Food Chains - A food chain illustrates the movement of energy through an ecosystem.

• Components of a Food Chain:
• Plants - 'base' of the food chain
• Herbivores - feed on plants; many are adapted to live on a diet high in cellulose
• Omnivores - feed on both plants and animals
• Carnivores - feed on herbivores, omnivores, & other carnivores
• lst level carnivore - feeds on herbivores
• 2nd level carnivore - feeds on 1st level carnivores
• Decomposers
• the 'final' consumer group
• use energy available in dead plants and animals
• transform organic material into inorganic material
• Food chains are more often called food webs because no organism lives solely on another:

Source: http://www.biology.iupui.edu/biocourses/N100H/ch41eco.html

• Types of Food Chains:
• Grazing food chain - The grazing food chain begins with the photosynthetic fixation of light, carbon dioxide, and water by plants (primary producers) who produce sugars and other organic molecules. Once produced, these compounds can be used to create the various types of plant tissues. Primary consumers or herbivores form the second link in the grazing food chain. They gain their energy by consuming primary producers. Secondary consumers or primary carnivores, the third link in the chain, gain their energy by consuming herbivores.Tertiary consumers or secondary carnivores are animals that receive their organic energy by consuming primary carnivores.
• Detrital food chain - The detritus food chain differs from the grazing food chain in several ways:
• the organisms making it up are generally smaller (like algae, bacteria, fungi, insects, & centipedes)
• the functional roles of the different organisms do not fall as neatly into categories like the grazing food chain's trophic levels.
• detritivores live in environments (like the soil) rich in scattered food particles. As a result, decomposers are less motile than herbivores or carnivores.
• Decomposers process large amounts of organic matter, converting it back into its inorganic nutrient form.

Source: http://soils.usda.gov/sqi/soil_quality/soil_biology/soil_food_web.html

Biogeochemical cycling:

• The transport and transformation of substances in the environment, through life, air, sea, land, and ice, are known collectively as biogeochemical cycles. These global cycles include the circulation of certain elements, or nutrients, upon which life and the earth's climate depend.

• Carbon cycle - the movement of carbon, in its many forms, between the biosphere, atmosphere, oceans, and geosphere
• plants obtain carbon dioxide from the air and, through photosynthesis, incorporate carbon into their tissues
• producers & consumers - transform part of the carbon in their food back into carbon dioxide via respiration
• decomposers - release the carbon tied up in dead plants & animals into the atmosphere
• Another major exchange of carbon dioxide occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis.
• Two other important processes are fossil fuel burning and changing land use. In fossil fuel burning, coal,

oil, natural gas, and gasoline are consumed by industry, power plants, and automobiles. Changing land use is a broad term which encompasses a host of essentially human activities, including agriculture, deforestation, and reforestation.

Source: http://www.biology.iupui.edu/biocourses/N100H/ch41eco.html

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The global carbon cycle is out of balance, making rapid global climate change more likely. Atmospheric CO2 levels are rising rapidly -- currently, they are 25% above where they stood before the industrial revolution. Carbon dioxide, a greenhouse gas,  forms when the carbon in biomass oxidizes as it burns or decays. Many biological processes set in motion by people release carbon dioxide. These include burning fossil fuels (coal, oil, & natural gas), slash-and-burn agriculture, clearing land for permanent pasture, cropland, or human settlements, accidental and intentional forest burning, and unsustainable logging and fuelwood collection. Clearing vegetation cover from a forested hectare releases much of the carbon in the vegetation to the atmosphere, as well as some of the carbon lodged in the soil. Logging or sustainable fuelwood collection can also degrade vegetation cover and result in a net release of carbon.

• Nitrogen cycle - Almost all of the nitrogen found in terrestrial ecosystems originally comes from the atmosphere. Small proportions enter the soil in rainfall or through the effects of lightning. Most, however, is biochemically fixed within the soil by specialized micro-organisms like bacteria. Members of the bean family (legumes) and some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacterial. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist in a moist environment. Scientist estimate that biological fixation globally adds approximately 140 million metric tons of nitogen to ecosystems every year.

Source: http://www.biology.iupui.edu/biocourses/N100H/ch41eco.html

Interactions among organisms in ecosystems:

• Predator-prey interactions - the interaction between predators and prey involve continuous evolutionary change; as predators evolve more efficient ways of capturing prey, the prey evolve ways of avoiding predation. For example:
• Warning coloration, mimicry, & cryptic coloration:
• warning coloration - conspicuous markings of an animal that make it easily recognizable and warn would-be predators that it is a poisonous, foul-tasting, or dangerous species.

Bright coloration in insects and other animals (typically yellow, orange, or red) can act as signal, warning other animals that they are poisonous or distasteful. Such color patterns are called "aposematic." When an animal attacks, eats, or encounters such a brightly colored animal and gets stung, bitten, or poisoned, it learns to associate these warning colors with a bad experience. Monarch butterflies have a chemical defense toxic to many natural enemies - they store poisonous compounds from milkweed called cardiac glycosides in their tissues. As a result, when an animal eats a monarch and gets sick, it learns to avoid potential prey with similar coloration.

• mimicry -  the advantageous resemblance of one species to another, often unrelated, species or to a feature of its own environment.
• cryptic coloration -  an organism matches its background, hiding (camouflaging) it from predators and/or prey.

