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Biology 1001
Laboratory 1
Read this exercise before you come to the laboratory.
Be sure to bring a Lab Coat to next week’s lab!
Campbell and Reece, Chapt. 52, 53.
After completing this laboratory exercise, the student should be able to:
1. Make a proper graph, if given a set of numerical data.
2. Explain or define the terms ecosystem, population, community, niche, competition.
1. Participate in the "species" competition exercise.
2. Plot the graphs using the data from this exercise. Ask your lab instructor to check them for
Final copies must be passed in for marking before you leave today.
3. Answer the questions on the lab assignment page.
Ecology is the study of the interrelationship of living organisms and their environment. The
environment includes both the physical environment - such as temperature, humidity. pH, and light intensity and the biotic environment of all of the other organisms that interact with one another. The interactions can
take place at various levels, such as populations (all members of the same species in an area), communities
(all of the populations of an area), or ecosystem (both the living communities and their nonliving
Populations of different species exhibit different distributional patterns. The most common type is a
clumped distribution, in which the members of a population are grouped together. Some aggregations are
short term, such as schools of fish or flocks of birds; others are seasonal, such as a frog chorus; and still others
are semipermanent, such as elephant herds or baboon troops. Some plants are found clustered around a
needed resource such as water or light. Others show an even distribution. This is commonly demonstrated by
territorial animals and plants such as the creosote bush, which secretes poisons from its root systems to prevent
competition. Many man-made communities exhibit even distribution. Random distribution is rare in nature
and occurs in areas where resources are somewhat evenly available and there is no biological or physical
control over distribution. One place where this pattern is observed is the tropical rain forests.
In addition to spatial distribution, many forms exhibit temporal patterns. Often these patterns are
associated with some aspect of reproduction, such as mating, hatching, flowering, seed set, and migration.
Population size is controlled by many factors, including immigration and emigration, birth rate,
death rate, and carrying capacity (ability of the environment to support a particular population size).
The maximum rate of reproduction of a species is called its reproductive potential if there are no
limiting factors (e.g., food or space) affecting its growth. Both the physical and biological environments place
limits on the reproductive potential. These limits, such as availability of nutrients, home sites, food, and
competition with other organisms, are collectively known as environmental resistance and exert a dampening
effect on growth. These limits tend to stabilize and balance a population at a level somewhat below the
carrying capacity of the environment.
Whenever addition to a population (from birth and immigration) exceeds subtraction (from death and
emigration), it will show growth. All successful species reproduce enough to ensure replacement. Unless
this happens, the species will be faced with extinction. As a population increases, more organisms join the
breeding population, and the number of offspring increases proportionately. A number of obvious factors
affect the rate of growth, including: (1) age of reproduction, (2) frequency of reproduction, (3) number of
offspring, and (4) number of times during a lifetime that the organism reproduces. All organisms have the
reproductive potential for exponential growth. In this form of growth, more organisms are added to the
population during each succeeding time period, causing it to increase at faster and faster rates.
These exponential J-shaped growth curves are short-lived phenomena, characterized by explosive, rapid
growth followed by a massive die-off called a population crash. The spring turnover in lakes, the addition of
fertilizer, or the addition of a new ingredient to the environment may trigger a massive response in the biotic
community. Also, if a species is introduced into a new environment, it may explode; this has occurred many
times. If a population has been held in check by a biological factor (e.g., parasite or predator) or a physical
factor (e.g., lack of oxygen), the population may experience exponential growth when the restricting factor
has been removed.
Eventually, environmental resources become limiting factors once more, competition becomes greater,
the death rate increases, the birth rate declines, and the growth rate approaches zero. Exponential growth has
ended, and the population levels off close to a sustainable level. This sustainable level is usually referred to as
the carrying capacity of the environment for the species being considered. The level is controlled by
competition for the limiting environment factors. If the population rises above this level, the ecosystem will
become damaged and eventually the population level will drop. If the damage is not too great, the system can
recover (environmental homeostasis).
