DIVERSITY IN ECOSYSTEMS

In some places Earth is a hot and in others it is cold.  Depending on your geographical location on Earth, you will experience varying amounts of daylight, winds and moisture.  These differences affect the diversity of living things across our planet.

ECOSYSTEMS AND ECOLOGY

·        An ecosystem is the result of all the relationships among the living and non-living parts of a particular environment.

·        An ecosystem with a large biodiversity will contain many types of organisms.

·        In a healthy ecosystem, each organism fills a niche, i.e., each has a certain place and role in the ecosystem. For example, owls live in wooded areas and eat rodents, worms live in the soil and digest its nutrients while keeping it loose for the growth of plants, and trees provide cover for all of these.

·        In a healthy ecosystem, resources remain properly distributed and competition among the organisms is at a level that does not decrease too many of their resources too quickly. But, competition for a niche may increase if a new organism enters an ecosystem and encroaches on the space and food already used by an existing species. In that case, there may be a loser as one of the competitors experiences a population decrease or perhaps even a local extinction.

·        Human activity often allow species to come in contact that would otherwise hardly impact one another. Think of the rabbits introduced to Australia. With no natural predators, their numbers exploded. Native grass eaters suffered as the rabbits ate large percentages of their food plants.

·        Another example is the development and accidental release of experimental Africanized bees in Brazil in the 1950's. As they spread northward, they pushed out or took over colonies of native bees.

·        On a personal level, just about any time we enter some new area, we may be unknowingly importing some organism with us that remains there when we return home. What is the effect of this? Sometimes, nothing obvious but we must be aware of our potential to upset ecosystems.

HW. P. 44 # 1-4 (ref.1.12)

·        Non-living things like sunlight, temperature, and wind levels are abiotic elements of the ecosystem.

·        The biotic elements of the ecosystem are all its living things.

·        Animals that feed on plants are herbivores, those that feed on other animals are carnivores and animals in the chain that can feed on both plants and animals and are called omnivores.

·        A general term for an animal is heterotroph because it can not make its own food as can a plant which is an autotroph.

·        One indicator of the overall health of an ecosystem is the health of its indicator species.  An indicator species is an organism whose health reflects the state of balance among the other components in that environment.

·        Some researchers use a common amphibian, the frog, as an indicator species. Frogs and other amphibians can be found in a wide variety of environments from warm swamps to city parks to mountainous terrain.

HW p. 13 # 1-4 (ref.1.1)

Their body structure allows them to live in the ecotone (zone) where terrestrial and aquatic environments meet. As tadpoles they are part of an aquatic food chain; as adults they fit into a terrestrial food chain. Because they are part of two worlds and part of two food chains, frogs are especially useful as living measuring sticks of the health of their environments.

HW p.23 # 1-6 (ref.1.5)

FOOD CHAINS AND FOOD WEBS

·        A food chain is a diagram depicting a step by step sequence of who eats whom in an ecosystem (fig. 2 pg 34)

·        A food web is a diagram that shows the interconnectedness of organisms in an ecosystem. (fig. 3 pg. 35)

·        It has a number of trophic levels.

·        Plants form the foundation of the food web. They are in the 1^st trophic level and are called producers. Plants we often forget about are the microscopic ones living in fresh or salt water.

·        The bases of some food chains include detritus, e.g., the sludgy matter at the bottom of ponds. Detritus contains wastes (from living animals and plants) and the remains of dead plants and animals.

·        Food webs containing detritus also contain decomposers that feed on it. In doing so, they create nutrients that feed plants and algae.

·        Moving up through the chain or web we encounter the 2^nd trophic level containing the primary consumers that feed on the plants.

·        Above them are secondary consumers, in the 3^rd trophic level.

·        The 4^th trophic level contains the tertiary consumers and finally, the 5^th trophic level contains a single top predator.

The following is a possible food web.  Note that the arrows are drawn from food source to food consumers ... in other words, you can substitute the arrows with the words ‘ by’
 

HW p.39 #1-6 (ref. p 34-36)

ENERGY IN ECOSYTEMS

·        The sun is the source of energy for all ecosystems (fig. 1 p32)

·        One billionth of the suns energy reaches Earth (150 million km trek)

·        The Earth’s atmosphere filters out most of the suns harmful radiation (cosmic rays, gamma rays, X-rays, UV) by reflection or absorption of chemicals in the atmosphere.

·        How is the sun’s energy broken up?

·        30% reflected by clouds

·        70% warms the surface of the Earth causing:  Water evaporation, weather patterns.

·        Albedo is a measurement of the percentage of light that an object reflects.  The higher the albedo, the greater the object’s ability to reflect sunlight (fig. 2 p. 32)

ENERGY FLOW THROUGH  Food CHAINS

PHOTOSYNETHSIS

·        The process by which green plants use sunlight energy to produce carbohydrates (sugar)

·        We can write the overall reaction of this process as:

6H₂O + 6CO₂ ----------> C₆H₁₂O₆+ 6O₂

·        the above chemical equation translates as:    six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen  

·        Only 0.023% of the Sun’s energy is used by plants for photosynthesis.

AEROBIC RESPIRATION

·        This is the process whereby living things release the chemical energy in sugar for their use.

·        The process occurs inside the cells of living things and requires oxygen (hence it is called aerobic) that has been gained by the organism from its surroundings.

·        All of the energy that was stored in the sugar when it was made during photosynthesis is released during aerobic respiration.

·        Some of the released energy is radiated from the organism as heat.           

