Ecology Part 3 Food chain is the sequence

Ecology Part 3

Food chain is the sequence of organisms including producers (autotrophs), primary consumers (herbivores), secondary consumer, (herbivore eating carnivores), tertiary consumers (carnivore eating carnivores), and decomposers, through which energy and materials may move in a community. In most communities the food chain are called trophic levels.

These are 2 food chains for two different environments, terrestrial and marine.

In most communities the food chains are completely intertwined to form a food web. The direction of the arrow indicates the movement of energy and material.

The successive levels of food and energy in the food chains are called trophic levels. The producers constitute the first trophic level, and the primary consumers, the second and so on. Since many species eat a varied diet, trophic levels are not hard-and-fast categories. At each trophic level there is a loss of energy from the system. Only a small percentage of the energy at one trophic level is available for the next.

Less than 10 % of the energy can make it from level to the next. There are reasons why only 10% of the energy can move from one level to the next. 1. Lack of complete consumer harvest of available biomass. 2. The inability to assimilate all that is consumed. 3. Loss of energy due to dissipation of heat energy. 4. Energy used for growth and reproduction.

This is represented by the pyramid of productivity with the producers at the base and the last consumer at the top. Usually producers are engage in photosynthesis but includes chemosynthesis. In general only 10% of the energy from one level can move to a successive level. The right is showing the flow of energy.

The pyramid of productivity is the basis that a pyramid of biomass exists. In general the decrease of energy at each successive trophic level means that less biomass can be supported at each level. Hence the total mass of carnivores in a given community is almost always less than the total mass of herbivores. However the size, growth rate, and longevity of the species at various trophic levels are important determining factors.

Because of the energy flow, in general moving from the producers to the tertiary consumers, there is a decrease in biomass. However in certain aquatic ecosystems this is not the case because the reproduction of the algae occurs at a fast rate, and consumed at a fast rate. In addition it has a small size.

The pyramid of productivity and the pyramid of biomass support the pyramid of numbers. This is because in general, carnivores are larger than the herbivorous prey. Since total biomass tends to decline at successive trophic levels, it follows the number of individuals must decline at each level (except decomposer which outnumber all other groups combined).

Gross primary productivity is the ability of producers to “fix” or convert carbon dioxide into organic material. Consumers reduce gross primary productivity by consuming the producers. Producers also reduce gross primary productivity because they also engage in cellular respiration. Net primary productivity is the amount of organic material that is produced beyond what is needed by the living organisms in an ecosystem. A dominant species in an ecosystem are species which are present in the greatest numbers or greatest biomass. A keystone species is one that exert an important species that can exert an effect on regulating other in a community.

Sea otters are considered to be a keystone predator species. Sea otters prey on sea urchins. Sea urchins eat kelp. Where sea otters are plentiful, sea urchins are rare and kelp beds are plentiful. Where sea otters are population is low, sea urchins are plentiful and kelp beds are almost absent. Whales in the last 20 years have been preying on sea otters, this has increased the sea urchin population and decreased the kelp beds off the coast of western Alaska.

Foundation species are species that exert their effect by changing their environment profoundly. Ex. Beavers can profoundly change the environment by damming a creek or river. Species diversity refers to the different number of species in a given area. One should also looks at relative numbers of each species as well. This factor is called species richness. In general, the greater the species diversity of an ecosystem, the more stable the ecosystem. An ecosystem with fewer species may be more susceptible to damage from some sort of disturbance, however it may recover quickly. An ecosystem with more species may be more stable and less resistant to change from a disturbance, however it may be more difficult for the ecosystem to recover when a serious disturbance does occur.

While both of these ecosystems have the same number of species of trees, the first community is more stable because of the relative number of individual trees is almost equal unlike the second community where one species dominates. This first community is described as having species richness.

Succession: is the process of change in which one community of organisms replaces another. This happens after some sort of change- volcano, fire, tornado, etc has disturbed the environment. As each community is established, the environment is modified and change making it possible for another community to become establish.

Primary succession: begins with bare rock or sand involves first the building of soil. Once organisms colonize an area, they change it so that other organisms may follow. Examples include what happens after a volcano erupts or glacier retreats.

Primary succession: begins with bare rock or sand involves first the building of soil. Once organisms colonize an area, they change it so that other organisms may follow. e. g. The first organisms to colonize the area may be mosses and lichens. These plants may produce acids as a waste produce to break down rocks in the formation of soil. Once soil formation is begun, ferns may come in and colonized the area. Its rhizoids helping to form more soil, and as they die and decompose, the soil may become more rich suitable for different types of organisms. It is easy to see that organisms can change the environment they interact with.

