13. Ecosystem relationships
Contents
13.1 Interactions between organisms
Organisms that inhabit a certain area make up the area's community of organisms. Organisms living within a community have various kinds of interactions and relationships with each other.
Some organisms live in a predator-prey relationship. For example, a common roach eats water fleas, whereas a pike eats roaches. If the population of water fleas suddenly increases, so will the population of roaches. As a result of the increased roach population, the size of the water flea population begins to decrease once again. In turn, the size of the roach population is kept in check by the pike population. Therefore, the different populations of a community affect each other in terms of population size.
Food chain: water fleas → roach → pike.
The individuals of the same species compete with each other. Competition can also arise between species with similar ecological niches. Having a similar ecological niche means that the two species have similar adaptations and lifestyles: for example, they can have similar diets or make use of similar mating locations.
Some species live with each other so closely that they are dependent on each other. This is called symbiosis. For example, lake fungi live in symbiosis with tiny algae. This symbiosis is mutually beneficial for the two species: the fungus receives sugar from the photosynthetic alga, whereas the alga receives a sheltered and stable growing surface from the fungus.
13.2 Energy in a lake's organism community
13.3 Food chains and food webs
When studying the interactions between the organisms of a community, we can distinguish food chains, where the chemical energy produced in photosynthesis moves from one organism to another. Food chains are comprised of organisms that act the parts of producers, consumers, and decomposers. When combined, food chains make up food webs.
Food webs are arrived at by conceptualizing all the food chains of a community, and the individuals within these food chains. When these relationships have been discovered, one notices that all the species of an ecosystem have relationships with all the other species within that same ecosystem.
Food webs consist of the food chains of an ecosystem.
13.4 Food pyramid
Producers (such as blue-green alga or water lilies) produce energy and oxygen to the ecosystems through the process of photosynthesis. Producers are also the food of first degree consumers. Alga-eating water fleas are an example of first degree consumers.
Second degree consumers are species that eat use first degree consumers. For example, small plankton-eating fish species, such as the roach, are second degree consumers. In addition to first and second degree consumers, many food chains also have third degree consumers. These species eat consumers of the lower degree. Predator fishes, such as the pike, are a good example of third degree consumers. Food chains can also accomodate consumers of even higher degrees, but in reality such species are very rare. The reason for this is the fact that only a part of the energy of the previous level of the food chain will transfer to the next level.
When a eagle eats a large fish (which itself is a 3rd degree consumer), it is a 4th degree consumer.
The number of species and individuals that inhabit the top of the food chain is smaller than the number of producers or lower-degree consumers. Because of this, the number of organisms in an ecosystem can be conceptualized as a pyramid. Such a pyramid describes how the quantity of individuals within the food chain decreases when moving from the bottom to the top. For example, a small pond can only accommodate only a couple of third degree consumers (such as large pikes), whereas it can accomodate a large number of producers and first degree consumers.
13.5 Decomposers
In addition to producers and consumers, an ecosystem also accomodates organisms that act as decomposers. Organisms such as bacteria, fungi, and crayfish can all function as decomposers in their ecosystems.
Decomposers feed on dead organisms, their parts, and their fecal matter. By doing so, they decompose the dead organisms and their parts, releasing the nutrients contained in them into a form that is accessible to the producers of the ecosystem. Therefore, decomposers act as a kind of link between the "end" of the food chain and its "beginning".
A spotted crayfish functions as a decomposer when it eats dead organisms.
Decomposers play a vital role in the nutrient cycle of a well-functioning ecosystem. A producer, such as a cattail, uses its roots to gather nitrogen. This nitrogen is transferred to an organism that uses the cattail as its food source, such as the larva of a caddisfly. The nitrogen is then transferred to an organism that eats the larva, such as a perch. Finally, when the perch dies, the decomposers of the ecosystem recycle the nitrogen contained within the perch's body into a form that can be used by plants and other producers. This process is an example of the nutrient cycle in action.
13.6 Terminology
- The organisms of an ecosystem have various kinds of relationships with each other.
- In a predator-prey relationship a species gains food at the expense of the other species.
- Competition between species is harmful for both species.
- Symbiosis is a kind of mutually beneficial relationship between two species.
- An ecological niche is comprised of the resources (or needs) used by a species.
- A producer brings energy into its community through photosynthesis.
- A consumer gains energy by eating producers or other consumers.
- A decomposer gains energy by decomposing dead producers or consumers.
- Plants require nutrients in order to grow. Nitrogen and phosphorous are the two most important nutrients for many plants.