Open with the Guam brown tree snake (Boiga irregularis) story. In 1945, a few snakes arrived on U.S. military cargo from the Admiralty Islands. Within 40 years the snake had eliminated 10 of Guam's 12 native forest bird species. Ask: 'Guam still has trees. Is that the whole story?' Then reveal the twist — with the birds gone, spider populations exploded (~40× higher than nearby Saipan), and native trees now show ~60–90% reduced seed dispersal because the birds that ate and moved the seeds are gone. Prompt students to name at least two knock-on effects beyond 'fewer birds.' This sets up trophic cascades and previews that one disruption reshapes an entire community.

1. 6m

   Invasive species vs. 'just non-native'

   Content

   A non-native species is any organism outside its historic range. It becomes an invasive species only when it spreads AND causes ecological or economic harm. The mechanism is enemy release: in the new range, the predators, competitors, and pathogens that held it in check are absent, so growth approximates exponential (dN/dt = rN) instead of logistic (dN/dt = rN((K−N)/K)). Concrete cases: Burmese python in the Everglades has driven ~90–99% declines in mid-size mammals (raccoons, opossums, marsh rabbits); zebra mussels filter phytoplankton so aggressively they collapse pelagic food webs while boosting benthic ones; kudzu smothers native canopy in the Southeast. Contrast: honey bees are non-native to North America but are managed and not classified as invasive.

   Delivery

   Head off the biggest misconception first — 'non-native ≠ invasive.' Ask students to nominate a non-native species that ISN'T invasive (honey bee, most crop plants, house cats when contained). Emphasize the two-part test: spreads AND harms. Connect enemy release back to Unit 8 population growth — invaders behave exponentially precisely because K hasn't been set by predators yet. Quick check: 'Why does the same species behave logistically at home and exponentially in Guam?'

2. 6m

   Trophic cascades and keystone species

   Content

   Species are linked by feeding relationships, so removing or adding one species propagates through the web. A keystone species has an effect on community structure far larger than its abundance would suggest. Classic case: Robert Paine's Pisaster ochraceus removal — take out the sea star and Mytilus mussels outcompete every other intertidal species, collapsing diversity from ~15 species to ~8. Yellowstone wolves (reintroduced 1995): wolves suppress elk browsing on willow and aspen along streams → riparian vegetation recovers → beavers return → stream morphology changes. Sea otters eat urchins; urchins eat kelp; lose otters and urchin barrens replace kelp forests. Cascades can be top-down (predator → prey → producer) or bottom-up (producer → consumer).

   Delivery

   Anchor the abstract term in Paine's actual experiment — students remember stories. Walk the wolf cascade one arrow at a time on the slide's food-web diagram, asking students to predict the next step before you reveal it. Pre-empt the misconception 'losing one species is only a local effect' — every example shows community-level restructuring. Ask: 'If we lose the sea otter, why does the kelp — three links away — care?'

3. 5m

   Pollution: biomagnification and eutrophication

   Content

   Two disruption modes to distinguish. (1) Biomagnification — persistent, fat-soluble pollutants (DDT, methylmercury, PCBs) are not excreted, so concentration multiplies at each trophic level. Classic DDT data: water ~0.000003 ppm → zooplankton ~0.04 ppm → small fish ~0.5 ppm → large fish ~2 ppm → osprey ~25 ppm. That's ~10⁷ magnification, which thinned raptor eggshells and crashed bald eagle and peregrine populations before the 1972 U.S. ban. (2) Eutrophication — nutrient (N, P) runoff from fertilizer and sewage → algal bloom → algae die → decomposer respiration depletes O₂ → hypoxic 'dead zone.' The Gulf of Mexico dead zone driven by Mississippi River runoff reaches ~15,000 km² most summers.

   Delivery

   Contrast the two mechanisms explicitly — biomagnification concentrates UP the food chain (top predators worst); eutrophication kills from the BOTTOM (decomposers steal O₂). Have students predict which trophic level of a lake would show the highest PCB burden and justify with one sentence — this is a common AP MC stem. Emphasize the numbers: order-of-magnitude thinking is AP-level.

4. 5m

   Climate change, ocean acidification, and tipping points

   Content

   Atmospheric CO₂ has risen from ~280 ppm (pre-industrial) to ~420 ppm (2024), and global mean temperature is now ~+1.2 °C above the 1850–1900 baseline. This is NOT just 'warmer.' It also means: (a) precipitation shifts (droughts, extreme rainfall); (b) ocean acidification — CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ has dropped surface ocean pH from ~8.2 → 8.1 (a ~30% increase in [H⁺]), reducing CO₃²⁻ available for coral, mollusk, and pteropod shells; (c) range shifts — species move poleward ~17 km/decade on average; (d) phenological mismatch — pied flycatchers arrive at their old date but caterpillar peak now comes 2 weeks earlier, so chicks starve. Finally, ecosystems can cross tipping points. A coral reef that loses its herbivorous fish and warms past ~2 °C can flip to an algae-dominated state that persists even after conditions improve — the system has low resilience and multiple stable states.

