Biology 3.1 - Carry out an investigation
into an aspect of the ecological niche
of an organism with guidance.
“Investigating the ecological niche of
an organism using a fair test”
New Zealand half crab
Petrolisthes elongatus
Achievement Standard: AS90713 version 3
Credits: 4
INSTRUCTIONS AND CONDITIONS
This study is divided into two tasks.
Task 1 Selecting an aspect of the ecological niche to investigate – at the aquarium
In this task you will gather and process information on the ecological niche of the organism from
background reading and observations. The purpose of this task is to provide information that will
enable you to develop a fair test investigation relating to an aspect of the ecological niche of your
chosen organism.
Task 2 Carrying out the investigation – at the aquarium
In this task you will independently investigate in detail, one particular aspect of the ecological niche
of the chosen organism. This task requires the writing of a scientific report that introduces the
aspect of the ecological niche being investigated and records details of the fair test investigation.
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Study Animal - students will choose a crab species to study from: half crab, purple shore
crab
Time - Three days at Portobello Aquarium (for experimental design, lab work and write up,
plus a maximum of four Biology periods (for write up).
You are required to keep a portfolio – ( This is your crab study booklet)
 All ideas, rough notes, brainstorming, possible investigations, collection of data and
observations, research and planning, failures, successes, tentative conclusions go into
the logbook.
 It is your ‘rough’ copy and a working document. Its neatness is not important - its
function is to record all findings, show your skills in investigation and to record the
milestones for Task 2 that will be observed by your teacher. It will also be used to ensure
authenticity and to support your final assessment for this achievement standard..
 It is from this logbook that you will write your formal report.
TASK 1 - INVESTIGATING THE ECOLOGICAL NICHE OF A NAMED ORGANISM
The ecological niche of an organism includes the physical conditions of the habitat (abiotic
factors), the range of other organisms present (biotic factors) and how these link together to
provide opportunities and threats for the organism. As well, the niche includes the
adaptations that the organism has to allow it to exploit these opportunities and avoid the
threats.
Examine the ecological niche of the organism to provide information that could be used as
a starting point for the development of a fair test investigation.
(a) Habitat
Examine the habitat of the organism using quantitative and/or qualitative data for factors
(biotic and abiotic) such as:
 temperature
 aspect
 exposure
 light intensity
 other organisms present
 humidity
 density and age structure
 soil/substrate type
(b) Adaptive Features
Examine the adaptive features of the organism using background information and your own
observations and measurements. The adaptive features may be related to:
 movement
 growth
 gas exchange
 nutrition
 sensitivity
 predators
 reproduction
 competition
 excretion
Information on the ecological niche of the organism relevant to the aspect being
investigated will later be written up to form the introduction section of your report. The
introduction should be about one page in length.
Purple shore crab – Hemigapsus edwardsii
TASK 2 - INVESTIGATING AN ASPECT OF THE ECOLOGICAL NICHE OF A NAMED
ORGANISM
This task will form the main part of your Report.
Focusing and Planning
Using observations and information you have gathered in Task 1, select aspects of the
organism’s niche for possible further investigation. The aspects of the ecological niche
selected must be ones that are significant to the way of life of the organism. They must also
provide you with the opportunity to develop and carry out an investigation that is
appropriate to Year 13 Biology.
a) In your logbook record aspects of the ecological niche that could be investigated.
b) Formulate possible hypotheses for investigations relating to these aspects.
c) Record ideas of how you could investigate these hypotheses.
MILESTONE 1: Discuss your hypotheses and your ideas with your teacher.
Your teacher will approve before you continue.
d) Choose one hypothesis to investigate based on your discussion with your teacher.
e) Use the information collected in Task 1 to write a brief summary of the ecological niche
of your organism focussing on the aspect you are investigating and why it is significant to
the way of life of the organism. Include information relevant to the hypothesis you have
chosen to investigate.
f) Initial method. Develop a step by step method for an investigation that will lead to a
valid conclusion. Check that the equipment you want to use is available. You may need
to trial some aspects of your investigation to ensure your method will be workable.
