An ecosystem consists of both biotic and abiotic factors. But what exactly are these factors? How do they impact an ecosystem, and do changes in abiotic and biotic factors change the ecosystem? An ecosystem depends on the interactions of the living and nonliving elements in the system.
TL;DR (Too Long; Didn't Read)
The abiotic factors in an ecosystem are all the nonliving elements (air, water, soil, temperature) while the biotic factors are all the living organisms in that ecosystem.
Biotic Factors in an Ecosystem
In an ecosystem, biotic factors include all the living parts of the ecosystem. A healthy woodland ecosystem contains producers like grasses and trees, as well as consumers ranging from mice and rabbits to hawks and bears. The biotic components of an ecosystem also encompass decomposers like fungus and bacteria. A healthy aquatic ecosystem includes producers like algae and phytoplankton, consumers like zooplankton and fish, and decomposers like bacteria. Specific biotic categories include:
Plants: Most ecosystems depend on plants to perform photosynthesis, making food from water and carbon dioxide in the ecosystem. In ponds, lakes and the ocean, many of the plants are grasses, algae or tiny phytoplankton floating on or near the surface. Also in this category are the chemosynthetic bacteria that live at deep ocean vents, which form the base of that food chain.
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Animals: First-order consumers like mice, rabbits and seed-eating birds as well as zooplankton, snails, mussels, sea urchins, ducks and black sharks eat the plants and algae. Predators like coyotes, bobcats, bears, killer whales and tiger sharks eat first-order consumers. Omnivores like bears and rotifers (nearly microscopic aquatic animals) eat both plants and animals.
Fungi: Fungi like mushrooms and slime molds feed off the bodies of living hosts or break down the remains of once-living organisms. Fungi serve an important role in the ecosystem as decomposers.
Protists: Protists generally are one-celled microscopic organisms, and they are sometimes overlooked in the ecosystem. Plant-like protists use photosynthesis, so they are producers. Animal-like protists such as paramecia and amoebas eat bacteria and smaller protists, so they form part of the food chain. Fungus-like protists often serve as decomposers in the ecosystem.
Bacteria: In deep-sea vents, chemosynthetic bacteria fill the role of producers in the food chain. Bacteria act as decomposers, breaking down dead organisms to release nutrients. Bacteria also serve as food for other organisms.
Abiotic Factors in an Ecosystem
The abiotic factors in an ecosystem include all the nonliving elements of the ecosystem. Air, soil or substrate, water, light, salinity and temperature all impact the living elements of an ecosystem. Specific abiotic factor examples and how they may affect the biotic portions of the ecosystem include:
Air: In a terrestrial environment, air surrounds the biotic factors; in an aquatic environment, the biotic factors are surrounded by water. Changes in the chemical composition of the air, like air pollution from cars or factories, impacts everything that breathes the air. Some organisms are more sensitive to changes in the air. For aquatic organisms, both the chemical composition of the air and water but also the quantity of air and water impact anything living in the water. For example, when algal blooms become excessive, the algae reduce the oxygen in the water, and many fish suffocate.
Soil or Substrate: Most plants need soil for nutrients and to hold themselves in place with their roots. Plants in areas with nutrient-poor soils often have adaptations to compensate, like the insect-capturing Cobra Lily and Venus Fly-trap. Soil or substrate also impact animals, such as the filter-feeding nudibranchs whose gills would be clogged if the substrate suddenly included fine particles of sand and silt.
Water: Water is essential for life on Earth. Water is essential to the chemical reactions within living organisms, is one of the key components for photosynthesis and is the placeholder in cells. Water also serves as a living environment for aquatic creatures. As such, changes in quantity and quality of water impact living systems. Water also has mass, creating pressure in aquatic environments. Water's ability to hold temperature moderates temperature changes within its mass and in nearby areas. For example, heat from the equator moved to higher latitudes by ocean currents results in milder climates for the affected areas. Differences in rainfall mean the difference between desert and forest biomes. Clouds can even be the controlling factor in some ecosystems, such as the cloud forests of the tropics where plants draw their moisture from the air.
Light: Lack of light in the deeper ocean prevents photosynthesis, meaning that the majority of life in the ocean lives near the surface. Differences in daylight hours impact temperatures at the equator and the poles. The day-night rhythm of light impacts life patterns, including reproduction, for many plants and animals.
Salinity: Animals in the ocean are adapted to the salinity, using a salt renal gland to control the salt content of their bodies. Plants in high-salinity environments also have internal mechanisms to remove the salt. Other living creatures without these mechanisms die from too much salt in their environment. The Dead Sea and Great Salt Lake are two examples of environments where salinity has reached levels that challenge most living organisms.
Temperature: Most organisms require a relatively stable temperature range. Mammals even have internal mechanisms to control their body temperature. Temperature changes, especially extreme and sudden changes, that go beyond an organism's tolerance will harm or kill the organism. Temperature changes can be natural, due to sunspots, weather-pattern shifts or ocean upwelling, or can be artificial, as with cooling-tower outfall, released water from dams or the concrete effect (concrete absorbing heat).
Abiotic vs Biotic Factors
A major difference between biotic and abiotic factors is that a change in any of the abiotic factors impacts the biotic factors, but changes in the biotic factors don't necessarily result in changes to the abiotic factors. For example, increasing or decreasing salinity in a body of water may kill all the inhabitants in and around the water (except maybe bacteria). The loss of the biota of the body of water doesn't necessarily change the salinity of the water, however.