Loss of Generalist Plant Species and Functional Diversity Decreases the Robustness of a Seed Dispersal Network

Abstract

SummaryUnderstanding cascading effects of species loss is a major challenge for ecologists. Traditionally, the robustness of ecological networks has been evaluated based on simulation studies where primary extinctions occur at random or as a function of species specialization, ignoring other important biological factors. Here, we estimate the robustness of a seed dispersal network from a grassland–forest mosaic in southern Brazil, simulating distinct scenarios of woody plant species extinction, including scenarios where species are eliminated based on their evolutionary and functional distinctiveness. Our results suggest that the network is more robust when species are eliminated based on their evolutionary uniqueness, followed by random extinctions, the extinction of the most specialist species, functional distinctiveness and, at last, when the most generalist species are sequentially eliminated. Our results provide important information for grassland–forest mosaic management, as they indicate that loss of generalist species and functional diversity makes the system more likely to collapse.

Including rewiring in the estimation of the robustness of mutualistic networks

“…Our results demonstrate that vertebrate pollinator–plant tropical networks are more susceptible to the loss of generalist than specialist species, mirroring previous findings obtained for temperate plant–pollinator networks dominated by insects (Memmott et al, ) and other kinds of mutualistic interactions (e.g. seed dispersal networks, Bastazini et al, ). Besides affecting a larger number of partners connected exclusively to them, the loss of generalist species may affect network cohesiveness because they connect distinct network modules, that is, subsets of species interacting more among them than with other members of the community (Olesen, Bascompte, Dupont, & Jordano, ).…”

“…species interacting with few partners), while highly susceptible to loss of generalists (Memmott, Waser, & Price, ). However, despite the importance and frequent use of these methods, they rarely consider explicitly the ability of species to ‘rewire’, that is, switch partners, which is a remarkable feature of ecological networks (Bastazini, Debastiani, Azambuja, Guimarães, & Pillar, ; Costa et al, ; Kaiser‐Bunbury et al, ; Poisot, Canard, Mouillot, Mouquet, & Gravel, ; Ponisio, Gaiarsa, & Kremen, ; Timóteo, Ramos, Vaughan, & Memmott, ; Vizentin‐Bugoni et al, ), therefore limiting the realism of the simulations. A major obstacle is the integration of rewiring based on the multiple mechanisms that determine species interactions (Bartomeus et al, ; Olesen, Bascompte, Elberling, & Jordano, ; Vázquez, Blütghen, Cagnolo, & Chacoff, ; Vizentin‐Bugoni, Maruyama, & Sazima, ; Vizentin‐Bugoni et al, ).…”

Searching for keystone plant resources in fruit‐frugivore interaction networks across the Neotropics

“…Removal simulations may not represent the real outcome compared to removal experiments in the field (e.g., for not accounting frugivore behavior and movement; Carlo & Yang, 2011; Morán‐López et al., 2020), but have the power to produce theoretical outcomes which improve our ability to predict changes under controlled conditions (Bastazini, Debastiani, Azambuja, Guimarães, & Pillar, 2019; Brose, Berlow, & Martinez, 2005; Memmott et al., 2004; Okuyama & Holland, 2008; Rezende et al., 2007). Simulations of species removal represent a robust procedure of addressing large‐scale assessments.…”

Employing plant functional groups to advance seed dispersal ecology and conservation

“…Functional group frameworks, in which species are categorized by ecological functions and the resulting groups treated as analytical units, have helped researchers confront complexity in other ecological subdisciplines and have been tentatively explored in seed dispersal (e.g. Dennis and Westcott 2006 ; Brodie et al 2009b ; Bastazini et al 2017 ). However, they have not yet been developed sufficiently to link empirical patterns of seed dispersal with theoretical predictions.…”

“… Zamora (2000) explored how the consistency of fitness benefits offered by seed dispersal across systems and groups of species permits generalization within functional groups. A key benefit of a functional group approach is that it could provide an understanding of the functions that may be lost when extinctions occur ( Blondel 2003 ; Bastazini et al 2017 ). This conservation-oriented conceptual application was highlighted by Schleuning et al (2014) in their call for more work examining the linkage between trait-based approaches such as functional group delineation and structural approaches such as network analysis ( Ruggera et al 2015 ).…”