MILESTONE 2: Submit your initial method and logbook to your teacher for checking. Your
teacher will approve before you continue.
Information Gathering
g) Carry out your investigation. Record all relevant raw data accurately and clearly. Make
sure you collect sufficient data to allow you to draw a valid conclusion
MILESTONE 3: Evaluate the quality of the information gathered and its degree of
relevance. Your teacher will approve before you continue.
Processing and Interpreting Data
h) Systematically record and process your data in a way that is appropriate to the type of
data you have collected.
i) Analyse your processed data to show trends, relationships or patterns relevant to your
hypothesis. You are expected to use appropriate statistical procedures to establish the
reliability of your data.
j) Write a conclusion for your investigation. This must link to your data and to your
hypothesis.
MILESTONE 4: Discuss your analysis and conclusion with your teacher. Your teacher will
approve before you continue.
Reporting
Using the information you have collated in your logbook, present your findings from Task 1
and 2 in a formal scientific report that includes the following sections:
Title
Aim
Hypothesis
Null hypothesis
Introduction
Method
Results
Conclusion
Discussion
Evaluation
References
Appendix
A simple, brief description of your investigation.
The purpose of your investigation.
A statement predicting the outcome of your investigation.
A corresponding statement that there will be no relationship between
your variables. You refer to this when doing your statistical analyses.
Relevant information on the species of crab you studied and its
ecological niche. When writing this section, use the information in the
Crab Study booklet, journal articles, and the initial investigations you
did at Portobello.
A set of instructions that clearly describes how your investigation was
performed. This should be in enough detail that someone else could
repeat your investigation.
The method should be written in past tense and avoid personal
pronouns, i.e., ‘I’ or ‘we’. Metric units should be used.
You should list and describe the factors that you have kept constant.
Present your raw data as a table or description.
Present your raw data as a graph. (Remember clear headings and axes
labels!)
Statistically analyse your raw data, e.g. average, standard deviation,
ANOVA. (Include a print out of your analysis as an appendix.)
Accept or reject your hypothesis.
Attempt to explain your results. Discuss your results, possible
interpretations, what your results could mean,… Remember to link
your results to the ecological niche of your species of crab! Refer back
to your introductory essay.
Justify the validity and reliability of your investigation.
A list of all the sources you used. These must be footnoted in the body
of your report.
Your raw data and statistical analyses must be included as an appendix.
Hand in your logbook with your report.
Assessment schedule AS90713 version 1 Bio/3/1 – A version 2
To be awarded the grade (A, M or E) the student must meet the holistic judgement statement at
the top of the column.
Evidence towards Achievement
The report and logbook show
development of an investigation
into an aspect of the ecological
niche of an organism, appropriate
recording and processing of data
and conclusion and explanations
linked to the purpose of the
investigation.
Development of an investigation:
 hypothesis linked to the
ecological niche
 Independent and dependent
variables
 Some other aspects of the
investigation identified or
described.
Evidence towards Merit
The report shows development of
a feasible investigation into an
aspect of the ecological niche of
an organism, appropriate
recording and processing of
sufficient data, conclusion and
evaluation or discussion linked to
the purpose of the investigation.
Investigation is feasible i.e.
method can be followed to obtain
relevant data. The method lacks
some detail and cannot be
independently followed without
further clarification.
Appropriate recording and
processing
 Measurements or data from
samples relevant to the
purpose
 Data is accurately processed to
enable a trend or pattern (or
absence) to be interpreted.
 Method of processing is
suitable to the hypothesis and
type of data
Sufficient data appropriately
recorded and processed
 Data range or number of
repeats will enable a reliable
trend or pattern (or absence)
to be identified.
Conclusion links the findings of the
investigation to the hypothesis
and explains aspects of the
investigation
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Conclusion links the findings of
the investigation to the
hypothesis.
Evaluation OR Discussion
 Discussion: Knowledge of
biological concepts or
processes is used to discuss
the biological significance of
the results and how they
relate to the ecological niche
of the organism.
