Biotic and Abiotic Factors Together The difference between biotic and abiotic factors may seem to be clear and simple. But if you think carefully, you will realize that many physical factors can be strongly influenced by the activities of organisms. Bullfrogs hang out, for example, in soft “muck” along the shores of ponds. You might think that this muck is strictly part of the physical environment, because it contains nonliving particles of sand and mud. But typical pond muck also contains leaf mold and other decomposing plant material produced by trees and other plants around the pond. That material is decomposing because it serves as “food” for bacteria and fungi that live in the muck.

Taking a slightly wider view, the “abiotic” conditions around that mucky shoreline are strongly influenced by living organisms. A leafy canopy of trees and shrubs often shade the pond's shoreline from direct sun and protect it from strong winds. In this way, organisms living around the pond strongly affect the amount of sunlight the shoreline receives and the range of temperatures it experiences. A forest around a pond also affects the humidity of air close to the ground. The roots of trees and other plants determine how much soil is held in place and how much washes into the pond. Even certain chemical conditions in the soil around the pond are affected by living organisms. If most trees nearby are pines, their decomposing needles make the soil acidic. If the trees nearby are oaks, the soil will be more alkaline. This kind of dynamic mix of biotic and abiotic factors shapes every environment.

In Your Notebook In your own words, explain the difference between biotic and abiotic factors. Give three examples of each.

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