Data from: Shrub encroachment is linked to extirpation of an apex predator

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.