Lab 7:
Ecological Communities; Predator-Prey Interactions 

Learning Objectives
In this lab students will:
- Define an ecological community.
- Describe different ways organisms in a community interact.
- Describe how the attributes of both predator and prey develop in the process of natural selection.
- Communicate how predator and prey populations over successive generations modify one another in a continuous process.
- Simulate the predator-prey relationship between populations.
- Record, collect and analyze the data from the simulation.

Evolution, Adaptations & Natural Selection

Image shows a diverse array of beetle species.

Evolution is the change in a species overtime. It seeks to answer the question why Is life so diverse?
There are about a half million species of beetles. Some of those are shown in this image.
Why so many different types of beetles?!
Why are there lions, tigers, leopards, cheetahs, and pumas?
Why so many different large cats?
Natural selection is the process by which organisms with certain inherited characteristics are more likely to survive and reproduce than individuals with other characteristics
As a result of natural selection, a population, a group of individuals of the same species living in the same place at the same time, changes over generations.
Charles Darwin envisioned nature as a “struggle for existence”. Those with the best adaptations will probably survive. Those who do not have the best adaptations will probably die.
Those that survive will be likely reproduce and pass their successful adaptations on to their offspring.

Image shows poisonous or inedible plants including poison ivy, Mancinelle, Dumb cane and Jimson weed

For example, plants whose leaves are foul-tasting or toxic (like the one in this image) are more likely to be avoided by plant eating animals and are more likely to survive and pass on their ability to produce foul-tasting leaves to the next generation.
All organisms that possess characteristics that enhance their survival are more likely to survive, reproduce and pass their genes to the next generation..
These characteristic are called adaptations.
• There are many observable examples of natural selection.
• The evolution of antibiotic resistant bacteria is one example.

Image shows two color variants of the peppered moth on the bark of a tree before and then after the industrial revolution, Before the industrial revolution the black color variant is more obvious on the bark of the tree. After the industrial revolution the light-colored peppered moth is more obvious on the bark of the soot covered tree.

• Another example is the change in the Peppered moth population.
• There are 2 color variations of the Peppered moth; a dark color and a lighter color.
• Before the industrial revolution the dark colored moths stood out against the lighter colored bark and were eaten more often. This made the dark colored moths rare.
• After the industrial revolution the soot covered tree barks camouflaged the dark colored moths and their numbers increased.
•This is evolution - a change in a population over time.
• Species evolve, not individuals.


• Ecology is the scientific study of the interactions between organisms with each other and their environment.
• Ecology can be divided into four increasingly comprehensive levels:
1. Organismal ecology - the study of an individual organism's morphology , physiology and behavioral adaptations that allow it to live in a particular environment.
2. Population ecology - the study of the number of individuals of a particular species in an area and how that population changes over time.
3. Community ecology - the study of how different species in the same area interact with each other.
4. Ecosystem ecology - the study of how all the living things in an area interact with each other and their environment. Often when we refer to "ecology" we are referring to ecosystems ecology.

Community Ecology

• In this lab we will focus on Community ecology.
• When populations share space with other populations this leads to interactions among them and makes them interdependent.
• Let’s look at how different species interact with each other in an ecosystem.
Competition - occurs when two populations are using the same resource. This is usually bad for both species (-/-).
Predation - occurs when one population uses the other as a food source (like a lion eating a gazelle of the gazelle eating the grass). One species benefits at the expense of the other(+/-).
Symbiosis - an extremely close interaction between populations. Usually occurs when one population lives in or on the other population. There are 3 types of symbiosis.
- Parasitism - a much smaller organism lives in or on another organism. One organism benefits and the other may be harmed (+/-)
- Mutualism - both populations benefit from the interaction (+/+).
- Commensalism - one population benefits while the other is neither harmed, nor does it benefit (+/0).
Watch the video to better understand Community Ecology.

Click here to watch Community Ecology Video


• When populations interact they influence each others evolution. One obvious example of this is the predator-prey interaction.
• The relationship between predator and prey is a powerful force of natural selection, selecting against prey unable to evade their predators and for those that can.
• These pressures exert a force on the predator too. Selecting for traits that allow it to catch the evading prey.
• In this lab you will simulate a predator-prey interaction.
• Watch the video to better understand the predator-prey interaction.

Click here for Predator Prey Interaction Video
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Non-majors College Biology Lab Manual © 2021 by Marie McGovern Ph.D. is licensed under CC BY-NC 4.0