1. Chapter 5 Higher Level Ecology

2. Pyramid of Numbers – the number of organisms at each trophic level in a food chain.
Pyramid Shape: Two conclusions
1. The number of organisms declines as you go up a pyramid (this happens because of the large energy losses at each level).
2. The body size of the organisms increase as you go up the pyramid (because animals eat smaller animals).
Limitations
Does not take into account the size of the organisms.
Parasitic food chains often give rise to an inverted pyramid.
The pyramid of numbers may not be drawn to scale because of a large number of organisms.

3. Population Control
A population comprises all the members of a species living in an area.
e.g. population of rabbits in a field.
Factors which reduce population when numbers are high or increase populations when numbers are low include:
Competition
Predation
Parasitism
Symbiosis

10. Predator Prey Relationships
Number of predators (e.g. foxes) and prey (e.g. rabbits) are inter-related.
As the number of prey increase the number of predators will rise. This will result in more prey being killed and so the number of prey will fall. The predator number will then fall because they have no food. Eventually the number of prey will begin to rise and the cycle starts again.
Factors that contribute to predator-prey interactions include:
1. availability of food
2. Concealment of prey
3. Movement of predators

11. Human Population Growth
World population is increasing by 75 million people per year
And increases by 205,000 additional people each day.
Some experts predict that the world population will be 10 billion by the year 2100.