The diet of the Pilliga mouse, Pseudomys pilligaensis (Rodentia: Muridae) from the Pilliga scrub, northern New South Wales

11 Pages·2001·3.9 MB·

by  E A Jefferys

The Diet ofthe Pilliga Mouse,
Pseudomyspilligaensis (Rodentia: Muridae) from
the Pilliga Scrub, Northern New South Wales
Elizabeth A. Jefferys and Barry J. Fox
School ofBiological Science, University ofNew SouthWales, SydneyNSW 2052
Jefferys, EA. and Fox, B.J. (2001). The dietofthe Pilliga mouse,Pseudomyspilligaensis
(Rodentia:Muridae)fromthePilligaScrub,northernNewSouthWales. Proceedings
oftheLinneanSocietyofNewSouth Wales 123, 89-99.
ThecontentsofthedigestivetractsfromfivePilligamice(Pseudomyspilligaensis),
collectedovertwelveyears, wereprocessed. Seedwasthe most abundant food in the diet
andwasrepresentedbyfiveorsixseedtypesin Spring/Summerandaccountedfor95%of
the diet, with leafcontributing less than 2%. InWinter, seed contributed 62% ofdiet,
representedby more thantwelve seedtypes with leafcontributing 38% ofthe diet. These
results indicate that P.pilligaensis is a specialised granivore, although it may be more
opportunisticinwinter.
Manuscriptreceived21 May2001,acceptedforpublication 19 September2001.
KEYWORDS: diet,granivore,Pilligamouse,Pseudomyspilligaensis.
INTRODUCTION
ThePilligamouse,Pseudomyspilligaensis(Rodentia: Muridae)wasfirstcaptured
in 1975 and was thought then to be an unusually small specimen ofthe New Holland
Mouse (Pseudomys novaehollandiae). However, material collected over the following
yearsrevealed significantmorphologicaldifferencesbetweentheanimalsfromthePilliga
andotherConilurinerodents andanewspecieswasdescribedbyFoxandBriscoe(1980).
Briscoe, et al (1981) used electrophoretic analysis to clearly demonstrate genetic
differentiationbetweenPseudomyspilligaensis andrelatedPseudomys species.
VerylittleisknownaboutthePilligamouseexceptthatitisterrestrialandappears
to live in burrows, often in sandy substrate. It apparently has an extremely restricted
distribution, and is known only from the Pilliga Scrub including Pilliga State Forests.
This area is situatednorth ofCoonabarabran innorthernNew SouthWales. It is a forest
onanisolatesandsubstrate,supportingamixedCallitris-Cypress-Pine-Eucalyptusforest
andheathcommunities (FoxandBriscoe 1980).Allknownindividuals capturedupuntil
1988 appeartohavebeenwithina50kmradius.The statusofthePilligamousehasbeen
listedasrare,limited,vulnerableandperhapsatriskbutpossiblyunderestimated(Strahan
1995). The Pilliga mouse is nocturnal and inhabits areas with sparse ground cover. The
Pilliga mouse is similar in appearance to the New Holland Mouse, Pseudomys
novaehollandiae which has a coastal distribution and is restricted to sandy areas. Both
are nocturnal and inhabit areas with sparse ground cover.
Proc.Linn. Soc.N.S.W., 123.2001
90 DIETOFTHEPILLIGAMOUSE
novaehollandiae which has a coastal distribution and is restricted to sandy areas. Both
are nocturnal and inhabit areas with sparse ground cover.
Incaptivity, animals live in family groups. The breeding season ( in captivity )
extendsatleastfromOctobertomid-Februaryandthegestationperiodisbetween24and
31 days.Young are bornwiththe incisors erupted and eight laboratory-born littershad a
modal size ofthree young (Fox and Briscoe 1980).
There areno publisheddataonthe dietofthis species.This studyexaminedthe
dietoffivewild-caughtindividualsofPseudomyspilligaensis,usingmicroscopicanalysis
offaecal samples whichwere collectedoveratwelve yearperiod.Anyknowledge ofthe
natural dietandcues forhabitatselectionare crucial inunderstandingthebiologyofany
rare native rodent (Cockburn 1981a,b). This information could substantially contribute
to the understanding ofits habitat requirements and to the conservation management of
this rare and endangered species.
