2nd National Koala Conference

June, 2017

Disease mediated mortality cycles in a free-ranging koala

population.

Steve Phillips

“Diseases in the form of Chlamydiosis and/or KoRV

collectively present one of the greatest threats to the

continued survival and viability of free-ranging koala

populations in Australia”

True or False?

1. Matters of demographic equilibrium

What might demographic equilibrium at local population level say about the

contemporaneous impacts of disease in wild koala populations?

2. The quandry of female reproductive output

What might arguably optimum levels of reproductive output by female koalas

at local population level say about the impacts of disease in wild koala

populations?

3. Shades of Lotka-Volterra

What if mortalities due to disease ‘cycled’ in local populations over time in a

way that was independent of other potential drivers?

4. The population growth paradox What might koala population growth and range expansion in the face of a

chronic disease burden say about the impacts of disease – or is it more

about genetics, or even something else?

Going against the tide….

What is the local population?

One or more aggregations of koalas,

the majority of which comprise

individuals with established home

range areas to which long-term fidelity

is maintained.

1.The quandry of demographic equilibrium …

0

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1 2 3 4 5 6 7 8 9 10

Tooth Wear Class

No.

anim

als

Local populations of disease +ve, free-ranging

koalas exist along a spectrum of demographic

profiles.

For recovering / expanding populations,

profiles are skewed to the right.

For declining populations, profiles are skewed

to the left

For populations at demographic equilibrium,

profiles approximate the normal distribution.

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n

Tooth-wear class

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Tooth-wear class

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Tooth-wear class

The local population at equilibrium.

The male cohort at equilibrium(?)

The female cohort at equilibrium.

2. Female reproductive output.

Oestrus cycle: ~ 4 – 5 weeks

Gestation: ~ 4 – 5 weeks

and then….

Pouch life: 19 – 21 weeks.

Dependent back-young: 24 – 36 weeks.

Back young (semi - dependence ): 37 – 48

weeks.

Dispersal: 52 – 80 weeks.

Source: Smith (1979); Handasyde (1986).

If this is true, then in populations that are at demographic equilibrium, we

might expect that the numbers of adult female koalas reproducing on an

annual basis should approximate 50%.

Pilliga: 9/13 (69%)

Port Macquarie: 7/12 (58%)

Gold Coast: 9/17(53%)

Ballina: 13/29 (45%)

Chi-square: 2.285, P = 0.52

On average, female koalas produce < 1 joey /year over the term of their

reproductive lives. This number approaches (but cannot exceed) 1 in

younger females, while progressively approaching (but never reaching)

zero in older females.

3. Shades of Lotka - Volterra

dN1/dt = r1N1[(K1 - N1)/ K1]

Where:

N = population size

t = time

r = rate of increase

K = carrying capacity

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1989 1994 1999 2004 2009 2014

No

. kn

ow

n m

ort

alit

ies/

ann

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Year

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1989 1994 1999 2004 2009 2014No

. re

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rte

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oad

-ki

lls

Year

0

1000

2000

3000

198919941999200420092014ann

ual

rai

nfa

ll (m

m)

Year

Analysis of 217 koala

mortalities in the

Ballina LGA over time

period 1989 – 2014.

In cases where cause

of death was

attributable to a

known cause,

‘disease’ accounted

for 36% of mortalities.

Source: Phillips et al 2015.

Mortality cycle was independent of rainfall (or lack of it) and other incidental

harvesting events such as vehicle strike.

4. The Lismore Paradox

Lismore is located on far north coast of NSW between Ballina and Casino. Area

has a long history of community / scientific engagement with koalas.

Home of the Friends of the Koala and the Koala Care Centre. Run entirely by

volunteers, the care centre treats between 300 – 400 koalas per year from the

local area.

Time Period n nd nm

28/02/15 – 26/05/15 69 36 (52.1) 24 (66.7)

27/05/15 – 31/08/15 101 40 (39.6) 29 (72.5)

1/9/15 – 30/11/15 94 32 (34) 26 (81.3)

1/12/15 – 29/02/16 103 32 (31) 28 (87.5)

From these data and on average, 39% of all admissions to the FoK Care

Centre are disease related, while of all koalas admitted for disease, 77% are

doa or euthanised.

Why is it then, that over the 3

consecutive koala generations

1993 – 2010 areas of the Lismore

LGA that are occupied by resident

koala populations has increased

by ~ 600%?

What does it all this mean?

Some alternative hypotheses….

There is an inherent capacity for koalas to maintain optimum population

parameters in the presence of disease.

Koala populations are capable of growth and/or recovery in the face of

chronic disease burdens.

I think it means that there is more to the koala disease equation than what

might be perceived by the average academic eye.

A way forward (perhaps)

Further research on disease requires big picture thinking that includes a

review of current paradigms, as well as a more integrated approach amongst

the various scientific disciples that are working on koala conservation and

management.

Understanding the disease equation as a fundamental aspect of koala

ecology is paramount to better conservation and management of the species

generally.

Balancing the disease equation is straight forward – yes it’s out there, it is

complex and we do need to understand and manage it, but as a symptom not a

cause.

There is little justification for working to improve koala reproductive output in

the interests of assisting recovery if we haven't addressed the real factors

driving decline in the first instance.

Human activity is the catalyst, disturbance is the key variable ….. .

Acknowledgments:

NSW Roads & Maritime Services, Friends of the Koala, John Callaghan,

Maria Matthes & Grant Brearley.

Thankyou