Ecosystems

Food Chains and Webs

Biotic factors:

  • Living

  • Examples:

    • plants

    • animals

    • fungi

    • bacteria

Abiotic factors:

  • Non-living

  • Examples:

    • water

    • sunlight

    • soil

    • air

    • temperature

Food chain

  • only one animal for each level

  • Arrows indicate the direction of energy flow (i.e. what eats the organism)

Flower (producer) → caterpillar (consumer) → Frog (consumer) →Snake (consumer) → Owl (consumer)

Food webs

  • much more complicated

  • shows a number of different animals on each level

  • Arrows still show direction of energy flow

Decomposers

They consume dead plants and animals and decompose them. Primary decomposers are fungi and bacteria.

Without decomposers, all the raw materials of life would remain wastes and the remaining bodies of dead organisms. That wouldn’t be good for our environment, because those remains would rot and produce odours.

Scavengers

Scavengers are carnivores who feed on the bodies of dead organisms. Once a scavenger is done, the decomposers take over and finish the job by breaking down the wastes of the dead organisms and returning it to the ecosystem.

Changes in the food chain

Nearly every species of animal is dependent on a number of other species for survival — this is called interdependence.

Current human activity is damaging the natural habitats of many animals. This will not only affect the animals in the area, but it could have far-reaching effects on the rest of the species in the food web. If the population of a species declines dramatically, it might affect the other species that rely on it.

Populations are interdependent. If the population of one organism changes, it will affect all the populations connected to it. Food chains/webs show interdependence. You can use it to predict how a change in one population will affect other organisms.

Ecosystems

When we talk about an ecosystem, we are referring to the living organisms that inhabit a specific region, how they interact with each other, and the effects on them of the non-living environment around them. Ecology is the study of an ecosystem, the interactions and organisms within it, and the interactions of organisms with the non-living organisms.

The term ‘living organisms’ includes all of the plants and animals that live in or visit the region. Together, they make up the community of the ecosystem. Each organism is also present in certain numbers, or in other words there is a population of organisms. Scientists study these populations to see what factors increase or decrease the population.

The non-living (abiotic) environment includes physical factors such as rainfall, temperature, wind, sunlight, soil, rocks and water.

Biospheres

Just as you have an address, so too can we give an address to the organisms that live in a specific area.

The biosphere is the broadest category in the address. It refers to that part of the Earth (including its atmosphere) in which living organisms can be found. The biosphere is then divided into a second level of biogeographical regions. For example, Australia and North America are biogeographical regions. Each region has its own unique plant and animal life. These interact with each other and depend on the unique physical conditions that are present there.

Biomes

The biome is the third level of an organism’s address and refers to areas that have similar climatic conditions; that is, similar soil types, rainfall, temperature and so on. Grasslands, deserts, the tropics, subtropics and arctic are all examples of different biomes. Scientists have observed that organisms living in the same type of biome have similar features, regardless of whether they are in the same biogeographical region. The Simpson desert, for example, is a desert biome in the Australian biogeographical region. The plants and animals found there show many characteristics similar to those found in other desert biomes around the world.

Habitats

Within each biome are different habitats, the fourth level of an organism’s address. This term defines an even more specific area. In a desert biome, the habitats could be the individual sand dunes, the clay pans between them, or a tussock of grass or scaggly tree growing on them. A tropical biome will have vastly different habitats from a desert biome, such as the moist, protected areas at ground level, or the very top of a leaf canopy.

Microhabitats

In every habitat there are areas where conditions vary from the rest of the habitat. In a tropical rainforest, same organisms may live between the roots of trees, others under the bark and others in the dirt itself. the microhabitat is the last and most specific part of an organism’s address. The microhabitat may also be known as the niche.

The address of a kowari can be written as:

  • Australia (biosphere)

  • Central Australia (biogeographical region)

  • Stony deserta (biome)

The kowari’s community includes:

  • the plants that the kowari uses for shelter and food

  • the plants that provide shelter to, or are eaten by animals that are then eaten by the kowari

  • the animals that the kowari eats

  • the other kowaris in the area

The non-living environment includes the soil type of the dunes, the rainfall and the temperature of the desert. Everything in the ecosystem is connected in some way.

