posted on 2017-02-15, 06:06authored byKatherine Selwood
Climate change is
becoming an increasingly significant driver of biodiversity loss. Changes to
climatic extremes, such as those associated with drought, may pose a more
severe threat to ecosystem functioning than gradual changes in mean conditions.
The duration and frequency of extreme droughts are projected to increase in
many parts of the world including Australia, especially in the south of the
continent. Identifying refugia that increase the capacity of biota to withstand
climate extremes such as drought (‘resistance’) and to recover if or when
adverse conditions abate (‘resilience’) will be critical for mitigating the
effects of climate change. Locations with reliable availability of water and
mesic microclimates, such as floodplains, are likely to be particularly
important for supporting species persistence during drought.
In this thesis, I conducted a global meta-analysis to compare
the relative effects of climate change and land-use change on demographic rates
in plant and animal populations. I measured the resistance and resilience of
floodplain bird assemblages to a thirteen-year drought (the ‘Big Dry’) in
southeastern Australia. I assessed the potential of floodplains as drought
refugia by comparing the resistance and resilience of birds in floodplains to
those in non-floodplain zones, and assessed whether floodplains moderate the
effects of aridity on bird occurrence. I investigated the importance of
landscape context, the physical landscape, vegetation structure and ecological
productivity in promoting the resistance of bird assemblages to prolonged
drought.
In the meta-analysis, I found, on average, that climate
variables had equally strong effects on demographic rates of plants and animals
as did land-use change. This is significant, given that the pressures of
climate change will continue to intensify in coming decades. In southeastern
Australia, where climate change is causing increased drought frequency and
severity, I found that bird assemblages were severely affected by the Big Dry:
a large proportion of species declined during the Big Dry, and few recovered
after the drought broke. Floodplains showed potential as drought refugia
because fewer species declined in floodplain zones than in non- floodplain
zones, and declines in floodplains were less severe for many species. I found
that floodplains moderate the effects of aridity on bird occurrence, extending
the distribution of many species into more arid regions than they would
otherwise be expected to occur. Vegetation productivity was the most important
factor for increasing the resistance of bird assemblages to drought across the
study region.
Climate change is an important driver of population
viability. Drying climate conditions, such as increased drought frequency and
severity, are likely to have significant effects on bird assemblages. However,
the effects of drought and aridity on birds may be reduced in highly productive
ecosystems such as floodplains.