Mechanisms underlying interaction frequencies and robustness in a novel seed dispersal network: lessons for restoration

Abstract

As human-caused extinctions and invasions accumulate across the planet, understanding the processes governing ecological functions mediated by species interactions, and anticipating the effect of species loss on such functions become increasingly urgent. In seed dispersal networks, the mechanisms that influence interaction frequencies may also influence the capacity of a species to switch to alternative partners (rewiring), influencing network robustness. Studying seed dispersal interactions in novel ecosystems on O‘ahu island, Hawai‘i, we test whether the same mechanisms defining interaction frequencies can regulate rewiring and increase network robustness to simulated species extinctions. We found that spatial and temporal overlaps were the primary mechanisms underlying interaction frequencies, and the loss of the more connected species affected networks to a greater extent. Further, rewiring increased network robustness, and morphological matching and spatial and temporal overlaps between partners were more influential on network robustness than species abundances. We argue that to achieve self-sustaining ecosystems, restoration initiatives can consider optimal morphological matching and spatial and temporal overlaps between consumers and resources to maximize chances of native plant dispersal. Specifically, restoration initiatives may benefit from replacing invasive species with native species possessing characteristics that promote frequent interactions and increase the probability of rewiring (such as long fruiting periods, small seeds and broad distributions).

Hawkmoths’ evolutionary history structures plant-pollinator interactions frequency, beyond its effect through ecological traits

“…While in the context of network ecology 'neutral models' have been typically estimated based on species' relative abundances (e.g, Krishna et al, 2008), we acknowledge that temporal overlap may also affect chances of encounter as species that occur in a community over longer periods of time may encounter (and thus interact) more partners (Vizentin-Bugoni et al, 2022). However, as stated in the introduction, in this case, phenological overlap appears to be related to pollinator-mediated selection in a diffuse coevolution scenario, and is therefore considered here as a niche-based process.…”

“…On the other hand, the absence of a phylogenetic signal for temporal distribution and relative abundances of hawkmoths reinforces the importance of temporal overlap in structuring interaction frequencies as it integrates the selected model even without the influence of phylogeny. This indicates that, for an interaction to be strong, hawkmoths and plants need to cooccur considerably over time (which may also represent a component of neutrality; Vizentin-Bugoni et al, 2022) while the lack of phenological overlap constrains interaction between species by generating forbidden links. Thus, our results suggest that there is likely a hierarchy in the importance of the processes influencing interaction frequencies.…”

“…other biological features do not determine abundance nor the chance of encounter) (Krishna et al, 2008). Recently it has been recognized that not only abundance should define neutral-based models as, for instance, partners that have longer overlapping flowering and foraging times are likely to interact more frequently as the extent of phenological overlap increases chances of encounter (Vizentin-Bugoni et al, 2022). On the other hand, a niche-based model of phenology would be expected when behavioral differences in the foraging time of some hawkmoth species and the time of some sphingophilous flowers anthesis indicate that time constraints may be mediated by pollinators.…”

To rewire or not to rewire: To what extent rewiring to surviving partners can avoid extinction?

“…Biella et al, 2019). On the one hand, in silico approaches may allow for testing the effects of more drastic species losses, for example, by simulating the sequential loss of several species over an entire continent (Schleuning et al, 2016; Sonne et al, 2022) or testing the relative importance of distinct rewiring mechanisms restructuring interaction networks (Vizentin‐Bugoni et al, 2020, 2022). On the other hand, the experimental approach allows for testing the effects of species removal at more realistic local conditions that incorporate many of the unforeseen parameters in simulation models, such as indirect effects and types of interactions other than those being investigated (e.g.…”

“…In conclusion, the study by Leimberger et al provides new insights into the potential of interacting species to respond to the loss of mutualistic species which besides contributing to our understanding of local community dynamics, could be used for more applied purposes as ecosystems restoration (Kaiser‐Bunbury et al, 2017; Vizentin‐Bugoni et al, 2022) or biodiversity maintenance (Vitorino et al, 2021) and improve the forecast at larger scales, for which field experiments are impractical (e.g. Schleuning et al, 2016; Sonne et al, 2022).…”