Large areas of Australian woodlands are subject to bushfire,
particularly eucalypt forests. Woodland forests comprise 67% of forest
vegetation in Australia, with scrublands, shrub and mixed forest types
dominating the northern and eastern coast (Fig. 1)(ERIN 2012 & ABARES 2013). An estimated 39 million hectares of Australian
forest was burnt from 2006 to 2011 (ABARES 2013). Animals inhabiting Australian
woodlands must be well-adapted to frequent changes in environmental conditions
in order to survive and successfully reproduce.
 |
| (Fig. 1 - Terrestrial Ecoregions of Australia (April 2012)) |
Bushfire is an important ecological process for the
germination of native plants, soil nutrient cycling and removal of obstructive
ground vegetation, including invasive weeds (IFA 2005). However, bushfire results
in increased environmental temperature, and the potential death of native fauna.
In the 1950’s, laboratory studies on thermoregulation of the short-beaked echidna
(Tachyglossus aculeatus) found that body
temperatures of 38°C resulted
in fatalities (Brice et al. 2002). However, recent field studies have shown they are able to
withstand ambient temperatures of above 40°C,
as well as survive large bushfire events (Brice et al 2002 & Nowack et al
2016).
Echidnas survive bushfire and increased environmental
temperature by seeking shelter, usually a log, cave or burrow, before entering
a state of torpor. Torpor significantly
lowers metabolic rate, and reduces breathing and heart rate. This decrease in
cardiovascular and metabolic activity results in effective loss of body
temperature (Heldmaier et al 2004). Echidnas subjected to bushfire in Dryandra
Woodland, south-east of Perth, reduced their body temperatures on average by 4°C as a result of
behavioural sheltering and torpor (Nowack et al 2016). One individual reduced body
temperature from over 30°C,
to below 20°C for four
days after the onset of bushfire. After a period of re-adjustment, body
temperature returned to normal as measured within the week prior (Fig.2). Possibly the
most important finding from this study was that none of the echidnas in the
sample left their home range as a result of the bushfire, although one did die
as a result of poor log choice (Nowack et al 2016).
 |
| (Fig. 2 - Body temperature traces of the same echidna (a) 7 days before and (b) 7 days after the fire on 21 April) |
The short beaked echidna enters a state of torpor as an
adaptation to bushfire, and subsequent increase in environmental temperature. This
adaptation is believed to have enabled their survival through global wildfire
events, such as those caused by meteoroid impacts during the
Cretaceous-Paleogene era, 65.5 million years ago (Nowack et al. 2016). Temperature variation and natural disasters will continue to occur, affecting
all species on earth. Thermal adaptations like torpor have and will continue to
benefit animals such as the short-beaked echidna as evolution continues over
time.
References:
Brice, P. Grigg, G. Beard, L. Donovan, J. 2002, ‘Heat
tolerance of short-beaked echidnas (Tachyglossus aculeatus) in the field’, Journal of Thermal Biology, Vol. 27 pg
449 - 457
Department of Agriculture (ABARES), 2013, ‘Australia’s State
of the Forests Report’, Five Yearly
Report, Australian Government
Environmental Resources Information Network (ERIN) 2012, Department
of Sustainability, Environment, Water, Population and Communities, Commonwealth
of Australia, Australian Government
Heldmaier, G. Ortmann, S. Elvert, R. 2004, ‘Natural
hypometabolism during hibernation and daily torpor in mammals’, Respiratory Physiology & Neurobiology,
Vol. 141 pg 317–329
Institute of Foresters of Australia (IFA), 2005, ‘The role
of fire in Australian forests and woodlands’, Forest Policy Statement 3.1, pg 1-3
Nowack, J. Cooper, C.E. Geiser, F. 2016, ‘Cool echidnas
survive the fire’, Proceedings of the
Royal Society B, Vol. 283, pg 1-8
Figures:
Figure 1:
Environmental Resources Information Network (ERIN) 2012, Department of Sustainability, Environment, Water, Population and Communities, Commonwealth of Australia, Australian GovernmentFigures:
Figure 1:
Figure 2:
Nowack, J. Cooper, C.E. Geiser, F. 2016, ‘Cool echidnas survive the fire’, Proceedings of the Royal Society B, Vol. 283, pg 1-8
That’s fantastic! I didn’t realise that echidnas showed torpor, which is pretty cool. I wonder if it could be an appropriate strategy for species as temperatures continue to increase, particularly in areas such as the tropics? Do you know if animals that are unknown to enter torpor naturally can be induced to enter it?
ReplyDeleteI'm not sure about animals that naturally don't undergo torpor, but theres research into naturally occurring compounds that induce torpor in mice and squirrels, tests could be done to see if it applies to other mammals too. Also i found a lot of research into inducing torpor in humans for space travel
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