4.4 part b Biotic Relationships

Biotic Relationships

click to find the answer to today's question What is biomass?

Biodiversity All organisms fit into a:

Energy enters an ecosystem from the sun and flows between organisms as one eats another.

Trophic levels: link to a local picture the flow of energy through an ecosystem. Energy is always lost from one trophic level to the next.

Primary productivity in an ecosystem - the rate at which solar energy is converted into organic compounds. The units of productivity are kilocalories per square meter per year.

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Food chain link to an Internet Website the specific sequence in which organisms obtain energy within an ecosystem.

 Food web link to an Internet Website interrelated food chains within an ecosystem.

As the diagram indicates, a food web may have many linked food chains and be very complex.



Competition - within any ecosystem, some organisms utilize resources and reduce the availability of those resources to other organisms.

Predation - refers to the relationship between a predator and its prey.

Predator and prey are often tied together in many ways. Each has traits that attempt to take advantage of the traits of the other. Moths are a good meal for many birds. Most moths are active at night, a time when most birds are not hunting. But the moth has to hide during the day to escape the birds. The protective coloration link to a local picture of some moths allow them to hide in plain view. Do you see the moth on the tree bark here? Would the moth be as well hidden on just any tree?

Have you ever seen a rabbit run onto the road in front of a car and suddenly stop? While this is not a good reaction at the time, it is the behavior that will most often save the rabbit from being caught by a predator. How?

Even predator and prey populations are related. If the predator population is low, the numbers of the prey species will increase. Most predator species will reproduce in larger numbers if food is abundant. As the numbers of the predator species increase, the prey population begins to decline.

Use this computer simulation link to an Internet Website to explore predator/prey populations.

Symbiosis link to an Internet Website the close association between two dissimilar organisms. link to an Internet Website

Ecological pyramid - a graph representing trophic level numbers within an ecosystem. The primary producer level is at the base of the pyramid with the consumer levels above.

regular ecological pyramid Most ecological pyramids would be like the one on the left. The pyramid on the right is "inverted".

Give an example of an ecosystem that would produce an inverted numbers pyramid.

Why would an energy pyramid never be inverted?

inverted ecological pyramid

the key points to useful information on this page
Population link to an Internet Website a group of individuals of the same species living in the same area.                      World population information link to a local webpage

  • Population density - the number of individuals in a population in a given area at a given time. link to an Internet Website
  • Carrying capacity - the maximum number of individuals that an ecosystem is capable of supporting.
      As population numbers increase, certain factors in the environment become limits to growth. All living things need a certain amount of space in which to live, food, water, and oxygen.
  • Biotic potential - the rate at which a population will grow if all individuals survive and reproduce at their maximum capacity. This is a theoretical number that is never realized in nature. While the term is not usually applied to human populations, health and census data are available for such calculations.
  • Realized intrinsic rate of growth - a measure of the difference between natality (birth rate) and mortality (death rate).
    • r = n - m
    • Since environmental conditions are rarely ideal, the maximum growth rate is almost never achieved in nature. For this reason, the realized intrinsic rate of growth more closely represents the actual growth of organisms in nature than does the biotic potential.

Use this computer simulation link to an Internet Website to explore human population dynamics.


4.4b Assignment - Biotic Relationships
Use the above information and included links to answer the following questions
Scoring criterialink to a local webpage
  1. Describe and give an example of the difference between a habitat and a niche.

  2. List two example of primary producers.

  3. Which of the trophic levels produces the most biomass? Which level the least?

  4. Visit this site link to an Internet Website  and play the food web game "Chain Reaction". List the order of each food chain from producer on up to the top consumer. What happens if on organisms is removed from the food web?

  5. Visit this site  link to an Internet Website  Blue Iceberg and play the "food web" game

    1. Record your best score here.

    2. List the names of the producers in the food web.

    3. List the names of the secondary consumers.

    4. List the names of the tertiary consumers.

    5. What is the difference between c and d above?

    6. Are there any omnivores in the food web?

  6. Describe an example of each type of symbiosis?

  7. Using this predator  prey data link to a local picture construct a graph showing the relationship between the two populations and place it here. Describe and support any comparison patterns you can see developing on the graph.

