Experimental Design in Ecology

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Questions and Answers

What is the independent variable in an experimental design?

  • The variable that is manipulated (correct)
  • Any variable that remains constant
  • The control condition
  • The variable that is being measured

What defines the dependent variable in an experiment?

  • A random variable that has no effect on the experiment
  • The variable that is constant throughout the experiment
  • The variable that is suspected to change due to the independent variable (correct)
  • The factor that influences the independent variable

What is the purpose of replication in an experimental design?

  • To isolate one variable from another
  • To ensure reproducibility and quantify natural variation (correct)
  • To minimize the number of samples needed
  • To eliminate the need for randomization

Why is randomization important in experimental design?

<p>It helps to control bias and other external effects (A)</p> Signup and view all the answers

What are treatments in an experimental design?

<p>The groupings compared in the experiment (B)</p> Signup and view all the answers

In what scenarios is it advisable to limit the number of samples taken in an experiment?

<p>When there are constraints like time, budget, or equipment (B)</p> Signup and view all the answers

Which of the following best describes an experimental unit?

<p>The individual item or subject that receives a treatment (D)</p> Signup and view all the answers

What does 'reducing noise' in experimental design refer to?

<p>Controlling extraneous variables to clarify treatment effects (B)</p> Signup and view all the answers

What is the independent variable in the experimental design described?

<p>The amount of light penetration/canopy coverage (A)</p> Signup and view all the answers

Which variable serves as the dependent variable in this experimental setup?

<p>Average understory plant species richness (C)</p> Signup and view all the answers

What defines an experimental unit in this study?

<p>The 5 m x 5 m quadrat used for sampling (B)</p> Signup and view all the answers

What type of sampling design is utilized in the experimental setup?

<p>Combination design with predetermined site characteristics (B)</p> Signup and view all the answers

Why is replication important in this experimental design?

<p>To allow for meaningful statistical analyses and confidence intervals (B)</p> Signup and view all the answers

How many plots of each treatment condition are suggested as a minimum for statistical analysis?

<p>Three of each type (A)</p> Signup and view all the answers

What is a key principle of the sampling design in this experiment?

<p>Randomization within predetermined characteristics is essential (D)</p> Signup and view all the answers

What characteristic separates the two treatment types in this study?

<p>Amount of light penetration/canopy coverage (A)</p> Signup and view all the answers

What best defines an experimental unit in an experiment?

<p>A physical unit that receives a specific treatment (A)</p> Signup and view all the answers

Which option describes pseudoreplication?

<p>Taking repeated measurements on the same experimental unit (C)</p> Signup and view all the answers

What characteristic is essential for a sample to be representative of the population?

<p>It must be unbiased and adequate in size (D)</p> Signup and view all the answers

Which sampling design is typically assumed by most statistical tests?

<p>Random sampling (A)</p> Signup and view all the answers

What is the role of replication in an experiment?

<p>To provide multiple independent instances of a treatment (D)</p> Signup and view all the answers

What advantage does systematic sampling provide compared to random sampling?

<p>It is usually simpler to conduct (B)</p> Signup and view all the answers

In which situation would you most likely employ the quadrat method?

<p>When sampling a defined area within a larger ecosystem (B)</p> Signup and view all the answers

Which of the following is NOT an accepted sampling design?

<p>Biased sampling (A)</p> Signup and view all the answers

What distinguishes a manipulative experiment from an observational experiment?

<p>It requires multiple treatment groups. (C)</p> Signup and view all the answers

Which of the following processes most directly supports a hypothesis in an observational experiment?

<p>Measurement and data collection from existing conditions. (B)</p> Signup and view all the answers

Which principle is crucial to ensure robust conclusions in both manipulational and observational experiments?

<p>Proper experimental randomization and data calibration. (C)</p> Signup and view all the answers

To effectively critique an experimental design, which criterion should be applied according to the FINER framework?

<p>The feasibility and ethical considerations of the design. (A)</p> Signup and view all the answers

What primary aspect differentiates manipulative experiments from observational experiments in ecological studies?

