Populations and Sustainability

Human pop. sustainable?

What is a limiting factor?

Examples of both abiotic and biotic limiting factors

The human population is predicted to reach 11 billion by 2100- this growth cannot be sustained indefinitely due to limiting factors, e.g. food availability

• An environmental resource or constraint that limits population growth

Abiotic: temperature, light, pH, availability of water/oxygen, humidity

Biotic: predators, disease, competition (most important- a result of interactions between living organisms)

What is carrying capacity?

Carrying capacity is the maximum population size that an environment can support.

Sigmoid Population growth curve

Migration affecting population size

• emigration- the movement of individual organisms away from a particular area decreases population size

• e..g. Norway lemmings leave areas of high population density

• immigration- the movement of individual organisms into a particular area

• e.g. Christmas Island red crabs yearly migration from forest to coast

What are Density Independent factors?

• factors that have an effect on the whole population regardless of its size.

• These can dramatically change population size e.g. earthquakes, fires, volcanic eruptions and storms.

What are the two types of competition?

Intraspecific competition

Interspecific competition

Competition between individuals of the same species For things such as food, water, breeding sites, mates, shelter.

Competition between individuals of different species 2 or more species compete for the same resource = a reduction of resource for both populations- if one is better adapted, the other can be outcompeted. The competitive exclusion principle: when 2 species are competing for limited resources- the one that uses the resources more effectively will ultimately eliminate the other e.g. Red and Grey Squirrels in the UK store more fat and can eat more varieties of food- they are bigger so have a higher chance of survival.