A simple ecological study: Proposed studies. Read the opening chapters in your lab manual (read all the sections on experimental design and hypothesis testing) and the material below before coming to class, and come prepared to go out in the field. If you need to review mean, standard error, and t-tests, do it. We will meet in the lab for a brief discussion of the scientific method and a planning session for our field work. Then, we will go to the nature reserve and you will begin making observations for your simple ecological study. Some of you may begin collecting data this week, but you will also have next week to continue. At the end of lab you will Hand in: Fill in the worksheet A simple ecological study: Proposed Studies and turn it in at the end of lab. 5 points based on (1) the clear statement of a testable descriptive hypothesis, (2) an appropriate sampling regime, and (3) a reasonable functional hypothesis.
General
Ecology Lab #4 A Simple Ecological Study
In
this lab you will conduct a simple ecological study that your group will initiate, design,
and carry out over the next two labs. The
goals of this lab are for you to understand basic ecological studies, design a sampling
regime, conduct statistical analysis of your results, and prepare a concise report of what
you did.
Designing
an Ecological Study: An ecological study usually begins with an
observation of a pattern in nature. For
example, you might observe that red squirrels are common in one area, while gray squirrels
dominate another. At this point your initial
observation is just subjective; you need to conduct a formal descriptive study to document
the pattern you observed. For this
descriptive phase you first need to formally state your question or descriptive
hypothesis: Are red squirrels dominate in
Area A? (or, stated as a hypothesis: Red
squirrels are dominate in area A, while gray squirrel are dominate in area B.) Now you would need to design a sampling protocol
that would accurately assess the squirrel populations (see section on Ecological Sampling)
followed by statistical analysis of the data (see section on statistical analysis).
abundance--the density of individuals in a habitat
might depend on the level of some resource that varies in distribution
morphology--the size, shape, or color of
individuals may be influenced by the environment (or you could have genetic differences in
different habitats).
reproductive
output--the
number of offspring produced is a critical ecological feature, and it could be influenced
by different habitats or the presence or absence of predators, herbivores, or parasites
You must know
what you are sampling; e.g., if you measure the seeds on an individual in August, have you
missed seeds that were produced back in June and have since fallen off? have some seeds
been eaten by mice? will more seeds be
produced in September? If you want to sample
seed production by an individual plant, you must be sure to actually sample what you think
you are sampling.
You must not
bias your samples. Which individuals will you
sample and which will be ignored? Random
sampling involves use of a random number table to select random plots to sample. The table will give you a number--say 6-- and you
sample plot 6. The problem with random
numbers is that everything you want to sample must have a number (i.e., you need to grid
off the study area so all points are numbered). Haphazard
sampling involves, for example, throwing a stake out and sampling the closest plant.
Your samples
must be replicated.
A student's t-test will allow you to statistically contrast the
two samples--in other words objectively answer the question of whether the samples are the
same or different. Small t values indicate a high probability that the two
population means are the same; by contrast, large t
values imply lower probability. The
calculated t value and probability (p)are given in SYSTAT. Ecologists consider a difference between
population means to be significant when the probability that they are the same is less
than 5% (p < .05)