Interactions among organisms can:



1. Interactions among organisms can:

- generate stability within ecosystems

- facilitate or restrain growth

- enhance or limit the size of populations, maintaining the balance between available resources and those who consume them

- change both biotic and abiotic characteristics

- Ecosystem hierarchy (smallest to largest): organism – population – community– ecosystem- biosphere

2. A stable ecosystem is one where:

- the population numbers of each organism change at a predictable rate.

- the supply of resources in the physical environment changes at a predictable rate.

- energy flows through the ecosystem at a fairly constant rate over time.

3. Interactions:

(a) Predation: one species (the predator) eats the other (prey)

Fill in the following blanks based on the graph below.

| | |

| |As the prey population increases, the predator population |

| |increases. |

| | |

| |As the predator population increases, the prey population |

| |decreases. |

(b) Competition: when two or more organisms need the same resource at the same time; can be among same or different species; usually occurs with organisms that share the same niche.

- Organisms and populations with similar requirements for food, water, oxygen, or other resources may compete with each other for limited resources.

- Niche: the role of an organism in its environment including type of food it eats, how it obtains its food and how it interacts with other organisms. Two organisms with the same ecological niches cannot coexist in the same habitat.

- Competition usually results in a decrease in the population of a species less adapted to compete for a particular resource. (natural selection/survival of the fittest)

(c) Symbiotic Relationships: exists between organisms of two different species that live together in

direct contact. Includes parasitism, mutualism and commensalism

- Parasitism: one organism (the parasite) benefits at the expense of the other (the host); host is usually not killed.

*Some parasites live within the host such as tape worms, heartworms, or bacteria.

*Some parasites feed on the external surface of a host, such as aphids, fleas, or mistletoe.

*If the host dies, this is devastating to both the parasite and the host populations. It is important that the host survive and thrive long enough for the parasite to reproduce and spread.

- Mutualism: relationship in which both organisms benefit. They help each other survive.

Examples: Bacteria, which have the ability to digest wood, live within the digestive tracts of termites; Plant roots provide food for fungi that break down nutrients the plant needs.

- Commensalism: where one organism benefits but the other is unaffected. For example, barnacles attach themselves to marine organisms which give them a place to live, and the organisms couldn't care less about this.

4. Energy is transferred through ecosystems: Energy entering ecosystems as sunlight is transferred by producers into chemical energy through the process of photosynthesis

- Energy then passes from organisms to organisms.

- Energy can change from one form to another in living things. Animals get energy from oxidizing their food, releasing some of its energy as heat; respiration releases CO2 and water.

- Almost all food energy comes originally from sunlight.

- Organisms at each trophic level use 90% of the energy and pass up 10% to the next trophic level.

5. Food provides molecules that serve as fuel and building material for all organisms.

- Plants, algae (including phytoplankton), and many microorganisms use the energy in light to make sugars (food) from carbon dioxide (CO2) and from the atmosphere and water through the process photosynthesis.

- Animals obtain food from eating plants (producers) or other animals (consumers). Within organisms, food moves through a series of chemical reactions in which it is broken down and rearranged to form new molecules, to support growth, or to release energy.

- In most animals, oxygen reacts with carbon-containing molecules (sugars) to provide energy and produce carbon dioxide (CO2) waste. Anaerobic bacteria get their energy needs in other chemical processes that do not require oxygen. Aerobic bacteria do require oxygen.

- The total amount of matter in an ecosystem remains constant, even though its form and location change.

6. The flow of energy through ecosystems can be described and illustrated in food chains, food webs,

and pyramids. (see class notes, diagram of energy pyramid, etc.)

- The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem.

- A food chain is the simplest path that energy takes through an ecosystem. Energy enters an ecosystem from the Sun.

- Each level in the transfer of energy through an ecosystem is called a trophic level.

- Organisms in each trophic level use some of the energy in the process of cellular respiration, lose energy due to heat loss, and store the rest.

- First Trophic Level: consists of producers (plants/autotrophs)

The autotroph uses some of the simple sugars for energy and some of the simple sugars are converted to organic compounds (carbohydrates, proteins, and fats)

- Second Trophic Level: consists of primary consumers (heterotrophs)

Herbivores – primary consumers that eat green plants; use some of the organic compounds for energy and some are converted into proteins, carbohydrates, and fats, much of the consumed energy is lost as heat. (i.e. grasshoppers, rabbits, zooplankton, etc.)

- Third Trophic Level or Higher: consists of consumers (heterotrophs)

Carnivores – consumers that eat other consumers

Omnivores – consumers that eat both producers and consumers

Carnivores or omnivores use some of the organic compounds for energy and some are converted into proteins, carbohydrates and fats; much is lost as heat (i.e. wolves, humans, frogs, minnows)

Decomposer – heterotrophs that break down organic material and return the nutrients to soil, water, and air making nutrients available to other organisms

- Food webs represent many interconnected food chains describing the various paths that energy takes through an ecosystem.

