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Interaction between
species
Maureen
To study an ecosystem the interaction
between species and their environment and
the unique conditions must be explored
Maureen Robertson Science
CQU MACKAY
S0202484
[email protected]
4/2/2012
Overview
To study an ecosystem the interaction between species and their environment
and the unique conditions must be explored (Fleer, Jane, & Hardy, 2007).
Applied ecology uses information to inform us over-harvesting and designing
land reserves for threatened species. Every ecosystem has a climate, culture,
environmental impact and symbiotic relationship between living and non-living
organisms (Gotelli, 2008). To answer these questions we used a digital field
measurement, counting and observing the behaviour of species in their habitats
along with analysing predation rates in a controlled setting. Since living
organisms in ecosystems are connected in complex relationships, it is not always
easy to anticipate how a step such as introducing a new species (Hardin, 1960)
will affect the rest of an ecosystem. Our finding concluded that species function
in ecosystems can be answered by looking at their niches.
Maureen Robertson
Page 1
Introduction
When the ecosystem contains plants only, one species of plant out-competes the
others and takes over. This illustrates the "competitive exclusion principle,"
which theorizes that no two species can occupy (Gause, 1934) the same niche at
the same time in a particular locale if resources are limited.
Can two plants happily co–exist (Fleer, Jane, & Hardy, 2007). Often; different
species within the ecosystem will compete for the resources that a niche
provides. However, certain species live well together (Gotelli, 2008)—
symbiotically, parasitically, or by staying out of each other's way. Then we
introduce a herbivore into the environment. In theory, an herbivore native to the
ecosystem should feed primarily on the dominant species. In this system, the
herbivore may consume enough of the dominant species to give the nondominant species a chance for proliferation and survival .Using a digital
experiment we will test these theories.
http://www.learner.org/courses/envsci/interactives/ecology/producers.php
The study of an individual ecosystem will involve the interaction between all the
species that inhabit the area. Each living species within the ecosystem was taken
into account (Fleer, Jane, & Hardy, 2007). Many key questions about how species
function in ecosystems can be answered by looking at their niches (Gause, 1934).
Species with narrow niches tend to be specialists, relying on comparatively few
food sources. As a result, they are highly sensitive to changes in key
environmental conditions, such as water temperature. In contrast; species with
broad niches are generalists that can adapt to wider ranges of environmental
conditions (Hardin, 1960).
Abbreviations
Phenotype - the way an organisms genes express themselves; either short, tall,
green, etc (physical type) (Gause, 1934).
Genotype - the gene type of an organism; the alleles of a certain characteristic:
TT, Tt, tt.
TT - means that the chromosomes that carry the alleles for a certain
characteristic both have a dominant gene.
Tt - means that one of the chromosomes of a pair has a dominant gene while the
other has a recessive gene for the certain characteristic.
tt - means that the chromosomes that carry the alleles for a certain
characteristic both have a recessive gene.
Maureen Robertson
Page 2
Method



You will need
Computer
Internet access
1. Click on web page to access simulator
http://www.learner.org/courses/envsci/interactives/ecology/producers.php
2. Read: The Lesson Producers-Challenge
3. Simulator Controls
Reset Button Returns to Day 0.Stop Button Stops the progression of the simulator at the moment it
is clicked. Step Simulates the progression of population as determined by the parameters for one
day. Run Simulates the progression of population as determined by the parameters for one hundred
days, or, if you have already run the simulator using "Step," "Run" continues the progression to day
100.Tableau Pull–down menu in the lower right–hand corner. There are two settings: Plants and
Many. The most visible difference among these tableaus is automatic changes in the food web (See
Food Web), which result in automatic changes in the interactive illustration (see Interactive
Illustration).
4. Open step 1. Given the two fictitious species of plants in the simulator, predict what will happen in
this young system and record your prediction in the Data Table. Then run the simulator to 100 time
steps and record the population numbers for both plants. Answer the following:


What assumptions does this model make about co-dominance as well as the general terrain
of the ecosystem? Figure 1
Do you find one producer to be dominant? Figure 2
Why might one producer be dominant over another? 2A
5. Open step 2. Introduce an herbivore into the environment. In theory, an herbivore native to the
ecosystem should feed primarily on the dominant species. In this system, the herbivore may
consume enough of the dominant species to give the non-dominant species a chance for
proliferation and survival. Click on herbivore A (the rabbit) and choose "eats plant A." Predict and
record what will happen to the population numbers in the ecosystem. Then, run the simulator and
record your results. Answer the following:


