The northern bettong (Bettongia tropica)

The northern bettong (Bettongia tropica) is a small rat-kangaroo (Potoroidae),

weighing in at an average of 1.2kgs. The claws on their forepaws are well

developed for digging and their tails can be used for carrying nesting material.

Their diet consists mainly of sporocarps (truffles) from hypogeous (underground)

fungi that they dig from the soil often around the bases of host trees. At least 35

different truffle species are on the menu. Truffles are eaten all year round, with

grass roots, herbs and lilies supplementing the diet at different times of the year.

The northern bettong is an endangered species that in recent times is known to

inhabit just four northeastern Queensland locations. It is found in the Lamb

Range, the Mt Windsor Tableland, Mt Spurgeon on the Carbine Tableland and

has recently been found near Paluma.

The Lamb Range population is the only one considered to be secure although it

is still limited to an area only 25km long and 6 kms across at its widest point.

Trial by fireSurvival of the northern bettong

A problem of balance

Fire has played an important role inshaping Australian ecosystems withmany native plants and animalsadapting to a fire-prone landscape.Little is known however, about theresponses of individual species tofire. An example of such adaptationis the relationship between fire,certain below ground (hypogeous)mycorrhizal fungi and fungi-eating(mycophagous) marsupials. KarlVernes examined this relationshipin his PhD studies.

Many trees in our forests depend onhypogeous fungi for healthygrowth. Primarily, hypogeous fungiprovide trees with mineralnutrients. They also enhanceresistance to disease and the abilityto take up water, as well as allowingtrees to withstand a greater range oftemperature, salinity and pH levels.

Mammals eat the nutritious fruitingbodies of hypogeous fungi whichare commonly known as ‘truffles’.When they do so, the spores of thefungus not only pass through thedigestive system of the animalunharmed but are more likely togerminate as a result of thispassage. In this way, mycophagousmarsupials help to maintain thehealth of our forest ecosystem bydispersing mycorrhizal fungalspores and increasing the likelihoodof new individual fungi forming.

January 1999

Objectives of the research

The research was designed toanswer two main questions:1. How does fire effect the

availability of hypogeous fungito the bettong?

2. What impact does fire-relatedchange in the hypogeous fungicommunity have on thebettong’s diet, home range andbroad-scale movement withinthe environment?

Past studies have indicated that firemay initiate changes to fruiting ofhypogeous fungi. Since these fungiare an important part of thebettong’s diet such informationcould lead to better ways ofmanaging bettongs and theirhabitat.

Playing with fire

In the study area at Davies Creek,experimental fires were conductedover two burning (dry) seasons in1995 and 1996. These fires were oflow to medium intensity andtypically only burned theunderstorey grasses and lowshrubs. Fires are a difficult tool tomanipulate, so experts from theDepartments of Environment andHeritage, Natural Resources andCSIRO were recruited to help withthe burning experiments, alongwith several volunteers.

Close inspection of the site showedthat low to medium intensity firesat Davies Creek were regularphenomena, occurring about everytwo to four years. However, theredid not appear to have been a fire atmost sites for at least three to fouryears or longer in some areas. Mostsites could be considered due for afire according to historic fireregimes.

Karl used data from trappedbettongs to estimate numbers andto record or monitor populationchanges, body weight andreproduction of his animals.Radio collars were fitted to trappedanimals so their locations could bedetermined at any time from theradio signal. Receivers were set upat different points around the studyarea and compass bearings taken tothe signal from each point. Thelocation where these bearingsintersect gave the locations of theanimals.

Responding to fire

According to Karl, radio-locationand trapping data indicated thatmost, if not all bettongs experiencedno ill effects from the fire itself.Bettong responses to the fire eventshowed:

• no change in the survival ofbettong pouch-young after thefires,

• home range size and locationdid not change following thefires, and animals still movedaround the area as previously,and

• when faced with a choice ofburnt or unburnt areas thebettongs preferred to forage inburnt areas.

The animals appeared to be moresuccessful in foraging after the fire,possibly because of the increasedavailability of fungi on the burntground and the decrease in ground-layer vegetation following the burnmade travelling easier for this smallanimal. Fungus remained the majorpart (56%) of the bettongs diet bothbefore and after the fire, throughoutall seasons.

Truffles of hypogeous fungiresponded to fires as follows:

• they were more available tobettongs immediately after thefire, mainly because theybecame easier for the bettongsto detect, and

• several months after the fire, theability of bettongs to detectfungi on the burnt sitedecreased to very low levels,whereas this increased on theunburnt control sites. Bothburnt and control sites hadreturned to normal levelswithin 12 months.

Conclusions

In this study bettongs appearmostly unaffected by fire, and arequite flexible in their response tochanging rates of truffle detection.This indicates that they may be afire-adapted marsupial, able tosurvive well under conditionswhere low to medium intensity firesoccur frequently. However, furtherstudies would need to be conductedto see how bettongs adjust to anenvironment where there werelonger intervals between fires orwhere fires are suppressedaltogether.

For further information pleasecontact:

Dr Chris JohnsonZoology & Tropical EcologyJames Cook University, TownsvillePh: (07)47814141 Fax: (07)47251570Christopher.Johnson@jcu.edu.au