Edexcel Biology Gcse - Adaptations,Interdependence and Competition Part 2

Tertiary consumers are also carnivores. They eat secondary consumers.

Light intensity

Temperature

Moisture levels

Soil pH content

Soil mineral content

Wind intensity and direction

Carbon dioxide levels for plants

Oxygen levels for aquatic animals

Levels of pollutants

Some plants have evolved for optimum growth in bright sunlight. An example of this is a cactus houseplant. Cacti originally come from deserts where they grow in bright sunlight. Other plants have evolved to grow in shade.

Many orchids, which are also kept as houseplants, grow on trees in the rainforest and have evolved for optimum growth in darker conditions. If you were to put an orchid on a bright windowsill and a cactus in a dark corner of your room neither plant would grow well

Both animals and plants have evolved to grow healthily at their optimum temperatures. If you planted either your cactus or orchid houseplants outside in cold temperatures, they would die. Similarly, animals that have evolved to live at the North Pole, such as the polar bear, could not survive in warmer conditions.

More people kill houseplants by overwatering than by under-watering them. Many plants cannot survive in waterlogged soils. Their roots are unable to respire, they rot and the plant dies. Other plants, such as pitcher plants, grow best in bogs where the moisture levels are high. Soil moisture meters can accurately determine how wet an area is.

The pH of soils can have a huge effect on the plants that are able to grow in them. Some plants, like azaleas, grow best in acidic soils and will quickly die if planted in alkaline soils. Others, like clematis, prefer alkaline soils. Some, like the hydrangea, can grow in both. These plants are unusual in that their flower colour changes in different soils. Just like universal indicator paper, hydrangea flowers are pink in acidic soils and blue in alkaline soils.

Many plants require high levels of soil minerals to grow well. An example of this is magnesium, which is required to produce chlorophyll. Plants with unnaturally yellow leaves may have a magnesium deficiency. Carnivorous plants, such as pitcher plants, have evolved to catch insects to supplement the low levels of minerals found in the soils in which they grow.

The strength of the wind and its direction has a huge impact on where organisms are found within ecosystems. Many organisms prefer more sheltered locations. Plant seeds are more likely to settle and germinate there, and animals which depend upon these are more likely to live close to where they grow. The strength of the wind can also affect the growth of individual organisms.

Carbon dioxide is a reactant in photosynthesis which means plants need it to survive. Areas with higher levels of carbon dioxide are more likely to have healthy plants growing. Farmers often release carbon dioxide within their greenhouses to maximise their crop yield. Woodlands often have higher carbon dioxide levels than open grassland, so many plants living in open areas have evolved mechanisms to overcome a shortage of carbon dioxide.

Oxygen from the air and oxygen produced by aquatic plants dissolves in water. Without this, aquatic animals would suffocate and die. Healthy lakes and rivers have high levels of oxygen, and polluted waters often have low levels of oxygen. This pollution means that only certain species can survive there such as sludgeworms. These are bioindicator species because their presence or absence informs us about the condition of the habitat.

Air pollutants such as sulfur dioxide are released from the burning of coal. Lichens cannot survive if the concentration of sulfur dioxide is too high. So lichens are considered to be indicator species for air pollution. If the air is clean there will be lots of lichens so that if the city and countryside are compared, there will be more lichen species further away from the city centre.

Stonefly nymph

| - mayfly larva

freshwater shrimp

| - caddis fly larva

bloodworm

| - water louse

sludgeworm

| - water louse

no living species

Abiotic factors are non-living. They include light intensity, temperature and moisture levels. The abundance and distribution of living organisms in an ecosystem are affected by abiotic factors.

A shingle beach has small stones instead of fine sand. Plant seeds can lodge between the small stones and start to grow, particularly at the top of the shore away from the waves. Two students set up a transect along a shingle beach. They started at the top of the beach and worked towards the sea. Every five metres they placed a quadrat on the beach and measured the height of all the plants found.

The abundance and distribution of organisms are affected by biotic factors, which are factors that are living.

The main biotic factors are predation and competition.

Availability of food

New predators

New pathogens

Competition

All animals require food to live. The availability of food is a major factor in how many animals live in an ecosystem. Areas like rainforests with rich food supplies have more species of life than other areas like deserts and the Polar Regions where there is less food.

The arrival of new predators in an ecosystem can have a devastating effect. In balanced ecosystems, predators and prey have evolved together. Predators can catch enough prey to survive, but not so many that they kill all of their food.

The arrival of a new predator can upset this balance. An example of this is the introduction of the red fox to Australia, which has caused concern over their effect on native birds and small mammals. Introducing new predators can cause a rapid decline in the numbers of prey, which then reduces the food supply for existing predators.

When organisms inhabit new ecosystems they often bring new pathogens.

As an example, Europeans first colonised North America, and introduced new pathogens, like the influenza virus. Many Native Americans had not developed immunity to new diseases such as this, and so many were killed by them.

Pathogens have also been introduced on purpose. Myxomatosis is a disease that affects rabbits. It is caused by a virus and infected rabbits develop skin tumours and may go blind. In the 1950s it was purposefully released into the wild in the UK to reduce the population of rabbits. It did exactly this and some people estimate that more than 99 per cent of rabbits in the UK died. However, our rabbits developed immunity to it and the population has now returned to previous levels.

The introduction of a new species into an ecosystem can result in it out-competing another native species. Several hundred years ago grey squirrels were brought over from North America by wealthy people and let free in their grounds. Our smaller native red squirrel couldn't compete with the newer, larger grey squirrel. Because grey squirrels are larger they can store more fat and survive harsher winters. So the numbers of red squirrels and the places they live has reduced dramatically.

Other examples of out-competition of native species by newly introduced species include the Canada goose in Europe and the cane toad in Australia, Himalayan balsam in Cambodia and harlequin ladybirds are also current concerns.