Density dependent factor Only affects the population once it has grown to a certain density (size) Density independent Affects the growth of a population regardless of the population density Give two examples of a density-independent factors Flood,drought (forest fire) Give 4 examples of an density-dependent factors Availability of food, disease, predators, build up of toxic wastes

As the density of the population increases what effect would each of the above factors have? As the density increases the availability of food could limit the growth of the population ie intra-specific competition would increase As the density increases then disease can spread quickly through the population and this will decrease the numbers As the density increases then predation will increase As the density of the population increases there will be a greater build up of toxic wastes which will decrease the population.

List 4 reasons why it would be useful to monitor the population of animals or plants Need the animal or plant as a food supply eg fish Species is endangered and in need of protection and conservation Species can be an indicator species and by its presence or absence it indicates the level of pollution They could be a pest like mosquitoes / locust

Succession begins with pioneer species List two pioneers Lichens and mosses Why can they grow at the start of succession and not other species? Pioneer species have adapted to tolerate adverse conditions eg a Hardy plant / shallow root system / use wind dispersal The area the pioneers are growing in will have very few nutrients What increases as succession moves towards the climax community? The nutrients will increase Organic matter will increase Ability to retain water will increase

Succession is unidirectional – explain this term Each group of species makes the soil suitable for the next group of species to grow and establish itself. Lichens/ mosses ---- small flowering plants---- bushes--- trees Climax community Increased stability - will not be taken over by other species Increased biomass – a lot mote living matter Increased species diversity