Components of Ecosystems:

Ecosystems are ecological units that include all the living or biotic factors and non-living or abiotic factors in an area. Examples
include regions such as ponds, caves, or portions of a forest or desert.

The abiotic factors determine the type of organisms that can successfully live in a particular area. Some of the major nonliving
factors of an ecosystem include:

• sunlight -- necessary for photosynthesis
• water -- all living things require some water, but some can live with lesser amounts
• temperature -- all living things have a range of temperatures in which they can survive; beyond those limits they will have difficult time
• oxygen -- many living things require oxygen; it is necessary for cellular respiration, a process used to obtain energy from food; others are actually killed by the presence of oxygen (certain bacteria)
• soil -- the type of soil, pH, amount of water it holds, available nutrients, etc determine what type of organism can successfully live in or on the soil; for example, cacti live in sand, cattails in soil saturated with water

Biotic factors include the plants, animals, fungi, bacteria and any other living things that live in an area. Categories include:

• Producers or autotrophs make their own food. Producers, such as plants, make food through a process called photosynthesis. In photosynthesis, plants use carbon dioxide and water to make sugar. This food is used by the plant for its own energy or may be eaten by consumers.
• Consumers or heterotrophs need to eat food that autotrophs have produced. There are different types of consumers. Herbivores eat plants. Carnivores eat animals. Omnivores eat both plants and animals.
• Decomposers are heterotrophs that break down dead tissue and waste products. They play a very important role in the ecosystem because they recycle nutrients. Bacteria and fungi are decomposers.

If events occur to change a habitat a series of changes may result in the ecosystem. For example, cutting the trees in the rainforest destroys the homes of some animals, increases the amount of light that reaches the forest floor, reduces the amount of food for organisms that depend on those trees, reduces the amount of carbon dioxide taken from the air and oxygen released into it. As a result of this habitat destruction, some organisms may become threatened, endangered and eventually extinct.

Important processes in ecosystems:

• Photosynthesis

• carried out by plants (with chlorophyll)
• rate is influenced by light intensity, temperature, and availability of water

• Decomposition
• reverse of photosynthesis, with organic matter being converted into inorganic compounds (like carbon dioxide)
• accomplished by decomposers:
• microorganisms like bacteria & fungi
• larger organisms like earthworms

• Herbivory - the eating of plants by animals of various types
• Carnivory - the eating of animals by other animals

What factors influence the distribution of plants and animals?

• Temperature - the ability to withstand extremes in temperature varies widely among plants & animals
• Animals respond to variation in temperature both physiologically and behaviorally. Birds and mammals are endotherms ('hot-blooded') & maintain relatively high body temperatures using the heat by their own metabolism. Other animals (such as reptiles, amphibians, fish, & insects) are called ectotherms & their body temperatures are largely set by the ambient (surrounding) temperature.
• Ectotherms - use sources of heat such as solar radiation (direct and indirect) & conduction to help adjust their body temperature

• Endotherms - may maintain body temperature by:
• changing the position of fur or feathers (like the Carolina Chickadee below)
• sweating & panting
• shivering
• behavioral means such as seeking shade or water, burrowing, or varying periods of activity

• Endotherms - may avoid extended periods of low or high temperatures by hibernating or estivating
• Hibernation - winter dormancy
• Estivation - summer dormancy
• common among some desert animals (permits conservation of water)

Many small and medium-sized mammals in north-temperate regions solve the problem of winter scarcity of food and low temperature by entering a prolonged and controlled state of dormancy. True hibernators, such as ground squirrels, groundhogs, & bats, prepare for hibernation by building up lots of body fat. Some, such as the groundhog, also store food in their burrow. Entry into hibernation is gradual. After a series of "test-drops" during which the temperature drops a few degree and then returns to normal, the animal cools to within a degree or less of the ambient (surrounding) temperature. Metabolism is greatly reduced. In ground squirrels, the respiratory rate drops from a normal of 200 per minute to 4 to 5 per minute, and the heart rate from 150 to 5. If the body temperature drops close to freezing, the animal will awaken. Hibernators also awaken at irregular intervals to eat and eliminate wastes and then return to sleep. Some mammals (such as bears, badgers, raccoons, and opossums) enter a state of prolonged sleep in winter with little or no drop of body temperature. This is not true hibernation.Their heart rates may drop, but their body temperature remains normal.  Mammals are not the only hibernators. Several another animals (such as toads and frogs) that also survive winter by hibernating.

