Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem. For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is converted by producers into stored chemical energy through photosynthesis, It then passes from organism to organism in food webs. The number of organisms an ecosystem can support depends on the resources available and abiotic factors such as quantity of light and water, range of temperatures, and the soil composition. Limitations of resources and other factors such as predation and climate limit the growth of populations in specific niches in the ecosystem.
Ecosystems are dependent on interrelationships within the environment.
There are millions of species of animals, plants, and micro-organisms living today that differ from those that lived in the remote past. Each species lives in a specific and fairly uniform environment. Although different species look very different, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry. Biological evolution accounts for a diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations.