Functional trait mismatch between native and introduced bee pollinators servicing a global fruit crop

Diversity’s link to ecosystem services, like pollination, can be better
understood with a shift from focusing on species richness to functional
trait-based approaches, which can provide more insight, particularly when
paired with comparative phylogenetics. Here, we assessed the functional
ecology and phylogenetic diversity of hymenopterans visiting apple flowers
in orchards surrounded by either ‘natural’ or ‘disturbed’ landscapes. We
investigated whether morphological and behavioural traits (hairiness, body
size, glossa length, pollen load purity, and probability of loose pollen)
exhibited non-random phylogenetic patterns. Then, explored whether bees,
the primary pollinators in this system, filled unique or overlapping
functional entities (FEs). For each landscape, we calculated phylogenetic
diversity and used FEs to assess functional richness, evenness, and
diversion. A phylogenomic matrix based on ultraconserved elements
(UCEs; 1,382,620 bp from 1,969 loci) was used to infer a fully resolved
and well-supported maximum likelihood phylogeny for 48 hymenopteran
morphospecies. Pollinator communities at natural sites had higher
phylogenetic complexity (X=2.37) and functional divergence (x̄=0.74 ± 0.02
s.e.) than disturbed sites (X=1.65 and x̄=0.6 ± 0.01 s.e.). Hairiness
showed significant phylogenetic clustering (K=0.94), whereas body size,
glossa length, and loose pollen showed weaker non-random phylogenetic
patterns (K between 0.3–0.5). Pollen load purity showed no association
with phylogeny. The assemblage of 17 bee morphospecies comprised nine FEs:
eight FEs consisted of native bees with three containing 65% of all native
bee taxa. The introduced honey bee (Apis mellifera) occupied a unique FE,
likely due to its different evolutionary history. Both landscape types
supported six FEs each with three overlapping: two native bee FEs and the
honey bee FE. Bee hairiness was the only functional trait to
exhibit a demonstrable phylogenetic signal. Despite differences in species
richness, and functional, and phylogenetic diversity between orchard
landscape types, both maintained equal bee FE numbers. While no native bee
taxon was analogous to the honey bee FE, four native bee FEs shared the
same hairiness level as honey bees. Health threats to honey bee
populations in Australia will likely disrupt pollination services to
apple, and other pollination-dependent food crops, given the low level of
functional redundancy within the investigated pollinator assemblages.