Download Introduction to population growth models

Introduction to population growth models
Scientific Theme(s):
Life Science
*Changes in Life Forms Over Time
*Natural History and Biodiversity
*Ecological Interactions
Grade Level(s):
6-8
9-12
Lesson Duration: One 60 minute lesson
Overview
Population biology is an important part of the life sciences. Population biology helps us understand the
regulatory mechanisms determining how different groups of organisms grow, or go extinct. This is critical in
many practical and applied situations such as managing natural or artificial populations of plants and animals,
determining harvest limits on organisms targeted for human consumption, or even examining human
population dynamics.
In this lesson, students will learn the basics of population biology through an introduction to exponential
growth using the roseate spoonbill (Platalea ajaja) as an example.
Objectives
1. Understand why the study of population dynamics is important.
2. Understand what defines a population.
3. Understand the concepts of birth rate, death rate, and exponential growth.
4. Understand how birth rate and death rate affect population dynamics.
5. Learn how to graph a simple exponential growth curve.
6. Extend concepts to more complex population models, such as logistic or predator-prey models.
Grade Level Expectations (GLEs) Addressed
1. Concepts of Life Science
a. [9] SC3.3 – The student demonstrates an understanding that all organisms are linked to each other
and their physical environments through the transfer and transformation of matter and energy by
identifying dynamic factors (e.g., carrying capacity, limiting factors, biodiversity, and productivity) that
affect population size.
Required Background
1. Concepts of population dynamics:
http://www.stanford.edu/group/stanfordbirds/text/essays/Population_Dynamics.html
2. Roseate Spoonbill biology: http://bna.birds.cornell.edu/bna/species/490/articles/introduction
Vocabulary
1. Population
2. Birth rate
3. Death rate
4. Exponential growth
Materials
1. Roseate Spoonbill PowerPoint presentation
2. Overhead projector or document camera
3. Laptop computer with internet access
4. Population Biology Exploration Sheet, 1 per student
5. Graph paper (PowerPoint slide 7), at least 1 per student
6. Pencils and erasers
Activity Preparation and Procedure
1. (10 minutes): Using the PowerPoint presentation, introduce the charismatic spoonbill, including important
aspects of its biology and ecology (slides 1-4).
2. (5 minutes): Using the PowerPoint presentation, introduce the discipline of population biology (slide 5).
a. Give students time to define the terms on the worksheet provided (population, birth rate, death rate).
3. (10 minutes): Ask the students to imagine they are scientists at Florida Everglades National Park. They are
tasked with monitoring and graphing the spoonbill population in the Park over time. To accomplish this, they
are provided with a hypothetical initial population size, birth rate, and death rate (slide 6).
a. Allow students time to come up with a hypothesis for population growth (see worksheet).
4. (15 minutes): Following the PowerPoint, walk the students through graphing the population level by year
(slides 8-24).
a. Use the blank graph paper template provided (slide 7 in the PowerPoint).
b. This would be a good time to teach or review graphing skills.
5. (10 minutes): Based on the observed relationship, have students guess what they think the population will be
in 20 years, then show them slide 25.
a. Introduce the concept of exponential growth and discuss factors that may limit it (food, resources,
space, predation, disease) (slide 26).
6. (10 minutes): Show students the online population dynamics program (slide 27, MathCS.org – Java).
a. Start with the example exponential model for the spoonbill (same birth and death rates).
b. After the model has run, allow the students to choose new initial conditions and predict the outcomes.
Assessment
1. Given different birth/death scenarios, ask students to predict whether a population will grow or decline, and
explain why.
Complementary Activities and Extension Ideas
1. Allow students to use the online program to examine additional models of population growth, including the
logistic and predator-prey models: http://www.mathcs.org/java/programs/PopDynamics/index.html
2. Challenge students to graph the growth of a population with different vital statistics (birth and death rates)
than provided in the example.
References
Dumas, Jeannette V. 2000. Roseate Spoonbill (Platalea ajaja), The Birds of North America Online (A. Poole, Ed.).
Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/490 doi:10.2173/bna.490
Ehrlich, P.R., Dobkin, D.S. and Wheye, D. (1999). Population Dynamics. Retrieved from
http://www.stanford.edu/group/stanfordbirds/text/essays/Population_Dynamics.html
Population Biology Worksheet
Name:_____________________________
Definitions
Population:
Individuals of the same __________ in a particular ___________.
Birth Rate:
The number of individuals (per capita) that are ________ in a _________.
Death Rate:
The number of individuals (per capita) that _________ in a ___________.
Spoonbill Scientist
5 Spoonbills
• Birth Rate = 2
• Death Rate = 1
Hypothesis?
The spoonbill population will decrease/increase at a slow/fast rate.
Why?______________________________________________________________________
___________________________________________________________________________
Unlimited growth is called “______________” growth.
List one factor that would prevent unlimited growth?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________