Evolutionary relationship between plants and insects: Insights from island communities

Interactions between plants and insects have long fascinated scientists.
While some plants rely on insects for pollination and seed dispersal,
insects rely on plants for food or as a habitat. Despite extensive
research investigating pair-wise species interactions, few studies have
characterized plant and insect communities simultaneously, making it
unclear if diverse plant communities are generally associated with diverse
insect communities. This work aims to better understand the historical and
evolutionary relationships between plant and insect phylogenetic diversity
(PD) on islands. We hypothesized that phylogenetically diverse plant
communities (i.e. high PD) support diverse insect communities, with the
relationship varying with island isolation, area, age, and latitude.
Species lists for plants and insects were compiled from the published
literature, and plant PD was calculated using ´standardized mean pairwise
distance´ (SES.MPD) and ´standardized mean nearest taxon distance´
(SES.MNTD). For insects, PD was estimated using the number of genera,
families, and orders. We found that plant diversity in evolutionary recent
times (SES.MNTD) is associated with recent insect diversity (number of
genera), but no relationship was found between plant and insect diversity
across whole phylogenies (plant SES.MPD vs. number of insect families).
Distant islands generally support high PD of plants (high SES.MPD and
SES.MNTD) and insects (low number of genera). Plant and insect PD was
generally high on small islands, except for plant SES.MPD revealing no
relationship with island size. Insect PD was somewhat higher on young
islands (low number of families), whereas there was no relationship
between island age and plant PD. Plant SES.MPD was higher on high latitude
islands, yet we did not find significant relationships between the
latitude and the metrics of insect PD, or plant SES.MNTD. These findings
suggest that protecting high plant PD may also help conserve high insect
PD, with a focus on small and distant islands as potential hotspots of
phylogenetic diversity across multiple taxa.