Deserts, grasslands, rainforests, coral reefs, and tundra may seem quite different, but they are all examples of biomes. A biome is characterized by abiotic (nonliving) factors such as geography and climate and by biotic (living) factors such as plant and animal species.
Life in any biome includes producers (plants and other photosynthetic organisms) and consumers (organisms that obtain their energy from producers). In addition, all ecosystems are dependent on detritivores (decomposers) — bacteria and other microorganisms that obtain energy from breaking down organic matter. Energy is lost in the form of heat at each level of a food chain, which means that the number of individuals at each successive level decreases. While food chains are a useful teaching tool, their simplicity doesn’t usually capture the complex relationships within a biome or the fact that any one organism may be part of several food chains.
Biomes (and their food webs) can change as a result of natural hazards or human activities. The tundra is a biome characterized by an extremely cold climate, little precipitation, poor nutrients, and a short growing season. Arctic tundra is found along the northern coasts of North America, Asia, and Europe, and in parts of Greenland. The tundra is known for cold conditions, with an average winter temperature of -30 degrees F (-34 degrees C), and an average summer temperature ranging from 37 degrees to 54 degrees F (3 degrees to 12 degrees C).
Another hallmark of the tundra is permafrost, a layer of permanently frozen subsoil and partially decayed organic matter. Approximately 1,700 species of vascular plants are found across the Arctic tundra, including flowering plants, low shrubs, sedges, grasses, and liverworts.
Animals found in the Arctic tundra include herbivorous mammals (lemmings, voles, caribou, arctic hares, and squirrels), carnivorous mammals (arctic foxes, wolves, and polar bears), fish (cod, flatfish, salmon, and trout), insects (mosquitoes, flies, moths, grasshoppers, and blackflies), and birds (ravens, snow buntings, falcons, loons, sandpipers, terns, and gulls). A generalized food web for the Arctic tundra begins with the various plant species (producers). The interconnected nature of a food web means that as numbers of one species increase (or decrease), other populations change in response. Much less extensive than Arctic tundra, Antarctic tundra is found on the Antarctic Peninsula and several Antarctic and subantarctic islands.
An overview of biomes and information on six major types: freshwater, marine, desert, forest, grassland, and tundra. General information about biomes and ecosystems, with links to pages about tundra, taiga, temperate forest, tropical rainforest, desert, grassland, and ocean biomes. The entire National Science Education Standards document can be read online or downloaded for free from the National Academies Press web site. A population consists of all individuals of a species that occur together at a given place and time. The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition.
When an area becomes overpopulated, the environment will become degraded due to the increased use of resources. Causes of environmental degradation and resource depletion vary from region to region and from country to country. Internal and external processes of the earth system cause natural hazards, events that change or destroy human and wildlife habitats, damage property, and harm or kill humans. Human activities also can induce hazards through resource acquisition, urban growth, land-use decisions, and waste disposal. These consumers may be further classified as herbivores (plant eaters), carnivores (meat eaters), or omnivores (feed on a combination of animals and plants).

For example, within a food chain there are always more producers than primary consumers, and more primary consumers than secondary consumers or tertiary consumers. A food web, which illustrates the overlap between multiple food chains, more accurately captures the flow of energy in an ecosystem. Changes in environmental conditions may limit the availability of resources (food, water, space or shelter), reducing the number of organisms that can survive in a given environment.
Other characteristics include low biodiversity, simple plants, limited drainage, and large variations in populations. Arctic tundra is located in the Northern Hemisphere; alpine tundra is located at high elevations on mountains throughout the world. Only the top nine or ten inches of soil thaw, leading to the formation of bogs and ponds each spring. Warming Arctic temperatures due to climate change are causing the permafrost to thaw, releasing the carbon in the form of carbon dioxide (a greenhouse gas). Herbivores (primary consumers) such as pikas, musk oxen, caribou, lemmings, and arctic hares make up the next rung. Thawing permafrost not only releases carbon dioxide but also leads to coastal erosion– an increasing problem in Alaska where villages are at risk.
These areas have rocky soil that supports minimal plant life: two flowering plant species, mosses, algae, and lichens.
For example, animals need air, water, and food; plants require air, water, nutrients, and light. When the environment changes, some plants and animals survive and reproduce, and others die or move to new locations.
Some of these changes are detrimental to the organism or other organisms, whereas others are beneficial. Humans change environments in ways that can be either beneficial or detrimental for themselves and other organisms.
Students should understand the different consequences of changing environments in small increments over long periods as compared with changing environments in large increments over short periods.
All populations living together and the physical factors with which they interact compose an ecosystem. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates.
Natural hazards include earthquakes, landslides, wildfires, volcanic eruptions, floods, storms, and even possible impacts of asteroids.
This material is based upon work supported by the National Science Foundation under Grant No. A change at any level of a food web will impact all other organisms in that web in some way. Tundra is also found to a limited extent in Antarctica – specifically, the Antarctic Peninsula. The division between the forested taiga and the treeless tundra is known as the timberline or tree line. The biome is also characterized by desertlike conditions, with an average of six to ten inches (15 to 25 cm) of yearly precipitation, including snow melt. Additional carbon dioxide in the atmosphere will intensify warming, leading to increased thawing and the release of even more carbon dioxide.
In general, tundra plants are low growing, have shallow root systems, and are capable of carrying out photosynthesis at low temperatures and with low light intensities.

While many of the mammals have adaptations that enable them to survive the long cold winters and to breed and raise young quickly during the short summers, most birds and some mammals migrate south during the winter. Omnivores and carnivores (secondary consumers) such as arctic foxes, brown bears, arctic wolves, and snowy owls top the web. Warming also means that seasons are arriving earlier – a shift not only in temperatures but also in the emergence and flowering of plants. Antarctic tundra does not support mammals, but marine mammals and birds inhabit areas near the coast. Pollution is a change in the environment that can influence the health, survival, or activities of organisms, including humans. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem. Some organisms coexist in mutually beneficial relationships (symbiosis), while others harm organisms for their own benefit (parasitism). Some species are considered keystone species because of the critical role they play in an ecosystem’s food web. This positive feedback loop thus has the potential to significantly increase the rate and effects of climate change. Bacteria and fungi play the important role of breaking down organic matter and returning nutrients to the soil for re-use. Populations of lemmings fluctuate radically (from large populations to near extinction) in regular intervals. Biologists suspect that a mismatch between plant availability and calving is increasing mortality rates of caribou calves.
All species in Antarctica and the Antarctic Islands (south of 60 degrees S latitude) are protected by the Antarctic Treaty.
The world has many different environments, and distinct environments support the life of different types of organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Still others benefit from a relationship that neither helps nor harms the other organism (commensalism).
Of course, the exact species involved in this web vary depending on the geographic location. While scientists believed that populations of lemming predators (foxes, owls, skuas, and stoats) also fluctuated in response to these changes, there is now evidence that suggests that the predators themselves drive the changes in lemming populations.
Finally, species distributions may change as birds and other animals shift their range or migration patterns in response to changing temperatures. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.
This work is licensed under anĀ Attribution-ShareAlike 3.0 Unported Creative Commons license.

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