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- [Narrator] Fueled by sunlight and rain, tropical rainforests are some of the most diverse, energy-rich ecosystems on the planet. A single hectare of rainforest, like this one in Peru, may contain over 50,000 species, housing a vast, interactive network of plants, animals, and insects. At the California Academy of Sciences, our mission is to explore, explain, and sustain tropical rainforests. Scientists, like Michelle Trautwein, are experts in these efforts, conducting research to help us better understand the structure and diversity of rainforest ecosystems. Entering a tropical rainforest, we find vertical layers of life, each with its own unique structure and composition. The forest floor receives very little sunlight. It is a hot, humid place where animals, like leafcutter ants, spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, we find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social groups. Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph. (calm bell music) The canopy is believed to house over 70% of species found in the rainforest, making in the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, and species evenness, the abundance of each species. Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, Community B has greater evenness, a more balanced number of individuals from each species. We recognize Community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances, like deforestation and climate change. Even with these findings, there are still many unanswered questions about tropical rainforests and the species that inhabit them, such as: Why are tropical rainforests so diverse? Why does the canopy have high species richness? You have the opportunity to explore and explain these incredibly diverse ecosystems.