A test of trophic and functional island biogeography theory with the avifauna of a continental archipelago

Abstract

The classical MacArthur–Wilson theory of island biogeography (TIB) emphasizes the role of island area and isolation in determining island biotas, but is neutral with respect to species differences that could affect community assembly and persistence. Recent extensions of island biogeography theory address how functional differences among species may lead to non‐random community assembly processes and different diversity–area scaling patterns. First, the trophic TIB considers how diversity scaling varies across trophic position in a community, with species at higher trophic levels being most strongly influenced by island area. Second, further extensions have predicted how trait distributions, and hence functional diversity, should scale with area. Trait‐based theory predicts richness‐corrected functional diversity should be low on small islands but converge to null on larger islands. Conversely, competitive assembly predicts high diversity on small islands converging to null with increasing size. However, despite mounting interest in diversity–area relationships across different dimensions of diversity, these predictions derived from theory have not been extensively tested across taxa and island systems. Here, we develop and test predictions of the trophic TIB and extensions to functional traits, by examining the diversity–area relationship across multiple trophic ranks and dimensions of avian biodiversity in the Ryūkyū archipelago of Japan. We find evidence for a positive species– and phylogenetic diversity–area relationship, but functional diversity was not strongly affected by island area. Counter to the trophic TIB, we found no differences in the slopes of species–area relationships among trophic ranks, although slopes varied among trophic guilds at the same rank. We revealed differential assembly of trophic ranks, with evidence of trait‐based assembly of intermediate predators but otherwise neutral community assembly. Our results suggest that niche space differs among trophic guilds of birds, but that differences are mostly not predicted by current extensions of island biogeography theory. While predicted patterns do not fit the empirical data well in this case, the development of such theory provides a useful framework to analyse island patterns from new perspectives. The application of empirical datasets such as ours should help provide a basis for developing further iterations of island biogeography theory.

Island area, not isolation, drives taxonomic, phylogenetic and functional diversity of ants on land‐bridge islands

“…However, although such species-area relationships have been intensively examined, phylogenetic-area and functional-area relationships have been less reported (but see Ross et al, 2019;Si et al, 2017;Whittaker et al, 2014). In our study, phylogenetic and functional diversity (PD, MPD, FD and FD_MPD) were both positively related to the island area, consistent with results from other studies (Ross et al, 2019;Si et al, 2017). Larger islands supported higher SR, as well as higher functional and phylogenetic diversity.…”

“…Jacquet, Mouillot, Kulbicki, & Gravel, 2017;Ottaviani et al, 2020 for the functional dimension; Pyron & Burbrink, 2014;Weigelt et al, 2015 for the phylogenetic dimension). However, efforts to understand the drivers of community assembly on islands that consider simultaneously both the phylogenetic and functional differences among species are limited (Patiño et al, 2017; but see Si et al, 2017;Ross, Friedman, Janicki, & Economo, 2019). Here, we use TIB to assess the phylogenetic and functional community structure of the ant fauna on an island archipelago in subtropical China.…”

Glacier influence on bird assemblages in habitat islands of the high Bolivian Andes

“…Communities are considered as overdispersed when the observed slope is significantly lower than the mean slopes from the null model and the SES score values higher than1.96, implying competitive exclusion. Inversely, communities are considered as underdispersed when the observed slopes is greater than the mean slopes from the null model and SES score values lower than −1.96, suggesting trait-based assembly (Petchey et al, 2007;Ross et al, 2019). SES also allows evaluating the relative strength of the assembly processes (i.e.…”

Relative Importance of Landscape and Climate Factors to the Species Diversity of Plant Growth Forms along an East Asian Archipelago

“…However, most of the previous studies analyzed the relative importance of area, distance from the mainland, and other landscape factors (e.g., habitat heterogeneity and structural connectivity) for species richness on islands. Research that simultaneously considers climatic and landscape factors is very rare [15,16]. It is therefore necessary to study the effects of climate factors on species richness in island ecosystems with landscape factors.…”