STUDY SITES
ThefiveindividualswereallcapturedfromlocalitieswithinthePilligaScrubarea
(Table 1). The specimens came from habitats in mixed cypress-eucalypt forest and
woodland.Thedominantcanopyspecieswereredstringybark{Eucalyptusmacroryncha),
scribbly gum (Eucalyptus rossii) and black cypress pine (Callitris endlicheri) with
Blakely'sredgum(Eucalyptusblakelyi)androughbarkedapple(Angophorafloribunda)
in creek lines, which also had stands of bottle brush (Callistemon) and tea tree
(Leptospermum) in the understorey Apart from creek lines the sparse understorey
comprisedheath-typeshrubssimilartothe She-Oak(Casuarinadistyla)dominatedheath
adjacenttotheforest. Moredetaileddescriptionsofthevegetationandaplantspecieslist
areprovidedbyFoxandBriscoe(1980).ThePilligaStateForestshaveaveryunpredictable
physical environment with annual rainfall around 625mm with a summer maximum.
Variation in annual rainfall is great, withperiods ofboth great drought and extreme wet
being common (Norris et al.1991; Hart 1995).
METHODS
The digestive tracts of five spirit specimens ofPseudomys pilligaensis were
carefullyremovedfromthebodycavityandopenedusingfinescissorsandfinejewellers
forceps. Three ofthe specimens contained faecel pellets only (BF 791 103; BE 791105
andNPWS 1-88)whiletheremainingtwospecimenscontainedmaterialinallsectionsof
the digestive tract (A.M. M10438; andA.M. M10602) (see Table 1,specimens No. 1, 3
and4 describedbyFoxandBriscoe 1980). Hencetobeconsistent, onlythe faecalpellet
,
datawere used in comparing the diets.
The contents ofeach section ofthe tract were flushed with 75% alcohol and
placed into separate containers and categories ( i.e. caecum, stomach, large intestine).
Faecal pellets when present were carefully removed from the rectum. Thus one sample
consists offive faecalpelletsthatwererandomly selected from onemouse. Each sample
was washed through a column offive different sieves with 0.58, 0.41, 0.26, 0.15, and
0.13mm mesh. Any material passing through the smallest sieve was collected on filter
paper was divided into six sub samples. Each subsample was transferred into a labelled
testtubetoallowmaterialstobehomogeneouslymixed.Thematerialwasthentransferred
from each tube with apipettetoacorrespondingly labelled slide (25.4 x 76.2mm)which
wasplacedon ahotplateat30C todry.Afterall moistureonthe slideswasevaporatedthe
slides were removed from the hotplate, placed on a flat surface and slowly covered with
modified Berlese mounting medium (Luo 1993). The completed slides were then left
PRrx:. Linn. Sex. N.S.W.. 123. 2001
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Proc.Linn. Soc.N.S.W.. 123. 2001
92 DIETOFTHEPILLIGAMOUSE
undisturbed for 2-3 days until the mountant set hard. This modified medium not only
clearsthematerialbutalsohasanabilitytopreserveandretaintheoriginalappearanceof
thefaecalpelletmaterial,whetherthatbe freshgreenmaterial oroldyellowmatureplant
material.Theamountofmaterialoneachslidewasstandardisedusingascoring(frequency-
of-occurrence) technique as described by Johnson 1982; Luo 1993; Fox, Read, Jefferys
andLuo 1994.
Estimation ofDietary Composition
GenerallythefoodmaterialinthesamplesofP.pilligaensiscouldnotbeidentified
tospeciesandwasclassifiedasleaf,stem,seed,insect,pollen,sandgranulesorunidentified
(followingtheprotocolofFox,Read,JefferysandLuo 1994).Asrodentstendtomasticate
their food very finely, positive identification of food items (e.g. epidermal tissue) is
extremely difficult. Some small pieces ofplant material could be identifiedto genus by
comparison with the plant slide collection in the ecology laboratory at the University of
New South Wales.
All six slides from each samplewere scoredbecause different dietary items were
bestrepresentedonslideswiththeappropriatesizedparticles.Atotalof50fieldsofview
at 40 x magnification were scored for each of the six slides from each sample. The
frequencyofoccurrenceofeachfoodcategorywasrecordedfromitspresenceorabsence
in each field. Next the number ofscores or frequency for each food item was summed
over all slides and the percentage ofeach category in the diet, from 300 fields ofview,
was calculatedas
p = )x 100%
- (/;•/!/;•
z
whereF- is the percentage and^-the frequency ofi food item.
