Ecological Relationships & Population Dynamic

Population (definition)

Group of individuals of the same species living together in a habitat

Population dynamics (definition)

Study of changes that occur in a population and factors that cause these changes

Why do organisms live in populations?

Safer. Breeding. Habitat provides food and shelter

How is the size of a population controlled? (5)

Competition. Predation. Symbiosis. Parasitism. Emigration

Competition (definition)

When two or more organisms seek a resource that is in short supply in a habitat.

Contest competition (definition)

An active physical confrontation between two organisms in which only one wins the resource.

Scramble competition (definition)

A struggle between organisms for a scarce resource in which each organism gets some of the resource

Adaptation of plants to reduce competition for water or minerals

Different plants take water from different soil depths

Example of plant adaptation to reduce competition

Grass has shorter roots near the surface. Dandelions have long tap roots which get water from deeper soil

Adaptation of animals to reduce competition

Occupy different food niches

Examples of animal adaptation to decrease competition

Caterpillars eat leaves while greenflies eat the sap of roses

Predation (definition)

The act of hunting, killing, and eating prey

Predator (definition)

The organism that hunts, kills and eats its prey

Prey (definition)

The organism that is eaten by the predator

Structural adaptations of predators

Keen eyesight, smell, and hearing

Behavioural adaptations of predators

Catch easiest prey. Live in groups. Change diet and location

Structural prey adaptations

Protective structures (thorns/stings). Camouflage and warning colouration

Behavioural prey adaptations

Stay in large groups

Function of predation in overall scheme of nature

Population control

Draw a graph of a predator and prey relationship

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Explain the predator prey graph

Increase in prey due to decrease in predators. Predators increase due to abundant food. Prey numbers decrease. Too little food decreases predators. Prey population increases again.

Why is there a time lag on the graph?

Accounts for the time taken for predators to respond to changes in their prey

Why do predator numbers increase?

Immigration. Abundant food. Mates

Why do predator numbers decrease?

Prey numbers decrease. Disease. Emigration

Symbiosis (definition)

A close relationship between two organisms of different species in which at least one of them benefit

Parasitism (definition)

A relationship between two organisms of different species living together where one benefits and does harm to the other.

Stage 1 of the population curve (lag)

Little increase in population due to adjusting to their habitat

Step 2 of the population curve (log)

Population rapidly increases due to higher breeding because of plentiful resources

Step 3 of population curve (stationary)

Population number no longer increases death rate = birth rate

Step 4 of population curve (decline)

Lack of resources. Death rate > birth rate

Draw a population curve

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Why does population growth slow down?

Food starts to run out. Not enough room for breeding/overcrowding causes disease. More predators due to higher numbers

What caused the sudden growth in the human population?

Fewer infant deaths. Better sanitation and medicine.

What causes the human population to decrease? (4)

Famine. Disease. War. Contraception

Ectoparasites (definition)

Parasites that live on the outside of the host e.g. lice

Endoparasites (definition)

Lives inside the host e.g. tapeworm