6.6 Ecosystems can be disrupted

6.6

Ecosystems can be disrupted

Learning intentions

By the end of this topic, you will be able to: • describe how natural disasters can impact ecosystems • describe how human activity can impact ecosystems.

carrying capacity the maximum number of organisms in a population that can be sustained by an ecosystem

natural disasters natural events such as oods, volcanic eruptions, tsunamis and earthquakes that can cause severe damage and fatalities

ood the over ow of a large body of water

Key ideas

• Humans compete with other organisms for resources. • New species can have environmental, social and economic impacts. • Understanding the impacts allow ecosystems to be maintained.

Limited resources

Animals use resources such as food and water and, in turn, become food for other organisms. The number of resources in an ecosystem is always limited. As the size of a population reaches its maximum carrying capacity (ability of the environment to support it), some of its resources, such as food, space and shelter, will become more limited. This means some organisms will either die or need to emigrate (leave). Once the population decreases, there will be enough resources for those remaining. When this occurs, the population will stabilise (reach its maximum size). The population will nd a new balance, or equilibrium.

Natural events such as the change in seasons, or natural disasters can disrupt the balance between the biotic (living) and abiotic Natural disasters (non-living) factors in an ecosystem. Australia has a widely uctuating environment. Seasonal changes Years of drought can be followed by ooding rains. When extreme natural change affects When the weather becomes colder, many humans, we call these changes natural disasters. animals migrate to warmer areas (Figure 1). As a result, their populations decrease in one environment and increase in another. During the breeding season, usually spring, the numbers of animals will increase. Flowering plants are pollinated and form seeds that spread throughout the environment, and later germinate into seedlings. As the population increases, so does competition for resources. As a result of this competition, some members of the population survive and others die, allowing the population to maintain its balance.

Figure 1 Short-tailed shearwaters leave their burrows on Montague Island on the southern coast of New South Wales and fly to feeding grounds in the area of the Bering Sea (between Russia and Alaska) during the northern hemisphere summer. They return to breed in late September. DRAFT Impacts of floods and droughts Floods are an over ow of water onto dry land, which has an immediate effect on the growth of plants and the germination of seeds. Marine ecosystems do not bene t from oods on land. When the water runs off the land, it brings sediment, pesticides and fertilisers into the marine ecosystem, causing some algal species to dominate the environment. Algal blooms are often deadly to other animals living in the ocean environment.

Figure 2 Flooding in Queensland in 2022

Human impacts

In an ecosystem with limited resources, humans must compete with other organisms for food and shelter. The human population has grown quickly over the last 200 years. This means we have needed to change the environment so that we can grow food, build homes and nd resources so that more and more people can live and work. Many of these changes can affect the local environment (environmental impacts), how people live (social impacts) and how we can work or earn money (economic impacts). Understanding the

Floods can be a hazard for some animal causes of these impacts will allow us to prevent further damage in the future. Deforestation Our landscape was once covered by patches of different types of landscapes, such as swamp, grassland, forest and heath. This variety of vegetation supported many species of animals that moved, reproduced and spread throughout their territories and beyond. life. Small mammals often escape to higher ground. Snakes are ushed out of their cover, as witnessed in the 2022 Queensland oods (Figure 2), and became a potential danger to humans. Aquatic animals bene t enormously from oods. Fish can breed in waters such as a lake. The increase in sh, insects and waterweeds are a food source for water birds. The extra food encourages the water birds to breed in great numbers, temporarily changing the balance in populations. Droughts pose an even greater challenge than oods (Figure 3). During a drought, animals migrate to nd water. Some animal populations ‘hang on’ during drought, but many populations will decrease until the land looks almost bare. Wind can blow the dry topsoil away from the drought affected area, removing many of the nutrients in the ecosystem. DRAFT

Figure 3 Drought poses a great threat to life. Figure 4 Only one specimen of the Hastings River mouse has ever been found. It is considered extinct due to changes brought about by European settlement.

Today, over 44 per cent of Australia’s original bushland has been cleared since European settlement. Much of that land is used for housing, to grow food or to manufacture products. The food webs that existed in these areas have been changed as new predators (dogs and cats) move in and the number of producers decreases.

drought a period in which an area experiences water shortage

urban sprawl the spreading and expansion of cities and houses into undeveloped land

Land degradation

Human activities have led to a degradation of the physical environment. Soil erosion is a major problem caused by the clearing of land for agriculture. In ecosystems with many trees, the soil is stabilised by a dense mat of plant roots. Its surface is covered by a layer of leaf litter, which protects the soil surface from erosion by wind and water. Water from rainfall is quickly absorbed through the top layers of soil.

Once land is cleared of trees for agriculture, there is little to protect the soil from the action of wind and water. Grazing by animals with hard hooves, such as cattle, compacts the soil. This slows the absorption of water into the soil and increases the amount of water runoff. This, in turn, erodes the soil. Wind also contributes to the removal of the nutrient-rich topsoil (Figure 5).

Urban sprawl

More than half of the world’s population lives in cities. The population in the world’s urban areas has grown by more than one billion people since the 1970s. Much of this growth has contributed to a phenomenon or process known as urban sprawl . Figure 5 In 1983, large amounts of topsoil were carried across Melbourne and into the Southern Ocean as a result of wind erosion.

Figure 6 Urban sprawl around many of Australia’s capital cities is on the rise. Urban sprawl means the spread of urban areas into rural areas, such as farmland, forests and coastal lands that lie on the outer edges of cities. Urban sprawl increases the distance between the city centre and its outer edge (Figure 6). Urban sprawl is common in rapidly developing cities or those with large populations. Some of Australia’s cities rate among the world’s worst in terms of their sprawling nature, particularly because everyone wants their own garden and local parks. DRAFT

A changing climate

Human activities are contributing to more signi cant changes to weather and climate. These changes can have a huge impact on ecosystems. In alpine areas, changing rainfall and temperature patterns alter the amount of suitable wet alpine habitat. This has made it dif cult for animals that need the cool environments to survive.

Retrieve 1 De ne the term ‘carrying capacity’. Comprehend 2 Describe two things you can do to reduce your personal environmental impact (your ecological footprint). 3 Describe a possible economic impact of a drought. 4 Describe a possible social impact that would occur if the environment surrounding a city was protected so that no new houses could be built 5 Each winter the cold weather causes the mountain pygmy possum to hibernate (deep sleep). This allows the possum to save energy when the food supplies are low during the winter. Describe how a warming climate could affect the mountain pygmy possum’s ability to hibernate and survive each winter.

6.6 Check your learning DRAFT Figure 8 Mountain pygmy possum Apply 6 Create a two-column table with the headings ‘Problems’ and ‘Solutions’. In the ‘Problems’ column, list the types of things that people do that affect wildlife, such as building homes and roads, and cutting down trees. In the ‘Solutions’ column, propose solutions to each problem. Quiz me Complete the Quiz me to check how well you’ve mastered the learning intentions and to be assigned a worksheet at your level. Figure 7 Alpine areas are reducing as the climate changes.