Edexcel Biology Gcse - Adaptations,Interdependence and Competition Part 3

availability of food

the presence of new predators and pathogens

Both the abundance and distribution of living organisms in an ecosystem are affected by biotic factors.

Red squirrels are native to Great Britain. They weigh around 300 grams, and about half the mass of the larger grey squirrel. The red squirrel species was introduced around a hundred years ago from America by wealthy land owners who wanted a fashionable addition to their forests.

The larger grey squirrel has provided competition for the native red squirrel, which has resulted in a lack of food for the species. Organisations like the Red Squirrel Support Trust have sampled the numbers of both squirrel types over time. Their results are shown below.

All animals require food which provides them with energy and raw materials to complete life processes, without which they may die. Because of these, competition for food can be fierce. There are many birds which eat insects in our gardens, and some have evolved to only eat certain types of insect to reduce competition from other species. Others like the blue tit and great tit compete with other members of their own species and as well as others for different insects. Because food is so vital, many animals will fight for it.

Animals within a species also compete for mates. This is essential so they can pass on their genes to their offspring. Animals have evolved to have an innate or natural drive to reproduce, and this competition often results in fights. This is seen each year when animals like red deer group together at the start of the mating season. Large male deer fight with each other by locking antlers and pushing hard, which is called a rut. In deer, and many others species, these fights competing for mates can often result in serious injury or death, but benefits the population as only the strongest pass on their genes to the next generation.

The territories of animals contain all of the resources and conditions they need to survive. These include abiotic factors such as light, temperature and water, and oxygen for aquatic animals. These are also biotic factors such as food and predators. Many animals, including the cats in back gardens, will fight for territory.

Example of intraspecific competition

An example of intraspecific competition over territory would be between lions on the grass plains of Africa whereas interspecific competition would occur when another predator like leopards lived close to the lions.

Often very small changes to ecosystems have large consequences, which can be difficult to predict. This means that all the organisms in an ecosystem are dependent upon each other. We call this interdependence.

All photosynthesis plants and algae in an ecosystem compete for light, space, water and minerals from the soil. Animals in an ecosystem compete for food, mates and their territory. Organisms which have more of these resources tend to grow more healthily and are more likely to have offspring. Competition can be interspecific or intraspecific depending on whether organisms from different species or the same species are competing for resources.

A stable community is one in which the size of the populations of all species remain relatively constant over time. In the example above the amount of grass and the numbers of rabbits and foxes all remain relatively constant. The different populations are living in a healthy balance with their environment.

Organisms depend on other species for resources such as nutrients. Parasites live in or on another organism, which is called the host. The parasite takes what it needs from the host but the host receives nothing in return and often suffers as a result.

Parasites are adapted so that they receive maximum benefit from the host but do not kill them.

An example of parasitism is the relationship between fleas and dogs. Fleas live on dogs and feed on their blood. The dog receives no benefit but the fleas are provided with food and a habitat. Fleas attach themselves to hairs and can spread from one host to another by jumping huge distances.

Tapeworms are parasites that live inside the small intestine of their hosts. Some human tapeworms have measured up to 15 metres in length. These worms have no digestive system and absorb the digested products of digestion from their hosts. They release eggs in the faeces which can infect other hosts. The host loses nutrition, and may develop weight loss, diarrhoea and vomiting.

Tapeworms have many adaptations such as strong suckers and hooks for attachment to the lining of the small intestine. Tapeworms are thin and flattened and have a very large surface area for absorption of nutrients. They have a huge reproductive potential and release lots of eggs because the chances of the parasite finding another host is very small and many eggs will die.

For example bees and flowering plants have a mutualistic relationship. Bees obtain nectar for food and spread the flower pollen from one flower to another, which helps reproduction in plants.

Different species of fish can display mutualism. Cleaner fish are smaller fish and swim near the gills of much larger species and eat the parasites around the fish gills of the larger fish. The smaller cleaner fish derive nutrition and protection and the larger fish have the gill parasites removed.

Lichens are another example of mutualism. They are formed by algae and fungi living together. Algae can photosynthesise and make food, which is shared with the fungus. The fungus in turn shelters the algae from a harsh climate.

Population

Plants

Pollutants are abiotic (non-living) factors

Interspecific

Interdependence

A parasite