For example, annual plants only experience the variations observed within a season, while large trees experience decade-long patterns such as the climatic fluctuations induced by El Nino. If a system is self-similar, i.e., there is some feature that is constant on all scales, it can be represented by something called a power law or scaling law. Power laws are a simple description of how a system's features change in proportion to the scale of the system. For organisms or individuals differing in size, scaling relationships among them are known as allometric laws. When viewed on a log-log plot the relationship is linear.
Similarity is central to the concept of scaling.
Basically, reality is size dependent. In biology, constancy in shape with change of size is called isometric growth or isometry. Isometry can then be used as a null hypothesis in scaling studies. If metabolic rate scaled isometrically with the surface area of mass it would be expected to scale to the 0.667 power. Since this is not the case, the scaling of metabolism in organisms violates isometry.