Together, abiotic and biotic factors make up an ecosystem. Abiotic factors are the non-living parts of an environment. These include things such as sunlight, temperature, wind, water, soil and naturally occurring events such as storms, fires and volcanic eruptions. Biotic factors are the living parts of an environment, such as plants, animals and micro-organisms. Together, they are the biological factors that determine a species' success. Each of these factors impacts others, and a mix of both is necessary for an ecosystem to survive.
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Abiotic and biotic factors together make up an ecosystem. Abiotic or non-living factors are those such as climate and geography. Biotic factors are living organisms.
Abiotic or Non-living Factors
Abiotic factors can be climatic, related to weather, or edaphic, related to soil. Climatic factors include air temperature, wind and rain. Edaphic factors include geography such as topography and mineral content, as well as soil temperature, texture, moisture level, pH level and aeration.
Climatic factors greatly impact which plants and animals can live within an ecosystem. Prevailing weather patterns and conditions dictate the conditions under which species will be expected to live. The patterns not only help to create the environment but also impact water currents. Changes in any of these factors, such as those that occur during occasional fluctuations such as El Niño, have a direct impact and can have both positive and negative effects.
Changes in air temperature affect the germination and growing patterns of plants as well as the migration and hibernation patterns in animals. While seasonal changes occur in many temperate climates, unexpected changes can have negative results. Although some species can adapt, sudden changes can result in inadequate protection from severe conditions (for example, being without a winter coat of fur) or without sufficient food stores to last through a season. In some habitats, such as in coral reefs, species may be unable to migrate to a more hospitable location. In all these cases, if they are unable to adapt, they will die off.
Edaphic factors impact plant species more than animals, and the effect is greater on larger organisms than it is on smaller ones. For example, variables such as elevation impact plant diversity more than that of bacteria. This is seen in forest tree populations where elevation, the slope of the land, exposure to sunlight and the soil all play a role in determining the population of particular tree species in a forest. Biotic factors also come into play. The presence of other tree species has an impact. The regeneration density of trees tends to be higher in locations where there are other trees of the same species nearby. In some cases, the presence of certain other species of trees nearby is associated with lower regeneration levels.
Land masses and elevation influence wind and temperature. For example, a mountain can create a wind break, which impacts the temperature on the other side. Ecosystems at higher elevations experience lower temperatures than those at lower elevations. In extreme cases, elevation can cause arctic or sub-arctic conditions even in tropical latitudes. These differences in temperature can make it impossible for a species to journey from one suitable environment to another if the path between requires traveling through changing elevations with inhospitable conditions.
Minerals such as calcium and nitrogen levels affect the availability of food sources. The level of gases such as oxygen and carbon dioxide in the air dictate which organisms can live there. Differences in terrain such as soil texture, composition and the size of sand grains also can impact a species’ ability to survive. For example, burrowing animals require certain types of terrain to create their homes, and some organisms require rich soil while others do better in sandy or rocky terrain.
In many ecosystems, abiotic factors are seasonal. In temperate climates, normal variations in temperature, precipitation and the amount of daily sunlight affect the ability of organisms to grow. This has an impact not only on plant life but also on the species that rely on the plants as a food source. Animal species may follow a pattern of activity and hibernation or may adapt to changing conditions through coat, diet and body-fat changes. Changing conditions encourage high diversity rates among species in an ecosystem. This can help stabilize populations.
Unexpected Climatic Events
The environmental stability of an ecosystem impacts the population of species that call it home. Unexpected changes may indirectly change the food web as changing conditions make it more or less hospitable and influence whether a particular species will establish itself. While many abiotic factors occur in a rather predictable manner, some occur infrequently or without warning. These include natural events such as droughts, storms, flooding, fires and volcanic eruptions. These events can have a great impact on the environment. As long as they do not occur with great frequency or over too large an area, there are benefits to these natural events. When spaced optimally, these events can be highly beneficial and rejuvenate the environment.
Extended droughts negatively impact an ecosystem. In many areas, plants cannot adapt to changing rain patterns, and they die. This also affect organisms further up the food chain that are forced to migrate to another area or make diet changes in order to survive.
Storms provide necessary precipitation, but heavy rain, sleet, hail, snow and high winds can damage or destroy trees and plants, with mixed environmental results. While damage to organisms can occur, this thinning of branches or forests can help strengthen existing species and provide room for new species to grow. On the other hand, heavy rains (or rapid snow melt) can cause localized erosion, weakening the support system.
Floods can be beneficial. Floodwaters provide nourishment to plants that may otherwise not get enough water. Sediment that may have settled in riverbeds is redistributed and replenishes the nutrients in the soil, making it more fertile. The newly deposited soil also can help prevent erosion. Of course floods also cause damage. High floodwaters can kill animals and plants, and aquatic life may be displaced and die when the waters recede without them.
Fire also has both harmful and beneficial effects on an ecosystem. Plant and animal life may be injured or die. The loss of live root structures can result in erosion and later sedimentation of waterways. Harmful gases may be produced and may be carried by winds, affecting other ecosystems as well. Potentially damaging particulates that end up in waterways can be consumed by aquatic life, negatively impacting the water quality. However, fire also can be rejuvenating to a forest. It fosters new growth by cracking open seed coats and triggering germination or by prompting tree pods in the canopy to open and release seeds. Fire clears the undergrowth, reducing competition for seedlings and providing a fresh bed for seeds that is rich in nutrients.
