ecology exam 4 pt 4 (community structure -> succession)

the changing nature of community structure across the landscape reflects the shifting distribution of populations in response to what?

A) changing environmental conditions

B) interactions among species

community structure is dynamic, meaning what?

shifting pattern of species’ dominance + diversity through time

community structure varies in time + space…

A) across the landscape (zonation)

B) in one position as times passes

succession

the gradual and seemingly directional change in community structure through time from field to forest

sere

sequence of communities from grass to shrub to forest

→ EACH of the change is called a “seral stage”

each seral stage has its characteristic structure and species composition. how long does it last?

may last only one or two years, or for several decades

patterns of succession are NOT random…

A) early successional species/pioneer species

B) late successional species

early successional species/pioneer species

usually characterized by high growth rates, smaller size, high degree of dispersal, and high rates of per capita population growth

late successional species

have lower rates of dispersal + colonization, slower per capita growth rate, they are larger + longer-lived

primary succesions

occurs on a site previously unoccupied by a community

secondary succesion

occurs on previously occupied (vegetated) sites after disturbance

→ the disturbance does not always result in the removal of all individuals

primary succession begins on sites that have _____ supported a community, like rock outcrops + cliffs, sand dunes, and newly exposed glacial till

never

alluvial soil

newly deposited soil on a floodplain

→ this is an example of primary succession meaning that this is necessary as a pioneer species for other things to get their footing like grass and shrubs

autogenic

environmental change is a direct result of the presence + activities of organisms within the community

→ i.e. trees blocking vertical light which changes vegetation structure

allogenic

environmental change is the result of a physical process/environment

→ i.e. decline with average temperature with elevation

in early stage of plant succession, shade-intolerant species will dominate. shade-intolerant species grow above + shade the slow-growing, shade-tolerant species. eventually, what will happen?

shade-intolerant species cannot grow + survive in the shaded conditions

succession results from what?

changes in the relative tolerances + competitive abilities of species under autogenically changing environmental conditions