Australia’s ecosystem

Australia is the most arid inhabited continent on Earth. It has unique ecosystems with unique communities living in them. Part of this uniqueness comes from these ecosystems being exposed to various human-made and natural events. The three main events affecting Australian ecosystems are:

  • flood

  • bushfires

  • drought

Although these events can devastate much of an ecosystem, they can also have some positive outcomes. Floods can deposit fertile new soil for plants to grow in and fire can trigger the germination of new plants. The effects of these events may be felt for many years, resulting in changes within the ecosystem.

Flood

Flooding can cover extremely large areas of Australia, affecting many varied ecosystems. After the initial devastation, floods can have positive ecological effects, such as:

  • replenishment of ground and soil water

  • increased breeding of water-dependent species such as fish and pelicans, and therefore an increase in numbers.

  • regeneration of long-living and slow reproducing trees in arid biomes

Bushfire

For millions of years, lightning strikes have sparked bushfires in Australia. Many native plants and animals have developed specialised ways to survive fires and respond quickly to its impact, such as:

  • Some native plant species need fire to release the seeds they need to regenerate. Others will die and never regenerate.

  • Highly mobile animals, such as birds, kangaroos and wallabies may be able to move out of the way of an approaching fire to safer regions. Slower animals may survive the fire by sheltering in burrows or logs. Reptiles and amphibians also take refuge underground.

  • Bushfire releases nutrients into the soil that allow plants to recover and seeds to grow quickly. Fire removes vegetation and exposes the soil to wind and water, making it very susceptible to erosion.

Drought

Although floods and bushfire bring rapid changes to ecosystems, drought creeps up over a number of years when rainfall is less than normal. The effects, however, can be devastating, particularly to humans and their farms. Droughts can have an impact on huge areas of land, effecting many more ecosystems than fire or flood. The ecosystems most prone to drought often have a low capacity to respond, and widespread death and famine is the result for the organisms in the ecosystem. Drought can also degrade the land and affect the way land is used in the future.

Definitions of drought vary widely. In the UK, 14 days without rain us considered a drought. In Australia, a drought is ‘official’ when rainfall over a year is in the lowest 10% ever recorded.

Physical Attributes of an Ecosystem

Adaptations

Organisms are affected by their environment in many ways. Predators might eat them and their young, while non-living factors such as extreme daytime temperatures might mean that they can only be active at night.

An organism can only live in an environment that it is suited for: it must have behavioural and physical adaptations that allow it to survive. These characteristics are called adaptations. The colour of the fur and the presence and colour of spines in an echidna are examples of physical adaptations.

When an echidna is being attacked, it will roll into a tight ball. Only the spines are exposed, making the echidna very unappetising and painful to the attacker. This is an example of a behavioural adaptation. Behavioural adaptations can be instinctive or learnt.

Effects of the non-living environment

Non-living or abiotic factors influence when an organism can live. They include:

  • Temperature: Biological processes such as digestion, respiration, excretion and reproduction take place at an optimum temperature range. When living things get too hot or too cold, they do not function properly.

  • Humidity: This is the amount of water vapour in the air. The amount of water lost from an organism into the air depends on humidity. If the air is very humid (as in tropical biomes), plants and animals will lose very little water. In contrast, desert biomes have very little. humidity. Plants and animals that live in this area have special features to help them retain as much water as possible.

  • Light energy: Light provides green plants with the energy they need to carry out photosynthesis. Light is readily available on land. In a water environment, however, most of the light is reflected at the surface 00 with only a small percentage (the green and blue colours of the spectrum) penetrating to any depth. This is called the photic zone and is where green plants such as seaweeds and kelp will grow. Plants are not found on the deep, dark ocean floor.

