Food Web : At each trophic level, there may be many more species than indicated in the table above. Food webs can be very complex.
Food availability may vary seasonally or by time of day. An organism like a mouse might play two roles, eating insects on occasion making it a secondary consumer , but also dining directly on plants making it a primary consumer.
A food web of who eats who in the southwest American desert biome might look something like this:. Keystone Species : In some food webs, there is one critical " keystone species " upon which the entire system depends. In the same way that an arch collapses when the keystone is removed, an entire food chain can collapse if there is a decline in a keystone species. Often, the keystone species is a predator that keeps the herbivores in check, and prevents them from overconsuming the plants, leading to a massive die off.
When we remove top predators like grizzly bears, orca whales, or wolves , for example, there is evidence that it affects not just the prey species, but even the physical environment.
Apex Predators : These species are at the top of the food chain and the healthy adults have no natural predators. The young and old may in some cases be preyed upon, but they typically succumb to disease, hunger, the effects of aging, or some combination of them. The also suffer from competition with humans, who often eliminate the top predators in order to have exclusive access to the prey species, or through habitat destruction, which is an indirect form of competition.
Decomposers : When organisms die, they are sometimes eaten by scavengers but the remaining tissues are broken down by fungi and bacteria. In this way, the nutrients that were part of the body are returned to the bottom of the trophic pyramid. Bioaccumulation : In addition to being less energy efficient, eating higher up the food chain has its risks. Pesticides and heavy metals like mercury, arsenic, and lead tend to be consumed in small quantities by the primary consumers.
This is so to keep the balance in the flow of energy, which you can see later. That is, the tertiary consumers are those who consume the most energy and those who produce less, so your group should be smaller. In any food web, energy is lost every time an organism eats another. Because of this, there must be many more plants than consumers of plants.
There are more autotrophs than heterotrophs, and more plant consumers than meat. Although there is intense competition between animals, there is also interdependence. When a species is extinguished, it can affect a whole chain of species and have unpredictable consequences. As the number of carnivores in a community increases, they eat more and more herbivores, and so the herbivorous population declines.
It then becomes more difficult for carnivores to find herbivores than to eat, and the carnivorous population in turn decreases. In this way, carnivores and herbivores are maintained in a relatively stable equilibrium, each limiting the population of the other. There is a similar balance between plants and plant-eaters. The organisms considered as tertiary consumers require a great amount of energy to be able to nourish themselves and to develop normally their vital functions.
This is due to the way in which the flow of energy between trophic levels occurs. Almost all the energy that drives ecosystems comes ultimately from the sun. The solar energy , Which is an abiotic factor, enters the ecosystem through the process of photosynthesis. The organisms in an ecosystem that capture the electromagnetic energy of the sun and convert it into chemical energy are called producers. Producers produce the carbon-based molecules, usually carbohydrates, that are consumed by the rest of the organisms in the ecosystem, including humans.
For instance, carnivores that feed on other carnivores are considered as tertiary consumers. Synonym s :. Freshwater ecology focuses on the relations of aquatic organisms to their freshwater habitats.
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