Some factors controlling population size are density dependent, and the larger the population, the greater
their effect. For example, limited food supply, predators, and parasites are much more debilitating when
populations are large. Other factors, such as freezing temperatures, are density independent and exert their
effects regardless of population size.
Organisms that have the same ecological requirements fit in the same ecological niche. If we let a circle
represent the niche of an organism, everything within it is required for the organism to survive. Thus, circle A
represents the niche of a squirrel and circle B the niche of a whale. The niches are completely separate, and it
would be hard to imagine anything in nature that the two have in common.
Concept of the niche.
If we compared the niche of the squirrel with the niche of a chipmunk, they would overlap.
The stippled area represents where the niches overlap and where the two organisms have the same needs.
This area represents a zone of competition between them (e.g., food, nesting sites, escape from predators, and
parasites), and the one with the best adaptations (fit) would have the greater chance of surviving. What
organism would have the greatest competition with the squirrel? The answer is another squirrel. We find that
the more closely two forms are related, the more competition there is between them. Intraspecific
competition (between members of the same species) is greater than interspecific competition (between
members of different species). This presentation is an oversimplification of the niche concept (which is more
like an ever-changing polygon), but it may enable you to visualize competition more clearly.
In this exercise we will look at some aspects of competition by examining the interaction of two artificial
"species" competing for a number of common resources.
-----------------------------------------------------LABORATORY ASSIGNMENT 1
The class will be divided into two groups corresponding to the two "species" - forks and spoons. Within
each species you will be working in groups of two - one will have the fork or spoon and the food pouch and the
other will do the counting and recording. (You may change jobs at any time you wish).
There are five "resources" - toothpicks, pasta noodles, string, pistachio nuts and rice, spread over a large
area. A unit of energy will consist of one toothpick, one pasta noodle, one string, two pistachio nuts or five
pieces of rice.
After each 30 second trial, the number of units collected by each individual will be counted and recorded.
Neither of these species is reproducing at this time and so an individual only requires enough "food" for its
own survival. If an individual collects less than 5 units in any one trial, it will die from lack of food. If it
collects 5 units or more, it survives. However, if it collects more than 7 units it also dies, this time from
overeating. The experiment will continue until one "species" becomes extinct.
Each pair of students will record the units of food they collect and will decide if they "survived" or
"perished". The lab demonstrator will keep track of the overall survival of the two "species" as well as time
the intervals.
------------------------------------------------------LABORATORY ASSIGNMENT 2
l. Using the data that were recorded from the "species-competition" exercise (which will be compiled on
the chalk board in the lab), plot extinction curves for both "species" (number surviving with respect to time).
See Appendix page A-3 for help in making graphs. You should be able to plot both species on the same graph.
Use a piece of graph paper from the front bench. After you have constructed your graph, have an instructor
check it.
2. Using the data you recorded yourself, make a bar graph (not a histogram) to show the total units 'eaten'
for each type of energy unit. Use a piece of graph paper from the front bench. After you have constructed your
graph, have an instructor check it.
3. Redraw your final corrected graphs on the graph paper provided in your lab manual. Pass
these in for evaluation before you leave today.
Be sure that you can answer the questions on page 1-7 before you leave the lab today.
-----------------------------------------------------TABLE 1-1 INDIVIDUAL FEEDING DATA: “SPECIES” FORK
# of
pastas strings
# of
# of
pistachio nuts
# of kernels
of rice UNITS (30 sec)
N.B. A “unit” consists of l toothpick or l pasta noodle or l piece of string or 2 pistachio nuts or 5 grains of rice.
Survived = 5 to 7 units;
Perished = under 5 units or over 7 units
(time in 30 sec
l. Which 'species' - forks or spoons - was more successful?
2. What was your reasoning in answering question 1?
3. Based on your own bar graph, state which energy units were easier to capture. Why?
4. Why is a histogram not an appropriate type of graph for these data? __________________
5. Look at the data from someone of the other ‘species’ than you. Compare it with your data.
Discuss the relative advantages and disadvantages of forks and spoons with regard to the
various kinds of energy units available.