In this lesson
- Video lesson (coming soon)
- Lesson notes
- Worked examples
- Big ideas
- NGSS alignment
Take it with you
- Lesson slides (PDF)
- Practice worksheet (PDF)
- Answer key (PDF)
Essential Question
Why do people depend on diverse ecosystems?
Food, clean water, and a stable climate all come from ecosystems, and ecosystems with more kinds of living things tend to supply them more reliably. In this lesson, you’ll learn how scientists describe and measure biodiversity, what ecosystem services are, and how data can show why protecting biodiversity matters to people.
Video lesson coming soon. In the meantime, read through the lesson below.
What Is Biodiversity?
- Biodiversity: the variety of life
- Genetic: variety of genes in a species
- Species: variety of species in an area
- Ecosystem: variety of ecosystems in a region
Biodiversity is the variety of life, and scientists describe it at three levels. Genetic diversity is the variety of genes within a species, such as the many varieties of one crop. Species diversity is the variety of different species in an area. Ecosystem diversity is the variety of ecosystems, such as forests, wetlands, and grasslands, in a region. A population with more genetic diversity is more likely to include some individuals that can survive a new disease or a change in conditions.
Measuring Species Richness
- Species richness: number of different species
- Count species, not individuals
- Compare areas of the same size
One simple measure of biodiversity is species richness, the number of different species in an area. To find it, count how many kinds of organisms there are, not how many individuals. Plots A and B each hold 20 organisms, but Plot A has 3 species and Plot B has 8, so Plot B has the higher richness. Bigger areas tend to hold more species, so scientists compare richness in areas of the same size. Richness is not the whole picture: in Plot A, one species makes up most of the individuals, and scientists also look at how evenly individuals are spread among species.
Ecosystem Services
- Benefits that people get from ecosystems
- Provisioning: food, water, timber
- Regulating: floods, water quality, climate
- Supporting: nutrient cycling, soil
- Cultural: recreation, learning, beauty
Ecosystem services are the benefits that people get from ecosystems. Scientists often sort them into four types. Provisioning services are goods taken from nature, such as food, fresh water, timber, and medicines. Regulating services control natural processes, such as soaking up floodwater, cleaning water, and storing carbon. Supporting services, such as nutrient cycling and soil formation, are the processes the other services depend on. Cultural services are non-material benefits, such as recreation, learning, and beauty.
Diversity and Stability
- A drought tests a community
- Plots with more species lost less biomass
- Species tolerate different conditions
- Diverse communities tend to recover better
Does biodiversity help an ecosystem keep working when conditions change? In grassland experiments, plots planted with more species have generally lost less plant biomass during a drought and recovered more completely afterward. The graph shows sample data modeled on those experiments: as the number of species rises from 1 to 16, the biomass left during the drought rises from 35% to 78% of a normal year. One explanation is that species differ in what they tolerate, so when drought hits, some species keep growing and make up for the ones that decline. Results vary with the ecosystem and with how stability is measured, so scientists say diverse communities tend to be more stable.
Services Have Real Value
- Many crops depend on animal pollinators
- Forests help filter water for cities
- Protecting nature can cost less than replacing it
Ecosystem services have real economic and health value. A global review found that 87 of the world’s 115 leading food crops depend to some degree on animal pollinators, such as bees. Those crops account for about 35% of global crop production by volume, because staples like wheat, corn, and rice mostly do not rely on animal pollination. Forested watersheds supply clean water, too. New York City protects land in the Catskill and Delaware watersheds that supply most of its drinking water, which has so far kept the city from needing a filtration plant for that water. The city has spent roughly $2.5 billion on watershed protection since the 1990s, and estimates for a filtration plant run from several billion dollars to $10 billion or more, plus yearly operating costs.
Worked Examples
Try each problem on your own first, then open the solution to check your work.
Example 1: Lawn or Meadow?
