Lesson 5

Designing an investigation

Lesson goals

Design an investigation to quantitatively measure plant and animal populations

Lesson description

Students conduct an initial qualitative survey to assess populations within the low and high tide zones. Using this information, students develop their variables and hypothesis before formulating a procedure to measure plant and animal populations with appropriate sampling techniques.

Estimated time

60 minutes

Supporting materials

Lesson 5 Worksheet - Designing an investigation

Outcomes

Working Scientifically - Questioning and Predicting

Develops and evaluates questions and hypotheses for scientific investigation
Develop and evaluate inquiry questions and hypotheses to identify a concept that can be investigated scientifically, involving primary and secondary data

Working Scientifically - Planning Investigations

Designs and evaluates investigations in order to obtain primary and secondary data and information
Justify and evaluate the use of variables and experimental controls to ensure that a valid procedure is developed that allows for the reliable collection of data
Evaluate and modify an investigation in response to new evidence

Module 4 - Ecosystem Dynamics

Measuring populations of organisms using sampling techniques

Worksheet access

Click on the image at below to access the Lesson 5 worksheet. Once opened, save to your personal google drive or download your own copy.

Once saved, use your current knowledge and resources below to complete the document.

APHS Lesson 5 - Field sampling techniques

Sampling methodology

When conducting an ecology investigation in the field, a scientist must ensure that the design is valid, accurate and reliable.

The following information, videos and activities will help you understand field sampling techniques used to ensure the validity, accuracy and reliability of an ecology investigation.

Experiment #1 - Pilot study

Qualitative survey

A pilot study is a preliminary, small-scale study that researchers conduct in order to help them decide how best to design and implement a large-scale research project. Using a pilot study, a researcher can identify or refine a research question, decide what methods are best to pursue it, and estimate how much time and resources will be necessary to complete the larger survey.

A qualitative survey is a study which obtains descriptive results. They are an effective tool for field ecologists as they allow a rapid assessment of an ecosystem to determine broad trends or patterns. They have the disadvantage of lacking fine scaled data, which requires a quantitative survey to obtain.

Use the 360 degree images below to complete your qualitative survey of the low and high tide zones. The data table to complete is found in worksheet 5.

Low tide qualitative survey

High tide qualitative survey

Experiment #2 - population dynamics

Collecting quantitative data

How to estimate populations in the field

Counting entire populations of plants and animals is near impossible and attempting to do so would lead to inaccuracies. This is why samples of populations are taken instead.

The sampling methods must be consistent because it must be conducted a number of times in order to gain reliable data.

If the experiment is not able to be repeated the data would not be considered reliable.

The size of the quadrat used is determined by the size and population of the study species. A quadrat of 1km x 1km may be used to study elephants using an aircraft, however would obviously be unsuitable for a smaller species which could not be seen at such distance.

Developing a hypothesis

Field experiment inquiry question: Do population dynamics differ between high and low tide communities?

What do we know?

An organism relies upon its adaptations to survive within an environment defined by a particular combination of biotic and abiotic factors, known as a niche.

Through our pilot study, we are able to describe the population dynamics of our study ecosystems eg: Grey Mangroves were abundant within the low tide zone, however they were not found in the above high tide community.

Complete page 3 in worksheet #5 to develop your experimental hypothesis.

Increasing validity

Issues with bias

Scientists in the field may be easily biased biased by various factors:

The easy option

Difficult terrain

Avoidance

Placing quadrats at random increases the validity of the experiment. Play the video below to learn more about random quadrat methodology.

Placing quadrats in the field

Coordinate placement

Coordinates are effective in a flat and small ecosystem. Two numbers are selected at random and the point where they intersect marks the quadrat site.

Grid placement

An aerial photograph of the study site may be divided into a grid. Individual segments are numbered. Individual quadrats may then be selected at random.

Haphazard placement

By throwing an object over one’s shoulder to position the quadrat, some human bias is removed from the quadrat placement.

Increasing reliability

Ecologists depend upon reliable results in order to make conclusions about population dynamics. In order to gain reliable data, the same experiment must be conducted a number of times.

A single quadrat is likely to provide an unreliable representation of a population size.

Increasing the number of quadrat samples provides a more reliable assessment of population size.

Increasing accuracy

This is achieved by using the correct methods and equipment consistently.

Watch the following videos on how to accurately estimate the vegetation cover and number of animals within quadrats.

Estimating vegetation cover

Estimating number of animals

Designing your experiment

Complete page 7 of Worksheet 5 to develop your experimental methodology.

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