• Chemical defenses
• serve to repel or inhibit potential predators
• commonly employed by arthropods, amphibians, & snakes
• also used extensively by various types of plants
• Predator satiation (or swamping)
  
• timing reproduction so that a maximum number of offspring are produced in a short period of time, thus satiating predators and allowing a greater percentage of young to survive
• examples of organisms that use this strategy include wildebeest, cicadas, caribou (below), and lots of plants

Source: http://polar.nrcan.gc.ca/kids/kidsanimals_e.html

Hunting ability of predators - As prey evolved better ways of avoiding predators, predators necessarily evolved better ways of hunting and capturing prey. These interactions between predators and prey have produced some complex adaptations. For example:

• the social hunting behavior of lions and wolves

• the fangs of some snakes

Source: http://www.geocities.com/Baja/Outback/3333/buzz.html

• spiders and their webs (click on the spider web for more information about spiders)

• the speed of many predators such as cheetahs and Peregrine Falcons (click on the cheetah for more information about cheetahs)

Not all relationships among organisms in an ecosystem involve eating or being eaten. Symbiosis refers to an association in which two species live together in a close relationship. The term symbiosis has usually been used to describe relationships that are mutually advantageous to the species involved. However, symbiosis is now used to describe any close interrelationship between species. The degree of benefit and harm varies considerably among the many symbiotic relationships that exist in nature:

• Protocooperation - association of mutual benefit to both species, but the cooperation is not obligatory, e.g., cattle and cattle egrets

• Mutualism -  a form of symbiosis in which two partners form a close relationship that produces equal benefits for both parties. Some ecologists may restrict their definition of mutualism to only those relationships that are obligatory, or required for an organism’s survival. Some examples of mutualism include:
• Clown fish and sea anemones-bright and colorful clown fish live in and amongst the tentacles of the sea anemone, which look like beautiful aquatic flowers, but bear poisonous stinging cells called nematocysts. A slime layer covering the clownfish make them immune to the stinging cells, and the stinging tentacles of the sea anemone deter potential predators. The clownfish in turn protect the sea anemone from other fish that would feed on the anemone. Clownfish lay eggs within the sea anemone, which offers protection during their incubation and development.

• Lichens are organisms that are made of two distinct species from two different kingdoms. Lichens are given their own species name even though separate fungi and blue green bacteria make up their body structure. The photosynthetic bacteria provide carbohydrate food products to the fungi, and the fungi provide a nice protective, nutrient rich housing structure. The fungal element is also thought to make available to the bacteria organic materials such as nitrogen, minerals water and gases.
• Legume plants such as beans, peas, alfalfa, and clover have root nodules, which contain bacteria in and amongst the root cells, and form ball-like lumps in the roots. These nitrogen-fixing bacteria get photosynthetic food products from the plant, and in exchange make nitrogen available to the plant for building molecules such as amino acids.
  

• Commensalism - a form of symbiosis in which only one of the partner species derives a benefit from participating in the symbiotic relationship. The other partner is unaffected, gaining neither benefit nor harm by the relationship. For example:
• Plants that grow on other plants are referred to as epiphytes. Typically the host plant is not harmed, nor does it benefit from this relationship. The epiphyte benefits from having a substrate to which it can anchor itself, and it is exposed to sunlight, gas exchange, water and nutrients.

Epiphytes are plants that grow on other plants, using them as a substrate. They
 are not parasitic but are taking nutrients from organic debris that accumulates
 on branches. In this photo the large, spreading tree central to the picture is
 supporting numerous fern-like epiphytes. Epiphytes are common in tropical
 forests where competition for light and substrate are intense.

• Birds and squirrels nesting in trees and shrubs can be thought of as examples of commensalism. The benefits are obvious - shelter from the elements and protection from predators. Host trees and shrubs are not affected by the presence of nests.
• Parasitism - In parasitism, one member of the relationship benefits while the other is harmed. Nearly all species of plants and animals are subject to parasitism by at least one species of parasite and usually by several. Parasites generally absorb food from their hosts but may also receive water, minerals, and shelter.  For example:
• Pathogens that cause diseases in plants and animals are parasites. Parasites are responsible for such diseases as malaria, polio, and influenza in humans. Plant diseases include wheat rust, corn smut, and Dutch elm disease. If a host dies prematurely from disease, however, the pathogen is also at risk of dying. As a result, many parasites and their hosts have evolved a form of mutual tolerance; nevertheless, the host is still harmed in some way.
• Fleas and lice
• Some parasites are classified as 'social parasites' because they depend on some aspect of the social structure or behavior of another organism, e.g., Brown-headed Cowbirds.

The eggs of the Brown-headed Cowbirds are usually white with a  fine speckling of reddish brown. In this photo of a nest of a Chipping Sparrow, the cowbird chick is in the process of hatching. Cowbird chicks usually hatch a day or two before the eggs of the host bird and grow rapidly, giving them a competitive head start.

Succession:

• the gradual and continuous replacement of plant and animal species by other species until eventually the community, as a whole, is replaced by another type of community. It is a gradual change, and it is the organisms present which bring about this change.
• involves the processes of colonization, establishment, and extinction which act on the participating species.
• occurs in stages, called seral stages, that can be recognized by the collection of species that dominate at that point in the succession.
• begins when an area is made partially or completely devoid of vegetation because of a disturbance. Some common mechanisms of disturbance are fires, wind storms, volcanic eruptions, logging, climate change, severe flooding, disease, and pest infestation.
• stops when species composition no longer changes with time, and this community is called the a climax community.

Primary succession vs. secondary succession:

• Primary succession - occurs on an area of newly exposed rock or sand or lava or any area that has not been occupied previously by a living (biotic) community.

• Secondary succession - takes place where a community has been removed, e.g., in a plowed field or a clear­cut forest

Primary Succession

Secondary Succession

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