50.351
Introduction
All populations have a spatial
distribution. Organisms may be randomly distributed; any point in space is as
likely to be occupied by an organism as any other point. Ecologists also recognize two types of non-random
distributions—clumped distribution and even distribution. In a clumped distribution, individuals are
aggregated and closer together than in a random distribution. Individuals may be clumped because points
with suitable abiotic and biotic characteristics are
not evenly distributed throughout an area. For example, plants may be clumped
in areas with sufficient soil moisture content.
On the other hand, in an even distribution, individuals are spread out
such that each individual is as far from others as possible. Even distributions are usually a result of
competition for resources. For example,
plants may use all of the nitrogen in the soil in their immediate areas. As a result, multiple individuals cannot grow
close to one another, and the plants become evenly distributed across a large
area.
In
today’s lab, we will determine the density and spatial distribution of eastern
white pine (Pinus strobus).
Methods
Data collection.—You will work in your teams. Your team will use T-square
sampling to measure density and spatial distribution of eastern white pine. Unlike other, more common plotless
methods, T-square sampling gives reliable density measurements even if the tree
distribution is not random (Greenwood 1996).
You
will be given a list of 12 randomly generated points. For each point, locate two white pines—1) the
white pine nearest to the random point and 2) the white pine that is the
first’s nearest neighbor on the side opposite of the random point (Figure 2.8).
Make the following measurements—
x: the distance from the random point to
the center of the nearest white pine
z: the distance from the center of the
first white pine to the center of its nearest white pine neighbor opposite the
random point.
Statistical
analysis.—When you return to
the lab, enter your data into the class data sheet. We will use Excel to
calculate the density and spatial distribution of white pines (Greenwood 1996).
Assignment
The written assignment should
include four parts: a descriptive title, a short introduction summarizing the
purpose of the investigation, the results (including the statistical analysis),
and a brief (a few paragraphs) discussion of the results. The discussion should include proposals for
additional investigations on this topic that would build on what we've done in
this lab.
Each person will turn in her/his own
assignment, even though you worked in teams.
The assignment should be word-processed.
The lab report is due in one week at the beginning of the lab meeting
time.
Literature Cited