- Ecological pyramids (energy pyramids) are models that show how energy flows through ecosystems. Energy moves up the pyramid and decreases by 90% at each level. Only 10% of energy is passed up from one trophic level to the next higher level. The base of the pyramid represents producers (autotrophs). Each step up represents a different level of consumer.

- A biomass pyramid represents the total mass of living organic matter (biomass) at each trophic level. Since the number of organisms is reduced in each successive trophic level, the biomass at each trophic level is reduced as well.

|Aquatic Energy Pyramid |- First Trophic Level: |

|[pic] |consists of producers (plants/autotrophs) |

|Only 10% of the energy available at each trophic level is passed up |- The autotroph uses some of the simple sugars for |

|to the next level. |energy and some of the simple sugars are converted to |

|* Producers are autotrophs. |organic compounds (carbohydrates, proteins, and fats) |

|* Consumers are heterotrophs. | |

| |- Second Trophic Level: consists of primary consumers |

| |Herbivores – primary consumers that eat green plants; use |

| |some of the organic compounds for energy and some are |

| |converted into proteins, carbohydrates, and fats, much of |

| |the consumed energy is lost as heat. (i.e. grasshoppers, |

| |rabbits, zooplankton, etc.) |

| |- Carnivores = eat animals/consumer |

| |- Ominvores = eat both plants and animals |

| | |

| |- Third Trophic Level or Higher: consists of consumers |

| |- Carnivores or omnivores use some of the organic |

| |compounds for energy and some are converted into |

| |proteins, carbohydrates and fats; much is lost as heat (i.e. |

| |wolves, humans, frogs, minnows) |

| |- Decomposers – heterotrophs that break down |

| |organic material and return the nutrients to soil, water, |

| |and air making nutrients available to other organisms |

|Terrestrial Food Chain |- The triangle shape of the energy/ecological pyramid demonstrates that most of the |

|[pic] |energy is available at the producer level. |

| |- As energy moves up the pyramid, less and less is available at each trophic level. |

| |This also explains why there are fewer organisms at the tertiary level. |

| |- The Sun is the source of energy for all food chains. |

| |- Disruptions to any physical (abiotic) or biological (biotic) component can lead to |

| |shifts in all populations. |

| |- Producers/Plants use sunlight and CO2 to produce food through photosynthesis; oxygen |

| |is the waste product. |

| |- Consumers eat food and oxidize it; cellular respiration releases carbon dioxide (CO2) |

| |as a waste product. |

| |- Matter in the environment remains constant, even though it changes form. |

| |- Decomposers recycle nutrients from dead plant or animal matter back to the soil |

| |and/or water. |

7. Regulation of a population is affected by limiting factors that include density-dependent, density-independent, abiotic (nonliving) and biotic (living) factors.

- Density-dependent Factors: those that operate more strongly on large populations than on small ones – (competition for food, water, shelter, and space, predation, parasitism, and disease

- Density-independent Factors: those that occur regardless of how large the population is and they may reduce the size of all population in the area; are mostly abiotic ( weather changes, human activities like pollution and urban sprawl, natural disasters like fires

[pic]

[pic]

energy pyramid and abiotic/biotic factors



energy mini-film

life science mini lessons

Maryland test items

[pic]

Energy Pyramids

What is an energy pyramid

[pic]

Energy pyramid

An energy pyramid is a graphical model of energy flow in a community. The different levels represent different groups of organisms that might compose a food chain. From the bottom-up, they are as follows:

• Producers — bring energy from nonliving sources into the community

• Primary consumers — eat the producers, which makes them herbivores in most communities

• Secondary consumers — eat the primary consumers, which makes them carnivores

• Tertiary consumers — eat the secondary consumers

In some food chains, there is a fourth consumer level, and rarely, a fifth. Have you ever wondered why there are limits to the lengths of food chains?

Why are energy pyramids shaped the way they are?

An energy pyramid’s shape shows how the amount of useful energy that enters each level — chemical energy in the form of food — decreases as it is used by the organisms in that level. How does this happen?

Recall that cell respiration “burns” food to release its energy, and in doing so, produces ATP, which carries some of the energy as well as heat, which carries the rest. ATP is then used to fuel countless life processes. The consequence is that even though a lot of energy may be taken in at any level, the energy that ends up being stored there – which is the food available to the next level — is far less. Scientists have calculated that an average of 90% of the energy entering each step of the food chain is “lost” this way (although the total amount in the system remains unchanged).

The consumers at the top of a food pyramid, as a group, thus have much less energy available to support them than those closer to the bottom. That’s why their numbers are relatively few in most communities. Eventually, the amount of useful energy left can’t support another level. That’s why energy flow is depicted in the shape of a pyramid. The energy that enters a community is ultimately lost to the living world as heat.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download