Epiphytes live on tall rainforest trees without affecting their health.

A tapeworm absorbs nutrients in a fox’s intestine, weakening the fox.

Wolves and bears both hunt elk in the same forest ecosystem.

Male penguins compete for limited nesting space during breeding.

Fungi assist plants in nutrient uptake; plants provide sugars in return.

A smaller fish eats parasites off a larger fish’s gills. Both benefit.

Cattle egrets eat insects disturbed by grazing cattle, which are unaffected.

A cuckoo lays its egg in a warbler’s nest. The warbler raises it at a cost.

A lion hunts and eats an antelope. Scavengers later eat leftovers.

Ants protect an acacia tree from herbivores and feed on its nectar.

Two protist species introduced into a lab compete until one is eliminated.

Wolf numbers drop due to a long-term prey shortage.

An orchid tricks insects into pollinating it by mimicking a female scent.

Two reef fish fight for the same hiding spots. One species relocates.

Predator and prey populations rise and fall together in a repeating cycle.

An invasive snake drives native bird populations to collapse.

A crab carries a sea anemone, gaining protection; the anemone gains food scraps.

During a drought, a group of the same species fights for remaining food.

A fox eats a rabbit; a flea lives on the fox and feeds on its blood.