                         The Connection between biotic and abiotic factors on Earth

HW p. 33 #1,3,4 (ref.1.10)

ENERGY TRANSFER

·        Producers use energy from sunlight to make molecules of sugar.

·        Consumers use this sugar as a form of chemical energy to do work.

·        Every time energy is transferred within an ecosystem, some energy changes form.

·        Not all of the chemical energy (food) that a plant creates can reach the animal that eats it.

·        In every ecosystem, there is less energy available to secondary consumers than primary consumers.

THE LAWS OF THERMODYNAMICS

·        Thermodynamics is the study of energy transformations.

1.  The first law of thermodynamics states that energy may be transformed from one form to another, however it cannot be created or destroyed.

2.  The second law of thermodynamics states that during any energy transformation, some of the energy is converted into an unusable form, mostly thermal energy that cannot be passed on.  Each transfer of energy results in a loss of energy from the system.  Therefore, in each step of a chain of transformations energy becomes less available.

GRAPHING ENERGY IN ECOSYSTEMS

·        A well developed food web looks like a pyramid - the biomass decreases as we move up the web.

·        It takes thousands of plants to support a few dozen primary consumers which can support just a few secondary consumers which are food for even fewer tertiary consumers, etc. This is because transferring energy up through the food web is an inefficient process.

·        Graphs called pyramids can be used to represent energy flow in food chains and food webs or the populations of organisms in a food chain.  (Figs 6, 7, 8 p.37)

Pyramid of energy – energy found in the organisms at each tropic level is measured and graphed

Pyramid of numbers – at each tropic level the number of organisms is measured and graphed

Pyramid of Biomass – at each tropic level the dry mass of all organisms is measured and graphed

 Examples of Energy Transfer

Think of how much of a plant's energy is needed by a rabbit to chew, digest, produce wastes, create the body heat it needs to live, race away to safety, or to breed. If the rabbit just ate slowly and frequently, created minimal wastes, slept often, and moved about slowly, it would be much fatter when it was eaten, perhaps by a fox. But, since the rabbit has a more active life than this, much of the energy that entered the rabbit as plant tissue is unavailable to the fox.

Similarly, when an eagle catches a fish, much of the energy the fish absorbed in its food will have been used up during its normal life processes and is not available to the eagle.

Cattle farmers do not want their cows running around because too much of the energy the cows absorb from eating hay would be lost as it changed into heat energy and muscle motion and so the cows would become too lean. In the bygone days of the huge cattle drives across the Great Plains of the United States, a major concern of the cattle owners was how thin the cattle would be when they reached the markets in distant cities. A person eating beef from one of those cows would be getting hardly any of the energy the cow got from its food. The cattle owners hoped there would be time to let the cows stand around and eat for a few weeks to fatten them up. Beef from those cows would contain much more of the energy the cows took in when they ate.

Eating mostly plants may not be for all of us but is certainly an efficient route to obtaining energy for our life processes!

Eating shark meat is one of the most useless ways of getting energy. Now of course a shark could provide many meals but, if we ate the fish lower in the food chain that were needed to support the shark, we would have food for weeks.

Think of farming and cows again: all the care, cost and time to raise a few cattle compared to the much lower cost of just the few weeks to grow the grain and corn that fed them. The cattle food would support more of us for a much longer period than the beef from the cows themselves.

HW p. 39 # 6-15 (ref. 1.11)

       FOOD PYRAMID ASSIGNMENT (handout)

DECREASING POPULATIONS AND EXTINCTION

·        When the population of an indicator species diminishes, the simplest reason is that its habitat is being negatively affected.

What is responsible?

·        Often it is a complex accumulation of effects related to human development. We drain swamps and clear woodlands. We build roads that crisscross the countryside. We develop industries that release a huge range of chemicals.

·        Some liquids are responsible for water pollution.

·        Certain gases cause air pollution. Still other gases are linked to climate changes and endangering the protective layer of ozone encircling the Earth.

Q. Amphibians have delicate, heat sensitive, moist skin through which gases can easily pass. How would the effects of human activity listed above affect a frog's health?

The continued loss of population leads to extinction   Extinctions are both natural and manmade.

Natural extinctions in the past have been dramatic, sometimes with about an 80% wipe out of species.

·        A common hypothesis about the disappearance of the dinosaurs is that an asteroid crashed into Earth, causing huge tidal waves, earthquakes and fires. Dust from the impact and from fires would blot out the sun for years - temperatures would plummet and plants would die off. Soon, so would most animals in the food chains.

Humans and their activities are the major cause of extinctions. Some predictions suggest that each half hour, another species becomes extinct. A major irony in this whole thing is the loss of species we have not even discovered, especially in sections of rain forest being destroyed for land development. And who knows what new medicinal cures may be lost because the plant whose bark or flower or root contained a special chemical has been cut down and burned.

EXAMPLES OF RESTORING BALANCE

Attempts to counterbalance population losses often center on breeding programs. In some situations, all members of a small, extremely endangered population are captured and held in protective custody (captive breeding) until careful management can help their numbers to increase to the point where of them can be released back into the wild.

There were, and still are, loud, nasty debates over the reintroduction of wolves into areas through which they historically had roamed for thousands of years, e.g., Yellowstone National Park in Montana. After the wolves had initially been driven and hunted out some years ago, the food chains in those areas had become very imbalanced as the populations of some organisms swelled and others declined.

HW p. 19 # 2-4 (ref. 1.3)      HW Chapter Review # 6,7, 10, 11, 12