1. ECOSYSTEMS ARE ALWAYS CHANGING POPULATIONS CHANGE OVER TIME –POPULATION GROWTH & DECLINE –MAINTAINING A BALANCE ECOSYSTEMS CHANGE OVER TIME –SUCCESSION: gradual change in an ecosystem in which one biological community is replaced by another (field  forest). PRIMARY SUCCESSION SECONDARY SUCCESSION –PATTERNS OF CHANGE

2. Population Growth & Decline Birth rate is 1 factor affecting population (unstable ecosystem-lack of food-may delay reproduction) Predator-Prey interactions affect population size. Limiting Factor = any factor/condition that limits the growth of a population in an ecosystem. A large # of predators will limit # of prey. Lack of nutrients for soil limits plant population; large population of algae in lake can use up oxygen & limit # of fish.

3. Maintaining a Balance Living things have certain minimum requirements for food, water & living space. CARRYING CAPACITY = when a population reaches a state where it can no longer grow (the maximum number of individuals that an ecosystem can support). An ecosystem’s carrying capacity is different for each population (a meadow can support more ants & bees than bluebirds; Isle Royale supports more moose (1 o consumer eating plants) than wolves (2 o consumer). Biotic factors can be limiting factors; interactions between populations (competition, predation, parasitism). Abiotic factors (temp., water, minerals, wind exposure) are limiting too.

4. PRIMARY SUCCESION Primary succession: establishment of a new biological community (plants starting to grow where a glacier retreated & left a barren area) Pioneer Species: the first living things to move into a barren environment (moss & lichen are common when no topsoil is available- have tiny rootlike anchors) As pioneers grow, they weaken rock, it breaks down & mixes with decaying plant matter to form soil. Now, new plants can move in & take root, eventually supporting small animals which in turn support larger ones.

5. Secondary Succession Takes place after a major disturbance to biological community in a stable ecosystem. (Soil remains after flood/fire/human activity) Seeds & plant roots survive, so after time grasses & small shrubs grow up among decaying remains. Birds, insects, rodents return. Alder trees (put nutrients into soil) take root and biological community grows & develops.

6. PATTERNS OF CHANGE Succession can establish forest, wetland, coastal or an ocean community. May happen over tens or hundreds of years. Pattern is same: community of producers forms first, then decomposers & consumers, then more producers and even more decomposers & consumers, leading to a stable biological community.

7. Patterns of Change con’t. Pioneer species can help other species grow or prevent others from establishing. –Alder trees have nitrogen-fixing bacteria on roots to improve nutrient content in soil-allowing other trees to grow. So pioneering species may stabilize soil, shade soil or add nutrients to soil when they die/decompose. –Plants may release chemicals to keep other plants from taking root. Or a new species may outcompete other species by using up resources or resisting dz.