aggregate size distribution The proportions of surface soil aggregates of different sizes in a given soil. The aggregate size distribution is affected by the application of fertilizers, the soil tillage system, and by wind erosion. It affects soil properties such as aeration, drainage, and water retention. See soil erosion; soil structure; soil texture.
aggregate species A group of species so closely related that it is very difficult to distinguish between them in the field. Such species usually arise through hybridization between closely related species. An example is the blackberry (Rubus frutico-sus agg.).
aggregation of risk A distribution of risk of attack from predators in which in some habitat patches the prey are at greater or lesser risk of predation than would be expected by chance alone. The term is usually applied to the risk of a host species being attacked by a parasitoid. See also aggregative response.
aggregative response The response of a predator to prey density in which it spends more time in habitat patches with higher densities of prey, leading to higher predator densities in these patches, or in patches with lower densities of prey, leading to lower densities of predators in these patches. See also aggregation of risk.
aggression A behavior pattern that intimidates or injures another organism, except for the purpose of predation. Aggression ranges from fighting over dominance in social animals to the singing of a bird in defense of its territory.
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