CHANGES IN ECOSYSTEMS

Chapter 16

Cabbage Tree Island

1. Read Pages 501-503 together and discuss.

2. Copy Figure 16.2 under heading CABBAGE TREE ISLAND.

3. Define the terms endangered, vulnerable and extinct.

4. Quick Check questions page 503 Qs 1-3.

Changes in ecosystems may be due to:

Regular and predictable events (tides and seasons)

Sporadic events (floods) One-off events (oil spill) Primary changes in ecosystems

may be due to natural agents or to human intervention.

Changes in ecosystems can be:

Short termFireCyclic changes: day/night, seasons, tides

Long termContinental driftClimate change ○ Deserts, ice ages, refuges○ Causes: ocean currents, atmospheric

change Irregular change

El Nino, tsunami, earthquake

Human Impacts on Ecosystems Changes due to human intervention

are usually associated with economic gain and meeting the needs of the growing population.

They can include:Fire preventionLand clearingFlood control measuresIntroduction of exotic species, deliberately

or accidentally.

Human Impacts on ecosystems

1. Introduction of exotic species2. Over-harvesting: lack of

sustainability3. Waterways: damming,

recreational and waste pollution

HUMAN IMPACT

Exotic species Overharvesting Waterways Choose one species to

study

Biological control

Biotechnological control

Dams Eutrophication

In each box:

1. Definition2. Example of where it is occurring.3. Important point(s) that need to be

made. 4. Solution that we have reached.

Human Impacts on Ecosystems

Introduction of exotic species

Introduction of Exotic Species Not all exotic species become major

ecological pests. E.g. cereal and fruit crops.

However, when some exotics are introduced to local ecosystems, displacement and loss of native species usually occurs.

Exotics in Australia

Key term: Biological controlIs the use of a natural predator or parasite to limit the population of a pest species.

For example, prickly pear is successfully controlled by the moth Cactoblastis cxactorum. The cane toad was introduced to control cane beetles but became a pest species itself.

Impacts of invasive exotic species How do natives become lost or

displaced?When introduced species are

successful predators of native species (feral cats and foxes).

New diseases are brought in which natives are not resistant to (fungal diseases).

Exotics use the same limited resources as natives.

Exotics change the environment of an ecosystem.

Rabbits

Rabbits

The introduction of rabbits began with several dozen brought to a property in Victoria in 1859 for hunting. They quickly spread to New South Wales, Queensland and the west by the 1900’s.

They have a high reproductive rate; one female can produce 30 kittens a year.

In their natural environment, their numbers are controlled by food shortages in winter and the presence of predators, parasites and competitors.

Rabbits

Rabbits compete more efficiently than native species for food and have displaced many native species.

Many attempts have been made to control numbers:Myxoma virus (killed many rabbits however

rabbits become resistant to the virus).Calicivirus (causes hemorrhagic disease

and numbers have dramatically reduced).

Cane Toads

Cane Toads

Originally from South and Central America, 100 toads were brought to Queensland to control greyback beetles.

Cane toads have now spread and are estimated to be increasing by about 35 km per year.

They have few natural predators in Australia.

They secrete venom from glands and cause the death of many native animals.

Carp

Carp

Carp were brought to Australia and escaped from the Victorian fish farms into the Murray-Darling River system.

They feed at the bottom of water. They take up mouthfuls of mud, spit it out so that the material becomes suspended in the water, then swallow particles of organic matter or small organisms.

Carp

Because of this behaviour, they destroy water plants and change aquatic habitats. Sunlight cannot penetrate through, thus some plants are lost from the aquatic environment.

Carp excretions increase the levels of dissolved nutrients leading to algal blooms (and eutrophication).

Human Impacts on Ecosystems

Over-harvesting

Over-harvesting

Over-harvesting is an unsustainable use of biological resource.

Harvesting of any species must be carried out at sustainable levels that allow the species to recover its numbers naturally between harvesting.

Important biological knowledge to prevent over-exploitation includes:where, when and at what age a species

breedsits rate of growththe time required for sexual maturity.

Salinity

Salinity

Salinity refers to the salt content of water or soil at a level where the salt content damages soil and degrades water quality.

Salinity causes economic loss through loss of productive agricultural land and damage to roads and buildings and puts the supply of acceptable drinking water at risk.

Dry land Salinity

Soils over much of Australia have naturally high salt levels and this salt is stored below the soil surface.