Althoughsomeauthorshavecalculatedfrequencypercentagesasthenumberof
fields in which a food category occurred out of 100 fields, then converted them into
relative percentage ofoccurrence (e.g. Sparkes and Malechek 1968; Cockburn 1980;
Carron,HappoldandBubela. 1990),theaboveequationdeterminestherelativepercentage
ofoccurrence ofeach food item irrespective ofthe number of fields scored. Detailed
discussionofthetechniqueswehaveusedarepresentedinLuo 1993; Fox, Read,Jefferys
and Luo 1994; Luo Fox and Jefferys 1994.
,
RESULTS
Table2 showsthepercentagedietarycompositionofthefivefaecal samplesofthe
Pilliga mice collected in the wild. Overall plant material (stem, seed, and leaf) was the
mostabundantfoodinthedietofP.pilliagensis, accountingformorethan94%ofitstotal
diet. There was no pollen present in any ofthe samples. The bulk ofthe plant material
was seed, over80%, and22 seedtypeswererecognised, 12 ofwhichweremonocotsand
1 seedtypesrecognizedasdicots.Table3 showsseedtypesfoundinthedietofPseudomys
pilligaensis. The seed types 16 to 22 ocurred only at trace levels. The seeds were finely
masticated but some particles were large enough to make some general identifications.
The Monocot seed material appears to come from the genera ofCyperus,Lepidosperma
andSchoenus,(Cyperaceae);Poa,Juncus,Aristida, Cymbopogon,Dichelachne Digitaria,
,
Entolasia, Eragrostis, Imperata, and Triodia spp. (Poaceae) all ofwhich are found in the
Pilliga Scrub area.
Leafmaterial found in the diet varied from 1% in spring to 52% in winter. Stem
material varied from4% in springto 1% inwinter SampleNo. 3 (BE 791103) contained
small traces ofleafofthe plant speciesAotus subglauca, family Fabaceae. Most ofthe
PRrjc.Linn. Soc. N.S.W.. 123. 2001
E.A.JEFFERYSANDB.J. FOX 93
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94 DIETOFTHEPILLIGAMOUSE
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Proc.Linn. Soc.N.S.W., 123. 2001
E.A.JEFFERYSANDB.J. FOX 95
leafmaterialwasMonocotandwasassociatedwiththeseedeaten(i.e.glumesandlemma).
Alloftheleafmaterial insampleNo. 1 AM.Ml0438wasMonocotmaterial andis either
Poaceae orCypeaceae family. Some ofthe leafcells were identified as belonging to the
family Poaceae (grasses) by the dumb-bell shaped silica bodies in the cells. Dicot leaf
was observed.
Fungal spores were present in one individual (No. 4 BE 791105) but as onlytwo
single spores were present it would appear that this was accidentally ingested and does
notappearto bepartoftheirdiet. Dirtandsandgranuleswerepresent inall samplesbut
ininsignificantproportions. Howeverasthere isno evidence ofanyrootmaterial orany
soil invertebrates,thissuggeststhatthemicewereprobablynotdiggingtoacquireanyof
the food in theirdiet atthese times.
Insect material was found in all five individuals but only four ofthe samples
were abletobe identified. Larval skinfromthe same species ofLepidopterancaterpillar
wasfoundinbothdietsfromspring(BE 791103 andBE 791105)winter(AM.M. 10602).
Hymenopteranmaterial identified as ant (Formicidae) alate wings was found in winter
(AM. M. 10602) and spring (NPWS. 1-88), and a section of ant gaster (Formicidae)
appears in spring (BE 791103). A section ofleg ofOrthopteran (grasshoppertype) was
found in winter. (AM. M.10602) so they appear to be consuming similar material over
this time period.
Pseudomys pilligaensis appears to have a strictly granivorous diet during the
spring/summer months (September to November), consuming from 91% to 95% ofits
dietas seed.This seedmaterialismainlyyellowtobrownandappearstobemature dried
seedfrom4to 6 species. Onetypeofseed(No.6, agrasstype)appears infourofthe five
samples, and it appears in the diet in the years 1976, 1977 and 1979. However in the
wintermonthstheybroadenthe dietto include amuch greaterrange ofseedtypes anda
higherproportion ofleafmaterial.
