Ecology

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Slide 1

In this presentation, we’re going to talk some more about ecology. In particular, we’re interested in the relationships between organisms within ecosystems. We’ll talk about different classes of organisms called producers and consumers, and which types of organisms feed on which other types of organisms. Finally we’ll be interested in a special class of organisms called the decomposers. These are nature’s recycling depots. They release energy from dead organisms and return it to the ecosystem.
 
Slide 2

So, what is ecology? It’s the study of the relationships between organisms and their environment. In other words, ecology is the study of ecosystems. Ecosystems are parts of the environment that occupy a certain area. They include all the living organisms in that area, and the non-living components of their environment such as the climate, water, the atmosphere, the soil and rocks. Ecologists, the scientists who study ecology, are interested in the interactions between the different living things in each ecosystem.
 
Slide 3

Ecologists divide organisms up into three groups, depending on the ways in which they obtain their food from their environment. Producers are found at the bottoms of many food chains. In the examples on the right, they are the plants and the phytoplankton. They take energy from sunlight to produce their own food. Consumers get their food by eating other organisms in their environment. We shall see later that there are different levels of consumers in any ecosystem. For example, in the food chain on the left, the grasshopper, bees, frog, snakes and hawk are all examples of consumers. The food chains on the right don’t show any examples of decomposers. These are organisms like bacteria that eat dead and decaying organic matter. They’re useful because they return the energy and nutrients from the dead organisms to the ecosystem.
 
Slide 4

The energy driving most ecosystems comes from the Sun. Without the Sun, there would be no life on Earth. Green plants and phytoplankton take the energy from the sun and turn it into a form of
food called sugar using a chemical process called photosynthesis. We call green plants and phytoplankton producers because they don’t require any other organisms to make their food. Other organisms eat the green plants and algae or phytoplankton.
 
Slide 5

Producers are an extremely important part of any food chain. They capture energy from the Sun and release it into the ecosystem. Other organisms in the ecosystem eat the producers, and transfer their energy further along the food chain. Producers absorb carbon dioxide, and release oxygen into our atmosphere, maintaining our atmosphere. Without producers, there could be no ecosystem. We require producers to turn the energy from the Sun into food for higher level consumers. If there are insufficient producers in an ecosystem, the number of consumers will also fall as there will not be enough food for them.
 
Slide 6

Just as plants are the producers in an ecosystem, animals are the consumers. Animals cannot make their own food from sunlight, and thus must rely either directly or indirectly on plants. Herbivores eat plants directly, while carnivores eat herbivores and other carnivores. Ecologists talk about three different types of consumers. The primary consumers are the animals that eat plants, or the herbivores. The secondary consumers eat the herbivores – they may be carnivores or omnivores. The tertiary consumers eat the secondary consumers. Again, they may be herbivores or omnivores.
 
Slide 7

Animals such as snails, grasshoppers, giraffes and cows feed directly on plants. Pandas also feed on plants, but they are omnivores as they also eat small insects. We call animals that feed only on plants herbivores, and they are the primary consumers in our ecosystem. Omnivores like the panda can act both as primary and secondary consumers.

Slide 8

Secondary and tertiary consumers are placed higher in the food chain than primary consumers. They are animals that eat other animals. Secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Secondary and tertiary consumers can be omnivores (eating both plants and animals) or carnivores, which eat only animals. Some examples of secondary and tertiary consumers are tigers, lions, wolves, cats, toads, hawks, seagulls and human beings.

Slide 9

Consumers such as this tiger are organisms that eat other organisms. Consumers make up the majority of each food chain. You might think that consumers are unnecessary, but in fact, they play a very important role in food chains. Without consumers, the populations of animals at lower levels of the food chain could explode. Any environment can only sustain a certain number of organisms. For example, herbivores might eat all the plant life in the ecosystem. This would mean that there would be no food for any of the organisms in the ecosystem, and the ecosystem would collapse.
 