<p>The active alteration of variables under study. (B)</p> Signup and view all the answers

How does an observational experiment typically operate in an ecological context?

<p>By gathering data on naturally occurring variables and conditions. (C)</p> Signup and view all the answers

Which statement reflects a critical component of the design process for effective ecological experiments?

<p>Testing multiple levels of one treatment variable may enhance results. (B)</p> Signup and view all the answers

Which element is NOT typically considered a characteristic of a strong experimental design?

<p>In-depth reliance on anecdotal evidence. (A)</p> Signup and view all the answers

What is a significant advantage of using randomization in experimental design?

<p>It helps neutralize other confounding effects. (A)</p> Signup and view all the answers

Which factor greatly influences the choice of measurement techniques in ecology?

<p>The available budget for the research. (B)</p> Signup and view all the answers

Why is replication considered necessary in experimental design?

<p>To account for variations and enhance result accuracy. (C)</p> Signup and view all the answers

How can one effectively 'reduce noise' in an experiment?

<p>By controlling external factors that might influence the results. (D)</p> Signup and view all the answers

In experimental designs, which of the following is considered an independent variable?

<p>The treatment conditions applied to experimental units. (C)</p> Signup and view all the answers

What defines a treatment in experimental design?

<p>The specific conditions applied to experimental units. (C)</p> Signup and view all the answers

What is a key consideration when determining how many samples to take in an experiment?

<p>The balance between resource constraints and statistical validity. (C)</p> Signup and view all the answers

Which statistical assumption is commonly linked to randomization in experimental design?

<p>The effects observed are independent of external variables. (B)</p> Signup and view all the answers

What is the primary purpose of using a sampling design in experiments?

<p>To achieve representative estimates of the population (B)</p> Signup and view all the answers

What is a key disadvantage of pseudoreplication in experimental design?

<p>It may lead to misleading results due to lack of true independence (B)</p> Signup and view all the answers

Which method is particularly useful when aiming for bias reduction in sampling?

<p>Random sampling (C)</p> Signup and view all the answers

How does systematic sampling differ from random sampling?

<p>Systematic sampling can introduce bias if population patterns are present (B)</p> Signup and view all the answers

Which characteristic is essential for the adequacy of a sample in an experiment?

<p>It must be random and large enough to represent the population (C)</p> Signup and view all the answers

What aspect of sampling does 'combination sampling' involve?

<p>Using random and systematic methods together for better coverage (D)</p> Signup and view all the answers

In the quadrat method, what is essential for making accurate measurements?

<p>A known and defined size for the quadrat is necessary (D)</p> Signup and view all the answers

What role does replication play in experimental design?

<p>To collect data from distinct experimental units under the same treatment conditions (B)</p> Signup and view all the answers

Which sampling method is most suitable for plants that are small and non-motile?

<p>Quadrat sampling (A)</p> Signup and view all the answers

What is a primary characteristic of the mark/recapture method?

<p>It estimates populations of large and/or mobile organisms. (A)</p> Signup and view all the answers

In the FINER framework, which component assesses if a research design is achievable within available resources?

<p>Feasibility (B)</p> Signup and view all the answers

What does the 'Novel' component of the FINER framework emphasize in experimental design?

<p>Research should resolve gaps in existing literature. (A)</p> Signup and view all the answers

When studying how light availability affects plant biodiversity, which hypothesis could be derived?

<p>Higher light availability will increase species richness. (D)</p> Signup and view all the answers

Which of the following would not be a consideration within the 'Ethical' component of the FINER framework?

<p>Providing adequate funding for research (D)</p> Signup and view all the answers

What sampling method is indicated for a wide diversity of organisms when specific characteristics are desired?

<p>Stratified sampling (B)</p> Signup and view all the answers

What aspect does the 'Relevance' component of the FINER framework specifically address?

<p>The ability to generate knowledge for future research. (C)</p> Signup and view all the answers

What would be an inappropriate choice for the measurement unit in this experimental design?

