“Communities in Transition” All communities change over time in response to environmental conditions. This gradual change in species composition is called. All communities change over time in response to environmental conditions. This gradual change in species composition is called ecological succession. = establishment of life on a “life-less” ground or area. Primary Succession = establishment of life on a “life-less” ground or area. Examples: lava flow, glacier retreating = biotic community established in an area where some type of biotic community is already present. 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******** TWO TYPES OF SUCCESSSION

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

Bare Rock ! Lichen/Moss Small herbs, shrubs Pines, 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 present) HAPPENS MUCH FASTER!! early succession mid succession late succession

GLACIERS RECEDING - northwest LAVA FLOW - Hawaii PRIMARY 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=K Population Growth=r Asexual Sexual