Reading Questions 6A

Reading Questions 6A

  • New England Forests Come Full Circle
  • Nature exists at several levels of complexity.
  • Population ecologists study the factors that regulate population abundance and distribution.
  • Growth models help ecologists understand population changes.
  1. Fill in 5 key events in the re-establishment of the New England forest in the Opening Story:

1. Farmers begin leaving

2. Many people abandoned farms to take jobs in growing textile farming

3. birds and wind brought seeds to abandoned farmland which resulted in many new plant species

4.goldenrods dominated the fields, outcompeting other species for sunlight

5. white pine tree grows tall and casts shadow over other plants including goldenrods

6. white pine trees harvested for lumber, made room for broadleaf tree species

7. Broadleaf forest re-established

  1. Distinguish between each level of analysis:

What does this level consist of?

What do scientists study at this level?


A single organism

Natural selection


All the individuals of a single species living in a given area at one time



All of the populations of organisms in a given area

How species interact with one another


All of the biotic and abiotic components in a particular location

Flows of energy and matter or a large scale (ex: the cycling of C/N/P/H2O in a lake)


All of earth’s ecosystems

Movement of air, water, and heat around the globe.

  1. Which level of analysis would be most appropriate for a scientist to use in each scenario?
    1. Monitoring the Grey Wolves of Yosemite


  1. Investigating the connections among organisms in a soil sample


  • Determining whether or not natural selection favors light or dark coloration in mice


  1. Evaluating the status of the Florida Everglades


  1. How does the Opening Story demonstrate the importance of community-level analysis and interactions between species?

Different plants have different needs, for example, plants like goldenrods are very sunlight reliant. When they do not get the sunlight they need and they die off, so do the insects and animals that eat them and eventually the cycle is messed up. Each organism is connected to each other in some way in a community.

  1. When considering a population as a system, what 2 processes are inputs that increase population size and what 2 processes are outputs that decrease population size?

Input 1 (+): birth                                                                              Output 1 (-): emigration

Input 2 (+): immigration                                                                Output 2 (-): death

  1. Key Idea: Five major characteristics help us understand how populations change over time:

Why is this factor important?

How could this factor apply to the New England forest in the Opening Story?

Population Size

Informs us which species are nearing extinction and which are abundant.

The populations of each species increased as the farmland grew back in

Population Density

Useful measure for wildlife managers who must set hunting or fishing limits on a species

Goldenrods were dominant over other species

Population Distribution

Helps us understand an ecosystem and how a population occupies space

Competition between species because they were so compact

Population Sex Ratio

Helps scientists estimate the number of offspring a population will produce in the next generation

Ecologists may study the percentage of female Microrhopala vittata beetles

Population Age Structure

Determines future growth potential (via individuals of reproductive age)

Shows how fast forest grew back in

  1. Key Idea: Density-dependent factors & density-independent factors can affect population sizes and growth rates:
    1. True/false: Wildfires occurring in the Southern California chaparral (shrubland biome) influence populations of local species in a density-dependent way.


  1. What variable served as the limiting resource in Gause’s paramecium experiment?


  1. Explain how the carrying capacity (k) of an environment is determined:

Population growth slowed as population size increased because there was a limit to how many individuals the food supply could sustain. This tells us about  the limit to the number of individuals that can exist in a population.

  1. What are common limiting resources for terrestrial plants?

Water and nutrients

  1. What are common limiting resources for animal populations?

Food, water, shelter

  1. True or false: Density-independent factors deal with limiting resources


  1. Predict what would happen to the population sizes of aurelia and P. caudatum if Gause had continued his experiment by alternating between high-food and low-food conditions each day:
  2. Aurelia and P. caudatum populations are going to continue to increase over time. Alternating between high food and low food conditions is normal in an environment.
  3. The Exponential Growth Model
    1. What does the intrinsic growth rate (r) for a species measure?

A populations maximum potential for growth.

  1. Chart the growth of the following population of mice at a growth rate of 10% per year:

























  1. The Logistic Growth Model
    1. Why is the exponential growth model usually insufficient to describe real populations?

Formula that allows us to estimate future population.

  1. How does the population growth rate CHANGE as it approaches the carrying capacity of its environment, and why?

The population growth rate changes because it is reaching its max population potential with the same amount of resources so a population is trying to surviving

  1. What factors prevent the continued growth of populations beyond the carrying capacity?

They are struggling to survive.

  1. Variations on Logistic Growth
    1. Why is population overshoot always followed by a die-off?

There is a population die-off because because it has reached its capacity and is no longer thriving as a population.

  1. True/false: during population overshoot, the environment’s carrying capacity increases.


  1. Reproductive Strategies and Survivorship Curves
    1. Characteristics of k-selected and r-selected species:


Reproduction Speed

Likely to overshoot?


Survivorship Curve Type

k-selected species

Large mammals

Late, produce few



Type I

r-selected species

Small, short lives, many offspring

Early, produce frequently


Mice, pests

Type 3

  1. Which type of species can evolve faster? Explain why.

r-selected species because they produce more frequently and have more offspring at a time than k-selected species.

  1. True/false: Most organisms show strict k-selected or r-selected reproduction strategies


  1. Which type of species is at greater risk for extinction? Explain why.

K-selected species because these populations have slow growth rates and cannot respond quickly to trauma.

  1. What is a metapopulation, and why is it important to study them?

A group of spatially distinct populations that are connected by occasional movements of individuals between them. This is an important part of each populations overall persistence. Small populations are more likely to go extinct than large ones and metapopulation provides protection from diseases and other threats for these populations.

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