Covers the entire section on interactions within an ecosystem. Includes notes from the textbook, as well as additional class, video and research information, diagrams and practice questions.
Applicable to all IEB Grade 12s.
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Interactions within an ecosystem
- Predator prey
- Food webs
- Competition between organisms
- Symbiotic relationships
Predator prey relationships
All living organisms within an ecosystem are interdependent.
Changes in the population of one species drastically affects others.
Predation is a biological interaction where one species, the predator, kills and eats another
species, the prey.
e.g. Great white shares - keystone species
= top of food chain and are very important
Role that predators play in their environment helps to create and maintain greater diversity
within an ecosystem.
They do this by:
- Regulating the abundance and distribution of prey species.
. As the predator population increases, the prey population decreases.
- Increasing the biodiversity of communities by preventing a single species from becoming
. dominant.
- Keeping the prey population genetically fit by removing sick, injured and weak individuals.
. (selecting agents)
- Providing vital food sources for scavengers.
- Prevent prey from destroying habitat.
- Reduce potential for epidemic disease.
Predators tend to be larger than prey and have evolved adaptations for capturing prey.
e.g. Special structures such as spider web, improved speed, well-developed eyesight and
camouflage
The feeding relationship between predator and prey determines the size of two populations by
means of a negative feedback mechanism.
As the prey population decreases due to predator killings, the food available to the predators is
less, so their numbers decline.
With the predator population reduced, the numbers of prey can increase once again.
= a cyclical rising and falling of the numbers of the prey population, with a slightly later cyclical
rising and falling of the predator population
These fluctuations may occur seasonally or over a number of years.
, The Graph
- Always more prey than predator, so may need two y-axes’
- Make sure you know where they cross over (half up)
- Be able to draw
- Predator numbers always follow
Number in prey population
Prey
Number in prey population
/ 100
/ 1000
Predator
Time
Sudden out of pattern drops in the graph could be a result of:
- Natural disaster
- Disease
- Predators being introduced
All examples:
- The predators and prey depend on one another.
- Both evolve to outwit the other (both organisms become more adapted, but their relationship
. still stays the same). .
e.g. in the lion and zebra relationship the adaptation is speed of movement.
. The fastest lions are able to catch and eat their prey more easily, so these survive and
. reproduce, rather than slower lions.
. The fastest zebras are escape the lions, so these survive and reproduce, rather than slower
. zebras.
- The relationship will be advantageous for the fitness of both species when they compete with
other species in the same ecosystem. (Known as co-evolution)
- Keep the populations of others healthy and in balance.
- Prevent the spread of disease, by keeping the density down.
- Strengthen the gene pool by removing the sick and weak.
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