Diet of a reintroduced marsupial 759
TABLE 1 Linear mixed-effects models, with a Gaussian distribution, used to investigate brushtail possum Trichosurus vulpecula diet over time.
Response variable
Frequency of occurrence over time2 Proportion over time3 Dietary richness4
Shannon’s index of diversity5
Explanatory variables1 Preference, Time
Preference, Time
Time, Sex, No. of genera available Time, Sex, No. of genera available
Interaction
Preference × Time Preference × Time
Time × No. of genera available Time × No. of genera available
Random effect Genus
Genus
Possum ID Possum ID
1Preference: preferred, no preference, non-preferred (derived from Jacob’s Index results); Time: months since release; Number of genera available was
determined from vegetation surveys. 2Number of scats in which genus was present. 3Proportion of genus within a scat (averaged from rbcL and ndhJ results; see Methods). 4Number of genera within an individual scat. 5Calculated as (H′) =(pi In(pi)), where pi = the proportion of each genus within the individual scat (averaged from ndhJ and rbcL results; see Methods).
samples: Eucalyptus, Petalostylis, Maireana, Zygophyllum, Callitris, Acacia, Silene, Austrostipa, Stackhousia, Melaleuca, Senna and Sonchus (Table 3, Supplementary Tables 2 & 3). Only four of those were not readily available at the source site (YookamurraWildlife Sanctuary) prior to translocation: Petalostylis, Silene, Stackhousia and Sonchus (H. Crisp, pers. comm., 2017). The diet of males and females did not differ greatly during the 12 months (Pianka overlap overall = 0.73, monthly overlap values 0.65–0.84).Overall, nine (13.4%) gen- erawere preferred, occurring in a significantly higher propor- tion of scats than expected based on their availability at the study site, 22 (32.8%) generawere consumed in the same pro- portion as their availability (neutral), and 36 (53.7%) genera were non-preferred, being consumed in significantly lower
proportion compared to their availability (Supplementary Table 4). Of the nine preferred genera, fourwere readily avail- able at the source site (Melaleuca, Zygophyllum, Pittosporum and Maireana;
H.Crisp, pers. comm., 2017).
Foraging habits Of the plant genera recorded in the pos- sums’ diet, most (72%) were ,0.5 m in height. However, these genera made up a relatively small proportion of the diet (frequency of occurrence in scats 11.4%), along with mid storey plants (0.5–2.5 m, frequency of occurrence in scats 9.5%), which made up 21% of plant genera consumed. The highest frequency of occurrence in scats was genera .2.5 m in height (32.6%; Fig. 3), despite comprising only 7% of genera available. Although taller plants made up a small proportion of genera, per cent cover was relatively similar to that of small plants (.2.5 m, mean % cover 41.7 ± SE 1.8; ,0.5 m, mean % cover 45.9 ± SE 5.6), with mid storey plants providing considerably lower per cent cover (0.5–2.5 m, mean % cover 13.4 ± SE 1.8). Mid storey genera including Acacia, Pittosporum and Eremophila were found in a higher proportion of scats with increasing time since release. No bird DNA was detected in any of the pos- sum scats. We were unsuccessful in amplifying invertebrate DNAand thus the consumption of invertebrates by possums in the National Park remains unknown.
Discussion
FIG. 2 Dietary richness (a) and Shannon’s index of diversity (b) for plant genera consumed by possums after their release (August 2015–July 2016). Both relationships are statistically significant.
The diet of reintroduced brushtail possums changed signifi- cantly with time since release, independent of changes in the availability of genera. Presumably, possums consumed a wider variety of foods (higher dietary richness and diversity) after release because the location of preferred and nutri- tious food plants was unknown. Flora at the source site (YookamurraWildlife Sanctuary) differed from the release site, although many of the same genera were available (H. Crisp, pers. comm., 2017). Over time, possums probably dis- covered sources of preferred plants within the release area.
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
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