Shrub Encroachment as a Legacy of Native Mammal Decline

Shrub Encroachment as a Legacy of Native Mammal Decline

Invasive native scrub cover in arid Australia has increased dramatically over the past century coincident with declines of native mammal species in the critical weight range. Hypotheses to explain the increase in shrub cover and associated land degradation range from increased CO2 emissions to overgrazing but none adequately explains all elements of invasive native scrub encroachment. This project considers the role of declining native mammals in shrub encroachment, as recent experiments in our lab have suggested that these mammals may play an important role in inhibiting growth and spread of invasive native scrub species.

We have study sites throughout arid and semi-arid NSW and SA and are running field trips throughout the year. If you would like to know more about this project or to volunteer please contact Charlotte Mills.

Research Program: 
Threatened Species
Research Themes: 
Terrestrial Ecosystems

Publications for this project

Author Date Title Description PDF
Gordon et al. 2017 Shrub encroachment is linked to extirpation of an apex predator

Abstract The abundance of shrubs has increased throughout Earth's arid lands. This ‘shrub encroachment’ has been linked to livestock grazing, fire-suppression and elevated atmospheric CO2 concentrations facilitating shrub recruitment. Apex predators initiate trophic cascades which can influence the abundance of many species across multiple trophic levels within ecosystems. Extirpation of apex predators is linked inextricably to pastoralism, but has not been considered as a factor contributing to shrub encroachment. Here, we ask if trophic cascades triggered by the extirpation of Australia's largest terrestrial predator, the dingo (Canis dingo), could be a driver of shrub encroachment in the Strzelecki Desert, Australia. We use aerial photographs spanning a 51-year period to compare shrub cover between areas where dingoes are historically rare and common. We then quantify contemporary patterns of shrub, shrub seedling and mammal abundances, and use structural equation modelling to compare competing trophic cascade hypotheses to explain how dingoes could influence shrub recruitment. Finally, we track the fate of seedlings of an encroaching shrub, hopbush (Dodonaea viscosa angustissima), during a period optimal for seedling recruitment, and quantify removal rates of hopbush seeds by rodents from enriched seed patches. Shrub cover was 26–48% greater in areas where dingoes were rare than common. Our structural equation modelling supported the hypothesis that dingo removal facilitates shrub encroachment by triggering a four level trophic cascade. According to this model, increased mesopredator abundance in the absence of dingoes results in suppressed abundance of consumers of shrub seeds and seedlings, rodents and rabbits respectively. In turn, suppressed abundances of rodents and rabbits in the absence of dingoes relaxed a recruitment bottleneck for shrubs. The results of our SEM were supported by results showing that rates of hopbush seedling survival and seed removal were 1·7 times greater and 2·1 times lower in areas where dingoes were rare than common. Our study provides evidence linking the suppression of an apex predator to the historic encroachment of shrubs. We contend that trophic cascades induced by apex predator extirpation may be an overlooked driver of shrub encroachment.

Online: http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12607/full

Check out the cartoon! https://kapowecology.wordpress.com/2017/01/20/dingoes-run-the-show-right-down-to-the-shrubs/

News for this project

08/03/2016

Arid field season off to a roaring start in 2016

The 2016 field season has kicked off with a big start for researchers in the Landscape

Updates for this project

Good kinds of records

In complete contrast to last trip - where we had record-breaking temperatures of 40+ degree days for 10 consecutive days - this trip we had perfect weather and hit a record of 5 fences built in 3.5 days!

Home again, back again

I’m writing this from the relative safety of my desk back at UNSW, although preparing to head back to the field next week.

More than just field work

We survived the hot weather in Scotia to arrive in a soggy Roxby Downs, the town nearby Arid Recovery Reserve.

2016's adventures begin!

Last Tuesday I set off from Sydney for a five week adventure in the red sand at Scotia Wildlife Sanctuary and Arid Recovery Reserve.

November Field Trip - All systems go!

The time has come around again so soon! We were only just out in June!

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