Download At high densities kangaroo grazing can reduce biodiversity

HOT TOPICS IN ECOLOGY
https://www.ecolsoc.org.au/hot-topics/high-densities-kangaroo-grazing-can-reduce-biodiversity
At high densities kangaroo grazing can reduce biodiversity
Over-abundant kangaroos reduce the diversity of native wildlife and are a danger to threatened species
Brett W A Howland, Australian National University, Pr. Don A. Driscoll, Deakin University
Eastern grey kangaroos
reach very high densities
in south-eastern Australia
due to the absence of
predators and ready
access to permanent
water in farm dams.
At high densities,
kangaroos reduce
abundance and diversity
of plants and reptiles,
degrade bird habitat and
threaten an endangered
mammal.
Detection of the
vulnerable striped legless
lizard declines
dramatically with high
kangaroo densities.
The literature
recommends that grazing
pressure be reduced
where kangaroos are
over-abundant to prevent
biodiversity loss.
Ecological Society of Australia
https://www.ecolsoc.org.au
Further information about
this topic contact:
Overabundant kangaroos graze away the habitat that other native species depend on for survival. Photo by
Graeme Coulson
Over-grazing by herbivores can simplify the structure, composition and function of
vegetation communities by reducing vegetation cover and diversity, increasing soil
degradation and driving biodiversity loss. European colonisation has created ideal
conditions for the eastern grey kangaroo in south-eastern Australia, thanks to dingo
eradication, new permanent watering points, protection from hunting and increased pasture
availability. Consequently, in some areas, kangaroo population densities have risen to
levels where impacts on other native species are occurring. At high densities, kangaroo
grazing can: (1) reduce the occurrence, height and seeding rates of some native grasses;
(2) reduce the diversity and cover of native shrubs following fire; (3) reduce the abundance
and diversity of beetles; (4) reduce the overall abundance and diversity of reptiles; (5)
reduce the quality of habitat for some species of legless lizards and the three-toe earless
skink; (6) reduce the occurrence of the vulnerable striped legless lizard; (7) reduce the
quality of habitat for many species of bird; and (8) reduce the quality of habitat for
endangered eastern barred bandicoots, threatening a reintroduction program. In particular,
the striped legless lizard appears very sensitive to high grazing. One recent study
suggested that detection of this species more than halved with each doubling of kangaroo
density. The impacts of high density kangaroo grazing on biodiversity in Australia are
consistent with studies on native herbivores overseas, where predation and hunting that
regulated herbivore density have diminished. Managing grazing pressure is often required to
prevent biodiversity loss and ecosystem degradation.
Brett Howland
[email protected]
03 92517609
Chair, Hot Topics Editorial
Board
Dr Rachel Standish
Status: approved ; Last updated: 22/07/2016
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HOT TOPICS IN ECOLOGY
https://www.ecolsoc.org.au/hot-topics/high-densities-kangaroo-grazing-can-reduce-biodiversity
At high densities kangaroo grazing can reduce biodiversity
Over-abundant kangaroos reduce the diversity of native wildlife and are a danger to threatened species
Brett W A Howland, Australian National University, Pr. Don A. Driscoll, Deakin University
Supporting Evidence
Title
Aim
Key Results
Barton, P. S., A. D. Manning, H. Gibb, J. T. Wood, D. B. Lindenmayer
and S. A. Cunningham (2011). "Experimental reduction of native
vertebrate grazing and addition of logs benefit beetle diversity at
multiple scales." Journal of Applied Ecology 48(4): 943
(i)Do differences in vertebrate grazing
affect the trophic structure of beetle
assemblages?(ii) Does the addition of
logs interact with grazing level to
affect beetle diversity at the hectare
scale? (iii) Does microhabitat structure
provided by logs interact with grazing
level to affect beetle diversity at small
scales because of a localized ‘refuge’
effect?
A reduction in grazing level had benefits for the
abundance and species richness of beetles at the
site scale. Further benefits were achieved at both
site and microhabitat scales when logs are used in
combination with exclosure fencing.
Brown, K., Paczkowska, G., & Gibson, N. (2016). "Mitigating impacts
of weeds and kangaroo grazing following prescribed fire in a Banksia
woodland." Ecological Management & Restoration 17(2): 133-139.
Investigated (i) how native and weed
species richness and cover changed
following autumn prescribed fire and (ii)
effectiveness of management
techniques at reducing the impacts of
grazing by western grey kangaroos.
Fencing significantly increased cover of native
shrubs and grasses through prevention of kangaroo
grazing. However, kangaroos also appeared to play
a role in suppressing weedy annual grasses post-fire
in these woodlands.
Howland, B. W. A., D. Stojanovic, I. J. Gordon, D. Fletcher, M. Snape,
I. A. Stirnemann and D. B. Lindenmayer (2016). "Habitat preference of
the striped legless lizard: Implications of grazing by native herbivores
and livestock for conservation of grassla
Investigated habitat preferences of
Delma impar at multiple spatial scales
The occurrence of Delma impar was not affected by
the size of grassland remnants, but was negatively
related to the density of native grazers. This result
was likely a consequence of the negative effect of
high grazing intensity on grass structural
complexity, as the probability of encountering a
Delma impar was positively related to grass
structural complexity at the fine scale (1m2).