<p>Total biomass of plants in a quadrat (C)</p> Signup and view all the answers

Which characteristic best describes the sampling design mentioned?

<p>Combination of predetermined location and random allocation (D)</p> Signup and view all the answers

Which of the following best describes the purpose of the experimental unit in this study?

<p>To serve as the fundamental unit of observation for comparison (C)</p> Signup and view all the answers

Why is it necessary to define the area size for sampling in this experimental design?

<p>To standardize the measurement impacts of external variables (B)</p> Signup and view all the answers

What is the primary challenge in observational/mensurative experiments compared to manipulative experiments?

<p>Determining causal relationships between variables (A)</p> Signup and view all the answers

What statistical analyses can be performed given the described setup with three plots for each treatment?

<p>Inferential statistics such as t-tests or ANOVA (A)</p> Signup and view all the answers

What is a critical factor in determining the richness of understory species in the described experiment?

<p>Degree of canopy closure affecting light availability (B)</p> Signup and view all the answers

Which principle is NOT emphasized in the guidelines for conducting experiments?

<p>Using multiple variables to assess their interactions (A)</p> Signup and view all the answers

Flashcards

Experimental Unit

A physical unit that receives a particular treatment, like a plot in a field or a plant.

Measurement Unit

Where observations are taken. Often it's one per experimental unit, but repeated measurements are possible, but don't increase statistical power if the measurements are on the same unit (pseudoreplication).

Replication

Independent instances of a treatment in an experiment (e.g., separate plots with the same treatment).

Unbiased Sample

A sample that fairly represents the entire population, ensuring good estimates.

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Adequate Sample Size

A sample large enough to accurately represent the population.

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Random Sampling

Sampling method where each member has an equal chance of being selected, best for unbiased samples.

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Quadrat Method

A sampling method where a defined area (quadrat) is used to measure organisms within the area.

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Sampling Design

The plan for how areas will be sampled, often using random, systematic, or combined methods.

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Independent Variable

The factor you manipulate in an experiment to see its effect on another variable.

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Dependent Variable

The factor you measure in an experiment to see how it responds to changes in the independent variable.

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Treatment

A specific condition or variation of the independent variable applied to experimental units.

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Combination Design

Uses a combination of pre-determined groups (like open v. closed canopy) and random sampling within groups.

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Experimental Design

A planned approach to answer a research question, focusing on what to measure, how to measure it, and how many samples to take.

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Randomization

Randomly assigning treatments to experimental units, preventing bias and allowing for statistical analysis.

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Reducing Noise

Controlling extraneous factors to ensure the observed changes are due to the treatment, not other influences.

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Trade-offs in Sampling

Balancing the need for replications with limitations like time, budget, and effort.

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Experimental Design Goal

To answer three key questions: what to measure, how to measure it, and how many samples to take to ensure reliable results.

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Observational Experiment

A study where you simply observe what's happening in nature without manipulating anything. You gather data from existing conditions.

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Manipulative Experiment

An experiment where you actively change something (like a variable) to see how it affects something else. You have a control group and a treatment group.

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Control Group

The group in an experiment that doesn't receive the treatment being tested. It acts as a baseline for comparison.

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Treatment Group

The group in an experiment that receives the treatment being tested. It's the group you are actively changing.

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FINER Criteria

A set of guidelines for evaluating the quality of a research question. It stands for Feasible, Interesting, Novel, Ethical, and Relevant.

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Pseudoreplication

Making repeated measurements on the same experimental unit and treating those measurements as independent. This can lead to inflated statistical significance because you're not truly getting independent data points.

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What is a measurement unit?

The level at which observations are made in an experiment. It's usually one measurement per experimental unit, but you can also make repeated measurements on the same unit.

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What is pseudoreplication?

Taking repeated measurements on the same experimental unit, which doesn't increase the statistical power of the experiment.

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What is an experimental unit?

A physical unit that receives a specific treatment in an experiment. Examples include an individual plant or a plot of land.

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What is replication in an experiment?

The number of independent instances of a treatment in an experiment. For example, separate plots receiving the same fertilizer treatment.

