Ecosystems (HSC SSCE Biology): Revision Notes

Ecosystems

Introduction to Australian ecosystems

Australia contains a remarkable diversity of ecosystems, each shaped by different environmental conditions. These varied environments support different combinations of plant and animal species.

Looking at New South Wales alone, we can see how environmental factors create distinct ecosystems:

The Blue Mountains region features sandstone tablelands carved by deep canyons and gorges. The biodiverse forests contain over 90 plant species and provide habitat for large numbers of animals, including 186 vertebrate species, 105 bird species, 14 bat species, 28 reptile species, and 10 frog species.

The Hunter Valley, north-east of the Blue Mountains, has soils with high clay content. This region supports four dominant eucalypt species and woodlands containing native shrubs, grasses, daisies, lilies and orchids. Animals such as the brush-tail rock wallaby, spotted-tail quoll and speckled warbler live here.

Coastal areas near Sydney have increasingly sandy soil with drier and windier conditions. This environment favours plants such as banksia scrub, acacia, spinifex, Leptospermum and Xanthorrhoea (grass tree) species.

What is an ecosystem?

An ecosystem is a system that includes all the living organisms (biotic factors) in a community, along with all the non-living features (abiotic factors) with which they interact. Let's break down these key terms:

• Biotic factors: All the living components in an ecosystem (plants, animals, fungi, bacteria)
• Abiotic factors: All the non-living physical and chemical components (temperature, water, light, soil, minerals)
• Community: A group of different populations living together in an area
• Population: All individuals of the same species living in a particular area
• Habitat: The specific place where an organism lives
• Environment: Made up of all the non-living (abiotic) factors in an ecosystem

Australia has many diverse ecosystems. The distribution of these different ecosystems across the continent results from variation in both biotic and abiotic factors in each particular area.

The Australian arid zone

The arid zone (shown in light tan on the map) is distinguished by several key features:

• Ancient and infertile soils with low levels of phosphorus and nitrogen
• Unpredictable rainfall patterns
• Plants adapted to harsh conditions, such as Sturt desert pea, saltbush and spinifex
• Fire as an important ecological process, with patch burning creating spaces for ephemeral plants (plants with short life cycles)
• Invertebrate animals dominating, including grasshoppers, crickets, beetles and termites
• Loss of native medium-sized mammals (desert bandicoot, lesser bilby, long-tailed hopping mouse) to extinction in the last 200 years, partly due to competition from introduced species like rabbits and camels

Types of ecosystems

Ecosystems can be broadly classified into two main categories based on whether they are land-based or water-based.

Terrestrial ecosystems

Terrestrial ecosystems are land-based environments. The abiotic factors within terrestrial ecosystems significantly influence which organisms can survive there. These factors include temperature, rainfall, soil type, and light availability. Examples include deserts, grasslands, woodlands, and rainforests.

Aquatic ecosystems

Aquatic ecosystems are water-based environments. Key abiotic factors affecting aquatic ecosystems include:

• Salt concentration (salinity)
• Light availability
• Water pressure
• Temperature
• Dissolved oxygen levels
• pH

Examples of aquatic ecosystems found in Australia include:

• Wetlands and mangrove swamps
• Rock platforms
• Estuaries, rivers and lakes
• Oceans and coral reefs

Australian terrestrial ecosystems

Australia has six main types of terrestrial ecosystems, distinguished primarily by their rainfall levels. These range from the driest deserts to the wettest tropical rainforests. Understanding the characteristics of each ecosystem type helps us understand which organisms can survive in each environment.

Terrestrial ecosystem	Annual rainfall	Temperature	Canopy cover	Typical organisms
Desert	Less than 250 mm	High during day (approx. 40°C), low at night (approx. 0°C)	Minimal	Sparse grasses, saltbushes, spinifex hopping mouse, insects, lizards, snakes
Grassland	250-750 mm	High or mild	Low	Grasses (e.g. spinifex), kangaroos, rabbits, snakes
Shrubland	200-400 mm	High	Low to moderate	Mallee trees, mulga, kangaroos, rabbits, snakes
Woodland	400-750 mm	Mild, sometimes high	10-30%	Grasses, shrubs, eucalypt trees, mice, birds, insects, spiders, wallabies
Temperate forest	More than 750 mm	Mild	30-70%	Various types of eucalypt trees
Tropical rainforest	More than 1500 mm	High or mild, humid air	Dense 70-100% with distinct layers (canopy, understorey, forest floor)	Bird's nest ferns, palms, lianas, bracken ferns, diverse leaf litter organisms

Soil characteristics: Often sandy soil in deserts, sometimes rocky. Soil type varies across other ecosystems and influences which plants can grow.

Canopy cover: Refers to the percentage of ground covered by the overhead plant canopy. This increases from minimal coverage in deserts to almost complete coverage (70-100%) in tropical rainforests. Dense canopy creates distinct vertical layers or strata in rainforests.

Biotic and abiotic interactions

Biotic and abiotic factors differ significantly between different ecosystems. This variation is crucial for understanding biodiversity and species distribution.

How abiotic factors influence ecosystems:

Abiotic factors create selection pressures that favour certain types of organisms over others. This means the underlying abiotic factors of an ecosystem must be studied to understand which organisms can survive there.

An organism's ecosystem provides it with:

• Nutrients
• Water
• Shelter
• Opportunities to mate

However, other living things compete for these same resources. This competition means some organisms successfully survive and reproduce, while others cannot compete effectively. Successful species develop a range of favourable characteristics (adaptations) that are uniquely suited to the specific environmental factors in their habitat. We say the population is adapted to this habitat.

Remember!