predationAn interaction where a predator gets food by eating all or part of another living thing, its prey. In this lesson the word covers plant eaters as well as hunters.Divers counted far fewer purple sea urchins on reefs where sea otters hunt, which is the signature of predation.
predatorThe organism that does the eating in predation. Hunters such as owls count, and so do grazers such as deer, because both take resources from another living thing.A deer browsing an oak seedling is a predator of that seedling, even though the seedling usually survives the meal.
preyThe organism that gets eaten in predation, whether it is an animal, a plant or a microbe.When prey becomes scarce, a predator population usually shrinks a few seasons later.
carnivoreA predator whose food is mostly other animals.A Cooper's hawk in a city park is a carnivore that takes pigeons and starlings.
herbivoreA predator whose food is mostly plants or plant parts, such as leaves, seeds or nectar.Desert tortoises are herbivores that strip wildflowers in spring and reduce how many seeds those plants set.
omnivoreA predator that regularly eats both plants and animals. The mix does not have to be equal: black bears eat mostly plant food and are still omnivores.A raccoon that eats crayfish one night and fallen figs the next is an omnivore.
competitionAn interaction in which two species need the same limited resource, so each one gets less than it would alone. Both are harmed.Starlings and bluebirds compete for the few nest holes in a park: every hole one species takes is a hole the other cannot use.
mutualismAn interaction between two species in which each partner gains something that helps it survive, grow or reproduce. Each partner is acting for itself, not out of kindness.The yucca moth pollinates the yucca while laying its eggs, and the yucca feeds the moth's young with a few of its seeds, a mutualism neither can do without.
commensalismAn interaction that helps one species while the other shows no measurable gain or loss, as far as scientists can tell.Lichens growing on oak bark use the trunk as a surface, and the oak's growth rings look the same with or without them, so ecologists call it commensalism.
parasitismAn interaction in which one species, the parasite, lives on or inside another living species, the host, and takes resources from it. The host is weakened but usually not killed.Winter ticks drinking blood from a moose are parasites; a moose carrying tens of thousands of them loses weight and may die in a hard winter.
hostThe living organism that a parasite lives on or inside and feeds from.A pigeon is the host for feather lice that chew on the barbs of its feathers.
criteria and constraintsCriteria are the requirements a design must meet to count as a success; constraints are the limits, such as cost, size, time or effects on living things, that narrow down which designs are allowed.A criterion for the frog-call sensor shield was cutting highway noise by at least 5 decibels; a constraint was that nothing could block the pond side.
