Complexity and Energy Cycle of Food Chains - Coursework Example

Food Chain Food chains illustrate the feeding relationships betweens species to another within the ecosystem in which organisms are linked to the other organisms. A food chain is an arrangement of the organisms of an ecological community according to the order of predation in which each member uses the next member as a food source (Kretch 543). A food chain can also be defined as the interaction of animals and plants in their quest for survival. History Although the term was not used until 1913 by the American ecologist Victor Shelford, the concept had already been anticipated by Charles Darwin in 1859 as “the tangled bank” metaphor and developed by the zoologist Karl Semper in 1881 (Kretch 143). Charles Elton further developed the concept and promoted food chains as one of the basic principles forming the basis of community ecology. Since the 1950’s much research has been conducted on food webs (the totality of interacting food chains in an ecological community). Food Chain A food chain starts with a plant that is able to use energy from the sun and the nutrients from its surrounding, to make food. Small organisms can eat the plant for food, and in turn, the small organisms become food for larger animals. They may then become food for even larger animals and so on up the food chain. The animals that are eaten in the food chain are called prey while the animals that eat other animals for food are called predators. A food chain can be as simple as three organisms or very complex with many predator/prey interactions. When an organism in the food chain dies, it becomes nutrients for the plants at the base of the food chain. In most healthy food chains, there is a mix of healthy organisms on each level of the food chain and many organisms at the base of the food chain and lower at the top. A food chain is a straight line sequence of steps by which energy originally stored in autotroph tissues moves to a higher trophic levels (Starr 733). In one tall grass prairie food chain, energy from a plant flows to a cutworm that eats its juicy part, then to the snake that eats the cutworm, to sandpaper that eats the snake, and finally to a marsh hawk that consumes the sandpaper (Starr 733). When you eat fish from the sea, such as tuna, you are taking part in the food chain that began somewhere in the ocean There tiny floating animals and plants called plankton were eaten by tiny fish. The tiny fish were eaten by larger fish, and these fish were eaten by even larger fish such as tuna. Every living thing has its place in the food chain and most belong to the several different food chains (Hoare 123). A food chain begins with green plants, which manufacture their own food from water, chemicals in the soil and air, and sunlight, which is called photosynthesis (Hoare 123). Unlike plants, animals cannot make their own food, instead some of them eat plants, and the rest eat other animals. When animals or plants die, bacteria that live in the soil break down the animals or plant tissues, and the chemicals that make up the animals or plants are released in the soil (Hoare 123). These chemicals act as fertilizers to enrich the soil and help the green plants to grow. Energy Cycle Since all life requires the input of energy, the energy cycles within the ecosystem are central to its well being. On earth, the sun provides the energy that is the basis of life in most ecosystems (an exception is the hydrothermal vent communities that derive energy from the heat of the Earth’s core) (Callihan 96). Without the constant influx of solar energy into our planetary system, most life would cease to exist. Energy generally flows through the entire ecosystem in one direction which is from producers to consumers and on to decomposers through the food chain. Photosynthetic organisms such as plants, some protest and some bacteria are the first link in most food chains in which they use the sunlight to combine carbon dioxide an water into sugars, releasing oxygen gas. Photosynthetic organisms are called producers, since they synthesize sugar and starch molecules using the sun’s energy to link the carbons in the carbon dioxide (Callihan 97). Primary consumers which are also known as herbivores are species that eat photosynthetic organisms. Consumers utilize sugars and starches stored in the cells or tissues for energy. Secondary consumers feed ob primary consumers, and on the food chain goes, through tertiary, quaternary (etc,) consumers. Finally, decomposers (fungi, bacteria, some animals) are species that recycle the organic material found in dead plants and animals back in the food chain. Animals that feed only on other animals are called carnivores also known as meat-eaters), whereas those that consume both synthetic and other animals are called as omnivores. The energy cycle of the food chain is subject to the laws of thermodynamic which states that energy can neither be created nor destroyed (Callihan 97). However, every use of energy is less than 100% efficient because 10% is lost as heat. When we call photosynthetic organisms producers, we mean that they produce food using the sun’s energy to form chemical bonds in sugars and other biomolecules. Other organisms can use the energy stored in the bonds of these biomolecules. The steps in the food chain are also known as trophic levels. Grasses are on the bottom of the pyramid; they are the producers, the first trophic level. Producers are also known as autotrophs, as they produce their own food. Each trophic level is greater in biomass (total mass of organisms) than the level above it (Callihan 