Changes in Biotic Factors

Changing the population size of one species often has an impact on the population size of other species. Give examples:

• Introduced species.

• Loss of inter-species relationships.

• Introduced species.

- Introduced competitors

- Introduced predators

- Introduced pathogens

- Loss of species that control abiotic factors

- Introduced competitors

- Grey squirrel was introduced to the UK from North America.

- In many areas, they have out-competed the indigenous red squirrel.

Why are grey squirrels better adapted to exploit the available food than red squirrels?

- Grey squirrels can digest acorns from oak trees which the red squirrels cannot.

- They're also larger and can compete more successfully for nest sites.

- Introduced predators

- Cane toads were introduced to Australia to control beetle pests of sugar cane

- However, they also ate other species, and are very toxic, so have few predators and have colonised a huge area

- Introduced pathogens

Humans may introduce pathogens, causing a decline in wildlife populations.

The pathogens are often carried by other introduced species.

When the Grey Squirrel was introduced from North America to the UK, it brought the squirrel pox virus which does not kill the Grey Squirrel but it does kill the indigenous Red Squirrel.

Introduced tree pathogens

Many tree pathogens have been introduced into the UK.

- Dutch Elm Disease

- Ash Dieback

- Sudden Oak Death.

Most tree pathogens were brought into the UK on vegetation or in the soil when plants were imported.

What is ash dieback?

A serious fungal disease of the European ash, characterized by the progressive death of the tree's branches.

- Loss of species that control abiotic factors

- Some species change habitats and produce abiotic features that other species need for survival. If these species are lost then many other species may decline

- African Forest Elephants

- Beavers

African Forest Elephants

They create clearings and water-holes that many other species rely on for water.

Beavers

They build dams, creating small lakes which are colonised by many aquatic species.

• Loss of inter-species relationships.

- Pollinators

- Seed dispersal species

- Food chain impacts

- Pollinators

- Many plants rely on their pollen being transported between their flowers by insects.

- If the insects were to die out, then the plants would not be able to reproduce.

How is the interspecies relationship of pollinators to plants lost?

The use of pesticides and loss of wild flowering plants reduces the populations of many insect species (like bees)

- Seed dispersal species

- Animals that eat seeds and fruit can be vital in the successful dispersal of seeds and therefore future plant survival.

- Many large herbivore species are endangered, for example, elephants, rhinos, hippos, gorillas, and many monkey species.

- Conservation of these herbivores would help to protect the plant species that rely on them.

Elephants as a seed dispersal species

- Elephants disperse the seeds of most tree species where elephants are found.

- They are not ruminants so they do not repeatedly chew their food and thus destroy the seeds.

- In addition, they are not territorial so they spread seeds over larger areas than most herbivores.

- Food chain impacts

The decline in the populations of some species has been caused by the over-exploitation of their food by humans

Puffins have declined because sandeels have been over-fished.

Can the overexploitation of one species cause another species to actually increase?

Yes

The over-collection of turtle eggs has caused a decline in turtle numbers, therefore leading to an increase in their food species, like jellyfish