Understanding the changing pollination of Acacia brachybotrya in mallee woodland
Abstract
Pollination is of vital importance to the reproduction of flowering plants. Insects are by far the most
important pollinators and the vast majority of terrestrial plants are predominantly insect pollinated.
However, insect pollinator declines are being observed around the world, and increasing numbers of
plant species are being found to show signs of pollen limitation in their reproduction. There is evidence
that land use changes and habitat fragmentation are changing the species and functional composition of
pollinator communities and plant-pollinator interactions, but little is known about the mechanisms with
which such changes are affecting pollen transport and pollination success.
Acacia brachybotrya is a plant species found in mallee woodland environments that shows signs of
increased pollen limitation of plant reproduction as a result of habitat fragmentation altering pollination
services. However, little is known about the pollinator community of A. brachybotrya or its pollination.
Therefore, it is unknown by what mechanism fragmentation is changing pollination services. nor of
how pollen transport is changing for A. brachybotrya as a result of fragmentation. The two main ways
pollination services may be changing include in the interactions between plants and pollinator
community, and changes in plant-plant interactions via pollen transport. Changes in pollinator
community may affect functional traits composition and thus pollinator pollination efficiency. Changes
in plant-plant interactions affect heterospecific pollen interactions, whereby pollen of a heterospecific
plants species can interfere with pollination.
Through the collection of insect visitors to A. brachybotrya and identification and counting their
conspecific and heterospecific pollen loads, my study attempts to analyse the A. brachybotrya pollinator
community and their changing pollen transport. I found evidence that bees are by far the most important
A. brachybotrya pollinator as indicated by high visitation, floral constancy, and significantly higher
conspecific pollen loads compared to beetles and flies. Beetles and flies were the next most important
A. brachybotrya pollinators, although a wide variety of pollinators was observed. The community of
pollen found on insect pollinators of A. brachybotrya appears to be changing with fragmentation, and
pollen species richness was found to be significantly higher in highly fragmented habitat remnants
compared to larger remnants for flies, and lower in highly fragmented habitat remnants for bees, with
moderate significance. Pollinator body size was not tested due to limited sample size, but trends
indicated that fragmentation leads to community shifts to larger bees in mallee woodland, which may
affect the amount of pollen being transported and the distance pollen is being transported.
These findings have implications for land management of environments experiencing pollen
limitation. Priorities for future research should include analysis on how insect functional traits and
pollen community composition may be changing with habitat fragmentation.