This is the final exam for Ecosystems & Niches. It pulls the whole course together: what a niche really is (a how, not a where — an occupation across many dimensions, with the fundamental-vs-realized split), the competitive exclusion principle and why a tiny compounding edge makes it inevitable (Gause), how species escape exclusion by resource partitioning (Darwin’s finches, MacArthur’s warblers) and character displacement, the generalist–specialist trade-off and which wins in stable vs. disturbed worlds, food webs and the ~90%-per-level energy leak, keystone species as referees against exclusion and the trophic cascades their removal unleashes, and the transfer to strategy — a market is an ecosystem — together with the failure modes (invasive species, disturbance, and non-durable niches) where the model stops giving good advice. Take your time; several questions look easy until you spot the trap — habitat masquerading as niche, “the loser was weak,” or “we dominate the niche, so we’re safe.”
How this exam works
Read carefully — this exam is final. Each question appears one at a time. Once you submit an answer it is locked for good: there’s no going back, no retry, and no restart. Your score is hidden until the end, where you’ll see a pass/fail verdict. The pass mark is 70%. A few questions ask you to select all correct answers.
What is the single sharpest difference between a species' habitat and its niche?
Select an answer to continue.
Course Recap
Big picture
Ecosystems & niches, in one picture
- Ecosystems & Niches
- The niche
- How a species makes its living (occupation), not where it lives (habitat); multi-dimensional; fundamental (potential alone) vs. realized (what competitors leave you)
- Competitive exclusion
- Two species on the exact same limiting resource can't coexist — a small edge compounds to total victory (Gause). The loser isn't weak; limiting similarity is the max survivable overlap
- Partitioning & specialization
- Escape from exclusion: divide the resource (finches by beak, 5 warblers by tree-zone); character displacement pushes rivals apart. Specialist (stable worlds) vs. generalist (disturbed worlds)
- Food webs & keystones
- Energy leaks ~90% per level (short chains, rare apex). Keystones have outsized effect, act as referees against exclusion; removing one triggers a trophic cascade — you can't do just one thing
- Markets are ecosystems
- Companies=species, customers=resources; exclusion, partitioning, moats transfer. "Find a niche" = Gause in a suit; a moat enforces the partition
- Where it breaks
- A niche guards only against co-evolved neighbors: invasive species (outside invaders) and disturbance (board reset) bypass it, and a niche must be defensible, durable, and big enough
- The niche
Key takeaways
An ecosystem stays diverse because no species wins everywhere — each survives by fitting a niche, a how (occupation across many dimensions), not a where (habitat); what competitors leave you is your realized niche, narrower than your fundamental potential. The load-bearing law is competitive exclusion: two species on the exact same limiting resource can’t coexist, because even a tiny edge compounds into total victory (Gause) — the loser isn’t weak, it just overlapped too much, and limiting similarity sets how close two coexisting species can get. Species dodge exclusion by resource partitioning (Darwin’s finches split by beak; MacArthur’s five warblers split one tree by zone), visible as character displacement, which drives specialization — and the generalist–specialist trade-off means narrow specialists win stable worlds while flexible generalists inherit disturbed ones. Zoom out and species knot into a food web where energy leaks ~90% per level and a few keystone species hold up far more than their weight (often as referees against exclusion), so removing one sends a trophic cascade far past its neighbors — you can’t do just one thing. It all transfers to strategy: a market is an ecosystem, “find an unoccupied niche” is Gause’s principle in a suit, and a moat enforces your partition — but the model breaks on invasive species and disturbance, and “find your niche” is a cliff unless the niche is defensible, durable, and big enough.