Ng, Katherina
Description
The intensification of agriculture for increased food production
is leading to new challenges for biodiversity conservation,
particularly managing complex changing landscapes for mutually
beneficial outcomes for agriculture and the environment. My
thesis aimed to understand the diversity and distribution of
beetles (Coleoptera), and the mechanisms shaping beetle
assemblages across a dynamic and fragmented agricultural
landscape. I used a landscape-scale study...[Show more] in south-eastern
Australia to examine beetle assemblages in remnant woodland
patches and four types of adjoining farmlands: crop, fallow,
plantings, and fine woody debris applied over harvested crop.
My thesis comprised four chapters written as journal articles. In
Paper I, I examined seasonal differences in beetle assemblages
between the woodland interior and four adjoining farmland uses. I
found that overall species richness was significantly lower in
woodlands than farmlands, although both habitats supported
significantly different assemblages. Abundance responses were
taxon-specific, and influenced by interactions between land-use
and season. These results suggest the importance of maintaining
farmland heterogeneity with a mix of low-intensity land-uses,
with further agricultural intensification a likely threat to
beetle diversity in the region.
In Paper II, I examined temporal patterns of edge responses and
movement of beetle assemblages between woodlands and the four
farmland uses. The use of directional pitfall traps allowed
inference of cross-habitat movement. Farmland use and season
interactively affected beetle abundance across
farmland–woodland edges. Applying woody debris was a novel way
of reducing seasonal fluctuations in edge responses and
increasing permeability for cross-habitat movement. Edges likely
provided resources for beetles in adjoining habitats, but
seasonal movement of predators into edges might negatively affect
prey assemblages.
In Paper III, I quantified relationships between ground-layer
structure, plant species richness and plant composition, and the
diversity and composition of beetles from different habitats or
seasons. Plant composition better predicted beetle composition
than vegetation structure. Plant richness and vegetation
structure both significantly affected beetle abundance and
composition. The influence of these vegetation attributes often
varied depending on habitat and season for all trophic groups.
These dynamic plant–beetle relationships suggest a need for
targeted ways of managing vegetation to improve beetle diversity
in different parts of the landscape.
In Paper IV, I disentangled the effects of farmland use, edge
effects and vegetation structure on the morphological traits of
Carabidae species. Carabid body size increased across a distance
from edges between woodlands and farmlands, and there were strong
mediating effects of farmland use on this association. Vegetation
structure was associated with traits relating to body size,
flying ability and body shape, and helped explain some of the
effects of farmland use and edge effects on body size. These
results provide evidence of vegetation- and land-use-mediated
filtering of traits as an important factor shaping carabid
assemblages in human-modified landscapes.
My results indicate that farmlands can provide important habitat
for many beetle species. However, spatio-temporal changes in
farmland habitat strongly influence beetle assemblages across the
landscape. Conservation strategies, therefore, need to take a
whole-of-landscape approach, and exploit heterogeneity of
mixed-farmlands over space and time to maximise outcomes for
biodiversity.
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