Another example of succession is that found in a pond. First the pond is barren but then the aquatic plants die and sediments begin to fill in and begins to be ringed by vegetation.

The beginnings of pond succession. It is barren with little vegetation. 50 yrs. the pond is bordered by mature cottonwood trees. 2 yrs. the pond is ringed by vegetation including cotton wood saplings. 150 -200 yrs. the pond has become a meadow, the pond is ringed by vegetation.

Secondary succession- Soil is present and occurs at a much more rapid rate. Can be the result of fire, tornados, floods and other like events. Examples abandoned crop lands, unused rail roads etc.

Ecological succession may lead to a stable community of plants and animals called the climax community. Catastrophic events (hurricanes, volcanoes, fires, etc. ) may disturb a climax community, causing the process of succession to occur again. A biome is an environment that has a characteristic climax community. The earth has two main types of biomes, land biomes and aquatic biomes.

Most land biomes are named for their climax community or dominant type of plant life. The major types of biomes are the tundra, taiga, temperate deciduous forest, grassland, tropical rain forest, and desert.

TUNDRA Where Found: northern North America, Europe, Asia Plants: mosses, lichens, grasses, a few stunted trees Animals: caribou, reindeer, wolves Other Characteristics: permafrost – creates freezing and thawing cycle

TAIGA Where Found: most of Canada and Asia Plants: pine trees Animals: bears, wolves, moose, elk, voles, wolverines, Characteristics: long and cold winter, summers completely thaws the soil.

TEMPERATE DECIDUOUS FOREST Where Found: southern Canada, eastern U. S. , Europe, and Japan Plants: trees that lose their leaves (oak, maple, birch) Animals: huge variety, including fox, deer, moose, etc. Characteristics: lands cleared by hunting and farming

GRASSLANDS Where Found: interior of many continents Plants: grasses and small leafy plants Animals: grazers and browsers Characteristics: Large variation in temperature and seasonal changes. Grazing and prairie fires halts succession.

TROPICAL RAIN FORESTS Where Found: South America, S. E. Asia, Central Africa, Central America Plants: rich vegetation in canopy and undergrowth Animals: colorful insects, lizards, amphibians, reptiles, small mammals Characteristics: 200 – 400 cm rain, constant (25 o C)

DESERTS Where Found: northern Africa, southern Asia, central Australia Plants: cactus and other non-leafy plants Animals: lizards, small rodents Other Characteristics: very little rainfall, although some deserts have seasonal rain

Nutrients are recycled into the ecosystem unlike energy. The major nutrient cycles are water, carbon, nitrogen and phosphorus.

In the carbon cycle, carbon is recycled mainly through the process of photosynthesis, cellular respiration and burning of fossil fuels. Carbon dioxide (CO 2) and carbon monoxide emissions have been increasing and increasing in the atmosphere. It allows light energy in but traps the reflected heat energy in atmosphere so that it does not go back into space. It causes global warming.

Nitrogen used for proteins and nucleic acids. The air is over 75% N 2, but this nitrogen can not be used because of its triple bond. N 2 is broken down by bacteria into NH 4 (ammonia), then NO 2 (nitrite) and finally NO 3 (nitrate). Plant roots absorb this NH 4, NO 2 or NO 3 and then make amino acids and then proteins. Animals get their nitrogen from eating plants or other animals. Nitrogen also gets into the soil when man uses fertilizers made from factories. Nitrification is the process of putting N 2 into the ecosystem. Another way to get nitrogen into the ecosystem is through decaying organisms and wastes.

Plants absorb water through their roots. Land animals absorb water from their food or drink it. Aquatic animals are bathed in it. Water gets into the atmosphere from cellular respiration, transpiration and evaporation from the oceans. Water vapor condensing will result in precipitation (rain or snow). The excess nitrogen and sulfur in the air (pollution) combines with the water. This results in acid rain. This leech minerals from the soil killing plants.

The phosphate cycle is the one nutrient that does not have an atmospheric component. It cycles through the soil and water. The main source of phosphorous is the weathering of rocks.

There are times when unwanted chemicals accumulate in organisms through the food chain. In the 1960's, cities sprayed with DDT, a chemical to get rid mosquitoes. This chemical accumulated in the lakes. It found its way into the aquatic plants. Fish ate the plants and DDT accumulated in the fish. Eagles ate the fish. DDT accumulated in the eagles. It affected their eggs as the shells were not hard. The chicks would not hatch. As a result, eagles became endangered. This process is called biological magnification.