182 Monitoring Threatened Species and Ecological Communities
(B. penicillata (Fig. 13.2a), Ps. occidentalis (Fig. 13.3), D. geoffroii (Fig. 13.4), Ph.
tapoatafa, N. eugenii and I. obesulus, but not M. fasciatus or quokka Setonix
brachyurus).
The abundances of most mammal species have changed markedly (Fig. 13.5).
The most conspicuous results were: the increase and subsequent decline of three
native species (I. obesulus, B. penicillata (Fig. 13.5a) and Ps. occidentalis (Fig. 13.5d));
the decline of four native taxa (Ph. tapoatafa, dunnarts Sminthopsis gilberti and S.
fuliginosus, mootit or southern bush rat Rattus fuscipes (Fig. 13.5c) and kwara or
western brush wallaby Notamacropus irma (Fig. 13.5d)); and the recent increase of
three native species (N. eugenii, T. vulpecula, D. geoffroii (Fig. 13.5b)). The activity
index for V. vulpes increased and the activity index for the cat Felis catus decreased
between 2006 and 2013, when sand plot monitoring was being conducted (Fig.
13.5e). There were no clear trends in the detection rates for the western grey
kangaroo Macropus fuliginosus (Fig. 13.5d) and European rabbit Oryctolagus
cuniculus (Fig. 13.5e). The similar rates and magnitudes of decline in the seven
native taxa suggest similar causes or processes may be common across the species.
Furthermore, a pattern of successive decline of native mammals according to size
(from small to larger species, 18–8000 g mean adult body mass) was also evident
(Wayne et al. 2017).
Explanations for the drivers behind differences in species abundances include
anthropogenic threats such as timber harvesting, prescribed burning and wildfire,
habitat fragmentation, proximity to agriculture and road densities, for Ps.
occidentalis (Wayne et al. 2006) and B. penicillata (Yeatman 2015). A series of
population comparison studies have investigated the possible causes of the recent
declines of B. penicillata within the region and elsewhere, including staple food
(a) (b)Fig. 13.2. (a) Adrian Wayne releasing a woylie or brush-tailed bettong Bettongia penicillata after capturing
it in a cage trap. Photo: L. O’Rourkes, WA DBCA. (b) Sand plot preparation for monitoring introduced and
native mammals. Photo: M. Maxwell, WA DBCA.