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Why did caribou in Alaska start moving to new places when the temperature got warmer? Let's investigate how environmental changes affect the organisms that live there.
But scientists noticed something surprising. Over the past 20 years, spring has been coming earlier in Alaska because temperatures are warming. The plants now grow and bloom before the caribou arrive. By the time the caribou get to their calving grounds, the most nutritious plants have already finished growing. The caribou mothers have less food, and their babies are smaller and weaker than they used to be.
Some caribou herds have started changing their paths to search for better food. Other herds have not changed — and those herds are shrinking.
Every organism lives in a habitat — a place that provides the food, water, shelter, and space it needs to survive. When the environment changes, organisms are affected in different ways. Some changes happen quickly, like a wildfire or a flood. Other changes happen slowly over many years, like a climate getting warmer or a forest being cut down. Let's explore the key ideas scientists use to understand how these changes affect living things.
What scientists do: Scientists construct explanations using evidence from observations. They study how populations of organisms change over time when their environments are altered. They collect data by counting organisms before and after a change occurs.
Our investigation: Imagine scientists are studying a pond ecosystem. For three years, they counted the number of frogs, dragonflies, and cattail plants living in and around the pond. Then, a new road was built nearby, and rainwater runoff carried pollution into the pond. The scientists continued counting for two more years after the pollution began.
What they observed: The data they collected tells an important story about how each population responded to the environmental change.
| Year | Frogs 🐸 | Dragonflies 🪰 | Cattail Plants 🌾 | Environment Notes |
|---|---|---|---|---|
| Year 1 | 120 | 200 | 85 | Clean water, healthy pond |
| Year 2 | 125 | 210 | 90 | Clean water, healthy pond |
| Year 3 | 118 | 195 | 88 | ⚠️ Road built — pollution starts |
| Year 4 | 70 | 140 | 95 | Polluted water from road runoff |
| Year 5 | 35 | 90 | 110 | Polluted water from road runoff |
The data from the pond investigation tells us a clear story. Before the road was built, all three populations were stable — the numbers stayed about the same from year to year. The frogs had around 120 individuals, the dragonflies had about 200, and the cattail plants had about 85 to 90.
But after the pollution from the road started flowing into the pond in Year 3, each organism responded very differently. The frogs were affected the most — their population dropped from 118 to just 35 in two years. This makes sense because frogs breathe through their skin, and polluted water can harm them very quickly. Frogs also lay their eggs in the water, so their babies (tadpoles) are surrounded by pollution from the moment they hatch.
The dragonflies also decreased, but not as much as the frogs. Dragonflies spend part of their life in the water as larvae, but as adults they can fly to other ponds if conditions get bad. Some dragonflies may have moved away, while others that stayed had fewer young survive.
The cattail plants actually increased! This is because the pollution from the road contained nutrients (like nitrogen from fertilizers) that helped the plants grow faster. The environmental change that was harmful to animals was actually helpful to the plants. This shows us that the same environmental change can affect different organisms in completely different ways.
This is exactly what happened with the caribou in Alaska. The environmental change (warmer temperatures making spring come earlier) caused the plants to bloom before the caribou arrived. Some caribou herds responded by changing their migration route — they moved. Other herds didn't change, and their populations got smaller. The same kind of environmental change caused different responses in different groups.
The crosscutting concept in this lesson is Cause and Effect. Scientists study cause and effect to understand what makes things change. In our lesson, the cause is an environmental change (like pollution or warming temperatures), and the effect is how organisms respond (moving, surviving, or declining). This same pattern of cause and effect shows up in many areas of science!
| Science Area | Cause (Environmental Change) | Effect (What Happens to Organisms) |
|---|---|---|
| Life Science — Forest | A wildfire burns through a forest | Deer and birds move away; plants with fire-resistant seeds grow back first; some small animals don't survive |
| Life Science — Ocean | Ocean water temperature gets warmer | Coral reefs bleach and die; some fish move to cooler waters; algae may grow faster |
| Earth Science — River | A dam is built across a river | Fish like salmon can't swim upstream to lay eggs; the fish population shrinks; plants along the river change |
| Earth Science — Arctic | Ice melts earlier in spring | Polar bears have less time to hunt seals; caribou food timing changes; some insects appear earlier |
Do you see the pattern? Every time the environment changes — whether it's fire, temperature, water, or something built by humans — the living things in that habitat are affected. The cause (the change) always leads to effects (responses by organisms). Some organisms benefit, some struggle, and some leave. Scientists design tests and collect data to figure out exactly which causes lead to which effects.
Understanding how environmental changes affect organisms isn't just something scientists study in labs — it helps people make important decisions in the real world. Here are some ways this science is used every day:
You can think like a scientist and engineer too! Next time you notice a construction site in your neighborhood, ask yourself: What plants and animals lived here before? How will this change affect them? What could people do to help? That kind of thinking is exactly what environmental scientists do every day.