Many small poisonous animals are brightly colored, including the poison dart frog and some species of fish, octopi, and insects. What is common in their environments that would lead to these different animals having a similar trait?

Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating.[1] This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature. Aposematism always involves advertising signals