 Evaluation: analysis of the
validity of the investigation
Evidence towards Excellence
The report shows development of a
workable investigation into an aspect
of the ecological niche of an
organism, appropriate, systematic
recording and processing of sufficient
data, conclusion, critical evaluation
and discussion linked to the purpose
of the investigation.
Investigation is workable i.e. method
can be independently followed to
obtain reliable data.
 hypothesis linked to the
ecological niche
 appropriate range for the
independent variable
 valid method for measuring the
dependent variable
 describes how other variables
will be controlled
 recognises the need for sufficient
data eg repeated measurements,
controls.
Sufficient data appropriately and
systematically recorded and
processed
 Data presented can be
interpreted without reference to
the method
Conclusion links the findings of the
investigation to the hypothesis.
Discussion: Knowledge of biological
concepts or processes is used to
discuss the biological significance of
the results and how they relate to
the ecological niche of the organism.
Critical evaluation: Shows analysis
and justification of the validity of the
investigation OR reliability of the
data (statistical analysis)
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Excellence exemplar for Biology achievement standard 3.1
Introduction: The ecological niche of the crab Hemigrapsus edwardsi.
The crab is a member of the Crustacea phylum and is in the family Grapsidae. This crab species is
found only in New Zealand on rocky shores. The rocky shore, where the crabs studied in this
investigation were found is quite exposed. There is a large rock platform that provides small
crevices and small rocks which help to protect them from wave action and predators. There are
also sea lettuce, and other algae growing on parts of the rocks.
The crab has many adaptations that allow it to live on the rocky shore
including:
 grey/black colour for camouflage
 food detection structures (antennae on its head and hairs on the mouth parts to sense
chemicals in the sea water)
 4 pairs of legs with muscles that allow it to move sideways, as well as forwards and backwards
 behavioural adaptations such as scuttling under rocks when the tide goes out or to avoid
predators
 freezing when being attacked (we noticed this when we touched some of them on their backs).
This might confuse predators.
 gills for gas exchange.
The rock pools provide a micro-climate where the temperature and salinity of the
water will change, depending on the weather. If it was a really hot day, the rock pools
will get warmer, more water will evaporate and the salinity will increase. The crab
would have to be adapted to cope with these changes in salinity, otherwise, as the
concentration of salt in the water around it changes, it will gain or loose mass due to
osmosis. Through the process of osmoregulation, the crab is able to maintain a
constant water balance in its body, but to do so requires energy and this could be
measured by an increase in the respiration rate. This is what I am going to investigate.
Explains
aspects of the
ecological niche
related to the
investigation.
The respiratory rate of the crab, Hemigrapsus edwardsi, in different salinities
Aim: To determine whether the respiratory rate of the crab changes in different salinities.
Hypothesis: The respiratory rate of the crab will increase as the salinity changes away Hypothesis linked
to ecological niche
from “normal” salinity.
Controlled variables
Method:
Thirty crabs of similar size, were collected from the rocky shore. The salinity was varied
by diluting the 200% conc. seawater provided in to five different concentrations. The
volume of the solutions was 200mL each. The concentrations were 150%, 125%, 100%,
75%, 50% conc. Water with 100% concentration is equivalent to the concentration of
Independent
normal seawater.
variable altered
Sixty-five mL of the 150% solution was poured into a petri dish. The petri dish had a
over an
thin layer of stones in the base to recreate the natural environment of the crabs.
appropriate range
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One crab was put into this petri dish and left for five minutes to allow them to adjust
to the conditions.
Controlled variables
The petri dishes were floated on a water bath which was set at 180C. The water bath
was placed in the room where the light intensity was the same for all petri dishes.
Dependent variable
An indirect method of estimating respiration was used. This was to count the number
of currents seen on the surface of the water. I assumed that a higher number of
currents indicated a higher respiration rate. A little bit of carmine red was sprinkled
onto the solution in the petri dish in order to see the movement of water more clearly.
The crabs were left in the petri dishes for five minutes before counting the respiratory
currents. The respiratory currents were counted for 30 seconds. This amount was
doubled to give the rate per minute.
