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University of New South Wales (2017)

Cascading effects of dingo Canis dingo control on bird assemblages in Australian deserts

Rees James

Titre : Cascading effects of dingo Canis dingo control on bird assemblages in Australian deserts

Auteur : Rees James

Université de soutenance : University of New South Wales

Grade : Doctor of Philosophy (PhD) 2017

Résumé
European settlement brought radical changes to Australian ecosystems, including near-eradication of dingo Canis dingo populations from 500,000 km2 of desert. Dingo eradication directly and indirectly affected assemblages of introduced and native mammals and the composition and structure of vegetation. Coinciding with these changes, many birds’ ranges and abundances shifted markedly. I investigated whether compositional changes to bird assemblages related to the absence of dingoes’ predatory influence in arid ecosystems. Surveys of birds in desert areas with and without dingoes revealed that dingo absence disadvantaged cover-dependent, low/ground-nesters, small granivores and specialist rodent-feeders and benefitted scavengers. To identify processes linking dingoes to the patterns of bird occurrence I had observed, I surveyed kangaroo and small mammal populations and native pasture plants, constructed large herbivore exclosures and monitored plants within them, provisioned carrion and monitored bird responses and investigated barn owl Tyto alba diets by dissecting regurgitated pellets. Where dingoes were functionally extinct, red kangaroo Macropus rufus abundance increased by a factor of 99 and kangaroo grazing reduced both pasture biomass and grass seed production by between 85% and 98%, likely explaining the association of small granivorous birds with dingo populations. Abundant carrion resources, as produced by kangaroo irruptions, increased populations of scavenging corvids by 50%, likely explaining these scavengers’ negative association with dingo populations. Furthermore, these localised increases in corvids affected a co-occurring small bird, white-winged fairywren Malurus leucopterus. Populations of barn owls and their preferred small mammal prey were greater by factors of 97 and 99 respectively in areas with dingoes than in areas without dingoes, where owls were rare and transient and consumed greater proportions of non-mammalian prey to compensate for the scarcity of small mammals. This research shows that the functional extinction of dingo populations has pervasive ecosystem effects, including transformation of avian assemblages, net losses of avian species, disintegration of ecosystem processes and degradation of desert landscapes. My results suggest current and future expansion of dingo control will entail a cost to ecosystem integrity and biodiversity, but, encouragingly, that reintroducing and conserving dingoes in arid areas has the potential to restore degraded ecosystems, buffer declining bird species against their key threats and improve rangeland productivity.

Présentation

Page publiée le 8 février 2018