Invasive species modulate the structure and stability of a multilayer plant-pollinator-seed dispersal network

VITALI, AGUSTIN; RUIZ-SUAREZ, SOFIA; VÁZQUEZ, DIEGO P.; SCHLEUNING, MATTIAS; RODRÍGUEZ-CABAL, MARIANO A.; SASAL, YAMILA; PILOSOF, SHI

Metz

Congreso; SFE2-GfÖ-EEF, International conference of Ecological Science; 2022

SFE2-GfÖ-EEF

Invasive species alter ecological networks by initiating cascading effects within and between trophic groups. However, field-based studies evaluating multitrophic cascades triggered by invasive species are rare. We explored whether invasive ungulates influence the structure and stability of pollination-plant-seed dispersal mutualisms. We have previously shown that ungulates disrupt a hummingbird-mistletoe-seed disperser marsupial keystone interaction, affecting its ability to maintain community complexity in the temperate forest of Patagonia. Non-native ungulates alter the tight interactions among the partners of this keystone interaction by consuming the main host of the mistletoe and changing the vegetation structure, leading to extinction of the seed disperser marsupial. We took advantage of an ongoing invasion scenario and compared invaded and non-invaded sites with historical records of this interaction. For each site (non-invaded vs. invaded), we built a multilayer network with pollination and seed dispersal interactions represented as two layers. We calculated the connectivity between interaction types, modularity and the role of species in connecting within and between modules. We further tested the effect of structure on stability in two ways. First, we used a stochastic coextinction model of disturbance propagation to evaluate the tolerance of the network to a single random removal of species. Second, we removed species sequentially according to their structural role (robustness). The non-invaded sites had a higher number of plant species connecting both interaction types, a greater number and proportion of indirect interactions between pollinators and seed dispersers, and a higher modularity. Species changed their structural role, evaluated as connectivity within and between modules, after the invasion of non-native ungulates. These differences in the community structure led to alteration of stability. The propagation of disturbances was greater in invaded sites. Moreover, robustness was lower in invaded sites when less connected species were removed first. Our results demonstrate that the disruption of a keystone interaction by invasive species triggers changes to the structure of a multilayer mutualistic network, producing multitrophic extinction cascades. This highlights the importance of considering multitrophic structures when studying the effects of invasive species on stability.