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 (fieldforest).

• PRIMARY SUCCESSION

• SECONDARY SUCCESSION

– PATTERNS OF CHANGE

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.

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 (1o consumer eating plants) than wolves (2o consumer).

• Biotic factors can be limiting factors; interactions between populations (competition, predation, parasitism). Abiotic factors (temp., water, minerals, wind exposure) are limiting too.

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.

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.

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.

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.