   Delivery

   The critical AP move here is to break the 'climate change = just hotter' frame. Walk through the four consequence channels — temperature, precipitation, chemistry, timing — and give a named biological example for each. Slow down on the acidification equation; students should be able to read that CO₂ literally makes seawater more acidic. Close with the tipping-point idea: recovery is not guaranteed. Ask: 'If we cut CO₂ tomorrow, does every reef come back? Why not?'

1. 28m

   Kelp Forest Disruption Lab — Food-web cascade + CO₂/SST data argument

   Students work in pairs. Part 1 (12 min): they annotate a North Pacific kelp-forest food web for a keystone-removal scenario (sea otter collapse), then do the same web for an invasive-predator scenario (Pycnopodia sea star wasting disease + purple urchin explosion). Part 2 (10 min): they analyze paired CO₂ and Bering Sea SST data and connect the abiotic trend to a biological indicator (kelp canopy loss). Part 3 (6 min): they write a short AP-style argument. Circulate and check that arrows show DIRECTION of population change (↑/↓) not just 'affected.' Targets SP2 Visual Representations, SP4 Representing and Describing Data, SP6 Argumentation, SP1 Concept Explanation. Student handout — Kelp Forest Under Stress Background. North Pacific kelp forests (giant kelp Macrocystis pyrifera, bull kelp Nereocystis luetkeana) support one of the most productive ecosystems on Earth. The food web below shows the key links. The food web (arrows → mean 'energy flows to'): - Kelp → Purple urchin (Strongylocentrotus purpuratus) - Kelp → Abalone - Kelp → Kelp bass (fish) - Purple urchin → Sunflower sea star (Pycnopodia helianthoides) - Purple urchin → Sea otter (Enhydra lutris) - Abalone → Sea otter - Kelp bass → Sea otter - Kelp bass → Harbor seal - Harbor seal → Orca - Sea otter → Orca Part 1A — Keystone removal (sea otter collapse, 1990s Aleutians). Orcas began preying on sea otters; otter numbers dropped ~90%. - On the food web, mark the sea otter with a red X . - Use ↑ or ↓ next to each of the following to predict its population change, and write ONE sentence citing the web link that drives it: - Purple urchin: ______ - Reasoning: ______ - Kelp: ______ - Reasoning: ______ - Kelp bass: ______ - Reasoning: ______ - Abalone: ______ - Reasoning: ______ - Name this cascade type (top-down or bottom-up): ______ Part 1B — Invasive/disease disruption (sea star wasting disease, 2013–present). A wasting disease collapsed Pycnopodia populations by >90% along the West Coast. Assume sea otters are ALSO scarce in this region. - Predict and justify: - Purple urchin: ______ - Reasoning: ______ - Kelp canopy cover: ______ - Reasoning: ______ - The resulting state — bare rock covered in urchins with almost no kelp — is called an urchin barren. Explain in ONE sentence why an urchin barren is an example of a tipping point, not just a temporary dip: ______ Part 2 — Data analysis. Use the paired data below (northeast Pacific, 2013–2019 marine heatwave 'The Blob'). - Year — Atmospheric CO₂ (ppm) — Bering Sea SST anomaly (°C) — Bull kelp canopy area (% of 2008 baseline) - 2008 — 385 — +0.2 — 100 - 2013 — 396 — +0.6 — 78 - 2014 — 398 — +1.4 — 45 - 2015 — 401 — +2.1 — 22 - 2016 — 404 — +2.3 — 12 - 2019 — 411 — +1.8 — 9 - Percent change in bull kelp canopy from 2008 to 2019: ______ % - Describe the trend in CO₂ from 2008 → 2019 in one sentence: ______ - Describe the relationship between SST anomaly and kelp canopy area: ______ - Name TWO mechanisms (beyond 'it's hotter') linking rising CO₂ to kelp loss: 1. ______ 2. ______ Part 3 — AP-style argument (4–6 sentences). Claim, evidence, reasoning. - Prompt: A resource manager proposes reintroducing sea otters to a site that has been an urchin barren for 15 years. Predict whether the kelp forest will recover to its pre-disturbance state, and defend your prediction using BOTH the food web (Part 1) and the data (Part 2). - Your response: ______

   Materials

   • Printed student handout (content below)
   • Colored pencils or pens (red + blue)
   • Ruler
   • Calculator (or phone) for percent-change math

