760 H. Bannister et al.
TABLE 2 Model results for assessing brushtail possum dietary changes over time since release. Response variable
Explanatory variable 1
Frequency of occurrence in scat
ANOVA output Time
β estimate (95% CI) −0.004 (−0.006–−0.001)
χ2
Proportion within scat
β estimate (95% CI)
ANOVA output Dietary richness
β estimate (95% CI)
ANOVA output Dietary diversity
β estimate (95% CI)
ANOVA output *Significant at P,0.05.
An investigation of the diet from the time of release, rather than 1 month later, may have uncovered stronger changes, but scats from the first month after release were not col- lected because some animals were fed supplementary food (Bannister et al., 2020). Trends suggested that either the acclimatization period had not ended 12 months after release, or that seasonal effects on food consumption were taking place. Both explanations suggest that the diet of this possum is flexible and varied, and thus it can adapt to changes in the availability of food resources. Although other studies have suggested that possum diet changes seasonally, most studies have not spanned .12 months (Freeland & Winter, 1975; Fitzgerald, 1984; Statham, 1984; Cruz et al., 2012). In one exception, differences were found between the wet and dry season diet of brushtail possums in the trop- ics, with some sex effects also observed over the 29 month study period (Gloury & Handasyde, 2016). Although these studies suggest that the post-release dietary acclimatization in our study could have included some seasonal effects, more long-term dietary studies are needed to differentiate between normal fluctuations in possum diet and post- release effects. Post-release acclimatization time is often measured using
metrics such as reproduction, movement (establishment of a stable home range) and body mass (Bright &Morris, 1994;
Hardman & Moro, 2006; Facka et al., 2010). Possums re- leased into Ikara-Flinders Ranges National Park retained all pouch young and continued to breed after release, despite initial loss of body mass (Bannister et al., 2020; Moseby et al., 2020). Mass was generally regained (or increased) within 30–60 days of release and possums settled into home ranges within 2–6weeks (Bannister et al., 2020). How- ever, our study suggests that although most post-release acclimatization parameters were met relatively quickly, changes in the diet were still occurring 12 months after re- lease, and thus total acclimatization may have been incom- plete, although not a barrier to short-term reintroduction success (Table 4). An alternative explanation is that the diet is highly variable and thus the concept of dietary accli- matization does not apply, but the direction of change sug- gests this is unlikely. Research usually focuses on the initial post-release period, when starvation is most likely, and during this period body condition may provide a more informative and rapid measure of foraging success than an investigation of diet (Soderquist, 1995). However, good food resources and successful breeding are vital for long-term population persistence through difficult condi- tions such as drought, and thus diet should be viewed as an important metric for measuring population viability and reintroduction success. For brushtail possums, total
Oryx, 2021, 55(5), 755–764 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000991 1 = 5.9
(P = 0.015*) Time
−0.00028 (−0.001–,0.001)
χ2 1 = 0.3
(P = 0.600) Time
1.81
(0.860–2.76) χ2
1 = 10.8
(P,0.001*) Time
χ2
−0.051 (−0.160–0.062)
1 = 10.1 (P = 0.002*)
Explanatory variable 2
Preference
0.140 (0.096–0.180) χ2
1 = 185
(P,0.001*) Preference
0.0029 (−0.009–0.015)
χ2 1 = 20.2 (P,0.0001*)
No. of genera available 0.17
(0.073–0.270) χ2
1 = 1.4 (P = 0.240)
No. of genera available
,0.001 (−0.012–0.012)
χ2 1 = 0.5 (P = 0.470) Sex
−0.42 (–1.40–0.560)
χ2 1 = 0.7
(P = 0.400) Sex
χ2
−0.074 (−0.190–0.042)
1 = 1.5 (P = 0.210)
Explanatory variable 3
Interaction
0.004 (−0.002–0.009)
χ2 1 = 1.8 (P = 0.180)
Trend
Time × Preference Frequency of occurrence changed significantly over time. Preferred genera present in higher number of scats; this did not change significantly over time.
0.002 (,0.001–0.004) χ2
1 = 6.0 (P = 0.014*)
Time × No. of genera available
−0.033 (−0.048–−0.018)
χ2 1 = 18.9 (P,0.001*)
Time × No. of genera available
0.00029 (−0.002–0.002)
χ2 1 = 0.1 (P = 0.750)
Diversity significantly decreased with time. Diversity was not significantly influenced by sex.
Richness significantly decreased with time. Genera available changed significantly over time. Richness was not significantly influenced by sex.
Time × Preference Preferred genera made up larger proportions of scats, & increased in proportions over time.
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