Question

You have been asked to determine on what types of grasslands two species of birds, northern harriers and short-eared owls, build nests. The types of grasslands to be used include undisturbed native grasses, managed native grasses, undisturbed nonnative grasses, and managed nonnative grasses. You are allowed a plot of land \(500 \mathrm{~m}\) square to study. Explain how you would determine where to plant the four types of grasses. What role would randomization play in this determination? Identify any confounding variables. Would this study be considered an observational study or an experiment? (Based on the article "Response of Northern Harriers and Short-Eared Owls to Grassland Management in Illinois," Journal of Wildlife Management \([1999]: 517-523 .)\)

Short answer

Divide the plot of land into four equal parts and assign grass types randomly to these sections. Observations on birds' nesting preferences are made in these sections. The role of randomization is to avoid bias in experiment. Potential confounding variables could be weather, availability of food and presence of predators. The study is an experiment since we control the environmental conditions.

Step-by-step solution

Determine the Design

Initially, divide the \(500 \, m^2\) plot into four equal quarters. Each quarter will represent a different type of grassland: undisturbed native grasses, managed native grasses, undisturbed nonnative grasses, and managed nonnative grasses.

Role of Randomization

Randomization is crucial in experimental design to prevent bias. Assign the location for each grassland type randomly to the four quarters. This way, any other variable that might affect the bird's nesting behavior will be distributed randomly and not linked to a certain type of grassland.

Identify Confounding Variables

Any variable that influences both the dependent variable and independent variable can act as a confounding variable. In this case, variables like weather conditions, availability of food, and presence of predators might affect both the grassland type and the bird's preference for nesting spots.

Classify the study

This study is an experiment because we are deliberately changing the condition (types of grasslands) to observe the effect on the birds' nesting behaviors. Observational studies do not involve manipulating the environment, which is not the case here.

Key concepts

Randomization in Experiments

The concept of randomization is pivotal in conducting effective scientific experiments, including the investigation of bird nesting preferences across different grassland types. Randomization involves assigning subjects, or in this case different grassland types, to treatment groups on a purely chance basis. This technique acts as a safeguard against bias, ensuring that any potential influence outside of the manipulated variable is equally distributed.

For example, if a researcher were to non-randomly allocate grassland types to different areas, they might unintentionally select sunnier spots for one type or wetter areas for another, skewing the results. To prevent this, the assignment of grassland types to the quarters of the plot must be random. A simple approach could be using a random number generator or drawing lots. Through randomization, one hopes that variables such as soil fertility and exposure to natural elements will be balanced among the experimental groups, making it more likely that any differences in nesting patterns observed are actually due to the type of grassland itself, rather than extraneous factors.

Confounding Variables

In the context of the grassland experiment, a confounding variable is any additional variable that might influence the outcome - which in this case is where birds choose to nest - but is not the intended focus of the study. These are troublesome because they can provide alternative explanations for the findings.

>Understanding and identifying confounding variables is crucial for the integrity of the experiment. In the bird-grassland scenario, external factors such as the distance to water sources, the height of the grass, or the abundance of insects can all influence bird nesting behavior, and thus act as confounders. These variables could potentially be controlled or accounted for, for example, by making sure each type of grassland has similar access to water or by measuring and statistically adjusting for the grass height across the different plots. Recognizing these variables allows researchers to employ methods such as stratification or multivariate analysis to mitigate their effects on the study's outcomes.

Observational Study vs Experiment

Distinguishing between an observational study and an experiment is essential in understanding the level of control an investigator has over the variables in question. In an observational study, researchers simply observe and measure things as they are, without actively intervening or manipulating the environment. Such studies are valuable for hypothesis generation and identifying correlations, but they cannot establish causation due to a lack of control over variables that might influence the outcome.

In contrast, experiments like the one planned for studying bird nesting preferences involve manipulating one or more variables - here, the type of grasslands - to ascertain their causal effect on another variable, the nesting behavior of birds. By controlling the types of grasslands planted in each plot, researchers aim to isolate the influence of grassland type on nesting location choices. This direct intervention characterizes the study as an experiment rather than an observational study, and it is key in allowing researchers to draw conclusions about cause-and-effect relationships.