   Example outputs

   • Part 1A: Purple urchin ↑ (otter no longer eats them); Kelp ↓ (urchin grazing unchecked → urchin barren); Kelp bass ↓ (loss of kelp habitat and food); Abalone ↑ short-term then ↓ (release from otter predation, then starve as kelp disappears). Cascade type: top-down.
   • Part 2: Kelp change = (9 − 100)/100 × 100 = −91%. CO₂ rises steadily from 385 → 411 ppm. SST anomaly and kelp area are strongly negatively correlated — as warming spikes in 2014–2016, kelp collapses. Two mechanisms: (1) warm water stresses kelp thermally and reduces nutrient upwelling, (2) warming enabled sea star wasting disease, removing urchin predators.
   • Part 3 sample: Claim — reintroduction alone is unlikely to restore the kelp forest. Evidence — the food web shows otters suppress urchins, but the data show SST is still elevated (+1.8 °C in 2019) and CO₂ continues to rise. Reasoning — even if otters cut urchin numbers, warm, low-nutrient water limits kelp regrowth, and 15 years of urchin barren has crossed a tipping point with low resilience; the system may sit in an alternative stable state.
   • Part 1B: Purple urchin ↑↑ (two predators, Pycnopodia and otter, both gone); Kelp canopy ↓↓ (unchecked grazing). Tipping-point reasoning: once urchins strip kelp, no larval kelp can settle, urchins persist on drift algae, and the community remains in an urchin-barren stable state even if predators return.
   • presentation_text: sample student annotation showing red X on otter, ↑ next to urchin, ↓ next to kelp and kelp bass, with 'top-down' circled.

1. A lake receives heavy fertilizer runoff from surrounding farms for three consecutive summers. Which sequence best describes the resulting disruption? (Targets SP1 Concept Explanation.) A) ↑ N/P → ↑ top predators → ↓ algae → ↑ dissolved O₂ B) ↑ N/P → ↑ algal bloom → ↑ decomposition → ↓ dissolved O₂ → fish die-off C) ↑ N/P → ↓ algal biomass → ↑ dissolved O₂ → ↑ fish biomass D) ↑ N/P → biomagnification in top predators → eggshell thinning

   multiple choiceB. Nutrient loading drives an algal bloom; when the algae die, decomposer respiration depletes O₂, producing hypoxia and fish kills (eutrophication). A and C get the O₂ direction wrong; D confuses eutrophication with biomagnification of persistent pollutants like DDT.

2. The following data are from a temperate forest lake, showing PCB concentration (ppm, wet weight) by trophic level: phytoplankton 0.025; zooplankton 0.123; smelt (small fish) 1.04; lake trout (large fish) 4.83; herring gull eggs 124. Describe the pattern in ONE sentence, name the process, and explain the mechanism in 2–3 sentences. (Targets SP4 Representing and Describing Data and SP1 Concept Explanation.)

   short answerPattern: PCB concentration increases by roughly 5,000× from phytoplankton (0.025 ppm) to gull eggs (124 ppm) as trophic level rises. Process: biomagnification. Mechanism: PCBs are lipid-soluble and not readily excreted, so each consumer retains the toxin from all prey it eats; because energy transfer between trophic levels is ~10%, a predator must consume roughly 10× the biomass of its prey to gain the same energy, concentrating persistent toxins at each step up the food web.

3. Corals reared in tanks bubbled with future-scenario air (800 ppm CO₂) build skeletons ~30% more slowly than corals in present-day air (420 ppm CO₂), even at identical temperature. Construct a claim–evidence–reasoning argument (3–4 sentences) explaining the mechanism, and predict ONE community-level consequence for the reef. (Targets SP6 Argumentation.)

   short answerClaim: Elevated CO₂ suppresses coral calcification through ocean acidification, independent of warming. Evidence: at fixed temperature, doubling CO₂ (420 → 800 ppm) reduced skeletal growth ~30%. Reasoning: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ lowers seawater pH and reduces available CO₃²⁻, the substrate corals use to precipitate CaCO₃ skeletons. Community consequence (any one): reduced 3-D reef structure lowers habitat for reef fish and invertebrates, decreasing biodiversity; or, weakened reefs cross a tipping point to an algae-dominated alternative stable state.

4. Lionfish (Pterois volitans), native to the Indo-Pacific, were released into Atlantic waters in the 1980s. In heavily invaded Bahamian reefs, small reef-fish abundance dropped ~65% within 5 years, while lionfish density grew exponentially. Which statement best explains the outcome? (Targets SP2 Visual Representations and SP1.) A) Lionfish are non-native, so by definition they are invasive. B) Lionfish population growth follows dN/dt = rN((K−N)/K), because Atlantic reefs have set a low carrying capacity. C) Lionfish grow near-exponentially (dN/dt = rN) because Atlantic predators, competitors, and parasites do not suppress them, and their predation drives a top-down cascade on reef-fish prey. D) The reef-fish decline is caused by ocean acidification, not by lionfish.

   multiple choiceC. Enemy release in the new range removes population controls, so growth is near-exponential rather than logistic, and heavy predation on small reef fish produces the observed top-down cascade. A is the classic misconception (non-native ≠ invasive without harm); B contradicts the observed exponential growth; D ignores the direct predation evidence.

• ☐Printed student handout (kelp food web + data table + argument prompt) — 1 per student
• ☐Red and blue pens or colored pencils
• ☐Ruler
• ☐Calculator or phone for percent-change math
• ☐Projector for slide deck (visuals auto-generated)
• ☐Timer visible to class