  • Acidity of the soil and water: Plants have a preferred soil acidity in which they like to live, as do organisms that live in the water. We measure the acidity using the pH scaled

  • Salinity of the water surrounding, or available to the organism: Salinity is a measure of the saltiness of the water. Freshwater and marine organisms experience very different salinity and show marked differences in the ways their bodies function.

  • Mineral salts and trace elements available: Where a plant lives is determined by the nutrients that are available in the soil.

  • Wave and wave currents: The intertidal area is that area that lies between high and low tides. At low tide, it is exposed to the air, while at high tide it is completely submerged. Those organisms that live in this region must be able to live in both conditions. They may also need to develop ways to stop being washed away. Likewise, organisms that live i fast-flowing streams require great strength as they battle against the force of the water.

  • Shelter: Shelter gives protection from factors such as predators ad the weather and can be found in many places in an ecosystem — under rocks, bark or leaf; inside hollow trees or hollow logs on the ground and even underground burrows. Different animals and plans require different types of shelter to survive.

  • Wind and air currents: Areas that are heavily buffeted by strong winds can be inhabited only by plants that have strong root systems.

Effects of the living environment

The living or biotic factors that influence where an organism can live include all of the other plants and animals that it comes into contact with directly , or is influenced by indirectly. Sometimes the relationship is beneficial; at other times it isn’t. Biotic factors include:

  • Competition: Often, animals living in the same area have the same food or nesting requirements. This means that the amount of available food or nesting materials must be shared. Plants compete with each other for nutrients in he soil and for the light that is available.

  • Dispersal: This refers to how an organism is scattered throughout an ecosystem. While animals can move freely by themselves, plants rely on wind, insects or animals to disperse them. Their seeds are often shaped to help them in this process.

  • Predation: The term ’predation’ refers to the act of one animal catching and eating another. Every organism in an ecosystem needs nutrients and many will get them by consuming other inhabitants in that area. They might be eaten, too.

  • Human intervention: Human beings are the most powerful and influential biotic factors in an ecosystem.

Food Chains and Food Webs

Energy for life

The sun is the source of all energy on Earth. Plants, green algae and a number of microorganisms are able to use light from the Sun to provide the energy they need for life. They do this by converting carbon dioxide and water into glucose and oxygen. This process is called photosynthesis.

Those organisms that produce their own food are referred to as autotrophs. They are essential because they provide oxygen and food for all the other organisms in the ecosystem.

The flow of nutrients through an ecosystem

Not all organisms produce their own food. Those that do not are called consumers or heterotrophs. Animals that eat plants are referred to as primary consumers or herbivores. Often, these animals provide food for other animals. The animals that eat the herbivores are called secondary consumers or carnivores. Those consumers that are able to eat both plants and animals are referred to as omnivores.

This nutritional sequence is referred to as a food chain. It is called a chain because each living organism in the chain is like a ‘link’, and each one depends on the organism that comes before it. In general, food chains rarely have more than six links (called trophic levels). In every ecological community several food chains are interrelated because the organisms that make up those food chains have various food sources. This interaction of food chains is known as the food web.

Biodiversity

Biodiversity refers to the number of different species present in a community. Communities with high biodiversity, where there are many different species of plants and animals living together, survive environmental changes better than communities with low biodiversity, where there are few. There are usually many different sources of food in a community of high biodiversity: there are alternatives if one food source is destroyed. The community is more stable and is able to survive changes in the environment more easily.

If the herbivores in a community rely on one particular plant species for all their food needs, then their fate is determined by the fate of that plant. If the plant were to be wiped out by disease then the herbivores would be wiped out, too. In turn, the carnivores that ate them would be wiped out, too. If, on the other hand, the herbivores have a variety of plants to choose from, they can possibly survive the loss of one particular species. Humans have reduced the biodiversity of many ecosystems by removing the natural vegetation and replacing it with one specific type of plant, for example wheat. As a result, many species are now extinct.

