Grade by Grade
B. Diversity of Living Things · Diversity of Living Things

Human Interventions: Weighing Risks and Benefits to Biodiversity

B1.1 A1.9 A2.1About 75 minutes
Learning goals
  • I can analyse the risks and benefits of human interventions such as fish stocking, tree plantations, pesticide use, fire suppression and biological control.
  • I can explain biomagnification and why some pesticides harm top predators.
  • I can evaluate sources of information on an environmental issue for accuracy, reliability and bias.
  • I can describe careers that manage biodiversity and the training they require.

Words to know

human intervention
A deliberate action by people that changes an ecosystem, such as stocking fish, planting trees, spraying pesticides or putting out fires.
stakeholder
A person or group affected by, or interested in, a decision.
biomagnification
The increase in concentration of a persistent toxin at each higher level of a food chain.
biological control
Using a natural enemy (predator, parasite or disease) to control a pest or invasive species.
fire regime
The natural pattern of how often, how intensely and in what season fires occur in an ecosystem.
serotinous cone
A cone sealed with resin that opens to release seeds mainly after the heat of a fire (e.g. jack pine).
prescribed burn
A planned, controlled fire set by trained crews to restore fire-dependent habitats and reduce fuel.
integrated pest management (IPM)
Controlling pests with a combination of methods (monitoring, crop rotation, biological control, targeted pesticides) to minimize harm.

Good intentions, complicated results

In the 1900s, people introduced fish to lakes to improve fishing, planted rows of pine on eroding land, sprayed insecticides to protect crops and forests, and put out every forest fire as fast as possible. Each action solved a problem. Many also caused new ones that took decades to notice.

The curriculum asks you to analyse the risks and benefits of human intervention in aquatic and land ecosystems. Today you will practise a structured way to do that, using real Canadian cases.

A risk-benefit framework

For any intervention, ask:

  1. What problem was it meant to solve?
  2. Benefits: ecological, economic, social and cultural. Who gains?
  3. Risks: to native species, genetic diversity, food webs, people's health. Who bears them?
  4. Short term vs long term.
  5. Evidence: how strong and how reliable are the sources?
  6. Alternatives: is there a lower-risk way to reach the same goal?
  7. Recommendation: continue, change or stop, with reasons.

Case 1: Fish stocking

Ontario raises fish in hatcheries and releases them into lakes and rivers.

  • Benefits: supports recreational and commercial fishing (and the jobs and tourism tied to it); restores species that have disappeared, such as the long-running effort to bring native Atlantic salmon back to Lake Ontario streams; can rebuild populations after overfishing.
  • Risks: stocked fish compete with or eat native species; non-native fish (for example, Pacific salmon species stocked in the Great Lakes) change food webs; hatchery fish can carry disease; and when hatchery fish breed with wild fish, they can reduce the wild population's genetic diversity and local adaptations.

Case 2: Tree plantations

In the late 1800s and early 1900s, clearing and over-farming parts of southern Ontario, such as the sandy soils of Norfolk County, left land so bare that it turned into blowing sand. Ontario began large reforestation programs; the St. Williams nursery in Norfolk County, opened in 1908, grew millions of seedlings, many of them red and white pine.

  • Benefits: stopped soil erosion, protected water, produced timber and stored carbon. Many of today's southern Ontario forests began as plantations.
  • Risks: rows of same-age trees of one species have low structural and species diversity (recall the forest-layers diagram in the first lesson) and are more vulnerable to pests and disease.
  • Today: managers often thin plantations and let native hardwoods grow in, gradually turning them into mixed forests.

Case 3: Pesticides

DDT, a powerful insecticide used widely after the Second World War, controlled mosquitoes and crop pests. But DDT is persistent (it breaks down slowly) and fat-soluble, so it builds up in body fat. Through biomagnification, its concentration rises at each step of a food chain. Top predators such as peregrine falcons, bald eagles and ospreys received the highest doses. A breakdown product of DDT caused thin eggshells that broke during incubation, and these birds declined sharply. After Canada and the United States restricted DDT in the 1970s, and with captive-breeding release programs, these birds have largely recovered; peregrines now nest on tall buildings in Toronto and other cities.

Neonicotinoids are newer insecticides often applied as seed coatings. Research linked them to harm in bees and other pollinators, and in 2015 Ontario introduced rules to reduce the use of neonicotinoid-treated corn and soybean seed.

