6.3.2(b) interactions between populations

spec points

interactions between populations

To include predator-prey relationships considering the effects on both predator and prey populations AND interspecific and intraspecific competition.

competition for

• mates/pollinators

• food/sunlight

• territory/space

• dominance

• water

what is competition?

When two or more individuals share any resource that is insufficient to satisfy all of their requirements fully, then competition results.

(e.g light, food, space)

interspecific vs intraspecific

• interspecific: different species

• intraspecific: within species

interspecific

Individuals competing for resources who are different species. One population size will grow, and the other shrink.

squirrels

Grey squirrel (Sciurus carolinensis) was introduced to Britain over 100 years ago and has been out competing the red squirrel (Sciurus vulgaris)

INTERSPECIFIC

ecological niche

habitat that an organism lives in and also it’s role in that habitat (what it eats)

• e.g. ladybirds live on trees and eat greenfly

Carl Gauss (1934)

Grew two species of paramecium. First separately, then together

What do the graphs show and how can you explain this?

When together there is greater competition for food. The P.caudatum are out competed by the P. aurelia. 

• The more overlap between two species’ niche, the more intense the competition. 

• If they have the same niche then one species is out-competed by the other. 

• Two species cannot occupy the same niche.

intraspecific

Individuals competing for resources who are the same species.

Availability of the resources will determine the size of that population.

The larger the availability of resources, the larger the population.

• competing for water

• eventually water dries up

• competing for food

intraspecific competition

Describe the graph at each stage:

1. Lots of resources, all organisms have enough to survive and reproduce – population size increases

2. Resources now limited, not enough for all to survive, population decreases in size

3. Smaller population means less competition, can survive and reproduce. Population grows

Can this be linked to natural selection?

predator-prey relationships

• lady birds and aphids

describe + explain stages 1-4 on graph

1. Increase in rabbits means the population of the foxes grows. More food available = survive = reproduce

2. High number of foxes means a decline in the rabbit population

3. Less rabbits mean that there is less food for foxes so the number of foxes decreases 

4. Less foxes mean that less rabbits get eaten and numbers can increase. Cycle starts over!

There are many other factors that determine the size of these populations can you list them?

• Environmental Factors

  • Availability of food and water resources.

  • Changes in habitat or vegetation.

  • Weather conditions (e.g., droughts or extreme winters).

• Disease

• Inter/Intraspecific Competition

• Migration

• Human Influence:

  • Hunting or trapping of foxes or rabbits.

  • Changes due to urbanization or farming.

• Genetic Factors/variations

• Predator-Prey Dynamics