  8. Find or draw an example of each type of ecological pyramid and place it here (or one that contains all). Label each pyramid.

    1. What patterns do you see in each of the pyramids?

    2. How would the reduction on the bottom of the pyramid effect the top?

    3. What might cause a reduction on the bottom?

  9. What is the current human population for earth?

  10. Calculate the realized intrinsic rate of growth for humans in the United States.

  11. What is the estimated carrying capacity for humans on earth?

    1. What will ultimately limit there growth?

  12. What is the estimated population of humans by the year 2050?

Honors biology: Complete the above questions along with these

  1. What is the earth's total area?
  2. What is the current human population density for earth?
  3. What is the area of the earth land mass?
  4. What is the current human population density for earth's land mass?
  5. Read the information about shrews below and do the calculations:

    Shrew Mathematics Exercise:

    The short-tailed shrew is a ravenous predator that is found throughout the plains states. Although it is seldom seen, it is common. There can be as many as 50 shrews living on one acre of land, with 10 to 20 shrews per acre common. Few animals are as hungry as a shrew. It must eat 11/2 times its own body weight in insects and other small animals in a single day. Solve the following problems so you can picture how much a shrew really eats.

    You must clearly show where the numbers come from and what the calculations represent.

    1. The short-tailed shrew must eat 11/2 times its own body weight in insects each day. If a shrew weighs 18 grams and a grasshopper weighs 3 grams, how many grasshoppers must a shrew kill and eat in one day? (Count each grasshopper killed in a day. If only part of a grasshopper needs to be eaten, count the whole grasshopper. For instance, 21/2 grasshoppers needed in a day would be three grasshoppers killed and eaten).
    2. How many grasshoppers must it eat in one week?
    3. If three shrews live in your garden, how many grasshoppers can they eat in one growing season? (Consider June, July, August, and September as the growing season).
    4. If you had to eat as much as a shrew (11/2 times your body weight), how many quarter pound hamburgers would you have to eat in one day?


  6. Use this information about prairie dogs to answer the questions below:

    In January of 2000, all members of a population of black-tailed prairie dogs in a field of native short-grass prairie north of Red Rock were counted. The population contained 50 prairie dogs. This population is isolated from other prairie dog populations and cannot expand far due to the fact that there are irrigation systems in the adjacent fields and wheat is grown there. Since the black-tailed prairie dog is now considered an endangered species, a wildlife biologist is monitoring this population. During 1999, 5 prairie dogs died and 10 were born. The field containing the prairie dog town measures 250 square meters.

    Prairie dogs are herbivores, feeding on several types of small plants found around their burrows. They are preyed upon by small carnivores as well as hawks and falcons. These same hawks and falcons feed on other small rodents round in the prairie dog town.

    1. What is the intrinsic growth rate, r, for this population in 2000?
      a. 0.01 prairie dogs per
          prairie dog per year
      b. 0.05 prairie dogs per
          prairie dog per year
      c. 0.10 prairie dogs per
          prairie dog per year
    2. If there are no predators or diseases in the area, what would you expect the population of prairie dogs to be at the end of December 2001?
      a. 56 prairie dogs b. 61 prairie dogs c. 67 prairie dogs
    3. What was the initial density of the prairie dog population?
      a. 0.2 prairie dogs
          per square meter
      b. 2.5 prairie dogs
          per square meter
      c. 5 prairie dogs
          per square meter
    4. What is the source of the energy that keeps prairie dogs alive?
      a. prairie grass b. glucose c. sunlight
    5. The wildlife biologist monitoring the prairie dogs suspects that the prairie dog town has been polluted with heavy metals, that cannot be excreted or metabolized by plants and animals. In which of the following organisms would you expect the biologist to find the highest concentration of heavy metals?
      a. small plants b. prairie dogs c. hawks & falcons


Research Links:

Biology Class










Biomass is the weight of all the living matter in a particular area.