Low functional diversity promotes niche changes in natural island pollinator communities

Abstract

Functional diversity loss among pollinators has rapidly progressed across the globe and is expected to influence plant-pollinator interactions in natural communities. Although recent findings suggest that the disappearance of a certain pollinator functional group may cause niche expansions and/or shifts in other groups, no study has examined this prediction in natural communities with high plant and pollinator diversities. By comparing coastal pollination networks on continental and oceanic islands, we examined how community-level flower visit patterns are influenced by the relative biomass of long-tongued pollinators (RBLP). We found that RBLP significantly correlated with pollinator functional diversity and was lower in oceanic than in continental islands. Pollinator niches shifted with decreasing RBLP, such that diverse species with various proboscis lengths, especially shorttongued species, increasingly visited long-tubed flowers. However, we found no conspicuous negative impacts of low RBLP and the consequent niche shifts on pollinator visit frequencies to flowers in oceanic island communities. Notably, fruit set significantly decreased as RBLP decreased in a study plant species. These results suggest that niche shifts by other functional groups can generally compensate for a decline in long-tongued pollinators in natural communities, but there may be negative impacts on plant reproduction.

Plant-pollinator interactions in East Asia: a review

“…Animal pollinators play significant roles in the sexual reproduction of many flowering plants (Ollerton et al 2011;Ratto et al 2018). The ecological and evolutionary consequences of plant-pollinator interactions are geographically variable (Hiraiwa & Ushimaru 2017;Johnson et al 2017;Ollerton 2017;Zanata et al 2017). However, the worldwide variation in plant-pollinator interactions is still poorly explored (Ollerton 2012).…”

Functional compensation by insular scavengers: the relative contributions of vertebrates and invertebrates vary among islands

“…Bars with the same letters are not significantly different, indicating that there is no difference among islands (GLMMs with Benjamini–Hochberg correction; p > 0.05). The green and red silhouettes of scavengers were modified from Sugiura ().…”

“…quadripunctatus per trap did not significantly differ among islands (GLMMs, p > 0.05; Supplementary material Appendix 1 Table A9). The silhouette of a burying beetle was modified from Sugiura ().…”

“…The original absence, decline or extinction of animal species may result in a reduction or loss of ecosystem functions in island environments (Boyer and Jetz 2014). However, other island species or introduced species can compensate for reduced or lost functions (Kawakami et al 2009, Pattemore and Wilcove 2012, Hiraiwa and Ushimaru 2017. In this study, we focused on the functional compensation by vertebrate and invertebrate scavengers in island environments.…”

“…For example, it was found that some plant species compensated for the functional reduction caused by experimental removal of dominant plant species on small islands (Wardle and Zackrisson 2005). Although functional compensation by island animals has been reported for pollination and seed dispersal (Kawakami et al 2009, Pattemore and Wilcove 2012, Hiraiwa and Ushimaru 2017, other ecosystem functions remain largely unexplored.…”