DISCUSSION
Itshouldbenotedthatthe sample size isverysmall andanyresultswill onlybe
a limited appraisal ofwhat the individuals were eating at the time ofthe sampling. The
five samplesrepresentonejuvenile and fouradults andwere collectedoveranumberof
years. Wintersamples comprised one adult inJuly 1976AM. M.10438 and onejuvenile
July 1977AM.M.10602.Whatwehaveclassifiedasthespring/summersamplescomprised
two adults collected in November 1979, i.e. BE 791103 and BE 791105 and one adult
from September 1988. Hence it is only possible to compare the diet for spring/summer
and winter in a very broad manner. The results from the other sections ofthe digestive
tractwereverysimilartothose fromthe faecalpellets.Thiswasalso foundtobethecase
with Pseudomys novaehollandiae diet analysis by Thompson (1980), with stomach
contents having a close similarity to faecal pellets.
Insectsdonotseemtobeaveryimportantpartofthediet, astheyonlyrangefrom
to 6%ofthetotaldiet. Insects, especiallyantsandtermites, arereadilyavailableinthis
habitat (Rolls 1981; Hart 1995 ) and would provide more calories per gram than seeds
(Golley 1961,Reichman 1975,RedfordandDorea 1984).Theinsectmaterialinallofthe
diets could possibly have been accidentally ingested as they all are associated with the
parts ofthe plants thatwere consumed. However, it would appearthat these rodents are
deliberately selecting plant material instead of insects at these times ofthe years. A
comparisonofthedietofPseudomyspilligaensiswiththoseofotherspeciesofPseudomys
inbothspring/summerandwinter(Table4)showsthatP.pilligaensislikeallotherspecies
demonstratedadropinthepercentageofseedfromspring/summertothewinterdiet,but
the magnitude of the shift differs. Pseudomys novaehollandiae is almost entirely
dependent on seed (97%) in summerbut drops to 45% in winter, while P. apodemoides
drops from 86% in summerto 55% inwinter(Table 4). These changes contrastwiththe
Proc.Linn. Soc.N.S.W., 123.2001
96 DIETOFTHEPILLIGAMOUSE
Table4,AcomparisonofdietitemsinthefaecesofP.pilligaensiswiththoseforfiveotherspecies
ofPseudomys in (A) Spring/summer and (B) winter. Values are the mean percentage occurence
±standarderror.Sources:Cockbum(1980);2Thomson(1980);3Cockburn(1981a),4Cockburn(1981b);
5Foxetal (1994);6LuoandFox (1994).
A) Spring/Summerdietitems
Species Leaf Stem Seed Fungi Insect Other Total
(n=samples)
Pseudomys 1.7 1.3 95.0 2.0 100.0
pilligaensis ±1.2 ±0.3 ±2.3 ±0 ±2.0 ±0
(3)
Pseudomys ' 1.5 _ 96.9 0.6 0.6 100.0
novaehollandiae ±0.9 ±1.5 ±0 ±0.6 ±0.6
(5)
Pseudomys2 4.9 a a 81.2 _ 3.8 10.0 99.9
novaehollandiae ±1.2 ±1.9 ±0.3 ±1.0
(35)
Pseudomy3 4.9 a a 85.8 1.0 1.0 100.1
apodemoides ±1.2 ±0.7 ±0 ±0.2 ±0.4
(15)
Pseudomys4 1.4 - 58.6 19.8 12.6 4.9 99.9
fumeus
(23)
Pseudomys5 44.6 0.3 44.2 0.3 7.3 3.4 100.1
oralis ±2.2 ±0.1 ±2.1 ±0.3 ±1.2
(29)
Pseudomys6 4.6 31.1 34.2 22.7 3.0 4.3 99.9
gracilicaudatus ±1.9 ±3.7 ±3.9 ±2.7 ±0.7 ±1.4
(25)
aLeafandstemconbined
Proc.Lfnn. Soc.N.S.W., 123. 2001
E.A.JEFFERYSANDB.J.FOX 97
B) Winterdietitems
Species Leaf Stem Seed Fungi Insect Other Total
(n=samples)
Pseudomys 38.0 1.25 61.5 1.0 100.0
pilligaensis ±14.0 ±0.5 ±14.5 ±0 ±1.0 ±0
(2)
Pseudomys1 18.9 44.6 3.3 17.0 15.7 100.0
novaehollandiae ±0.9 ±8.9 ±3.3 ±14.0 ±5.6
(7)
Pseudomys2 11.5 a a 54.7 - 7.3 26.6 100.1
novaehollandiae ±0.6 ±0.3 ±0.7 ±1.5
(22)
Pseudomys^ 8.1 a a 55.3 10.4 11.2 15.0 100.0