Slide 10

Decomposers such as worms, fungi and bacteria are also an important part of an ecosystem. Decomposers are the ecosystem’s recycling depots. They break down (or decompose) dead or decaying organisms and return the energy that is trapped in them to the ecosystem. They break down organic substances into simpler organic matter than can be used as food by the other organisms in the ecosystem.
 
Slide 11

Scientists classify decomposers into two groups. The fungi, like mushrooms and toadstools, break down dead organisms. This is the largest group of decomposers. Detritivores like worms and bacteria then scavenge the remains left behind by the fungi.
 
Slide 12

We often don’t think of decomposers as being very important, but, in fact, they’re a crucial part of ecosystems. They are the ecosystem’s recycling depot. They break down dead organic matter and return its energy to the ecosystem. This provides energy for other parts of the ecosystem, and also releases the physical space occupied by the dead organism back to the biosphere.

Slide 13

Decomposers clean up after everyone else in the ecosystem. They eat the things that no one else wants. If there were no decomposers, plants would not receive the essential nutrients that they need for their healthy growth, and the dead organic matter and animal waste would pile up, leaving less room for the other organisms of the ecosystem.
 
Slide 14

As animals process their food, they release carbon dioxide to the atmosphere. They also wee and poo. This releases waste materials to the ecosystem, which can be harmful for the other plants and animals, and reduce the available space in the ecosystem. Decomposers break these waste materials down into simple inorganic molecules that provide nutrients for the plants and help them to thrive. Plants use the carbon dioxide together with sunlight to create food, and release oxygen into the atmosphere. Without decomposers, the whole ecosystem would keel over.

Slide 15

Decomposers don’t always eat dead organic matter. They can also break down decaying tissues while they are still attached to a living organism. Some decomposers are microscopic, like bacteria, but others aren’t. Some common examples of decomposers are fungi, bacteria and earthworms.
 
Slide 16

Let’s start by looking at bacteria. Many bacteria are microscopic. Indeed, bacteria are among the smallest life forms on earth. They help to decompose dead plants and animals, but can also eat diseased tissue that is still attached to a living organism. One interesting type of bacteria is the rhizobium. They are nitrogen-fixing bacteria and have a special relationship with the roots of pea plants. We say that this relationship is symbiotic as the two organisms help each other to survive. You find them around the roots of peas and other legumes. They change the nitrogen in the air into nitrates. These are special compounds that act as fertilisers for plants, helping them to grow. The rhizobia leave some of the nitrates behind in the soil, helping the plants to grow.
 
Slide 17

Fungi are another class of decomposers. They aren’t only mushrooms. Some other types of fungi are mildew, mould and toadstools. They are not considered to be plants because they can’t make their own food. This is because they lack chlorophyll, a chemical that is found in the green leaves of plants and is required for photosynthesis.

Fungi release enzymes that break down (or decompose) dead plants and animals. At the same time, they absorb nutrients from these organisms.
 
Slide 18

The final group of decomposers are the earthworms. They also eat dead plants and animals. In addition, they aerate the soil. They take in nutrients from the microorganisms that are found in the material they ingest. They excrete a special type of waste product called a cast, which is rich in nutrients like nitrogen, phosphorus and potash. This enriches the soil and helps the plants to grow.
 
Slide 19

When plants and animals die, decomposers like bacteria, fungi and earthworms feed on them. They release chemical nutrients such as carbon and nitrogen as waste products. The waste products are released back into the soil, air and water of the ecosystem where they help plants to grow.

Slide 20

In summary, there are three main groups of organisms in ecosystems. Organisms are placed into these groups on the basis of the way they obtain their food from the environment. Producers such as plants and algae make their own food using energy from the Sun, and form food for other classes of organisms. Consumers are organisms that eat other organisms. All animals are consumers of one form or another. Herbivores eat the producers, while omnivores eat the producers and other consumers and carnivores eat consumers. The third group of organisms are the decomposers. These are organisms like bacteria, earthworms and fungi that break down dead or decaying organic matter into simpler inorganic chemicals.