Volcanic eruptions initially result in destruction, but the rich nutrients in volcanic soil later benefit plant life. On the other hand, an increase in water acidity and temperature can be harmful to aquatic life. Birds may experience lost habitat, and their migration patterns may be disrupted. An eruption also forces multiple gases into the atmosphere that can impact oxygen levels and affect respiratory systems.
Biotic or Living Factors
All living organisms, from microscopic organisms to humans, are biotic factors. Microscopic organisms are the most plentiful of these and are widely distributed. They are highly adaptable, and their reproduction rates are rapid, allowing them to create a large population in a short time. Their size works to their advantage; they can be dispersed over a large area quickly, either through abiotic factors such as wind or water currents, or by traveling in or on other organisms. The simplicity of the organisms also aids in their adaptability. The conditions needed for growth are few, so they can easily thrive in a greater variety of environments.
Biotic factors impact both their environment and each other. The presence or absence of other organisms influences whether a species needs to compete for food, shelter and other resources. Different species of plants may compete for light, water and nutrients. Some microbes and viruses can cause diseases that may be transmitted to other species, thus lowering the population. Beneficial insects are the primary pollinators of crops, but others have the potential to destroy crops. Insects also may carry diseases, some of which can be transmitted to other species.
The presence of predators impacts the ecosystem. The effect this has depends on three factors: the number of predators in a given environment, how they interact with prey and how they interact with other predators. The existence of multiple predator species in an ecosystem may or may not impact each other, depending on their preferred food source, the size of the habitat and the frequency and quantity of food required. The greatest impact is made when two or more species consume the same prey.
Things such as wind or water currents can relocate micro-organisms and small plants and allow them to start new colonies. This spread of species can be beneficial to the ecosystem as a whole as it can mean a larger food supply for primary consumers. However, it can be a problem when established species are forced to compete with new ones for resources and those invasive species take over and disrupt the balance of the ecosystem.
In some cases, biotic factors can prevent abiotic factors from doing their job. An overpopulation of a species can impact abiotic factors and have a negative effect on other species. Even the smallest organism, such as phytoplankton, can devastate an ecosystem if it is allowed to overpopulate. This is seen in “brown algal blooms” where an excessive number of algae collect on the surface of the water and prevent the sunlight from reaching the area below, effectively killing all life beneath the water. On land, a similar situation is seen when a tree canopy grows to cover a large area, effectively blocking the sun from reaching plant life below.
Extreme Environmental Conditions
The Arctic and Antarctic not only have extreme cold temperatures, but these temperatures also vary by season. In the Arctic Circle, the Earth’s rotation allows minimal sun to reach the surface, resulting in a short growing season. For example, the growing season in the Arctic National Wildlife Refuge is only 50 to 60 days with a temperature range of 2 to 12 degrees Celsius. With the Arctic Circle oriented away from the sun, the winters have short days, with temperatures ranging from -34 to -51 degrees Celsius (-29 to -60F). High winds (up to 160 km/hour, or about 100 miles per hour) pelt exposed plants and animals with ice crystals. While the snow cover provides insulating benefits, the extreme conditions do not allow any new plant growth.
Biotic factors are few in the Arctic. Conditions only allow for low-lying plants with shallow root structures. Most of these have dark green to red leaves that absorb more sunlight and reproduce asexually, through budding or cloning, rather than sexually via seeds. Most plant life grows just above the permafrost, as the soil is several inches below. Because of the very short summer, plants and animals reproduce quickly. Many animals are migratory; those that live in the Arctic National Wildlife Refuge tend to have smaller appendages and larger bodies than their southern counterparts that enable them to stay warm. Most mammals also have both an insulating layer of fat and a protective coat that resists cold and snow.
At the other temperature extreme, arid deserts also pose challenges for biotic factors. Living organisms need water to survive, and the abiotic factors in a desert (temperature, sunlight, topography and soil composition) are inhospitable to all but a few species. The temperature range of most major American deserts is from 20 to 49 degrees Celsius (68 to 120F). Precipitation levels are low, and rainfall is inconsistent. The soil tends to be coarse and rocky with little to no subsurface water. There is little to no canopy, and plant life tends to be short and sparse. Animal life also tends to be smaller, and many species spend their days in a burrow, emerging only during the cooler nights. While this environment is favorable for succulents such as cacti, poikilohydric plants survive by maintaining a dormant state between rains. After a rain, they become photosynthetically active and reproduce rapidly before again assuming the dormant state.
- The Regents of the University of California: FOSS Ecoscenarios: Arctic National Wildlife Refuge
- University of British Columbia: Abiotic and Biotic Factors Creating Variation Among Bromeliad Communities
- The National Academies Press: Environmental Impacts of Natural Disasters
- U.S. Forest Service: Relationships Between Biotic and Abiotic Factors and Regeneration of Chestnut Oak, White Oak, and Northern Red Oak
- University of California Museum of Paleontology: The Desert Biome