45-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Chapter 45: Human impacts

45-2Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Humans in Australia• The Australian biota evolved in an increasingly arid

climate following the break-up of Gondwana• Immigration of other fauna started when continent

approached South-East Asian plate (bats, rodents)• People entered northern Australia at least

40 000 yrs ago• Initial impacts were from fires• European colonisers came in 1500–1600s to

‘conquer and civilise’ the land

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Humans in Australia (cont.)• Grasslands were turned over to pasture• Forests were cleared• Cities were built without adequate planning for

wastes and effluents• Now, ecosystems are under threat by

– loss of biodiversity– coastal and urban development– inappropriate land and water use– over-exploitation of resources– spread of exotic species

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Losing biodiversity• It is likely that 20% of all species will become

extinct in the next 30 years• 27 mammals and 1 bird species have become

extinct since European settlement• Seagrass beds are at risk due to water quality • Biodiversity hotspots

– Examples: flora of south-western Australia, north Queensland rainforest, wet sclerophyll forest

• Hot spots may reflect the areas most studied, so relative sampling intensity must be considered

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Discussion question 1:

Why conserve biodiversity?

Why conserve biodiversity?• Ecosystem services• Bioresources• Aesthetics• Philosophy• Custodial reasons

• About 1.4 million species have been described, total unknown

• Functional classifications may be easier and more ecologically informative than taxonomic ones

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Tropical forests• Unparalleled diversity of species• Natural disturbances are tree fall and fire• Rapid nutrient cycling enables high production• Low nutrient storage in soil, high in biomass, so

clearing removes nutrients• Slash-and-burn agriculture uses small plots, but is

only productive for a short time• Rainforest regeneration is very slow

– affected by selective weeding and absence of animals for dispersing seeds

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Land clearance and habitat fragmentationMany land fragments are too small to support viablepopulations. Impacts of fragmentation depend on• Ecology and dispersal ability of organisms• Dependence of species on native vegetation• ‘Stepping stones’• For plants, small refuges may be important

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Habitat corridors link adjacent fragments• These links effectively increase habitat size• Facilitate movement of animals (and genes)

between patches, so encourage viable population sizes

BUT• They also help spread weeds, pests, diseases,

deleterious genes and fires

• Fragment shape and ratio of edge-to-middle are important factors

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Fig. 45.5a: Habitat fragmentation

Copyright © Byron Lamont, Western Australian Herbarium

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Introducing new species• Intentional and unintentional introductions have led

to ecological disturbances e.g. Phytophthora cinnamomi fungus (causes dieback disease), rabbits, foxes, feral animals, Japanese sea-star, black-striped mussel, cats

• Strict quarantine controls now apply• Successful invaders have

– high mobility, fecundity and survival– a lack of natural predators– a broad diet– tolerance to a wide range of conditions

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Integrated pest management• The coordinated use of several control techniques

– Example: rabbits viruses (myxomatosis and rabbit calicivirus) poisoning warren ripping fumigation

• Cane toad– failed to control sugar cane beetles, and became a pest

itself by out-competing native species for food– has toxic skin secretions that kill vertebrate predators– has now reached Kakadu—major ecological disaster

likely

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Fig. B45.3c: Spread of the cane toad

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Impact of weeds• A weed is a ‘plant growing in the wrong place’• Usually opportunistic species, e.g. blackberry,

Bitou bush• May grow rapidly and provide cover for foxes,

rabbits• May degrade native animal habitats• Ornamental (garden) species can become weeds

if they spread into native bush, e.g. Pittosporum undulatum

Fig. 45.6: The weed Spartina

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Fresh water is the key to life• A critical resource in Australia• River flows have been altered reduced biodiversity• Flood control death of terrestrial trees (Murray

River)• Water harvesting salinity, temperature, oxygen

changes, pollution• Watering points encourage hard-hoofed animals (that

compact the soil) as well as native grazers that reduce vegetation cover

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Holding on to soil• Land clearing no surface litter layer or root

mat greatly accelerates top-soil loss • Compaction by hard-hoofed non-native animals

reduces porosity increased water run-off • Reduced vegetation cover increased wind

erosion• Improved farming practices include

– no-till system– leaving stubble after harvest

Fig. 45.9: Wind erosion

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Discussion question 2:

What would cause soil acidification?

