Ecology and Habitat Study (Junior Cert Science): Revision Notes

Ecology and Habitat Study

What is ecology?

Ecology is the scientific study of how living organisms interact with each other and with their physical surroundings. It helps us understand the complex relationships that exist in nature.

Populations, habitats and ecosystems

To understand ecology, we need to know some key terms that describe where and how organisms live.

Population

A population consists of all the members of a particular species that live in the same area. For example, all the rabbits living in a field form a population of rabbits.

Habitat

A habitat is the specific place where a particular organism lives. It provides everything the organism needs to survive, including:

• Food and water
• Shelter and protection
• A suitable climate
• A place to breed

Organisms breed in their natural habitat, and the climate of the habitat, the food available, and competition from other species all affect whether a species will survive or not.

Ecosystem

An ecosystem is a community of living organisms that interact with each other and with their environment. Ecosystems can be large or small - a lake, a forest, or even a small pond can be an ecosystem.

Understanding the difference

The key differences between habitats and ecosystems are:

Ecosystem	Habitat
Can contain many habitats	Part of an ecosystem
Larger	Smaller
Contains many species	Contains one or a few species

Food chains and food webs

Food chains

A food chain shows the pathway that energy takes as it passes from one organism to another through food. Energy flows in one direction through a food chain.

The diagram shows a simple food chain where:

• The leaf is eaten by
• The caterpillar, which is eaten by
• The small bird, which is eaten by
• The hawk

In this example, energy flows from the leaf through to the hawk.

Food webs

In reality, organisms usually have more than one food source. They may also be eaten by more than one type of predator. A food web shows a number of interconnected food chains, giving us a more realistic picture of feeding relationships in nature.

If one organism at the beginning of a food chain dies off, the rest of the organisms in that food chain are also in danger of dying due to lack of food.

Energy flow in an ecosystem

How energy enters an ecosystem

For life to be sustained, organisms need energy to flow from one organism to the next. Light energy is trapped by plants during photosynthesis. These plants convert this light energy to chemical energy in carbohydrates.

Producers and consumers

Organisms that make their own food are known as producers. Plants are producers because they can make food through photosynthesis.

When a producer is eaten by a consumer (an organism that does not make its own food), only 10% of the chemical energy is passed on through the food chain. The other 90% of the energy is used by the organism for movement, reproduction, heat and other life processes.

The 10% rule

This diagram shows how energy flows through a food chain:

1. Energy from the sun is trapped by the producers (e.g. grass)
2. This is the energy that is taken in by the primary consumer (e.g. grasshopper)
3. Only 10% of the energy consumed by the primary consumer will transfer to the secondary consumer (e.g. frog)
4. Only 10% of the energy consumed by the secondary consumer will transfer to the tertiary consumer (e.g. owl)

Types of consumers

As a result of this energy loss, food chains typically have only three or four trophic levels:

• Primary consumers get their energy from the producers by eating them
• Secondary consumers get their energy from primary consumers by eating them
• Tertiary consumers get their energy from secondary consumers by eating them

Decomposers are a group of organisms that feed on dead plant and animal matter. They break down the dead matter and recycle their nutrients back into the food chains. Fungi and bacteria are among the main decomposers.

We can also classify consumers by what they eat:

• A carnivore is an organism that feeds on animals only
• A herbivore is an organism that feeds on plants only
• An omnivore is an organism that feeds on both plants and animals

Habitat study

Why study a habitat?

Studying a habitat can:

• Give us information about the different life forms that live in it
• Help us understand how different animals and plants are adapted to their habitat
• Help us prevent harmful conditions that can easily destroy that habitat

How to conduct a habitat study

We are going to describe the steps taken to carry out a study of a grassland habitat. The study of a grassland habitat will be different to a seashore habitat or a woodland habitat.

Steps in a habitat study

Step 1: Which habitat?

The first step is to identify which grassland area you will study. This could be a local park, a school field, school grounds, or even your garden. You need to clearly define the boundaries of your study area.

Step 2: Measure factors affecting the habitat

There are two types of factors that affect organisms in a habitat:

Abiotic factors are the non-living things that affect organisms in their habitats. Examples include temperature, soil temperature, soil pH, and light intensity.

Biotic factors are the living things that affect other living things. Examples include what organisms each organism feeds on, competition, interdependence, and adaptation.

Important abiotic factors need to be measured in a habitat:

Factor	Apparatus	Method
Air temperature	Thermometer/temperature sensor	Place a thermometer or sensor in the air and take the reading
Soil temperature	Soil thermometer/temperature probe	Place a soil thermometer or sensor in the soil and take the reading
Soil pH	Universal indicator/pH sensor	Collect a soil sample and test it with universal indicator or pH sensor
Light intensity	Light meter/light sensor	Expose a light meter/sensor and take the reading

Step 3: Identify the producers

Plants convert light energy into chemical energy in food. Plants are described as producers because they make the food that all the organisms in the habitat depend on for their energy.