Howland, B. W. A., D. Stojanovic, I. J. Gordon, J. Radford, A. D.
Manning and D. B. Lindenmayer (2016). "Birds of a feather flock
together: Using trait-groups to understand the effect of macropod
grazing on birds in grassy habitats." Biological Conservati
Investigated the potential of a traitbased approach to predict the
preference of birds utilizing the grassy
layers for different levels of grazing by
eastern grey kangaroos within grassy
habitats in south-eastern Australia.
Birds that utilized the grassy layer showed a varied
response to differences in grazing intensity. Ground
foragers, species with elevated nests, and birds that
rely on early detection of predators were more likely
to utilize the grassy layer under high grazing
intensities. In contrast, small aerial insectivores,
and a single ground-nesting species (that relies on
concealment to avoid predators) were more likely to
utilize grassy layer under lower grazing intensities.
Howland, B., D. Stojanovic, I. J. Gordon, A. D. Manning, D. Fletcher
and D. B. Lindenmayer (2014). "Eaten out of house and home: impacts
of grazing on ground-dwelling reptiles in Australian grasslands and
grassy woodlands." PLoS ONE 9(12): e105966.
Investigated the relationship between
(1) density of native eastern grey
kangaroos, Macropus giganteus, and
grass structure, and (2) grass
structure and reptiles (i.e. abundance,
richness, diversity and occurrence)
Reptile abundance, species richness and diversity
were highest where grazing intensity was low. No
species of reptile was more likely to occur at high
grazing intensities. Legless lizards (Delma impar, D.
inornata) were more likely to be detected in areas
subject to moderate grazing intensity, whereas one
species (Hemiergis talbingoensis) was less likely to
be detected in areas subject to intense grazing.
Manning, A. D., R. B. Cunningham and D. B. Lindenmayer (2013).
"Bringing forward the benefits of coarse woody debris in ecosystem
recovery under different levels of grazing and vegetation density."
Biological Conservation 157(0): 204-214.
Examined the effect of experimentally
adding Course Woody Debris, in four
different treatments, on reptile
abundance in temperate woodlands in
south-eastern Australia – one of the
most highly degraded vegetation types
on the continent. They investigated the
influence that varying grazing pressure
and vegetation density had on those
effects.
Reduction of grazing was the most effective way of
increasing small skink abundance in high density
vegetation.
Meers, B. T. and R. Adams (2003). "The impact of grazing by Eastern
Grey Kangaroos (Macropus giganteus) on vegetation recovery after fire
at Reef Hills Regional Park, Victoria." Ecological Management &
Restoration 4(2): 126-132.
(i) determine the grazing patterns of
the Eastern Grey Kangaroo after fire at
Reef Hills Regional Park, and (ii)
determine the impacts that grazing
might have on post fire woody shrub
recovery.
Preferential grazing by Eastern Grey Kangaroos
occurred on small burnt plots compared to adjacent
unburnt areas as determined by faecal pellet counts.
On burnt areas, there was a significant reduction in
shrub diversity on grazed plots compared to
ungrazed plots.
Mysterud, A. (2006). "The concept of overgrazing and its role in
management of large herbivores." Wildlife Biology 12(2): 129-141
Detailed discussion of what
overgrazing means under different land
uses and impacts of overgrazing in
conservation and production
landscapes.
There are several different ways of defining
overgrazing. Native and exotic herbivores can result
in overgrazing. Overgrazing can lead to new stable
ecosystems states and these new states may be
irreversible.
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HOT TOPICS IN ECOLOGY
https://www.ecolsoc.org.au/hot-topics/high-densities-kangaroo-grazing-can-reduce-biodiversity
At high densities kangaroo grazing can reduce biodiversity
Over-abundant kangaroos reduce the diversity of native wildlife and are a danger to threatened species
Brett W A Howland, Australian National University, Pr. Don A. Driscoll, Deakin University
Aim
Key Results
Neave, H. M. and M. T. Tanton (1989). "The Effects of Grazing by
Kangaroos and Rabbits on the Vegetation and the Habitat of Other
Fauna in the Tidbinbilla Nature Reserve, Australian-Capital-Territory."
Australian Wildlife Research 16(3): 337-351.
Title
Examine the present status of the
grassland vegetation in three areas in
which exclosures have provided
protection from grazing since 1979 and
compare the status with that in 198283.
Some plants declined, others increased under high
kangaroo grazing. Height and seeding rates declined
for many species, with implications for habitat
quality for other wildlife.
Winnard, A. L., & Coulson, G. (2008). "Sixteen years of Eastern Barred
Bandicoot Perameles gunnii reintroductions in Victoria: a
review". Pacific Conservation Biology 14(1): 34-53.
Examined characteristics affecting the
success of Eastern Barred Bandicoot
reintroductions, including competition
from herbivores.
A combination of drought and grazing pressure from
kangaroos and rabbits reduced the amount of
available habitat and possibly lead to population
decline of Eastern Barred Bandicoots at one
reintroduction site in Victoria.
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