The flow of energy through an ecosystem

Energy in an ecosystem moves in one direction only. During photosynthesis, glucose is produced inside the leaves of plants from CO2 and water. The energy for this reaction is provided by the Sun’s light. We can say that light energy from the sun has been converted into chemical energy inside of the plant. Plants only use a small amount (around 0.2%) of the Sun’s energy available to them, and at each level of the food chain only about 5%-20% of the energy available is transferred to the next level. For this reason, the number of plants in an ecosystem is greater than the number of herbivores and carnivores that eat them.

Decomposers

The term organic matter refers to all matter that comes from living organisms. All of this matter contains the element carbon. Organic matter is recycled within the ecosystem due to the activity of decomposers. This group of organisms breaks down the organic matter in dead bodies of plants and animals and releases the nutrients they contain for plants to use in their growth. Decomposers include bacteria and fungi. In effect, they are nature’s recyclers.

Fragments of dead organic material present in soil are referred to as detritus. These organisms that eat or ingest this material are called detritivores. Earthworms and dung beetles are examples of this.

Relationships between organisms

No plant or animal living in a community lives in isolation. This interaction may be by direct contact, especially when predators eat other animals. It can also be indirect as in the case of competition for food. The different types of interactions include:

  • Mutualism (symbiosis): Both organisms benefit by their relationship with each other. An example of mutualism is the relationship between the false clown anemone fish with the anemone. Slime of the fish’s body prevents it from being stung and it lives and feeds under the protection of its host. The anemone receives in return scraps of food from the fish, and is cleaned of parasites.

  • Commensalism: One species benefits from the interaction while the other is unaffected. Tropical fish called remora attach themselves to faster fish such as sharks using a sucker-like pad on the top of their heads. The sharks don’t benefit from the remora’s presence, nor are they harmed.

  • Amensalism: One species is harmed by the interaction while the other is unaffected. Cows and sheep commonly farm trails as they walk to and from feeding areas. They are unaffected by the trail, but the plants they trample are destroyed.

  • Competition: Different animals or plants may fight for the same food resource, water or nesting material.

  • Exploitation: One species benefits from the interaction while the other is harmed. This type of interaction includes:

    • Predation — One species kills the other for food.

    • Herbivory — Although herbivores eat plants, they rarely eat the whole thing and so do not actually kill them.

    • Parasitism — A parasite is an organism that lives in or on another, called the host. In most cases, the parasitic organism oes not kill its host, but it can cause severe problems.

Microorganisms

Microorganisms, or microbes, are living organisms that are so small that they can only be seen through microscopes. There are five different types of microorganisms: bacteria, viruses, fungi, protozoa and algae.

Bacteria

Bacteria are one-celled spherical, or rod-shape organisms. They are also called monerans. These organisms are some of the smallest and simplest living things. Bacteria are unique because they do not have a definite nucleus. Instead the chemical that makes up the nucleus is spread throughout the cytoplasm. Bacteria are made up of cytoplasm, a cell membrane and a cell wall.

Most bacteria cannot move on their own. They rely on air or moving liquids to help them move. However, some bacteria can move on their own. These type of bacteria have hair-like structures called flagella to move in liquids.

In order to survive, bacteria need water and the right temperature. Some also need oxygen. bacteria feed on dead plants and animals. Bacteria can be found all over the world. Bacteria can be found in the food you eat, in ai and soil, in oceans, and inside your body. Some examples of bacteria that you might have heard are Salmonella Eneritidis, which causes food poisoning, and Streptococcus, which causes strep throat.

Bacteria can be helpful. Bacteria help break down the remains of dead organisms, digest food, make foods such as yogurt or vinegar, and they help change nitrogen into something plants can use. In some cases plants are harmful, They cause food to spoil, diseases in plants and sickness in humans.

Viruses

Viruses are the smallest microorganisms and can only be seen through a powerful microscope. A virus is a parasite that can only live inside the cells of living things. A virus takes over the cell of a living organism by injecting its genetic material into the cell. It then uses this cell to take over other cells.