Integrated pest management aims to keep the benefits (protecting crops and forests) while reducing the risks: monitoring pests, rotating crops, using natural enemies, and spraying only targeted products when needed.

water0.000003 ppmzooplankton0.04 ppmsmall fish0.5 ppmlarge fish2 ppmfish-eating birdsabout 25 ppmDDTconcentrationincreasesDDT concentration up an estuary food chain
Biomagnification: approximate, rounded textbook values based on a 1960s study of a U.S. estuary. DDT barely detectable in water became millions of times more concentrated in fish-eating birds at the top of the food chain.

Case 4: Fire suppression

Many Canadian ecosystems are fire-adapted. Jack pine, common across Ontario's boreal forest, has serotinous cones that stay sealed until the heat of a fire opens them. Ontario's rare tallgrass prairies and oak savannas (for example on the Rice Lake Plains and on Walpole Island) depend on frequent fire to stop trees and shrubs from shading out prairie plants.

  • Benefits of suppression: protects lives, homes, communities and timber.
  • Risks: without fire, fire-dependent species decline, forests become denser and older, and fuel builds up, so when fires do come they can be larger and more intense.
  • Today: managers use prescribed burns and sometimes let remote fires burn. Many First Nations have long used fire deliberately to manage landscapes, and some communities are leading the revival of these cultural burning practices with conservation partners.
1. Cone sealed shutwith resin; seedsstored for years2. Fire's heatmelts the resin3. Cone opens andseeds fall4. Seedlings grow insunny ash-covered soil
How jack pine depends on fire. Its serotinous cones open after a fire's heat melts the resin, releasing seeds onto bare, sunny ground where seedlings thrive. Putting out every fire can stop jack pine stands from renewing.

Case 5: Controlling invasive species

  • Sea lamprey spread into the upper Great Lakes in the 1920s and 1930s and devastated lake trout. Since the late 1950s, a lampricide called TFM has been applied to streams where lamprey larvae live. It has reduced sea lamprey numbers dramatically and helped lake trout recover. Risk: TFM can also kill some non-target species in treated streams, such as native lamprey larvae and mudpuppies, so doses are carefully controlled.
  • Purple loosestrife, a Eurasian wetland plant, forms dense stands that crowd out cattails and other native plants. Since the 1990s, leaf-eating ***Galerucella* beetles have been released in Ontario as biological control**. They were tested beforehand to make sure they feed almost only on purple loosestrife. Risk: any introduced control agent might affect native species in ways not predicted, which is why careful testing is required (earlier biological controls elsewhere, such as cane toads in Australia, caused disasters).

Positive interventions also include protected areas, wildlife corridors (for example, ecopassages under highways for turtles), wetland restoration, and head-starting programs that raise young Blanding's turtles in safety before release.

Worked example

Let's analyse a fish-stocking decision

A township proposes stocking a lake with a non-native sport fish to attract tourists. Analyse risks and benefits and make a recommendation.

  1. Problem: declining tourism and fishing.
  2. Benefits: economic (tourism, bait shops, lodges), social (recreation).
  3. Risks: the new predator may eat or compete with native fish, frogs and invertebrates; it may carry disease; it may spread to connected waters and become invasive; the change is hard to reverse.
  4. Stakeholders: local businesses, anglers, cottagers, nearby First Nations with fishing rights and knowledge of the lake, provincial fisheries biologists, other species.
  5. Alternatives: stock a native species from local genetic stock; improve habitat (spawning beds, shoreline vegetation); adjust catch limits.
  6. Recommendation: do not introduce a non-native fish; choose native stocking with local genetic stock and habitat restoration, and monitor results.

The long-term ecological risks of a non-native predator outweigh short-term tourism benefits; lower-risk alternatives exist.

Worked example

Let's evaluate sources on neonicotinoids (A1.9)

You find four sources on whether neonicotinoids harm bees. Rank their reliability: (a) a peer-reviewed study in a scientific journal with field data from many farms; (b) a pesticide manufacturer's web page; (c) a social media post with a dramatic video of dead bees and no location; (d) a government agency's science review that summarizes many studies.

  1. Criteria: author expertise, evidence shown, review process, bias or conflict of interest, date.
  2. (d) Government science review: summarizes many studies, expert authors, public process → high reliability (check the date).
  3. (a) Peer-reviewed field study: strong evidence and expert review → high reliability, though one study is not the final word.
  4. (b) Manufacturer's page: may be accurate but has a financial conflict of interest → use with caution and check its claims.
  5. (c) Social media post: no source, no data, no context → low reliability; it may be true, but you cannot tell.

Most reliable: (d) and (a); use (b) with caution; (c) is not reliable evidence.

