AP Environmental Science

## Ecosystems and their parts An **ecosystem** is a community of living organisms together with the nonliving environment they interact with. The living parts are **biotic** factors (plants, animals, fungi, bacteria) and the nonliving parts are **abiotic** factors (sunlight, temperature, water, soil chemistry, salinity, oxygen). The two sets act on each other all the time: plants change the soil they grow in, and the soil's nutrients and moisture decide which plants can grow there at all. A **population** is all the individuals of one species in an area, and a **community** is all the populations living and interacting in that area. The interactions between species depend mainly on how much of each resource is available, since food, water, light, space and shelter are always limited somewhere, and how species deal with that shortage shapes who survives. ## Predator and prey In a **predator-prey relationship**, the predator is the organism that eats another organism, the prey. The two populations often rise and fall together in a pattern: when prey are abundant, predators have plenty of food and their numbers grow; more predators then reduce the prey population; the shortage of prey makes predator numbers fall; and with fewer predators the prey recover. Real populations are also affected by weather, disease and alternative food, so the cycles are rarely as tidy as this. Predation acts as a selective pressure on both sides. Prey that are faster, better camouflaged or better…