Does adding the herbivore establish a more equal field? Is one producer still dominant over
the other? Why might one producer be dominant over another? Figure 3
How do producer population numbers with the presence of an herbivore compare to the
primary colonizer model? Figure 4
Maureen Robertson
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Results
1. What assumptions does this model make about co-dominance as well as the general terrain of the
ecosystem?
5
5 5 5 5 5 5
5
5
5
5
5
5
5
5
3
3
2
Plant 2
100
95
0.1 0.1 0.1
0.1 0
Plant 1
90
0.1 0.1 0.1
85
0.1 0.1 0.1
80
0.2 0.1
75
0.4 0.3
65
0.6 0.5
70
0.9 0.8
Plant 1
5…
10
15
20
25
30
35
40
45
50
55
11
60
2
0
5
4
4
1
5
Figure 1
This graph can conclude that, after a short period of time Plant 2 becomes the dominant species.
2. Do you find one producer to be dominant?2A. Why might one producer be dominant over
another?
Parallel logic to that given above gives [N1 = 0:N2 = K2]
as the only stable equilibrium point, and at equilibrium species 2’s population will be at the
environment’s carrying capacity for species 2, while species 1’s population is at zero. Species 2 will
competitively exclude species 1 (Hardin, 1960).
2A. Inequality in plant size and variation in growth rates is likely to make one producer dominant
over the other. The interaction among several factors come into play too: genetic variation,
environmental heterogeneity, intra20 specific competition (Gause, 1934).
Maureen Robertson
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3. Does adding the herbivore establish a more equal field? Is one producer still dominant over the
other? Why might one producer be dominant over another?
The herbivour and plant 2 become
(TT)equally dominent
YES (Tt)
Does adding
the
herbivore
establish a
more equal
field
The herbivour eats and
stamples the plant
Plant 1 makes no come back and is equaly
dominated by the herbavour and plant 2(TTt)
No(TTt)
Figure 3
4. How do producer population numbers with the presence of an herbivore compare to the primary
colonizer model?
1/1/2000
50
1/1/2100
40
1/1/2010
30
1/1/2090
1/1/2020
20
10
Plant 2
0
1/1/2080
1/1/2030
1/1/2070
1/1/2040
1/1/2060
Maureen Robertson
Herbivore
1/1/2050
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Discussion
Ecological succession, a fundamental concept in ecology, refers to more-or-less predictable and
orderly changes in the composition or structure of an ecological community (Hardin, 1960). The
trajectory of ecological change can be influenced by site conditions, by the interactions of the
species present, and by more stochastic factors such as availability of colonists or seeds (Gause,
1934), or weather conditions at the time of disturbance. In general, communities in early succession
will be dominated by fast-growing, well-dispersed species (Gotelli, 2008). As succession proceeds,
these species will tend to be replaced by more competitive species.
The results were inconsistent with our first expectations, we at first felt that both the plants would
be even. By researching the Gause theory, and doing the simulated experiment, this confirmed
Gause theory. Introducing the herbivore showed that the dominant influence will prevail, tho this
time to a lesser extent. It was felt this was so because, it was plants verses herbivore thus the same
influences would not occur. Using a simulator gave us quick results, yet it was sensed that to get the
best results we would need to use real life experiment over a course of ten years. We will endeavour
to do this once funded.
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Conclusion
The competitive exclusion principle (Gause, 1934)sometimes referred to as Gause's Law of
competitive exclusion, states that two species that compete for the exact same resources cannot
stably coexist. One of the two competitors will always have an ever so slight advantage over the
other that leads to extinction of the second competitor in the long run,(as we saw in our digital
simulator) or (in the real world) to an evolutionary shift of the inferior competitor towards a
different ecological niche.
In ecology, a niche is a term describing the relational position of a species or population in an
ecosystem (Hardin, 1960). The niche in this instance was plant 1, plant 2 and a herbivore
(Rabbit).The niche told us how a population responds to the abundance of its resources and enemies
and how it affects those same factors. We saw the evidence when Plant 1 and 2 were affected by
resources and enemies, with plant 2 becoming the enemy to plant 1.
In conclusion we found that after two years plant 2 became the dominant plant, once we introduced
the herbivores (rabbits) Plant 2 had to fight for survival. Plant 2 and the herbivore lived relatively in
harmony. Plant 2 was not killed of like plant 1 but was reduced by a third after 1 year and then for
the next 100 years continued at a 1/3 less than the herbivore.
Maureen Robertson
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Referencing
Acara. (2011). Australian curriculum assesment and reporting authority. Acara.
Fleer, M., Jane, B., & Hardy, T. (2007). Science for Children,Developing a personal approach to
teaching. French Forest NSW: Pearson.
Gause, G. F. (1934). The Struggle for Existence. Baltimore: Williams and Wilkens.
Gotelli, N. J. (2008). A Primer of Ecology;4th Edition. Sunderland,Massachusetts: Sinauer Associates.
Hardin, G. (1960). The Cometitive Exclusion Principle. Science, 1292-1297.
Maureen Robertson
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