A hibernating Indiana Bat

• Plants - obviously cannot move to escape high or low temperatures
• photosynthesis slows down or stops when temperatures get too high or too low
• at high temperatures, leaves can lose some heat by evapotranspiration (loss of water through small holes in leaves)

• plants adapted to withstand low temperatures:
• may have hairs on leaves or stems
• have more solutes in cytoplasm to reduce freezing point
• tend to be short and grow closely together to resist the cold temperatures and wind
• tend to be dark-colored to absorb as much of the sun’s heat as possible

Lichens are composed of a sac fungus and a blue-green algae living and growing together. The association is symbiotic (mutually advantageous): the fungus cannot photosynthesize but is able to obtain food from the algae. The fungus absorbs and retains water, and the algae uses this to photosynthesise, therefore providing food for itself and the fungus. Lichens commonly grow on exposed rocks or trees. They can withstand severe temperature extremes, and as well as inhabiting the cold tundra, they may also be found in the scorching deserts. They are very slow-growing and vary greatly in size, from a millimeter to several meters across. In habitats where there is little else for animals to eat, lichens are a valuable food source. They have also been commercially used as dyes, medicines, poisons, cosmetics and perfumes; and are good indicators of pollution.

• Water
• precipitation determines, along with mean temperature, the world-wide distribution of

biomes

• Primary problem for plants in areas like deserts is a lack of water. Plants adapted for arid conditions include:
• Xerophytes, such as cacti and joshua trees (pictured below), that usually have special means of storing and conserving water. They often have few or no leaves, which reduces transpiration.
• Phreatophytes - plants that grow extremely long roots, allowing them to acquire moisture at or near the water table.

Cacti (like the saguaro cactus shown here)are among the most drought-resistant plants on the planet due to their absence of leaves, shallow root systems, ability to store water in their stems, spines for shade and waxy skin to seal in moisture. Cacti depend on chlorophyll in the outer tissue of their skin and stems to conduct photosynthesis for the manufacture of food. Spines protect the plant from animals, shade it from the sun and also collect moisture. Extensive shallow root systems are usually radial, allowing for the quick acquisition of large quantities of water when it rains. Because they store water in the core of both stems and roots, cacti are well-suited to dry climates and can survive years of drought on the water collected from a single rainfall.

• perennials, such as the Ocotillo, survive by becoming dormant during dry periods, then springing to life when water becomes available.
• ephemerals, such as the Desert Sand Verbena, that usually germinate in the spring following winter rains. They grow quickly, flower and produce seeds before dying. These seeds are extremely hardy. They remain dormant, resisting drought and heat, until the following spring -- sometimes 2 or 3 springs -- when they repeat the cycle, germinating after winter rains to bloom again in the spring.

• Animals survive in hot, dry areas by:
• avoiding the heat, for example:
• Costa's Hummingbirds breed in desert areas of the American southwest in late winter, then leave in late spring when temperatures become extreme.
• Many animals (especially mammals and reptiles) are crepuscular (active only at dusk and dawn)
• Bats, many snakes, most rodents and some larger mammals like foxes and skunks, are nocturnal, sleeping in a cool den, cave or burrow by day.
• dissipating heat, for example:
• the large ears of jackrabbits (like the black-tailed jackrabbit shown to the right) have lots of blood vessels that release heat when the animal is resting in a cool, shady location
• acquiring water, for example:
• from plants, particularly succulent ones, such as cacti. Many species of insects thrive in the deserts this way. Some insects tap plant fluids such as nectar or sap from stems, while others extract water from the plant parts they eat, such as leaves and fruit.