Soil acidification• Repeated application of ammonia-based fertilisers

without liming• Addition of organic acids• Growing legumes • Plant yield drops when pH reaches 5 or less• 12–24 million ha agricultural land is presently at or

below pH 4.8• Improved land management is vital • Acid sulphate soils are common in coastal areas

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Dryland salinity • Salt is naturally present in soil or groundwater, but

out of reach of plant roots• In wet areas rain washes salt out of soil; in dry

areas soil salinity is higher• Tree removal causes reduced evapotranspiration

(and hence discharge) of ground water, so water table rises

• When less than 2 m from surface it rises further, by capillarity

• Recharge (from rainfall) and discharge zones may be far apart

Need catchment-based management

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Fig 45.10: The salinisation process

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Irrigation salinity• Results from irrigating soils to grow crops• Excess water recharges ground water• Discharge is slow because there are no deep-

rooted trees• Water table rises and brings salt to surface• Signs of salinised soil

– replacement of salt-sensitive species with tolerant ones until no plants can survive

– salt scald occurs and then crust forms – salt drains into streams, into river system and the sea

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Prevention of dryland salinity• Stop clearing native vegetation• Replant using deep-rooted species, e.g. eucalypts• By 2050, approx 17 million ha in Australia are

predicted to be affected by dryland salinity – south-west WA is worst affected (> 4 million ha)– SA, Victoria and NSW are also affected– ground water levels are still rising in Murray–Darling

basin

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Polluting the atmosphereEven the Arctic icecap has black soot; global effectsof pollution are the ozone ‘hole’ and global warming

• Ozone (O3) layer is 13–20 km above earth• Shields earth from destructive UV radiation• Constantly created by action of sun on oxygen• Depleted by natural and man-made constituents in

the air, e.g. chlorofluorocarbons (CFCs)• When rate of destruction of ozone > rate of

formation, ‘hole’ forms

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Effects of UV radiation• Depend on the wavelength: A, B and C• UV-C and -B are the most harmful, but nearly all

filtered out by ozone layer• For each 1% decrease in ozone there is a

2% increase in UVB at earth’s surface• UV radiation reduces uptake of CO2 by

phytoplankton• UV-A causes sunburn and skin cancers• Montreal Protocol target is to get ozone levels

back to normal by mid-21st century

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Greenhouse effect• Natural warming of earth • Greenhouse gases CO2, N2O, CH4 and water

vapour absorb heat that would be lost to space, raising temp of earth by 30°C

• Post-industrialisation levels of these gases are rapidly increasing, mostly due to fossil-fuel burning

45-28Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Fig. 45.14: Mechanism of the greenhouse effect

45-29Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Global warming• Intergovernmental Panel on Climate Change

(IPCC) was established in 1988, and in 2001 concluded that warming over the last 50 years was due to human activities.

• Climate models project global surface temperature will rise 1.4–5.8°C, and sea levels rise 9–88 cm, by 2100

• Rainfall patterns will change in space and time• Changes in ocean currents may occur

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Coral bleaching• Coral polyps stressed by warm water expel their

symbiotic algae, and die • Bleaching has been reported in reef corals from all

tropical oceans • Coral distribution patterns may change as a result

of global warming

Rising sea levels• Sea levels are expected to rise due to heating and

expansion of seawater• Many low-lying cities are at risk, and some whole

nations, e.g. Nauru

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Reduction of emissions• 30% of Australian CO2 emissions are due to fossil

fuel use, agriculture, land clearing and forestry

Discussion question 3:What are the best ways to reduce CO2 emissions?

45-33Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Some ideas for reducing CO2 emissions• More efficient lighting, cars, industry• Change to cleaner fossil fuels (e.g. natural gas)• Adopt non-carbon fuels (solar thermal,

photovoltaic, wind, geothermal, tidal)

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Towards sustainability• Convention on International Trade in Endangered

Species (CITES): bans trade in listed species• Environmental Protection and Biodiversity

Conservation Act 1999 (Cwlth) conserves ecosystems and their components

• Victorian Flora and Fauna Guarantee Act 1987• Protection of whole habitats is achieved through

Nature Reserves and National Parks• Permits are now required for some activities, e.g.

clearing native vegetation

Fig. 45.17: Exotic wildlife trade

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Managing natural communities for conservation• Prevention of degradation is needed across a

variety of land tenures, not just reserves• Market-based approaches (i.e. farmers paid to

manage natural areas) are gaining popularity• Traditional use of fire to produce diversity of

habitat patches is being recognised

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Restoration ecology: resetting the clock• Whole landscapes may need restoring, e.g. wheat

belt in WA• Need data on habitats, species, patterns• Incorporate a suitable disturbance regime to

produce mosaic of habitat patches high diversity

• Replanting methods may include direct seeding of local species

• Soil fungi and bacteria should be incorporated from unmodified systems

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Ecologically sustainable development (ESD)• A sustainable society ‘all human activity takes

place within the limitations set by the environment’• In 1992 the Australian government adopted a

National Strategy for ESD (NSESD) to safeguard intergenerational equity, with seven main objectives

A global society developed along ESD principles is the only solution

Summary• The impact of humans on the Australian

environment has greatly accelerated over the last 200 years

• More than half of agricultural land in Australia is affected by land degradation

• Human impacts have effects on a global scale• Ecologically sustainable development is required if

the resources on which life depends are to be maintained

45-40Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University