Human impacts

Human impacts on food webs

Big idea: Human activities can disrupt food webs by adding pollutants that move through ecosystems and affect organisms at many trophic levels.

Humans are part of food webs, even when we are not directly eating plants or animals. Activities such as industry, transport, farming, and waste disposal can change how food webs function.

🔬 Human Impact: Consequences Deep Dive

Big Idea: Human impacts don't just remove species — they trigger chain reactions that weaken ecosystems and push them toward collapse. Understanding how damage spreads is key to predicting and preventing it.

⚡ Tipping Points

A tipping point is like leaning back in a chair — tip a little and you recover, but lean too far and you crash. No going back!

Real Example: Coral Reef Collapse 🪸: Coral reefs tolerate some warming and pollution. Cross the tipping point (too hot + too polluted), and corals bleach and die. The reef flips from colorful coral to slimy algae — and may stay that way for decades.

Real Example: Amazon Dieback 🌳: The Amazon creates its own rain. Cut too many trees (20-25% deforestation), and rainfall drops below the tipping point — the forest dries out, fires spread, and jungle could flip to savanna. Irreversible.

Once a tipping point is crossed, it may be irreversible — the ecosystem can't bounce back.

Connect tipping points to resilience — low resilience = closer to the tipping point!

🌍 Planetary Boundaries

Earth has 'safe limits' called planetary boundaries — like speed limits on a highway. Go too fast, and you risk a crash that affects everyone.

We've Already Crossed Some!: Scientists say we've crossed safe limits for biodiversity loss and nitrogen/phosphorus pollution. Climate change and land use are at the edge.

Staying within planetary boundaries keeps Earth stable and safe for ALL life — including us!

☠️ Bioaccumulation & Biomagnification

Some pollutants don't break down — they build up in living things and get more concentrated up the food chain.

Real Example: Mercury in Tuna 🍣: Tiny plankton absorb a bit of mercury. Small fish eat many plankton (more mercury). Medium fish eat many small fish (even more). Tuna eat many medium fish (most concentrated!). You eat tuna = you get the highest dose. That's biomagnification!

Real Example: DDT & Eagles 🦅: DDT pesticide accumulated in fish. Eagles ate the fish and concentrated DDT in their bodies. DDT made their eggshells so thin they broke — bald eagle populations crashed until DDT was banned.

Know the difference: Bioaccumulation = ONE organism. Biomagnification = UP the food chain. Top predators suffer most!

Bioaccumulation

Bioaccumulation happens when an organism absorbs pollutants faster than it can remove them.

Even when pollution levels in the environment are low, long-lived organisms can store increasing amounts of toxins in their tissues.

Biomagnification

Biomagnification occurs when pollutants are passed from prey to predator.

As energy moves up food chains, biomass decreases. Toxins become more concentrated because they are stored in body tissues rather than lost.

Bioaccumulation happens within one organism; biomagnification happens between trophic levels.