AP Biology: Ecology, Populations and Ecosystems

Organism → population → community → ecosystem → biome → biosphere

All the individuals of one species living in the same area.

All the populations of different species that live and interact in an area.

Biotic: living parts of the environment (predators, competitors, food). Abiotic: nonliving parts (temperature, water, sunlight, soil pH).

\frac{dN}{dt} = r_{max}N

\frac{dN}{dt} = r_{max}N\left(\frac{K - N}{K}\right)

The maximum population size an environment can sustain over time.

At K/2, half the carrying capacity.

Density-dependent factors get stronger with crowding (competition, disease, predation). Density-independent factors hit regardless of size (floods, fires, freezes).

r-selected: many small offspring, little parental care, early maturity (insects, weeds). K-selected: few large offspring, lots of care, populations near carrying capacity (elephants, humans).

Type I: most survive to old age (humans). Type II: constant death rate throughout life (many songbirds, rodents). Type III: very high early mortality (oysters, most fish).

Both species benefit, e.g. bees and flowering plants.

One species benefits and the other is unaffected, e.g. barnacles on a whale.

One species benefits at the expense of its host, e.g. tapeworms.

Two species competing for the exact same limiting resource cannot coexist indefinitely; one is eliminated or the niche is divided (Gause's principle).

Similar species divide a resource (feeding at different heights or times), which lets them coexist.

A species' role in its ecosystem: the full set of biotic and abiotic resources and conditions it uses.

Fundamental niche: everything a species could use. Realized niche: the part it actually uses because of competition and other interactions.

A species with a much larger effect on its community than its abundance suggests, e.g. sea otters keeping sea urchins in check in kelp forests.

A harmless species resembles a harmful one, e.g. hoverflies that look like wasps.

Two or more harmful species resemble each other, reinforcing the same warning to predators (different stinging bees and wasps).

Bright warning colors on toxic or dangerous animals, e.g. poison dart frogs.

Prey numbers rise, then predator numbers rise after a lag; predators cut prey numbers, and then predators decline (lynx and snowshoe hare).

Primary: starts on bare rock with no soil (after lava flows or retreating glaciers); pioneer species like lichens come first. Secondary: starts where soil remains (after a fire or on abandoned farmland); faster.

Producers → primary consumers (herbivores) → secondary consumers → tertiary consumers. Decomposers recycle nutrients from every level.

Most of the rest is lost as heat from cellular respiration, which is why food chains rarely exceed four or five levels.

10 kcal (10,000 → 1,000 → 100 → 10).

GPP: total energy captured by photosynthesis. NPP = GPP − energy producers use in their own respiration. NPP is what is available to consumers.

Increasing concentration of persistent toxins such as DDT or mercury at higher trophic levels.

Organisms such as bacteria and fungi that break down dead matter and wastes, returning nutrients to the soil.

A non-native species that spreads rapidly and harms its new ecosystem, often because it lacks natural predators (zebra mussels, kudzu).

More species means more redundancy in ecological roles, so the ecosystem can better resist and recover from disturbances.