A student surveys two 10 m × 10 m plots. Find the species richness of each plot and the number of individuals. Which plot has more species? Which has more individuals?
| Lawn species | Count | Meadow species | Count |
|---|---|---|---|
| Kentucky bluegrass | 170 | Little bluestem | 38 |
| White clover | 22 | Purple coneflower | 26 |
| Dandelion | 8 | Black-eyed Susan | 20 |
| Yarrow | 16 | ||
| Goldenrod | 12 | ||
| Aster | 8 |
Show the solution
- Richness is the number of different species. Lawn: 3 species. Meadow: 6 species.
- Individuals: lawn 170 + 22 + 8 = 200; meadow 38 + 26 + 20 + 16 + 12 + 8 = 120
- Compare: the meadow has 6 ÷ 3 = 2 times as many species, even though it has 200 − 120 = 80 fewer individuals.
- Lesson: richness counts species, not individuals.
- Answer: Richness: lawn 3, meadow 6. The meadow has twice as many species, but the lawn has more individuals (200 compared with 120).
Example 2: Drought and Recovery
Two grassland plots, one with 1 or 2 species and one with 16 species, were measured before, during, and after a drought in year 3. Which plot lost more biomass? Which recovered more? Write a claim, evidence, and reasoning.
Show the solution
- Read the graph: in year 3, the low-diversity plot fell to 38% and the high-diversity plot fell to 78%. They lost 62 and 22 percentage points of their biomass.
- Recovery: by year 6, the high-diversity plot was back to 100%, but the low-diversity plot had reached only 80%.
- Claim: in this data, the plot with more species resisted the drought better and recovered more completely.
- Evidence: in year 3 it kept 78% of its biomass compared with 38%, and by year 6 it was at 100% compared with 80%.
- Reasoning: a plot with more species is more likely to include species that tolerate drought. Those species keep growing and can fill in for the ones that decline.
- Answer: The high-diversity plot lost 22 percentage points compared with 62, and recovered fully by year 6.
Example 3: A City’s Water Supply
The model compares a city’s water supply when its forested watershed is intact and when the forest is cleared. Use the model to predict what happens to the water reaching the city if the forest is cleared. What might the city have to do?
Show the solution
- Intact forest: roots, soil, and microbes slow the water and filter it, so cleaner water reaches the streams and the reservoir. This is a regulating service.
- Cleared forest: pavement and bare soil let less water soak in and send more runoff over the surface. The runoff carries sediment and pollutants into the water.
- Prediction: dirtier water reaches the reservoir.
- Response: the city may have to build and run a filtration plant, or pay to protect and restore forest. Either way, a service that nature provided now has a cost.
- Answer: Dirtier water would reach the reservoir, and the city might need a costly filtration plant to replace the forest’s service.
Practice
Classify levels of biodiversity, calculate species richness, use pest damage data as evidence, and explain what a wetland does for a river. Try it on your own first, then check your work with the answer key.
- Biodiversity and Ecosystem Services Practice Worksheet (PDF)
- Biodiversity and Ecosystem Services Practice Answer Key (PDF)
Lesson Slides
Big Ideas
- Biodiversity includes genetic, species, and ecosystem diversity
- Species richness is the number of different species
- Diverse communities tend to resist and recover from disturbance
- Ecosystem services: provisioning, regulating, supporting, cultural
- Protecting ecosystems can cost less than replacing their services
Back to the essential question: people depend on ecosystems for food, clean water, pollination, flood control, climate regulation, and recreation. Diverse ecosystems tend to keep providing these services through droughts, pests, and other disturbances, and replacing a lost service with technology can be costly. Next, you’ll look at the large land communities, called biomes, and how climate shapes them.
NGSS Alignment
This lesson builds toward these Next Generation Science Standards (NGSS) performance expectations:
- HS-LS2-2: Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.
- HS-LS2-6: Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.
Disciplinary core ideas: LS2.A Interdependent Relationships in Ecosystems; LS2.C Ecosystem Dynamics, Functioning, and Resilience