“communities in transition” all communities change over time in response to environmental...

“Communities in Transition”

All communities change over time in response to environmental All communities change over time in response to environmental conditions. This gradual change in species composition is called conditions. This gradual change in species composition is called ecological succession..

Primary Succession = establishment of life on a “life-less” = establishment of life on a “life-less” ground or area. ground or area. Examples: lava flow, glacier retreating

Secondary Succession = biotic community established in an = biotic community established in an area where some type of biotic community is already present.area where some type of biotic community is already present.

Examples: fire, storms, landslides (natural disasters) or human causes: landscaping; deforestation

********Intermediate Disturbance Hypothesis********

TWO TYPES OF SUCCESSSION

Happens over a long period of time. (soil formation must Happens over a long period of time. (soil formation must happen first - this can take hundreds to thousands of years) happen first - this can take hundreds to thousands of years)

Soil formation (facilitation) begins when “pioneer species” Soil formation (facilitation) begins when “pioneer species” attach themselves to patches of bare rock. Over time they trap attach themselves to patches of bare rock. Over time they trap bits of wind blown detritus & begin to create the soil/nutrient bits of wind blown detritus & begin to create the soil/nutrient cycles.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 Once the soil is fertile and deep enough mid-successional plant species arise plant species arise (example: taller grasses, low shrubs).

Finally late successional plants such as trees replace many Finally late successional plants such as trees replace many early plant species. early plant species. (often referred to as climax or k-selected)

Bare RockBare Rock!!

Lichen/MossLichen/MossSmall herbs, shrubsSmall herbs, shrubs

Pines, aspen, sprucePines, aspen, spruce

early succession

mid succession

late succession

Starts with bare Rock. Must form soil before plants can colonize!!

Begins where life has been disturbed (soil is still Begins where life has been disturbed (soil is still present)present)

HAPPENS MUCH FASTER!!

early succession

mid succession

late succession

GLACIERS RECEDING - northwest

LAVA FLOW - Hawaii PRIMARY SUCCESION EXAMPLESPRIMARY SUCCESION EXAMPLES

Area has been cleared in the past 2 years = disturbance (early succession; pioneer species)

Area hasn’t been cleared in 50 years = late succession (climax community)

Area hasn’t been cleared for 10 years = mid succession

Environmental Resistance determines biotic potential.

Carrying Capacity=KPopulation Growth=r

Asexual

Sexual