Lesson Biomes and Population Dynamics - Balance within Natural Systems

Learning Objectives

After this lesson, students should be able to:

• Define the term "biome" and list the various types on our planet.
• Define population and carrying capacity.
• Explain why different species are found within different biomes.
• Explain why carrying capacity is determined by the limiting factors within the community.
• Explain how population data can be used to analyze growth rate curves.
• Identify the connection between ecological relationships of organisms and their effect on population to the fundamentals of engineering design.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Introduction/Motivation

Our planet, divided into northern and southern hemispheres, experiences differences in climate and seasons at latitudes and locations. These climatic factors, in large part, determine which plant species are capable of living where. As we now know, the producers are responsible for determining which consumers can be supported within any particular community's food web. Today's lecture concentrates on understanding why certain types of plant vegetation are associated with different parts of the world and how this contributes to a characteristic variety of associated consumers.

During this lesson, we will also study the population dynamics involved with the diversity of community life. What limits population size and are populations static or dynamic? What factors into this interaction and how do populations maintain an equilibrium or balance? Refer to the Computer Simulation of the Sonoran Desert Community activity to have students manipulate variables to better understand what impacts population dynamics. This continues the Research and Revise phase of the Legacy Cycle. Why, after thousands of generations, do communities continue to exist? Why have resources not become depleted? What actions do organisms conduct (and not conduct) in order to avoid risking their species' continual existence in this area? You should continue to question and analyze whether we, as humans, provide for ourselves in similar ways. Do organisms harm their communities? Do humans? As your assessment of the natural world broadens, so will the framework of your team's design.

Lesson Background and Concepts for Teachers

Legacy Cycle

This is the second lesson in the Research and Revise phase in which students are introduced to biomes, population dynamics, limiting factors and carrying capacity. The information covered in this lesson provides students with the understanding of ecological relationships necessary for them to approach the Challenge Question from the direction of sustainable design.

Lecture Information

The concepts of this lesson are provided in the Lesson 3 Population Dynamics Lecture Supplement, a PowerPoint® file. This information provides definitions and explanations as well as supplemental visuals. An outline of key points covered in this presentation is provided below:

Living World:

• Biosphere: A thin layer of the living world that surrounds the nonliving world - composed of air, organisms, soil and water.

Biomes:

• Major communities of organisms occurring together at relatively large scales, such as at the landscape-level. Biomes are generally characterized and identified by their vegetation - tundra, deciduous forest, taiga (conifers), chaparral (scrub), grassland, desert, tropical rainforest.

Why Do Biomes Differ?

• Great differences in climate of Earth.
• Living organisms require specific ranges in season, temperature, sunlight, rainfall and require interactions with other specific organisms.
• Each major type of climate develops a characteristic type of vegetation.
• Each type of plant life supports a characteristic variety of animal life.

Do biomes affect the size of populations? (Ask students to think about this as you discuss what a population is.) Populations:

• A population is a group of organisms of the same species that live and interact in the same place at the same time.
• A population is composed of individuals of the same species that interbreed.

Four Rates Determine Population Size:

• Mortality: death rate
• Natality: birth rate
• Immigration: movement of new individuals into the population
• Emigration: movement of current individuals out of the population

Size of a Population:

• Size of any population is the result of the relationships among these rates.
• Which factors most influence the trend of: humans, mule deer, red wolves? Why?

Population Rate Changes:

• What do mortality and emigration have in common?
• What do natality and immigration have in common?
• What must organisms be able to do to immigrate or emigrate?
• How does a plant incapable of movement establish a new population?

Passive Dispersal:

• Used by organisms incapable of movement (animal, wind, water).

In the same way that the web of life connects individuals, it also connects populations. The environment has two components::

• Biotic: All living parts (plants, animals)
• Abiotic: All nonliving parts (soil, space, sunlight, water, wind)

Population Numbers Limited:

• The environment limits a population's size.
• Environment may slow, kill or enhance an individual's growth/life and hence affect the population size.

Limiting Factor:

• Any biotic or abiotic factor that can affect (+/-) the growth of a population (temperature, moisture, amount of sunlight, food resources, etc.).
• Limiting factors may be measured alone, however each factor affects others, and together, they affect population size.
• The effect may be either direct or indirect.

Water:

• Water is an important abiotic factor.
• All organisms need water.
• Almost all chemical reactions needed to keep an organism alive take place in water.
• Water molecules are a part of many chemical reactions.

Populations and Limiting Factors:

• Limiting factors affect the density (number) of the population.
• Under optimum conditions, the population will be favored and be able to reach maximum numbers.
• Must limiting factors have a negative connotation?

Resources:

• Abiotic and biotic factors represent the resources available in the environment.
• Resources (limiting factors) are matter and energy.
• Explain how this can be both a positive and negative impact on a population.
• Affect the size of a population. (Pose the following questions to students.)
• Question: Why did bluebirds and wood ducks suffer population declines?
• Question: What was their environmental limiting factor?
• Question: How did humans rescue these two species?

Space as a Limiting Factor:

• Organisms require different amounts of space (abiotic factor).
• Space needs relate to a biotic factor – the availability of food energy.
• Why do space needs differ for plants and large meat-eating predators?

Limits to Population Size - Biotic:

• predators
• disease
• competition
• environmental stress (temperature, amount of light, erosion, etc)

Carrying Capacity:

• The greatest number of individuals that a space can support indefinitely without degrading the environment.

Growth of a Population (two types):

1. Sigmoid (S-shaped curve)

• Once carrying capacity is reached, # deaths should = # births.
• Environmental resistance builds up in form of disease, famine, predation.
• Results in slowed rate of increase.
• Population reaches equilibrium.
• Most common.

2. Exponential growth (boom and bust)

• #s increase exponentially (doubling)
• Exceeds carrying capacity
• CRASH (resources exhausted)

Boom and Bust:

• Exponential curves typical for:
• Insect plagues
• Lemming populations
• Blooms of algae
• Rodents

Exponential Patterns:

• Single housefly
• Lays ~ 120 eggs.
• Half are female.
• Each female capable of 7 generations per year
• 6,182,442,727320 flies in one year!!!

Carrying Capacity:

• Most important measure in determining population size.
• WHY??? - Represents the ability of abiotic and biotic factors in the environment to provide necessary resources.
• How do humans affect the carrying capacity of ecosystems?

Global Stability threatened by:

• Direct harvesting
• Pollution
• Atmospheric changes
• Habitat loss

Associated Activities

• Computer Simulation of the Sonoran Desert Community - Student groups manipulate the population numbers of five Sonoran Desert species through a computer program simulation of a Sonoran Desert community. As they take stewardship of an ecosystem, they strengthen their comprehension of what is required for a natural ecosystem to sustain itself (remain in balance). They become familiar with species' behaviors, niches and food resource needs for two producers (saguaro cactus, ironwood tree) and three consumers, and are challenged to identify species dependencies in order to keep the community in balance and sustainable, so all survive.

Assessment

Post-Lesson Assessment:

• Why do different types of biomes exist?
• What are some unique species adaptations that help them survive in different biomes?
• How do limiting factors differ between biomes?
• Why might the carrying capacity of a community change?
• What type of organisms exist in the greatest and least numbers within a community?
• What characteristics do species possess that follow an exponential growth curve?
• What regulates the gentle oscillation in population growth of any particular species when it reaches carrying capacity?
• How can you apply this knowledge to help solve the grand challenge posed in lesson 1?

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.