Transcript succession

“Communities in Transition”
All communities change over time in response to environmental
conditions. This gradual change in species composition is called
ecological succession.
TWO TYPES OF SUCCESSSION
Primary Succession = establishment of life on a “life-less”
ground or area. Examples: lava flow, glacier retreating
Secondary Succession = biotic community established in an area
where some type of biotic community is already present.
Examples: fire, storms, landslides (natural disasters) or human
causes: landscaping; deforestation
********Intermediate Disturbance Hypothesis********
Happens over a long period of time. (soil formation must
happen first - this can take hundreds to thousands of years)
Soil formation (facilitation) begins when “pioneer species”
attach themselves to patches of bare rock. Over time they trap
bits of wind blown detritus & begin to create the soil/nutrient
cycles.
Pioneer Species = r-selected species; early successional plants
examples: moss, lichens, small annuals, small perennial grasses & weeds
Once the soil is fertile and deep enough mid-successional
plant species arise (example: taller grasses, low shrubs).
Finally late successional plants such as trees replace many
early plant species. (often referred to as climax or k-selected)
late succession
mid succession
early succession
Pines, aspen, spruce
Small herbs, shrubs
Bare Rock!
Lichen/Moss
Starts with bare Rock. Must form soil before plants can colonize!!
late succession
mid succession
early succession
Begins where life has been disturbed (soil is still present)
HAPPENS MUCH FASTER!!
LAVA FLOW - Hawaii
PRIMARY SUCCESION EXAMPLES
GLACIERS RECEDING - northwest
Area hasn’t been cleared in
50 years = late succession
(climax community)
Area hasn’t been
cleared for 10
years = mid
succession
Area has been cleared in the past 2 years =
disturbance (early succession; pioneer species)
Environmental Resistance determines
biotic potential.
Carrying Capacity=K
Population Growth=r
Asexual
Sexual