Why are large carnivores so rare in nature and why is the population of herbivores higher than that of carnivores and omnivores?
Paul Colinvaux wrote a book on this: "Why big fierce animals are rare" in 1978. The reason was pointed out by Charles Elton in 1927 in "The ecology of animals" and it is now known as the Eltonian Pyramid. Every step on the pyramid goes down by 90%. Thus 1000kg of grass supports 100kg of rabbits, 10kg of cats eating rabbits, and a 1kg eagle. Omnivores like us may straddle several steps on the pyramid.
The top-level predators represent the carnivores like humans, lions, and eagles that do not act like prey and undergo predation by another organism. The position of top-level predators on the top of the food web is rare in a community due to the least amount of energy received by top organisms. Carnivores are wide-ranging, but rare because of their positions at the top of food webs. Most of the largest carnivore species, like lions, wolves, and bears, have experienced substantial population declines and range contractions throughout the world during the previous 200 years. The ratio of biomass of plants to herbivores to carnivores is typically about 100:10:1. This is why large carnivores are relatively rare: they get much less energy than the herbivores, and the herbivores get less energy than the original plants. Carnivorous predators have often been considered the most at risk of extinction, because they need to eat a large proportion of food and roam large territories, which increasingly overlap with human territories, causing conflict. Herbivores get energy directly from the source, which allows them to become bigger than carnivores. Carnivores may be at the top of the food chain, but herbivores are often the bigger guns on the ladder. This is because carnivores depend upon herbivores for their food and get energy by consuming herbivores. Some energy is wasted during the transfer from herbivores to carnivores. Consequently, less energy exists at the level of a secondary consumer. There are more herbivores than carnivores. An ecosystem cannot support a large number of omnivores without supporting an even larger number of herbivores, and an even larger number of autotrophs. Herbivores have longer small intestines than carnivores because they eat plant and grass-based foods high in cellulose and need a long time to digest. Bile is a digestive liquid that the liver secretes and stores in the gallbladder. Bile's purpose in the gut is to aid fat digestion and absorption. Because the energy that transfers up to each level is only 10% of what was available for the level below, it cannot support very large number organisms in the next trophic level. By the time you get to the top carnivores there is very little energy left and that supports a smaller number of organisms.Propose an explanation for why populations of top carnivores, such as hawks, are always smaller than the population of herbivores, such as caterpillars. Animals at the top have less energy because they only get 10% of the energy of the organism it gets it from. Energy is lost with each trophic level, so it takes more of the sun's energy to ultimately produce a pound of meat to feed a carnivore than it does to produce a pound of plants to feed an herbivore. 10% of energy is passed from one trophic level to the next.
- Badges
- Science topic