A key helps you ask questions about the organism you want to identify. By answering the questions, you are led to the identity of the organism.

Step 4: Identify the consumers

Animals can be identified using a key - this is similar to the plant key but focuses on characteristics of the particular habitat in which they are found.

This flowchart shows an example of how to identify animals by asking questions about their physical features.

Following the yes/no paths leads you to identify the organism.

Methods of collecting animals

Different apparatus and methods are used to collect small animals in the field:

Apparatus	How it is used	Organisms collected
Pooter	A pooter has two tubes. You place one tube near the organism and you suck through the second tube with gauze. The gauze prevents you swallowing the organism.	Small insects (such as greenflies and spiders)
Beating tray	A white sheet or tray is held under the leaves of a tree or shrub. The branches are shaken or beaten with a stick. This dislodges the animals and they fall onto the sheet.	Insects and small animals that live on the leaves of shrubs and trees
Pitfall trap	A jar is sunk into the ground at day in advance. The mouth of the jar must be level with the surface of the ground. A flat stone supported by small stones forms a lid. The lid prevents rain getting in.	Animals, e.g. ground beetles, that walk along the surface of the ground. Useful to compare animals that are around during the day with those that are around at night.

Step 5: Identify the decomposers

Decomposers in a grassland include earthworms, beetles, woodlice, bacteria, and fungi. These organisms break down dead plants and animals into materials that go back into the soil, recycling nutrients for new plant growth.

Step 6: Adaptation

Adaptation is the way an organism is suited to survive in its environment. Different organisms have different adaptations depending on their habitat.

Examples of adaptations in different habitats:

Habitat	Plant adaptation and benefit	Animal adaptation and benefit
Grassland	Buttercups have bright yellow petals to attract insect pollinators	Earthworms are a dark colour for camouflage. They are not easily seen by birds
Woodland	Primroses flower early in spring and get more light before the leaves come out on the trees	Sparrowhawks have large feet with needle-sharp talons for catching their prey
Rocky seashore	Seaweeds produce a slimy mucilage that prevents them drying out at low tide	Limpets have a muscular foot to anchor them to the rocks and prevent them from being swept away

Step 7: Competition

Competition is the struggle between organisms for resources that are in short supply.

Plants may compete for:

• Light
• Water
• Space
• Minerals

Animals may compete for:

• Food
• Shelter
• Mates
• Territory

Step 8: Interdependence

Interdependence is the way in which organisms rely on one another for survival.

Animals largely depend on plants for their food - either directly by feeding on plants or indirectly by feeding on other animals that feed on plants.

However, plants also depend on animals:

• For pollination - plants rely on animals to carry pollen from flower to flower to ensure the formation of fruit
• For seed dispersal - plants rely on animals to disperse (spread) their seeds to ensure germination of the next year's crop

Step 9: Counting populations

To carry out a direct count (counting every individual) of a species in a habitat is usually very difficult. There are two methods we can use to estimate the number of a particular species (population) in a habitat.

The quadrat method

Frequency is the percentage chance of finding a particular organism in one throw of a quadrat.

A quadrat is an open square of wood, metal, or plastic, usually a square of side 50 cm (i.e. $0.5 \text{ m} \times 0.5 \text{ m} = 0.25 \text{ m}^2$).

The steps to investigate the frequency of a number of plant species in a habitat are:

1. Choose the plants to be counted
2. Throw a pencil at random, then place a quadrat where the pencil lands
3. If the plant is in the quadrat, place a tick in the appropriate box in the results table
4. If a plant is not in the quadrat, leave the box in the results table empty
5. Repeat steps 2-4 nine more times
6. Calculate the frequency of each plant as shown in the table

The frequency can be calculated using:

$\text{Frequency} = \frac{\text{Total}}{10}$

$\text{Percentage frequency} = \frac{\text{Total} \times 100}{10}$

The capture-recapture method

This method can be used to count animals. The following steps are used:

1. As many woodlice as possible are captured, counted, and recorded
2. Each animal is tagged and released
3. A day or two later, as many woodlice as possible are captured and counted again
4. The number of tagged animals in the second capture is counted and recorded
5. The size of the population is estimated using the formula below

$\text{Size of population} = \frac{\text{number of animals caught on day 1} \times \text{number of animals caught on day 2}}{\text{number of animals caught on day 2 with the tag mark}}$

Remember!