Module 4: Ecosystem Dynamics

In this article, we will break down the various topics you will study in Year 11 Module 4: Ecosystem Dynamics to help you get ahead and ace Biology.

Ecosystem Dynamics

The biodiversity of the Earth has constantly changed since life first appeared on the planet.

In order to understand how our current ecosystems function and how they are changing, it is helpful to examine evidence of changes that occurred in these systems in the past.

Scientific knowledge gained from the fossil record and geological evidence enables scientists to study the complex relationships between biotic and abiotic factors.

You will look at ecosystem dynamics, past ecosystems and the models that can be used to predict future ecosystems so that human impact on biodiversity can be minimised.

The topics covered include:

• Topic 1: Population Dynamics
• Topic 2: Past Ecosystems
• Topic 3: Future Ecosystems

Topic 1: Population Dynamics

This module will expand on relationships between biotic and abiotic factors in an ecosystem.

Abiotic factors

Abiotic factors (shown below) impact the distribution, abundance, morphology and ultimately the survival of organisms in an ecosystem.

For example, water and light availability affects the distribution of plants.

Biotic factors

Complex biotic relationships exist between organisms in an ecosystem which impacts on the distribution and abundance of species.

During this module, you will look at specific examples of these relationships.

For example, predation affects the population of both prey and the predator ultimately.

The lynx population increases when the hare population is abundant as there is more food to sustain the lynx population.

This increase in predators decreases the hare population, to the point that Lynx run out of food and decline.

This eventually results in an increase in lynx and the cycle starts again.

During your class, you will cover the impact of such relationships in more detail.

Sampling techniques

The distribution and abundance of a population of organisms can be measured using sampling techniques including:

• Transect mapping, which involves surveying a line through a given area and recording which organisms are present. It is used to determine the distribution of organisms.
• Quadrat sampling is where the abundance of organisms is recorded within a set square area. This data can be used to calculate the total population and population density. You will practice some of these calculations during your class.
• Capture-mark-recapture is used to measure abundance of mobile organisms.

Extinction

Natural disasters or human activities can disrupt population dynamics and result in the extinction of species.

A recent case of extinction is the Thylacine (Tasmanian tiger) which was a carnivorous marsupial closely related to the Tasmanian devil.

The hunting of the Thylacine by farmers caused a major decline and ultimately the extinction of the species.

Video footage of this animal is rare and a short clip of the last animal in captivity was recently rediscovered.

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Topic 2: Past Ecosystems

Since ecosystems change over time, paleontological and geological evidence can be used to provide insight into past ecosystems.

This includes Aboriginal rock paintings, rock structure and formation, and ice core drilling.

Aboriginal rock paintings

Palaeontologists can use Aboriginal rock paintings as recordings of the species present in different regions tens of thousands of years ago.

The discovery of two emu-like paintings in Arnhem Land provided evidence that humans co-existed with the megafauna bird Genyornis which became extinct over 40 000 years ago.

Continental drift

Evidence of continental drift helps us understand how environments on different continents would have changed in the past.

Magma rising from the ocean floor pushes through the crust and eventually cools down forming new rocks. These mid-ocean ridges or spreading zones push continental plates apart.

The existence of mid-ocean ridges provides evidence that continents were once joined together.

The distribution of fossils also supports the idea of continental drift, as fossils of some organisms are found on continents that now are very far apart and have different habitats.

For example, fossils of the now-extinct Glossopteris plant are found across all of the continents shown below.

Ice cores

Ice cores taken from polar ice caps and glaciers can reveal information about past climates.

As snow falls, air is trapped under the layers of snow.

As the snow becomes ice, the gases, dust particles, ash and pollen in the air become trapped.

Scientists can extract this material from cores of ice which provide a chronological record of the Earth’s past climate.

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Gas analysis

Gas analysis is used to extract information from tiny bubbles containing atmospheric gas that becomes trapped in the ice cores.

The ice can be crushed to release the trapped gasses, which are then separated out by a gas chromatograph.

Isotopes can be identified by Isotope Ratio Mass Spectrometry.

Radiometric dating

Radiometric dating can be used to determine the absolute age of a material such as rocks or fossils.

An example of a radioisotope is Carbon-14 which is taken up by organisms while they are alive and upon their death begins to decay to become Carbon-12.

The ratio of Carbon-14 to Carbon-12 continues to change consistently over time, so this ratio can be used to estimate the age of the sample.

Evolution of Australian organisms

During Module 4 you will also look at how fossil animals, plants and pollen reveal how Australian organisms evolved after Australia became an island continent.

For example, Dickson’s Thylacine was a small carnivorous marsupial. It is the common ancestor of modern carnivorous marsupials such as the Tiger quoll, Tasmanian devil and Tasmanian tiger.

The modern-day prevalence of sclerophyll plants in Australia provides evidence that as Australia drifted North from Antarctica, its climate became warmer and drier.

While fossils indicate there were widespread rainforests across Australia in the past, the continent is now populated with sclerophyll plants such as Eucalyptus that have small leaves and a thick waxy cuticle as an adaptation for dry climates.

Topic 3: Future Ecosystems

Humans have been responsible for a variety of biotic and abiotic changes to ecosystems. This includes:

• Modified fire regimes used by Aboriginal Australians for hunting leading to a greater prevalence of fire-resistant sclerophyll plants.
• Farming practices that move species around or clear habitat for monoculture.
• Introduction of new species that outcompete native species leading to their extinction.
• Land clearing and deforestation leading to destruction of habitats.
• Inappropriate waste disposal leading to entrapment or ingestion of the waste by aquatic organisms.
• Air pollution such as carbon dioxide or methane emissions which contribute to climate change.

Modelling

The study of past ecosystems and understanding how they are changing now will enable scientists to predict future impacts on biodiversity.

Scientists can use modelling to depict processes and systems of future impact.

A simple example is a food web that shows how change to one species leads to flow-on effects for other species as a result.

Other examples include the use of computer models or manipulative experiments to observe how organisms and ecosystems respond to predicted future changes.

Restoration plans

In this module, you will examine some practices used to restore land that is degraded due to mining or agricultural practices.

Since mining is a highly destructive process, government bodies work with mining companies to implement a restoration plan once the mine is decommissioned. This includes:

• Planting local trees to restore vegetation.
• Planting local trees to restore vegetation.
• Creating habitats for plants and animals.
• Monitoring and controlling unwanted plants and feral animals.
• Working on conservation initiatives in partnership with local communities.

An example of such a restoration practice includes the Westside Mine in Lake Macquarie, New South Wales that was successfully restored post-mining in 2012.

The land now has many established native plants and animals and even some threatened species such as the squirrel glider.