apodemoides ±2.6 ±1.4 ±0.6 ±1.1 ±1.8
(15)
Pseudomys"' 1.6 - 26.7 55.0 6.6 10.2 100.1
fumeus
(23)
Pseudomys5 77.0 6.5 11.6 1.1 2.3 1.5 100.0
oralis ±2.2 ±1.5 ±1.8 ±0.6 ±0.4 ±0.8
(29)
Pseudomys6 12.2 29.1 31.1 22.8 1.3 3.4 99.9
gracilicaudatus ±1.5 ±1.7 ±1.8 ±1.9 ±0.6 ±0.9
(36)
aLeafandstemcombined
larger species, P. oralis which has seed as 44% ofits diet in summer and 12% in winter,
the lowest use of seed in winter, but consumes 77% leaf in winter. Pseudomys
gracilicaudatus shows little change in seed consumption from summer (34%) to winter
(31%), but this holds true for all diet items so that this species shows the least seasonal
change. Alltheotherspeciesincreasetheamountofleaforsteminthedietinwinterbut
P. oralis shows by farthe greatest change from 45% in summerto 77% in winter.
PseudomyspilligaensisappearstobeclosestindiettoP.novaehollandiaewithits
dependence on seed (95%) in summerto 62% in winter. The magnitude ofshift in the
diet is the lowest for the genus. Pseudomys pilligaensis had the highest percentage of
seed(62%) in its winterdiet , whichis followedclosestbyP. novaehollandiaewith45%
andP. apodemoides with 55%. These observations may be a reflection ofdifferences in
the availability ofseed in the habitats ofthese species, asP.pilligaensis occupies heath
and open forest, as does P. novaehollandiae, while P. oralis occupies forest, P.fumeus
subalpine heathland and woodland, with P. apodemoides found only in mature heath.
Proc.Linn. Soc.N.S.W., 123.2001
98 DIETOFTHEPILLIGAMOUSE
CONCLUSIONS
Pseudomys pilligaensis appears to be similar to other Pseudomys studied
(Cockburn, 1980, 1981a, 1981b; Thompson 1980; Luo and Fox 1994 and Fox ,Read,
Jefferys and Luo,1994) whichbroaden theirdiet in winterto incorporate agreaterrange
ofseedtypesandahigherproportionofotherplantmaterial(e.g. anincreaseinstem,leaf
or sporangia). It is not clear whether this reflects an active choice by P. pilligaensis to
selectforincreasedamountsofleafandawiderrangeofseedtypesoradefaultselection
causedbylackofalternativedietaryitemsinsucharestrictedhabitat.Theseresultsindicate
that P. pilligaensis is a granivore, as the diet is dominated by seed ( over 50%) both in
spring/summerandwinter.ThisisconsistentwithKerleyandWhitford's(1994)definition
"The term granivore, should refer to animals whose diet is dominated (>50%)
by[seed]."However P.pilligaensiscouldbeoperatinginageneralopportunisticmanner
(i.e.interpretingopportunisticspeciesasonethatisutilizinganunpredictableenvironment,
differently over the seasons and years) considering the very restricted habitat that the
species survives in today.
These results are important as they provide the only information to date on the
dietofP.pilligaensisinthewild.Asthe speciesisclassedasrare, limitedandvulnerable
(Strahan 1995) this information may contribute to better understanding of its habitat
requirements and conservation management.
ACKNOWLEDGEMENTS
WewouldliketothankJennyTaylorandMarilynFoxforconstructivecommentsonadraftmanuscript.
WethanktheAustralianMuseumforaccesstothetwospecimensfromtheircollectionandtheNationalParks
andWildlifeServiceforaccesstothespecimenfromtheircollection. Fundingforthisresearchwasprovided
inpartbygrantsfromtheAustralianResearchCouncil, mostrecentlyfrom(A1/9700994)
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Proc.Linn. Soc.N.S.W., 123. 2001