Download 11D Ecological Succession

Rhonda Alexander IC Science Robert E. Lee
B.11.D describe how events and processes that occur during ecological succession can change
populations and species diversity
Succession
Some of the organisms in an area are gradually replaced over time by new species. This succession is a
result of the changes to the environment brought about by the organisms themselves. Through
succession, the organisms tend to get bigger and more complex, as the biodiversity also rises.
Pioneer species are those that first colonize bare soil or rock. They can withstand the harsh
environment, and include lichens and mosses and Marram Grass on sand dunes. The process continues
in stages until the climax community is reached, which will remain stable until the abiotic factors
change.
If succession is halted (e.g. by fire, flood or by Man’s actions – such as plowing), then a secondary
succession will start. This is much faster than primary succession as there are many seeds in the soil
from which new plants can grow, whilst animals readily colonize the area as soon as the plants appear.
Ultimately, it does not matter very much what the starting point for succession is - rock, bog or pond - as
eventually the climax community will be much the same, since the climate is the main influence on it.
• Early Successional Communities
• A succession (or sere) proceeds in seral stages,
until the formation of a climax community, which is
stable until further disturbance.
• Early successional (or pioneer) communities are
characterized by:
Simple structure, with a small number of
species interactions
Broad niches
Low species diversity
Pioneer community, Hawaii
• Climax Communities
• In contrast to early successional communities, climax communities typically show:
Complex structure, with a large number of species interactions
Narrow niches
High species diversity
Climax community, Hawaii
•
•
Hawaii: Local plants are able to rapidly recolonize
barren areas
Primary Succession
When the starting point is an ABIOTIC environment
• Volcano
• Flood
•
Primary Succession
‣ Primary succession refers to colonization of a
region where
there is no pre-existing community. Examples include:
Newly emerged coral atolls, volcanic
islands
Newly formed glacial moraines
Islands where the previous community has
been extinguished by a volcanic eruption
‣ A classical sequence of colonization
begins with lichens, mosses, and liverworts,
progresses to ferns, grasses, shrubs, and
culminates in a climax community of mature forest.
In reality, this scenario is rare
• Secondary succession
occurs where an existing
community has been cleared by a
disturbance that does not involve
complete soil loss.
• Such disturbance events
include cyclone damage, forest
fires and hillside slips.