Scientists cannot agree on whether viruses are alive or not. Most scientists think that because they cannot reproduce without a host, or change food into energy, they are not living organisms.

Like bacteria, viruses do not have nucleus. They are found in the air, in water, and on skin. Sometimes, viruses attack and kill bacteria. Viruses can be dangerous. Some examples of dangerous viruses are chicken pox, measles and influenza.

Algae

Algae are simple plant-like organisms. Most have one cell, but some can have more than one cell. Algae that have more than one cell tend to be larger.

Algae make their own foo through photosynthesis like plants do. However, they are not considered plants because they do not have specialised parts like plants.

Algae is usually organised into groups by colour: red, green, brown, and golden-brown. Algae can be found in swimming pools, at the beach and in ponds and lakes.

While algae can be a nuisance at times, it is also helpful. Most of the oxygen we breathe is produced by algaee that floats near the surface of water.

Fungi

Fungi are similar to plants, but like algae they lack certain elements of plants. While they do grow in the soil like plants and have a cell wall, there are many differences:

  • they grow in dark moist places

  • they have large cells with many nuclei

  • Their cell walls are made with chitin, not cellulose like plants.

  • They cannot make their own food because they do not have chloroplasts or chlorophyll. Instead they feed on dead organisms.

Their sizes range from microorganisms like yeast to organisms that have many cells like mushrooms.

Yeast are single-celled, colourless fungi. They grow where sugar is present because they use sugar for food. Yeast is used to help bread rise.

Mold is a common type of fungi that grows on fruit and bread. Mold often looks like tiny green threads. Their roots called rhizoids, hold the mold to the bread. These roots then absorb nutrients to absorb the bread.

Mushrooms are similar to molds as they have man threads. The threads on a mushroom are packed tightly together. The rhizoids are connected to the stalks of the mushrooms. Above the stalk is a cap. The cap also houses the gills, which produce spores.

Protozoa

Protozoa are single-celled organisms that cause Malaria and sleeping sickness. Like other microorganisms, they also can be useful. Protozoa can be used to eat bacteria in sewage treatment plants. By adding protozoa, sewage is made safe for disposal.

Protozoa are heterotrophs. They cannot make their own food but they can move around to find food. They do not have a cell wall. They can be found in ponds, rivers, oceans and soil. Protozoa are very different. Scientists have further classified into four groups: amoebas, ciliates, flagellates, and sporozoans.

Amoebas: Amoebas produce extensions called pseudopods. Pseudopods surround the food they digest through special enzymes. The pseudopods then break down the food to be used as energy for moving around.

Ciliates: This group of protozoa are called ciliates because they are lined with tiny hairs called cilia. These hairs are used for movement. The hairs are also used in feeding. They carry the food to the mouth region. Enzymes then help break down the food. Ciliates can also be helpful to humans. They are used in sewage treatment plants to break down the bacteria in human wastes. If it wasn’t treated, we would become very sick. An example is the paramecium.

Flagellates: Protozoa that have more than one flagella are called flagellates. The flagella is used for movement. It is similar to a tail and moves in a whip-like motion. Flagellates are the cause of sleeping sickness, a deadly disease in East Africa that is caused by the Tsetse fly. If not treated in the early stages, it can lead to death.

Sporozoans: Sporozoans cannot move around at all. They only survive inside another living organism, or host. They are not beneficial in any way to the host. An example is a mosquito that carries malaria. The sporozoan then travels to the liver and red blood cells of the host and then infects them. An infected person suffers from a high fever and severe headaches.

Microorganisms (again)

Microorganisms play a role in making foods such as cheese, yogurt and sausages. Pickles are fermented by lactic acid producing bacteria; bread dough rises due to yeasts, which are single celled, microscopic fungi. Foods are preserved to stop microorganisms from spoiling them.

  • Canning first destroys bacteria through heating and then the food is placed in a sterilised container and sealed.

  • Drying removes water from the food; spoilage bacteria require water to grow and reproduce.

