal networks. Both alien plant and flower visitor species increased total interaction turnover through the flowering season by promoting interaction rewiring in the case of alien plants and by increasing species turnover in the case of alien flower visitors. Synthesis. This study provides one of the first empirical reports of alien species shaping the seasonal dynamics of plant–flower visitor networks. We demonstrate that the presence of alien species may simultaneously lead to a homogenization of plant species composition and increase the diversity of plant–flower visitor interactions through a flowering season. Additionally, we highlight the importance of considering the role of different trophic levels when analysing the impact of alien species in plant–flower visitor communities. Overall, our findings suggest that management strategies should pay particular attention to the timescale at which interactions with alien species dissolve or form, and to the consequences and drivers of such seasonal dynamics.

Temporal scale‐dependence of plant–pollinator networks

“…For example, mean annual temperature might dictate not only which species potentially can interact but also the length and the synchrony of the periods in which these interactions are realized. This perspective may also help to predict the consequences of climate change (Park and Mazer ), species invasions (Herron‐Sweet et al , Arroyo‐Correa et al ) or habitat degradation and restoration (Burkle et al , Ponisio et al ).…”

“…Additionally, even temporally co‐occurring species may switch interaction partners over time, thereby rewiring the links within the network (Poisot et al ). Understanding the influence of temporal dynamics – such as species turnover and link rewiring – on network structure at multiple temporal scales might be particularly important considering various drivers that alter the timing of species interactions, such as climate change (Park and Mazer ), habitat modification (Burkle et al , Ponisio et al ) and species invasions (Herron‐Sweet et al , Arroyo‐Correa et al ).…”

Trait matching and phenological overlap increase the spatio‐temporal stability and functionality of plant–pollinator interactions

“…In addition, interactions among specialised species had higher trait matching, such that specialisation indirectly favours interaction stability. These results suggest that the non‐random extinction of interactions among specialists (Aizen et al 2012) and biotic invasion (with invaders typically being generalists, Aizen et al 2008, Frost et al 2019, and promoters of interaction rewiring, Arroyo‐Correa et al 2020), can disproportionately increase the variability of interaction frequencies within communities, increasing ecological network variability and making more difficult the prediction of interaction networks. Furthermore, we show that the strong positive effects of species abundance on the spatio‐temporal stability of interactions are mediated by phenological overlap, such that temporal co‐occurrence, rather than abundance itself, appears to be stabilising.…”

Seeing through the static: the temporal dimension of plant–animal mutualistic interactions

“…For example estimating the flow and spread of perturbations through interaction networks (e.g. presence of an invader or a novel resource; Valdovinos et al ., 2009; Kaiser‐Bunbury et al ., 2010; Arroyo‐Correa et al ., 2020); assessing how the network roles of individual species change through time (e.g. Cirtwill et al ., 2018; Bramon Mora et al ., 2020); quantifying the temporal persistence of species, their interactions and structural components of networks (e.g.…”