Chapter 18Interactions

of Living Things

Mr. Perez

Important Vocabulary

• Ecology

• Abiotic factor

• Biotic factor

• Population

• Community

• Ecosystem

• Biosphere

• Population density

• Limiting factor

• Symbiosis

• Niche

• Habitat

• Producer

• Consumer

• Decomposer

• Food chain

• Food Web

Ecology

• The study of interactions among organisms and their environment.

• Ecologists organize the environmental factors that influence organisms into two groups• Abiotic factors- non-living parts of

the environment• Biotic factors- living or once-living

organisms in the environment

Abiotic factors

• Water• All organisms need water to survive• Organism bodies are 50%-95% water• Important in cytoplasm in cells• Respiration, photosynthesis, digestion

and other important life processes can’t happen without water

• More than 95% of the Earth’s surface water is found in the ocean

Abiotic factors• Light and temperature

• Sunlight is important for plants and other photosynthetic organisms

• Temperature can determine which plants/animals can live there

• Air• Composed of gases including nitrogen, oxygen

and carbon dioxide• Needed for respiration

• Soil• Soil type is determined by the amounts of

sand, silt and clay• Different kinds contain different nutrients,

minerals and moisture

Biotic factorsLevels of organization:

Organism

Population

Community

Ecosystem

Biome

Biosphere

Characteristics of Populations

• Population size can be difficult to measure because individuals are too widespread or move around too much

• Instead, we estimate the population size (sampling)

• The size of a population is always changing• Births• Deaths• Migration• Immigration

Characteristics of Populations• Population density- the number of

individuals in a population that occupy a definite area• Ex: If 100 mice live in an area of one

square kilometer, the population density is 100 mice per square kilometer

• Population spacing is how the organisms are arranged in a given area• Evenly- consistent distance between them• Randomly- each organism’s location is

independent of the locations of other organisms

• Clumped- resources such as food or living space are clumped

Limiting factors

• Any biotic or abiotic factor that limits the number of individuals in a population• Competitors• Weather• Predators• Fires• Available habitat• Disease/parasites

Carrying Capacity

• The largest number of individuals of a species that an environment can support and maintain for a long period of time• If a population gets bigger than the carrying

capacity, some individuals are left without adequate resources and will either die or be forced to move elsewhere

• Biotic potential• The maximum rate at which a population

increases when plenty of food and water are available, the weather is ideal, and no disease or enemies exist

Symbiosis and Other interactions

• Symbiosis: any close interaction between two or more different species• Mutualism: two different species of organisms

cooperate and both benefit (+ +)• Lichens = fungus + algae

• Commensalism: one organism benefits without affecting the other organism (+ 0)• Flatworm that lives in a horseshoe crab’s gills

• Parasitism: two different species in which one species benefits and the other species is harmed (+ -)• Mistletoe grows into a tree’s roots and takes

away nutrients

Symbiosis and Other interactions

• Predation is a way to regulate population size• Act of hunting, killing and feeding on

another organism

• Habitats and niches• Habitat: place where an organism lives• Niche: role, or job, of an organism in the

ecosystem

Classwork Questions

• On a separate sheet of paper answer the following questions. You do not have to write these questions, but the answers should be in complete sentences.

1. Compare and contrast abiotic factors and biotic factors. Give five examples of each that are in your ecosystem.

2. Describe a population and a community.

3. Explain how biotic factors change in an ecosystem that has flooded.

Classwork Questions

• Write down the following questions. Answer them as you watch the videos.

1. Name three pairs of animals that work together in the video.

2. Describe what each animal offers its partner (if anything).

http://www.youtube.com/watch?v=uxVMeLWzB_o

Energy Flow Through Ecosystems

• Organisms interact with members of their own species and other species

• Food chains or food webs consist of:• Producers- organisms that take in and use

energy from the Sun or some other source to produce food

• Consumers- organisms that take in energy when they feed on producers or other consumers

• Decomposers- take in energy as they break down the remains of organisms

Food chains

• Simple way of showing how energy, in the form of food, passes from one organism to another• Arrows indicate the

direction of energy transfer

• Usually only have three or four links because energy decreases/is lost as it is transferred • Lost as heat*

Food Webs

• Series of overlapping food chains that exist an ecosystem• Provides more

complete model of energy transfer in an ecosystem

• More accurate, because they show more organisms

Ecological Pyramids

• Most of the energy in the biosphere comes from the Sun• Producers take in and transform only a

small part of the energy that reaches the Earth’s surface

• Primary consumers eat producers• Secondary consumers eat other consumers• Tertiary consumers eat only secondary

consumers (usually at the top of the food chain/web)

Ecological Pyramids

• Organisms can be classified as:• Autotrophs- can produce

their own food• Heterotrophs- cannot

produce their own food• Carnivore- must eat

other organisms• Herbivore- must eat

producers (plants)• Omnivore- can eat both

plants and other organisms

Energy Pyramids

Only about 10% of the energy at each level of the pyramid is available to the next level

Classwork questions

• On a separate sheet of paper answer the following questions. You do not have to write the question, but the answers should be complete sentences.

1. Draw and label a food web that includes you and what you’ve eaten today (or yesterday).

2. Compare and contrast producers, consumers and decomposers.

3. Use your knowledge of food chains and the energy pyramid to explain why fewer lions than gazelles live on the African plains.

Videos

• http://www.vtaide.com/png/symbiosis.htm

Resources

• Florida Science Grade 8

Glencoe Science & McGraw Hill Publishing

• Google Images