average number of trophic level in the food chain of an ecosystem are
Trophic level The efficiency with which energy or biomass is transferred from one trophic level to the next is called the ecological efficiency. Consumers at each level convert on average only about 10% of the chemical energy in their food to their own organic tissue (the ten-percent law). For this reason, food chains rarely extend for more than 5 or 6 levels. At the lowest trophic level (the bottom of the food chain), plants convert about 1% of the sunlight they receive into chemical energy. It follows from this that the total energy originally present in the incident sunlight that is finally embodied in a tertiary consumer is about 0.001%[7]
Niche differentiation When species use different resources, this can help them to coexist. For example, some lizard species appear to coexist because they consume insects of differing sizes.[3] Alternatively, species can coexist on the same resources if each species is limited by different resources, or differently able to capture resources. For example, different types of phytoplankton can coexist when different species are differently limited by nitrogen, phosphorus, silicon, and light.[4] In the Galapagos Islands, finches with small beaks are more able to consume small seeds, and finches with large beaks are more able to consume large seeds. If a species' density declines, then the food it most depends on will become more abundant (since there are so few individuals to consume it). As a result, the remaining individuals will experience less competition for food.