Succession
This is the non-seasonal, directional and continuous pattern of
colonisation and extinction at a site by populations of species.
Pioneers
Climax community
r-strategists
K-strategists
Rapidly changing
stable communities
Toxic pollution
 E.g. pesticides, insecticides or heavy metals
 Loss of diversity
 Reduction in species richness
 Species present in large numbers due to lack of interspecific
competition in polluted habitats
Categories of succession
 Autogenic succession – natural sequence
 Primary succession
 Secondary succession
 Allogenic succession
 Degradative succession
Toxic pollution
 Problems with pesticides
o Kill non-target species
o target species evolve resistance to the insecticide
o some insecticides become concentrated up food chains
 PCB’s and heavy metals
o Egg shell thinning
o Interference with mammalian reproduction
o Damage to the immune system
o Carcinogenic
Changes in complexity
Limited complexity is typical of naturally stressed communities
Loss of complexity is also typical of stressed communities associated
with polluted habitats that may result from
 Eutrophication
 Toxic pollution
Reduction in complexity can also be a result of
 Monoculture
 Habitat destruction
Eutrophication
•“Enrichment of waters by inorganic plant nutrients, usually nitrogen
and phosphorous, which increases primary production”
Stages of Eutrophication
 Algal bloom – caused by the effect of fertilizers on the growth
of microscopic green algae
 Rapid growth of algae causes death of higher plants
 Flow rate of river slows down
 Older algae decompose, bacterial populations increase (BOD
increases)
 Fish are killed and the entire food web of the river is disrupted.
Monoculture
 Loss of diversity by modern agricultural practices
 A single crop species is grown over a large area, reducing the
complexity of the ecosystem to a single species.
 Unstable ecosystem, at risk from interspecific competition.
Habitat destruction
 Britain's wild orchids disappearing habitats
 Annual deforestation estimates
 Species extinctions
Essay question
Give an account of the types of succession and the changes in
complexity of ecosystems as a result of succession.