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Why is an unbiased sample important?

An unbiased sample fairly represents the entire population, ensuring good estimates based on the data collected.

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What are the three basic sampling designs?

Random, systematic, and a combination of both.

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What is random sampling?

A sampling method where each member of the population has an equal chance of being selected. It's usually preferred for unbiased results.

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What is the quadrat method?

A sampling method where a designated area (quadrat) of a known size is used to count or measure organisms within that area.

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Mark/Recapture Method

A technique used for estimating population sizes of mobile organisms by capturing, marking, and releasing individuals, then recapturing them to calculate an estimate of the total population.

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Quadrat Sampling

A method used for studying immobile organisms by dividing the study site into equal squares (quadrats) and counting the organisms within each quadrat.

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FINER Framework

A set of criteria for evaluating a research study's quality: Feasible, Interesting, Novel, Ethical, and Relevant.

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Feasibility

The practicality of conducting the study based on resources, time, and technical capability.

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Interesting

The study should be engaging and attract attention for both researchers and the wider community.

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Novel

The study should contribute new knowledge or perspectives beyond existing research.

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Ethical

The study should adhere to ethical principles of scientific research, respecting participants and ensuring safety.

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Study Notes

Experimental Design in Ecology

  • Objectives: Participants will be able to distinguish between observational/mensurative and manipulative experiments, define relevant terminology, apply principles of experimental design to research questions, and critique designs using the FINER criteria.
  • Connection to Broader Concepts: Understanding how the scientific method is used to answer ecological questions.

Types of Experiments

  • Observational (Mensurative): Measurements are made on existing conditions to determine patterns and draw conclusions. This includes simple measurements (e.g., deer density) to complex observations (citizen science projects).
  • Manipulative: Intentionally manipulating a variable to observe its effects. Requires at least two groups: a control group (no manipulation) and a treatment group (manipulation).

General Principles of Experimental Design

  • What to Measure: Variables should align with the research question and hypothesis.
  • How to Measure: Appropriate measuring tools are critical (e.g., clinometers, soil corers, CO2 meters). Measurements should accurately reflect the variable of interest.
  • Number of Samples: Replication increases accuracy and validity, but resources limit sample size. A tradeoff exists between sample size and other factors like time, budget, and effort.

Terminology

  • Independent Variable: The variable hypothesized to cause a change in another variable. Shown on the x-axis.
  • Dependent Variable: The variable expected to change due to the independent variable. Graphically shown on the y-axis.
  • Treatment: Groupings being compared (single factor or combinations of multiple factors).
  • Experimental Unit: The specific item or area that receives a treatment (e.g. a plot in a field, a single plant).
  • Measurement Unit: The level at which observations are made (e.g. one measurement per unit, or repeated, but not pseudoreplication).
  • Replication: Repeating treatments to quantify natural variation and increase accuracy.

Sampling Designs

  • Random Sampling: Ensures unbiased samples using random procedures (e.g., random number generators, tables, drawing numbers).
  • Systematic Sampling: Samples are taken at regular intervals. Less complicated than random, but bias can occur if the sampling pattern reflects a pattern in the population.
  • Combination Sampling: Combines random and systematic strategies for more representative samples (e.g., sampling only "representative" sites in a forest).
  • Quadrat Method: Used for stationary organisms, involves sampling a defined area (quadrat), typically counting the number of organisms within the area.
  • Mark-Recapture Method: Used for mobile organisms to estimate population sizes by marking individuals, releasing them, and recapturing them later.

Evaluating Experimental Design (FINER framework)

  • Feasible: Can the design be accomplished given available resources and time, appropriate sample sizes, and technical abilities?
  • Interesting: Will the research question pique the interest of the audience (relevant researchers or broader public)?
  • Novel: Does the research generate new findings, resolve gaps in existing literature, or create novel hypotheses?
  • Ethical: Does the design comply with ethical guidelines and research standards?
  • Relevant: Does the research answer a specific, relevant question that advances understanding or knowledge?

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BIOL208 - Lab 0: Experimental Design PDF

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