This document provides an overview of ecosystems and biomes. It begins by defining an ecosystem as a group of organisms along with their physical environment. Ecosystems are made up of biotic (living) and abiotic (non-living) factors. Biodiversity, or the variety of species in an ecosystem, determines how resilient the ecosystem is to change. Ecosystems go through successional changes over long periods of time as the environment and communities change. There are three main types of terrestrial biomes - tropical, temperate, and high-latitude - determined by factors like latitude and climate. Aquatic ecosystems include freshwater, wetlands, estuaries, and marine environments. The document concludes with a discussion of levels