Careers in biodiversity management (A2.1)

  • Fish and wildlife technician: collects field data, runs hatcheries and surveys. Usually a college diploma (several Ontario colleges offer fish and wildlife programs).
  • Fisheries or wildlife biologist: designs studies and advises on management. Usually a university degree in biology or environmental science, often a master's.
  • Registered Professional Forester: plans forest harvesting, regeneration and fire management. A forestry degree plus professional registration with the Ontario Professional Foresters Association.
  • Conservation officer: enforces fish and wildlife laws. Usually a college or university program in conservation or law enforcement.
  • Ecologist or environmental consultant: assesses the impact of developments on species and habitats.
  • Fire ranger and prescribed-burn specialist: fight fires and run controlled burns.
Just for fun

Biological control is like hiring the pickiest eater you know. The Galerucella beetles released to fight purple loosestrife were tested on dozens of plants to make sure they'd eat purple loosestrife and almost nothing else: the one guest at the buffet who will only eat one dish.

Hands-on activity

Analyse an intervention near you

You need: internet access with a grown-up's help, a notebook, and about an hour.

  1. Choose a human intervention in your area or province: for example, a fish-stocking program, a prescribed burn, invasive species control (phragmites, purple loosestrife, zebra mussels), a turtle ecopassage, a dam, a reforestation project or a pesticide ban.
  2. Find three sources, including at least one from a government agency, conservation authority, university or First Nation, and one that represents a different viewpoint.
  3. For each source, record the author, date, purpose and any bias, and rate its reliability.
  4. Fill in the risk-benefit framework (7 questions from the tip box above) and list at least four stakeholders.
  5. Write a one-paragraph recommendation, citing your sources.
  6. Optional: find one career connected to your intervention and describe the training it requires.

What to look for: specific ecological, economic and social points; risks and benefits for different stakeholders; honest evaluation of sources; a recommendation that follows from the evidence and considers alternatives.

Your turn

1

Give one benefit and two risks of stocking a lake with hatchery-raised fish.

2

Why are top predators most affected by DDT?

3

Explain how fire suppression can harm biodiversity.

4

What is biological control? Give an Ontario example.

5

State one benefit and one risk of using TFM to control sea lamprey.

6

Why did Ontario plant pine plantations in the early 1900s, and what is a drawback of them today?

7

Name two careers that manage biodiversity and the training each needs.

More practice: warm-up

1

What is a serotinous cone?

2

What is a stakeholder?

3

Which birds declined because of DDT eggshell thinning?

4

What is a prescribed burn?

5

What does IPM stand for?

More practice: on your own

1

Using the biomagnification figure, by what factor did DDT increase from small fish (0.5 ppm) to fish-eating birds (25 ppm)?

2

A town plans to spray an insecticide over a wetland to kill mosquitoes. Suggest two risks and one lower-risk alternative.

3

Explain why the risks of introducing a biological control agent must be tested before release.

4

Why might a peer-reviewed study still not settle a question?

5

Why might a First Nation be an important stakeholder in a lake-stocking decision?

Challenge

1

The peregrine falcon's recovery involved both a pesticide restriction and captive-breeding releases. Explain why both were needed.

2

Compare the risk-benefit balance of fire suppression near a town and in a remote boreal wilderness park.

3

Write a short argument for or against using a lampricide in a stream that also has a population of an endangered native lamprey species.

Check your understanding

Quiz

1.

Biomagnification means a toxin's concentration:

2.

Which is a RISK of stocking non-native fish?

3.

Jack pine depends on fire because:

4.

Galerucella beetles in Ontario are an example of:

5.

Which source about a pesticide is most reliable?

6.

Which training is required to become a Registered Professional Forester in Ontario?

For parents and teachers

Big idea (B1.1): human interventions such as fish stocking, plantations, pesticides, fire suppression and invasive-species control bring benefits and risks to biodiversity. Students use a structured risk-benefit framework, evaluate sources (A1.9) and explore careers (A2.1).

How to help: Discuss a local example together (a conservation authority project, a turtle crossing sign, invasive species in your area). Ask "Who benefits? Who bears the risk? What's the evidence?"

Common difficulties:

  • One-sided answers. Every case should list both risks and benefits.
  • Confusing bioaccumulation (in one organism over time) with biomagnification (up the food chain).
  • Trusting dramatic sources without checking evidence.

Sources: DDT concentrations are the rounded values that many textbooks use to summarize Woodwell, Wurster and Isaacson (1967, Science); St. Williams nursery (Ontario Parks / St. Williams Conservation Reserve); sea lamprey control (Great Lakes Fishery Commission); purple loosestrife biocontrol (Ontario Invasive Plant Council); Ontario neonicotinoid regulations (2015).