Exercise 2 Thursday Sept 22

IMPORTANT SUPPORTING CONCEPTS #1: The distribution of species is affected by abiotic and biotic components of the environment.

Today’s particular focus: The effect of abiotic components of the environment on the distribution of species.

Pre-reading assignment:
Campbell: All of 52.1 Earth’s climate varies by latitude and season and is changing rapidly. 1158-1164; Part of Concept 52.2 1164-1166. Stop just before the section entitled: ‘Disturbance and terrestrial Biomes”

In small groups of 3-4. Answer the following:

1)What according to our readings limits the geographic distribution of species?

2)Let’s take the environmental factor of temperature that we know affects the distribution of species. How might scientists investigate the tolerance of a tree species to temperature?

Write some ideas below.

3)Draw a hypothetical curve for Douglas-fir tree growth versus temperature. Assume 20°C is optimal growth. (Start by putting this curve on a whiteboard. We may discuss these ideas as a whole class discussion.) DON’T MOVE ON, UNTIL I HAVE SEEN YOUR CURVE.

4)What would a narrow/wide tolerance to suboptimal temperature look like? Draw two curves illustrating narrow tolerance/broad tolerance.

5)The mean annual temperature in which subalpine fir (Abieslasiocarpa) grows is 5oC. Make an educated guess as to what the temperature optimum might look like compared to Douglas fir. Draw a hypothetical curve of temperature (x axis) and growth (y axis).

6)Now draw both species on same graph. (Show your instructor your graph.)

7)The mean annual temperature at which pacific silver fir (Abiesamabilis) grows is 15oC. What might the temperature/growth curve look if added to the previous two curves?

8)Draw a temperature vs growth graph of all three species.

9)Let’s start with a very simple idealized scenario of what the forest composition might look like if you walked up a northwest coastal mountain from west to east. For the moment we will consider only three tree species: Douglas-fir, pacific silver fir and subalpine fir.

Subalpine fir

Pacific silver fi

Douglas-fir

As you hike up the slope you would first walk up through Douglas-fir trees, then there would be a region where you would be walking through Douglas-fir and Pacific silver fir. As you kept waking up the slope, the Douglas-fir trees would become fewer and fewer until only pacific silver trees would be found. As you kept walking further up the slope subalpine trees would start to appear among the pacific silver fir trees. Moving further up near the tree, you would only find subalpine fir. In what ways do the trees different tolerances to temperature as you showed on your temperature/growth curves above explain the distribution of trees up the slope of the mountain? Be specific and thorough as you can.

10)From your readings what other environmental parameter seems to have a substantial impact on the distribution of organisms on Earth? (Show your answer to your instructor.)

11)Draw what you think a generalized graph of growth versus moisture might look like for a typical tree species.

12)Examine the information under “Ecology” in Pojar and Mackinnon for Douglas-fir, pacific silver fir, and western red cedar. Pay particular attention to any information given that could help you determine the relative tolerances the trees have to soil moisture levels. Write below any inferences that your group has made.

13)Draw a set of hypothetical curves for those three species based on information that you gleaned from Pojar and Mackinnon.

14)Below shows a relative flat area partially up a mountain slope at an elevation that all three species can be found growing. Although this hypothetical stretch of ground is relatively flat the soil characteristics are quite different. As shown below, on the one side of the area the soil is made up of loose glacial till through which rain water runs right through and ends up below any level that the trees root systems can extend. On the other side is a soil that is a mixture of sand, clay, and silt called a loam. Rain water is actually retained in that area.

Glacial till ------Loam

Given the information that you got from Pojar and Mackinnon and the moisture vs growth curves that you drew, locate where you think the trees (Douglas-fir, pacific silver fir, and western red cedar) might be located.

15)Examine the climograph in Figure 52.9 of text (your instructor may put the figure on overhead). How do you think the authors made that figure?

16)Given the graphs you made for temperature versus tree growth and moisture vs tree growth, construct a hypothetical climograph for Douglas fir, pacific silver fir, and western red cedar.

17)Are there areas on the graph that are unique to each species? If so, give examples. If not, give examples.

18)Look at the graph of Robert Whittaker’s data for trees in the Siskiyou Mountains and/or Santa Catalina Mountains. What is the gradient that Whittaker used on the x axis?

19)How do you think Whittaker actually measured that gradient?

20)Name two plants that you recognize on Whittaker’s figures.

21) How do the conditions for optimum growth vary for Pinusjeffreyi versus Abiesnobilis?

I AM ON THE RIGHT TRACK IF:

  • Name the two most important abiotic factors affecting the distribution of terrestrial species.
  • Plot two or more tree species on a temperature/growth graph.
  • Use a plot of temperature/growth graph to explain the distribution of trees up a mountain slope.
  • From a plot of two or more trees on a temperature/growth graph, I can explain why temperature does or does not serve as an important axis that separate the niches of one or more of the organisms from the other.
  • Draw a climograph from temperature/growth and moisture/growth curves and vice versa.