By studying processes that move energy and matter throughout an ecosystem, ecologists can better understand how ecosystems function. One of these processes is photosynthesis. The process of photosynthesis begins with the Sun and it's solar energy (nearly all of the energy that powers ecosystems comes from the Sun). This solar energy is absorbed by plants, algae, and some bacteria so they can produce usable forms of energy. These organisms are known as producers or autotrophs. These autotrophs use solar energy to convert carbon dioxide (CO2) and water (H2O) into glucose (C6H12O6). Glucose is a form of potential energy which can be used by many organisms. Not only does photosynthesis produce glucose, but it also produces oxygen as a waste product. This is why plants and other producers are helpful to us humans and other organisms because they give us the oxygen we need to breathe.
Photosynthesis
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Cellular Respiration
Next is cellular respiration, a process by which cells unlock the energy of chemical compounds. Unlike photosynthesis which is used by autotrophs, cellular respiration is used by herbivores. Herbivores eat the tissues of autotrophs and gain energy from the chemical energy contained in those tissues. There are two types of respiration: aerobic and anaerobic. Aerobic respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water. Put simply, it’s the opposite of photosynthesis. Organisms undergoing aerobic respiration are running photosynthesis backward to recover the solar energy stored in glucose. In contrast, anaerobic respiration is a process by which cells convert glucose into energy in the absence of oxygen. Bacteria that live in muddy swamps will use this process since they cannot use oxygen.
Consumers
Consumers are organisms that are incapable of photosynthesis and must obtain their energy by consuming other organisms also known as heterotrophs. Consumers are different from producers in that they are incapable of photosynthesis and must obtain their energy by consuming other organisms. The first type of consumer is the primary consumer (or herbivore) which eats producers. Examples of these consumers include zebras, grasshoppers, tadpoles, and zooplankton. The other two types of consumers are considered carnivores because they eat other consumers. Organisms that eat primary consumers are considered secondary consumers. Examples of these consumers include lions, hawks, and rattlesnakes. Carnivores that eat secondary consumers are called tertiary consumers which include bald eagles and lions.
Food Chain and Food Web
Trophic levels can be seen within the different types of consumers. Trophic levels are the successive levels of organisms consuming one another. In a food chain, energy moves from one level to the next. A food chain is the sequence of consumption from producers through tertiary consumers. Because species are rarely connected in such a simple figure, a food web is more realistically accurate. A food web is a complex model of how energy and matter move through trophic levels. Food webs illustrate the main point that all species in an ecosystem are connected to one another.
Other Organisms
Along with producers and consumers, there are scavengers, detritivores, and decomposers. These three groups of organisms feed on the dead organic matter. Scavengers consume dead animals. For example, vultures are organisms that feed off of dead animals, so they would be considered scavengers. Detritivores are organisms that specialize in breaking down dead tissues and waste products into smaller particles. Examples include millipedes, slugs, and dung beetles. Once detritivores have broken down the dead tissues, decomposers come in. They are fungi and bacteria that convert organic matter into small elements and molecules that can be recycled back into the ecosystem. These three groups of organisms are essential to the recycling of organic matter and energy. Without them, the world would rapidly fill up.
GPP vs NPP
The amount of energy available in an ecosystem can vary depending on how much life that area can support. An ecosystem’s productivity is measured by scientists so they can better understand where the energy comes from and how it is circulated through an ecosystem. The gross primary productivity is the total amount of solar energy that producers in an ecosystem capture via photosynthesis over a given amount of time. One important point about GPP is that because it is gross, it accounts for the total amount of energy and does not account for the energy lost when the producers respire. Basically, GPP measures how much photosynthesis is occurring over some amount of time. This is different from net primary productivity. NPP is the energy captured by producers in an ecosystem minus the energy producers respire. Measuring NPP can help scientists compare the productivites of different ecosystems. Essentially, the greater the productivity of an ecosystem, the more primary consumers can be supported. NPP also helps measure the productivity after a change in the ecosystem by observing the stored energy (NPP).
Converting sunlight into chemical energy is not an easy or efficient process. Only about 1% of solar energy that reaches the producers in an ecosystem is converted into chemical energy through photosynthesis. The other 99% of solar energy is reflected or passes through producers without being absorbed. Out of that 1% that is absorbed, 60% is used to fuel the producer’s respiration. The other 40% is used to support the plant’s growth and reproduction (NPP).
For example: “A forest in North America might have a GPP of 2.5 kg C/m2/year and lose 1.5 kg C/m2/year to respiration by plants. Because NPP = GPP – respiration, the NPP of the forest is 1 kg C/m2/year. This means that the plants living in 1 m2 of forest will add 1 kg of carbon to their tissues every year by means of growth and reproduction. So, in this example, NPP is 40 percent of GPP. “
Ecological Efficiency
Ecological efficiency is the proportion of consumed energy that can be passed from one trophic level to another. The efficiencies are relatively low. Out of the total biomass at each level, only approximately 10 percent of energy can be converted into energy at the next higher trophic level. We represent this distribution of biomass among trophic levels through a trophic pyramid. Most of the energy is found at the producer level, which then decreases as you ascend the pyramid.