97). Grasshoppers represent the second trophic level, or primary consumers in an example of food chain. Grasshoppers consume plants and are consumed in the example by toads, the secondary consumers, which represent the third trophic level. Snakes consume toads, and are in turn consumed by owls making these the fourth and fifth trophic levels. In the example, bacteria are the decomposers that recycle some of the nutrients from dead owls (and other levels) to be reused by the first trophic level. The pyramid illustrates a food chain; however, in nature it is never actually as simple as shown. Owls consume snakes, but they may also consume toads (a lower level in the pyramid) and fish (from an entirely different pyramid). Thus, within every ecosystem there may be numerous food chains interacting in varying ways to form a food web (Callihan 98). Furthermore, all organisms produce waste products that feed decomposers. The food web represents the cycling and recycling of both energy and nutrients within the ecosystem. The productivity of the entire web is dependent upon the amount of photosynthesis carried out by photosynthesizers (Callihan 98). Food Web Food web is the collection of interconnected food chains in which materials and energy flow within an ecosystem (Food Web Encarta). The food web is separated into 2 broad categories such as the detrital web which starts with organic debris, and the “grazing web” which normally starts with green plants, Photosynthesizing planktons, algae (Food Web Encarta). In detrital web, substances pass from animal and plant matter to fungi (decomposers) and bacteria, then to detrital feeders (detrivores), and then to predators or carnivores, while in a grazing web, materials generally pass from plants to plant eaters or herbivores, to flesh eaters or carnivores (Food Web Encarta). Food Chains and Webs at Oceans Oceanic food chains, like those in all other ecosystems, begin with primary producers, the organisms that fix inorganic carbon from the atmosphere to produce organic matter. In oceans they range from microscopic bacteria and phytoplankton, drifting in surface waters, to large attached algae familiar along the shore as kelps and seaweeds. In the open ocean primary production is due partly to bacteria and very much more to phytoplankton, mostly single celled or colonial algae (Stonehouse 250). Primary producers are browsed by consumers of various kinds, mostly in the zooplanktons, including arrow-worms, polychaetes, crustacea, and the larvae of many organisms from hydroids to fish, and zooplankton is in turn feed on by fishes, birds, seals, and whales, so the energy fixed by the primary producers passes along the food chain (Stonehouse 250). A proportion of primary producers sink below the level of plankton, to be taken by a host of predators on the sea bed (Stonehouse 250). Complexity in Food Webs: Multitrophic Series According to Vicki Medland (Krech 544): Omnivory is one of the reasons food webs are so complex. Some species feed in many different trophic levels. This greatly increases the complexity and interactions present within the web. It was originally suggested that omnivory was rare in food webs because it lead to instability. More recent research especially that on complex detritus based food webs suggest that omnivory is quite common and doesn’t lead to instability in many cases. Detrivores are also difficult to categorize because they feed on dead organic matter accumulated from many trophic levels. Certain species feed on different trophic levels as juveniles. In some species each sex has different trophic level. The effects of feeding on many different levels greatly increases food web complexity. Complexity Few food webs are simple chain. Most involve consumers as omnivores that feed on more than one trophic level, such as coyotes, which are predators that sometimes feed on herbivores such as rabbits or on other predators such as lizards (Krech 544). Consumers can be herbivores (feeding on grasses or fruits) and are often detritivores (scavenging on dead animals. Some species feed at different trophic levels at different life stages like for example mosquitoes which are detritivores as larvae, whereas females are blood feeding predators, and males are nectivores (feeding on nectar) or may not feed at all (Krech 544). A measure of complexity called “connectance” has been developed to better understand food-web dynamics. Connectance is the ratio of the number of actual feeding interactions between the members of the food web to the possible number of interactions with a higher ratio indicating greater complexity (Krech 544). A second factor is interaction strength, which is the actual amount of influence one species has on another. By measuring connectance and interaction strength scientist are able to evaluate the stability of the food web or its ability to remain unchanged following different types of disturbance. It was believed that more complex food webs are less stable, but recent studies of food webs with high connectance but weak interaction strengths refute this belief Krech 544). Works Cited Callihan, Laurie Ann. Biology. New York: Research & Education Association 2004. “Food Web.” 2007. Food Web - MSN Encarta, 28 December 2007 . Hoare, Ben. The Kingfisher A-Z. New York: Kingfisher Publications 2002. Krech, Shepard.,Mcneill, John Robert., Merchant, Carolyn. Encyclopedia of World Environmental History. New York: Routledge 2004. Starr, Cecie. Biology Concepts and Applications. New York: Thomson Brooks/Cole 2005. Stonehouse, Bernard. Encyclopedia of Antarctica and the Southern Oceans. New York: John Wiley and Sons 2002. Read More