Section 4 – Community Stability

Ecological Succession Equilibrium: stable and balanced Disequilibrium: unstable and off balance Limiting factors shift – carrying capacities altered Population sizes change Succession: a somewhat predictable series of changes over time in a community Following a Disturbance Ex. Fire, Flood, Natural Disasters

Primary Succession Primary Succession: the somewhat predictable series of changes in a community that follows a disturbance so severe that no vegetation or soil life remains Starting from scratch – from rock, sand or sediment Glaciers retreat, lakes dry up, volcanic lava or ash spreads across a landscape Pioneer Species: one of the first species to colonize newly exposed land Well adapted for colonization Seeds can travel long distances to spread quickly

Primary Succession Lichens: formed by a mutualistic relationship between algae and fungi Algae provides food and energy – photosynthesis Fungi holds onto rocks and captures moisture Lichen grows – releases acid the breaks down rock Soil begins to form, small plants, insects and worms move in

Secondary Succession Secondary Succession: the somewhat predictable series of changes in a community that follows a disturbance (e.g., a fire, logging, or farming) that dramatically alters the community but does not destroy all vegetation or soil life Occurs faster than primary succession

Succession in Water Primary Aquatic Succession: when an area fills with water for the first time Glaciers retreat and leave depressions in the ground Over time, aquatic communities are established Secondary Aquatic Succession: follows disturbance to aquatic community Pond fills with organic matter Pond may fill in completely, and a terrestrial system begins

Climax Communities Climax Community: stable community that “completes” the succession process Climate, Soil Conditions and other factors influence a community’s composition These factors can also promote or inhibit a community’s progression between succession stages. Communities – temporary, ever-changing associations among species

Invasive Species Invasive Species: a nonnative (exotic) species that spreads widely in a community A community DISTURBANCE. Do not have sufficient limiting factors, and end up taking over.

What makes a species Invasive? Some nonnative species are NOT invasive Populations remain Small and Localized, eventually dying out. Others exist without causing problems Invasive when limiting factors are not present in their new environment. Limiting Factors: predators, parasites, competitors Population growth of exotic species is not held in check. Community thrown out of balance.