Because of Australia’s low rainfall, high evaporation rates and flat terrain, this salt has not been washed away but has been absorbed into the soil.

Dry land Salinity

The natural vegetation in Australia has deep rooted trees. These take up large amounts of water from the soil and this water is lost by transpiration.

Under these conditions, the water table has remained at a constant depth below the surface.

Since European settlement, native grasslands have been cleared for urban development and the deep-rooted trees have been replaced with shallow-rooted crop.

Dry land Salinity

As land is cleared, more water enters the soil and reaches the ground water, causing the watertable to rise. Dissolved salts are brought up to the surface and it causes many plants to die.

Dry land Salinity

Irrigation Salinity

Irrigation Salinity

This occurs when excess irrigation seeps into the soil, causing the watertable to rise.

Eventually the watertable reaches the root systems of plants and those they are not suited to salt are killed.

When the irrigation stops, the soil dries out and salt is left at the surface.

The surface soil gets more and more salty the more often the process is repeated.

Human Impact on Ecosystems

Waterways: damming and pollution

The damming of rivers and diversion of water from rivers The health of river systems depend on

natural water flow to maintain their biodiversity, if not the following may occur:The release of cold water from the bottom of

dams can lower water temps to a level where fish can no longer breed

Wetlands that depend on periodic flooding may begin to dry out and populations of native fish and water birds may decline

Movements of native migrating of river fish stop or slow with many species becoming extinct.

Nutrient overload

Nutrient Overload

The accumulation of dissolved mineral nutrients in a body of water is termed eutrophication.

Cyanobacteria can multiply rapidly and form a bloom that covers much of the water surface. As it spreads it reduces the light intensity in the water depths so that submerged plants die and the amount of organic matter in the water increases.

Decomposers feed on the organic matter and multiply and use up the dissolved oxygen.

Human Impacts on Ecosystems

Genetic Modification

Genetic Modification (GM)

Genetic modification is the use of modern biotechnology techniques to change the genes of an organism, such as a plant or animal.

GM is used because it can change the genes of an organism in ways not possible through traditional breeding techniques providing opportunities for new plant varieties and animal breeds.

Genetic Modification (GM)An example.. Products from GM soybean, canola, corn,

potato, sugar beet and cotton crops have been approved for use in food in Australia. These crops have been modified to be insect resistant, herbicide tolerant or both.

What are the advantages and disadvantages of these crops?

Advantages and Disadvantages of GM

Advantages GM crops that have been modified for

insect resistance or herbicide tolerance allow farmers to use less herbicide and pesticide on their farms.

These crops can grow without the impact of insects/herbicides meaning a stronger food economy for Australia.

Advantages and Disadvantages of GM

Disadvantages If too much herbicide is used it can

contaminate the soil, therefore impacting on other crops surrounding the GM products.

Weeds etc can become tolerant to the use of herbicides therefore the herbicide will not be effective any longer.

NATURAL CHANGE

Fire

Fire

Natural change agents: Fire

Species living in fire-prone ecosystems must be capable of surviving the effects of fires, either as individuals or through their offspring.

Mobile organisms escape by flying or running away.

Slower animals escape by retreating into burrows.

Soil is a good insulator.

Natural change agents: Fire

Plants cannot escape but have survival strategies:Vegetative reproducerObligate seeder

Vegetative Reproducer

Vegetative Reproducer

Plants using this method regrow through means of buds found in the bark or in underground stems; e.g. Eucalyptus.

Obligate Seeders

Obligate Seeders

They don’t usually survive bushfires, however their seeds germinate in the mineral-rich soil that is produced by fire.

Fire Frequency

After bushfires, the native plant population can either be replaced (OS) or can regenerate (VR).

The interval between fires can affect the diversity of a plant community.

If fire occurs frequently, some species may be lost.

If it remains absent for a while, certain animals and plants will die as they rely on the new shrubs as a resource.

As a result, controlled burns often take place to ensure the biodiversity remains.

Succession

Succession

Succession is the natural replacement over time of one community by another community with different dominant species.

Primary succession occurs in areas that have not been previously colonised. E.g. by lichen on a bare rock.

Secondary succession occurs in areas that were once colonised but have been disturbed. E.g. by clearing for farmland, then subsequently abandoned and recolonised.

A climax community is a stable community of consistent composition.

Stuff to do

NATURE OF BIOLOGY:1. Read page 528 – 5342. Complete quick check

questions page 533 & 534