Sufficiency of
data
5 more trials with different crabs were done at each concentration. Each time a fresh
65 mL of solution was added. The results were recorded and the rates per minute
were averaged. This process was repeated for the 4 remaining concentrations and the
results for these were averaged.
Workable
method outlined
Results:
Average respiratory rate of the crab in different concentrations of seawater.
% concentration of the water (100% = normal sea water)
50
75
100
125
150
Average number of
respiratory currents
per minute
7.92
6.75
6.00
7.50
Sufficient data
systematically
recorded and
processed.
(raw data is in
log book)
12.42
number of respiratory currents per min
Average respiratory rate of the crab in different seawater concentrations.
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y = 0.0016x 2 - 0.2908x + 18.648
r 2 = 0.9642
12
10
Data
appropriately
and
systematically
processed.
8
6
4
2
0
0
20
40
60
80
100
120
140
160
seawater concentration (%)
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Statistical analysis of results:
The graph of the results suggests that there is a significant relationship between the
concentration of the seawater and the respiratory rate of the crabs. This is confirmed
by the r2 value of 0.9642, which indicates that 96% of the variation in the results is
explained by the change in seawater concentration.
Conclusion:
The respiratory rate of the crab, as measured by respiratory currents, increased when
the concentration of the seawater either increased or decreased from the 100% conc.
(normal seawater).
Discussion:
This investigation was carried out to determine whether respiratory rates of the crab
increased as the salinity was changed from normal levels. The crab is a euryhaline
organism that lives on the rocky shore, often in rock pools. Because of the tidal
movements of water, the salinity of the crab’s environment fluctuates. To maintain
homeostasis, the crab osmoregulates. This means it actively controls the salinity levels
inside its body.
As the seawater concentration increased or decreased from the concentration of
normal seawater (100% conc.) the respiration rate increased. This is because the crab
is most comfortable at the concentration of normal seawater. As osmoregulation
involves the active transport of ions, it requires energy to adjust to higher or lower
seawater concentrations than 100% seawater. As the salinity of the crab’s
environment increases or decreases from the salinity of normal seawater it requires
more energy in order to osmoregulate. So in order to obtain that energy, it needs
more oxygen and its respiration rate increases. This is necessary for the crab as it must
deal with a range of salinity as the tidal pools dry out. If the concentration of the water
is greater than that of the crab’s internal environment, it will go through osmosis.
Although the crab has an exoskeleton, water can still leave its body through the space
around its joints and gills.
Evaluation:
Initially I found that there were several problems with my investigation. The most
significant one was that the crabs were out of their natural environment which made
them more fidgety. Some of mine even attempted to escape from the petri dishes
during the trials. This clearly shows that they were unsettled and perhaps not
responding as they usually would. If they decided to stay inside the petri dish, they
stayed close to the edge and moved away from the movement of people around them.
I moved my investigation to a more secluded position and screened them off with a
cover so that were not able to see what was around them. I also lined the petri dish
with a thin layer of stones to attempt to somewhat recreate the natural environment.
This change made the crabs calmer and produced a more natural response.
Conclusion related
to the hypothesis
and extends it to
reflect the range of
the independent
variable
Significance of
findings in relation
to the ecological
niche
Discussion of
results related to
niche
Critical evaluation limitations
discussed and
changes made to
the method justified
in relation to
validity of
investigation
The counting of actual respiration itself was difficult as it was a humid day and the
carmine red seemed to be congealing before being placed in the water. Perhaps in
humid conditions chalk dust or very fine sand would have been more suitable but
these were not available where I was carrying out the investigation.
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Critical evaluation
through analysis
of
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the validity of the
investigation
Where the crabs were sampled from may have biased the outcome of the results as
the position in the tidal zone might influence the levels of salinity that they were
accustomed to. Most of my animals appeared to be female, this may also have biased
my results. Further investigations would need to be carried out to determine if sex or
original location influences crab respiration rate.
Despite these limitations my results show that the increase in respiratory rates can be explained
by the changing concentration of the seawater.
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