Whither wildlife in an overpopulated world?

Chris R. Dickman

Aims of talk

• World population growth – trends and predictions• Population growth in Australia• Consequences for Australian wildlife:

1) the losers: large species, specialists• Direct impacts – loss of habitat, overkill, pollution, disruption

to life cycles • Indirect impacts – invasive species, disease, climate change

2) the winners: generalists, resilient native species• Consequences for people:

• Loss of resources and services, cultural memory loss, diminishing connection with remaining wildlife and its environment; accelerating loss of wildlife

• Conclusions: where to from here?

World population: growth

Source: UN Department of Economic and Social Affairs (2012)

Current population ~7.2 billionGrowth rate ~1.1%

World population: projections

Source: UN Department of Economic and Social Affairs (2012)

‘Low’ variant ‘Medium’ variant

‘High’ variant

‘Constant-fertility’variant

Australia: population growth

Current population ~ 23 millionLong term growth rate >1.3% (now 1.8%)

Source: UN Department of Economic and Social Affairs (2012)

Wildlife: recent changes in status

• Worldwide: 270 terrestrial vertebrates, 62 fishes, 384 invertebrates listed as extinct (IUCN Red List – 2013)

• Australia: 54 terrestrial vertebrates listed as extinct, +2 not listed, 290 more rated as threatened (EPBC Act 1999 – 2013); ~3000 ‘ecosystem types’ also at risk (Keith et al. 2013)

• Background rate of extinction ~1 species per million per year; exceeded by 1-3 orders of magnitude by some vertebrate groups, e.g. Australian mammals (Dickman et al. 2007)

Photo: T. Prete

Photo: D. Gialanella

Photo: A. Greenville

Australian wildlife: causes of loss

• Habitat loss: conversion of natural vegetation for human food (arable + grazing), shelter (towns, cities), roads, industry. Examples:

• 1) Victorian native grassland reduced by 99% for grazing and urban infrastructure → loss of eastern barred bandicoot

• 2) Logging in Victorian central highlands for timber → decline in Leadbeater’s possum

• 3) Mining, CSG fracking?

Photo: Museum Victoria

Photo: D. Harley

Australian wildlife: causes of loss

• Direct overkill: targeted destruction of wildlife to reduce competition (real or perceived) with humans. Examples:

• Thylacine, Tasmania• Marsupial Destruction Acts,

Queensland and NSW; bounties, Sydney rat cull

• Indirect overkill: roads, fence barriers, uncapped mine shafts kill >100 million terrestrial vertebrates / year → local population depletion

Photo: Murweh Shire Council

Australian wildlife: causes of loss

• Invasive species: human-associated sport, companion, commensal and other animals have wrought huge problems. Examples:

• Rabbit, red fox, domestic cat, black rat, common myna, cane toad

Effect size following predator removal

Salo et al. (2007)

Photos: P. German

Australian wildlife: causes of loss

• Pollution: air, water, soil contamination; noise, light pollution reduce habitat quality and disrupt species’ life cycles. Examples:

• Frogs (water pollution), bats, birds (light pollution); chronic elevation of stress hormones in many terrestrial vertebrates → reduced reproduction

Australian wildlife: causes of loss

Climate change, esp. extreme events: heat waves, droughts, floods and climate × environment interactions

Climate model: red-tailed phascogale

Average of Pseudomys hermannsburgensis

0

10

20

30

40

50

60

1990

1991

1993

1999

2001

2002

2006

2008

2011

Capt

ures

(100

trap

nig

hts)

Flood rain → resource pulse → rodents →predators (+ wildfire) → intense predation

Long-term rodent trapping results, Simpson Desert

Capture rate: sandy inland mouse

Flood rains Rains

Intense per capitapredation

predation

Australian wildlife and human overpopulation

• Australia has the world’s highest rate of extinction of native mammals in the last 200 years + high rates of loss of native birds and amphibians

• Rates far exceed background rates

• Many other vertebrates are threatened

• Humans—directly and indirectly—are the cause

Where to from here?• Predicting future

wildlife loss: 13 extinctions of Australian terrestrial vertebrates since 1950; 56 in total

• 0.95 species lost with every million additional people

• By 2100 (roughly!):– 63 species (IUCN

low)– 70 species (IUCN

medium)– 87 species (IUCN

high)– 124 species (IUCN

constant-fertility)

r2 = 0.96y = 36.5+0.95x

1950

2009

What will we lose?Rough estimates suggest many species (7-68) will go by 2100, most likely:– Currently threatened

species– Specialists (e.g. koala,

high altitude + latitude frogs and mammals)

– Boom and bust taxa and other arid-dwellers

– Coast-dependent species (seabirds, turtles), island endemics

– Any species with small geographical ranges

What will we lose?

• In addition to the species …• the integrity of ecological communities • co-evolved relationships • ecological services (e.g. soil turnover,

dispersal of seeds, fruits, spores of mycorrhizal fungi, pollination, control of some ‘pest’ species)

• current economic value (e.g. $1.8 billion / year in tourism; Hundloe & Hamilton 1997)

• future value (missed opportunity costs) • aesthetic, inspirational, iconic exemplars of the

Australian identity

What will we have?

Lots of these …

(resilient or generalist

native species)

and these …

(domestic +

invasive

species)

→ biotic

homogenisation Photo: R. Shine

Conclusions

• Many Australian mammals, birds and other vertebrates have been extirpated by human activity

• Potentially catastrophic losses of more species, populations, ecological processes and services are inevitable as the human population grows

• Cultural memory loss and disconnection to the environment are likely with more people (and increasing urbanisation), exacerbating problems for wildlife

• “All environmental problems become harder – and ultimately impossible – to solve with ever more people” Sir David Attenborough

• Can we avoid a Down Under dystopia? Solutions?