• Fire:
• Historically, humans have thought that all fires were detrimental because they blackened landscapes and burned trees.  In fact, plants and animals evolved together with fire, making it a necessary element in the survival of many ecosystems.
• Fire-dependent ecosystems in the U.S.:
• aspen and lodgepole pine (e.g., in Yellowstone National Park) - Aspens contain a growth enzyme that is released when the heat from a fire destroys a chemical inhibitor.  The sprouting ability of aspens is fierce.  Following the fires in 1988 (see videos of fires at Glacier National Park), aspens grew to 1 million per acre in Yellowstone.  One aspen tree can send out hundreds of sprouts that can grow to 10 feet tall in only 6 years.  Thus, one tree normally produces a group of aspens, which contributes greatly to the growth rate of the species.
• tallgrass prairie - Fires are important in the tallgrass prairie because they eliminate woody vegetation & foreign plant species.
• jack pine in the Great Lakes States have evolved to resist fire and use it for to their advantage for reproduction.  The jack pine depends on fire to open the thick scales of its cones that protect the seeds.  The seeds then fall to the ground where a seedbed has been formed as a result of a fire clearing out the underlying vegetation.  The charred material serves as nutrients for the nascent seedlings. In this case fire is the ultimate source for reproduction of jack pines as it clears a seedbed, reducing competition and providing nutrients for growth.

The Role of Fire in Ecosystems. -- Fire is an essential component of many ecosystems. In these ecosystems, plants and animals have adapted to periodic fire, and some are dependant on burning. For example, Lodgepole pine cones are held closed with a resin. Fire melts the resin and allows the cone to open and release seeds. Suppressing fire in fire-dependent ecosystems short-circuits their ecological processes as surely as removing water would. Fires in these ecosystems typically burn quickly. The fuel load is low because periodic fires prevent fuel build up & fires do not burn with great heat. Established plants and the soil are usually not adversely affected, & species dependant on fire retain their natural cycles. In contrast, fire suppression in fire-dependent ecosystems allows dead grass, brush, wood, leaves and needles to accumulate & may lead to abnormally big, hot fires that can do more damage. Fires are caused by lightening and people. Native Americans set fires to clear land for agriculture, to alter plant communities & attract a diversity of game species, and to improve access. Today, land managers use fire as an important tool in managing fire-dependent ecosytems.

• Effects of fire:
• plants - Many plants depend on fire to heat and scar their seeds as a process for germination. Decaying trees release nutrients into the soil and serve as a base for new plants to sprout. Much of the plant life in the United States has evolved to use fire directly as a catalyst for reproduction or benefited by the nourishment left in its path.
• animals - The specific effects of fire on animals depends on what kind of fire, the type of vegetation, and the individual animal.
• Larger animals generally survive more often than smaller ones; although a  burrowed animal can escape burning, usually it suffocates in the meantime.
• Many birds also thrive after a fire when the seeds of many trees are dispersed.  Birds, like woodpeckers, take advantage of burned out trees to make nests or forage for dead insects.
• Insects usually do not survive fires well because their escape range is too small.  This can affect birds if the specific insects are a food source for the aviators.  Trees can benefit from the death of insects that reside in their trunks.  Many insects, in this case the mountain pine beetle in lodgepole forests, kill the trees in which they inhabit.  A lot of these forest pests, like the beetle, or the spruce bud worm, which resides in Douglas and subalpine fir forests, are burned out by fires.

• Light
• influences daily and seasonal activity patterns of plants and animals
• necessary for photosynthesis which, in turn, is the source of energy in almost all ecosystems
• Energy flow through an ecosystem:

• Gross primary production = all the sun's energy that is assimilated (total photosynthesis)
• Respiration = energy needed for maintenance and reproduction
• Net primary production
• energy remaining after respiration & stored as organic matter
• energy available to other organisms in a food chain (or food web)

Ecological Principles 2

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