Trophic level is a step or division of food chain which is characterized by the method of obtaining its food. The number of trophic levels are equal to the number of steps in the food chain. The two fundamental trophic levels are producers and consumers.
A group of species belonging to a trophic level which exploits a common resource base in a similar fashion is known as ecological guild. Examples: Nectar feeding birds, grazing animals.
An ecad of a plant species is a population of individuals which although belong to the same genetic stock (genetically similar) but differ in vegetative characters such as size, shape, number of leaves, stem etc.