  • Freezing slows down the spoilage by changing that same essential water into ice, a form that bacteria can’t use.

  • Food additives are any substance added to food. Sugar, salt, and corn syrup are the most commonly used food additives. They are often used to keep food fresh, slow in microbial growth, give desired texture and appearance, and aid in processing and preparation.

  • Pasteurisation destroys most of the existing spoilage organisms by heating the food to a high temperature for a short period of time.

  • Pickling or fermentation (culturing) leaves tend to food with a higher level of acid, making it inhospitable for spoilage bacteria.

  • Vaccum packaging uses a vaccum sealed, moisture impermeable film that inhibits molds, yeasts and bacterial growth on the surface of things such as meat. Since there is no air in the package, vaccum-packaged meat will have a darker, purple colour before being opened. Once the meat is exposed to oxygen, it will turn the familiar bright red colour.

Human Impact on Ecosystems

Pollutant: Anything that makes the environment unfit or unhealthy for organisms to live there. Pollutants affect the atmosphere, lithosphere and hydrosphere.

Water pollution

  • Sewage: contains contaminants and human wastes

  • Agricultural runoff: contain fertilisers

  • Sediment pollution: caused by clearing land (soil runoff)

  • Inorganic chemicals: from industrial processes. Go into air and water

Air pollution creates smog and acid rain.

The greenhouse effect

Heat from the Earth is trapped by greenhouse gases in the Earth’s atmosphere. Greenhouse gases include carbon dioxide, methane, nitric oxide, ozone, and water vapour.

Conservation

  • Aimed at keeping alive all the plants and animals that live together in a specific habitat.

  • Usually by keeping the habitat undisturbed and free of human interaction.

Climate change is the gradual increase in the overall temperature of the Earth’s atmosphere, generally attributed to the greenhouse effect and caused by increased levels of carbon dioxide, CFCs and other pollutants.

The greenhouse effect is a natural effect caused by carbon dioxide and other gases in the atmosphere. Just the right amount of greenhouse gases are required to sustain life. Over the last 100 years the levels of greenhouse gases in the atmosphere, particularly carbon dioxide, have increased. Average temperatures have increased by 0.18ºC each decade.

Some solar radiation is reflected by the Earth and the atmosphere. Some radiation is absorbed by the Earth’s surface and warms it.

Infrared radiation is emitted by the Earth’s surface. Some of this infrared passes through the atmosphere. Some is absorbed by greenhouse gases and re-emitted in all directions by the atmosphere. The effect of this is to warm Earth’s surface and the lower atmosphere.

Causes of greenhouse gases

  • Carbon dioxide: fossil fuels (60%)

  • Methane (CH4): breakdown of vegetation (26%)

  • Nitrous oxide (N2O): car exhausts, fertilisers (6%)

  • Chlorofluorocarbons (CFCs): aerosol cans

  • Other: 8%

Indicators of chemical change

  • glaciers and ice sheets melting

  • air temperatures changing

  • arctic sea ice

  • changing southern ocean currents

  • ocean heat content

  • sea surface temperatures

  • ocean acidification

  • sea levels

  • changing rain pattern

  • no. of hot/cold days per year

  • intensity and frequency of extreme weather events

Coral reefs getting bleached

Increased greenhouse gases from activities like deforestation, and the burning of fossil fuels for heat and energy, cause ocean temperatures to rise, and when corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

Ice core CO2 levels

Ice cores can tell scientists about temperature, precipitation, atmospheric composition, volcanic activity, and even wind patterns. When snow falls it traps air into the ice. When scientists take a core of ice, it reveals the atmospheric gas concentrations at the time the snow fell. The ice can reveal the temperature of each year for the past 400,000 years.

The future

A temperature increase of 1-4ºC is expected by the end of this century. This could lead to:

  • continued melting of polar ice caps — rising sea levels

  • increase in number of severe storms and cyclones

  • more droughts and heat waves

  • less rain and snow

  • changing habitats