The species-interaction sign table — memorize this grid
5 rows| Interaction | Species 1 | Species 2 | Chapter example |
|---|---|---|---|
| Mutualism | + | + | Ants and acacias; mycorrhizae; lichens; bat pollinating a flower |
| Commensalism | + | 0 | Epiphytes such as Spanish moss on trees; barnacles riding on whales |
| Parasitism | + | – | Dodder on a host plant; tapeworms; Dicrocoelium in ants and deer |
| Predation (incl. herbivory) | + | – | Didinium eating Paramecium; a deer grazing grass; Pisaster on mussels |
| Interspecific competition | – | – | Semibalanus vs Chthamalus; P. aurelia vs P. caudatum; kangaroo rats vs other rodents |
Niche and competition vocabulary
7 rows| Term | What it means | Chapter evidence |
|---|---|---|
| Fundamental niche | Everything a species could use, set by physiological tolerance and resource needs | Chthamalus can live in both the shallow and the deep zone |
| Realized niche | What it actually uses once other species are present | Chthamalus is confined to the shallow zone by Semibalanus |
| Interference competition | Physical fighting or displacement over access to a resource | Semibalanus crowds off, undercuts, and replaces Chthamalus |
| Exploitative competition | Simply consuming the shared resource faster | P. aurelia grows ~6× faster than P. caudatum on the same food |
| Competitive exclusion | The more efficient user eliminates the other locally | P. caudatum declines to extinction with P. aurelia |
| Resource partitioning | Coexisting by using different parts of the resource | Five MacArthur warblers in five zones of one spruce tree |
| Character displacement | Evolutionary divergence where the two species co-occur | Finch beak depths differ in sympatry, match in allopatry |
Gause's three Paramecium tubes — what each one proves
4 rows| Setup | Result | What it demonstrates |
|---|---|---|
| Each species alone | All three grow to their own plateau density | None of them is intrinsically unable to live in the tube |
| P. aurelia + P. caudatum | P. caudatum declines to extinction | Competitive exclusion by exploitative competition |
| P. caudatum + P. bursaria | Both persist at reduced densities | Resource partitioning — different realized niches in the same tube |
| Either species with vs without a competitor | Density is much lower with a competitor present | Coexistence does not mean competition is absent |
Defenses and who uses them
9 rows| Defense | How it works | Example |
|---|---|---|
| Morphological | Physical structures that make eating difficult | Thorns, spines, prickles, sticky glandular hairs, silica in grasses |
| Secondary compounds | Chemicals outside primary metabolism that poison or derange herbivores | Mustard oils (Brassicaceae); cardiac glycosides (milkweeds, dogbanes) |
| Recruited defense | The plant calls in the herbivore's own enemy | Wild tobacco emits a volatile attracting a bug that eats the caterpillar |
| Acquired chemical defense | The animal stores the plant toxin instead of degrading it | Monarch keeps cardiac glycosides through chrysalis, adult, and eggs |
| Manufactured toxin | The animal makes its own poison | Poison-dart frogs, >200 alkaloids in the skin mucus |
| Warning coloration | Advertise a real defense so predators learn to avoid you | Dendrobatid frogs; orange-and-black monarchs |
| Cryptic coloration | Blend in; works only for undefended animals, and only if you do not group | Waved umber moth caterpillar resembling a twig |
| Batesian mimicry | Palatable species copies a defended model — a bluff | Tiger swallowtail copying the pipevine swallowtail |
| Mullerian mimicry | Several defended species converge, so predators learn one pattern | Sympatric Heliconius pairs |
Primary vs secondary succession
6 rows| Feature | Primary succession | Secondary succession |
|---|---|---|
| Starting substrate | Bare and lifeless — new rock, deglaciated ground, open water | A disturbed community where organisms still remain |
| Soil at the start | None; must be built by the pioneers | Already present, with seeds and roots surviving |
| Triggering event | Glacial retreat; a volcanic island rising from the sea | Fire, clearing, or other disturbance of an existing community |
| Typical pioneers | Lichens, then mosses — acid secretions break the rock down | Weedy plants regrowing from the surviving seed bank |
| Speed | Very slow — Glacier Bay takes about 200 years to reach spruce forest | Much faster, because the hardest step is already done |
| Chapter example | Glacier Bay: lichens → mosses → alders → spruce | A cleared or burned woods slowly becoming woods again |
Exam traps
11 pairsQuestions get built out of near-misses. If you can state each difference in one sentence, you will not lose those points.
Batesian mimicryvsMullerian mimicry
Batesian = a bluff. One palatable mimic copies one distasteful model (tiger swallowtail copying pipevine swallowtail); the mimic benefits and the model actually loses a little, because predators sample fakes. Mullerian = an honest alliance. Several genuinely protected species converge on one pattern (Heliconius pairs), so predators only have to learn one lesson and every species gains. Count the liars: Batesian has one, Mullerian has none.
Fundamental nichevsRealized niche
Fundamental = potential, set only by the species' own physiological tolerances and resource needs. Realized = actual, what is left once competitors, predators, and parasites are present. Realized is a subset. In Connell's experiment Chthamalus has a big fundamental and a small realized niche, while Semibalanus has identical fundamental and realized niches.
Interference competitionvsExploitative competition
Interference is physical contact: fighting over a territory, or Semibalanus crowding off and undercutting Chthamalus. Exploitative is indirect: just eating the shared resource faster, as P. aurelia does at six times the rate of P. caudatum. If two individuals never touch, it is exploitative.
Warning (aposematic) colorationvsCryptic coloration
Warning coloration is bright and conspicuous and only works if the animal is genuinely defended — organisms without chemical defenses are seldom brightly colored. Cryptic coloration is camouflage for the undefended. Bonus rule: camouflaged animals usually do not live in groups, because finding one reveals the rest.
Primary successionvsSecondary succession
Primary starts on bare, lifeless substrate with no soil — new rock, deglaciated ground, a new volcanic island. Secondary starts where a community was disturbed but organisms remain — a burned or cleared woods. Ask one question: was there soil and life to start with? If yes, it is secondary.
CommensalismvsMutualism
Commensalism is +/0; mutualism is +/+. The chapter warns there is no clean boundary, because it is hard to prove the second partner gains nothing. Oxpeckers on impala are usually called commensalism but are really mutualism (the mammal loses ticks); the same birds pick scabs and drink blood, which slides toward parasitism.
ParasitismvsPredation
Both are +/–. The chapter treats parasitism as a form of predation in which the organism preyed on does not necessarily die, and the relationship is typically long-term and intimate. Parasitoids are the bridge case: eggs laid in or on a living host, larvae that eat it and usually kill it.
Resource partitioningvsCharacter displacement
Resource partitioning is the ecological pattern — species right now using different portions of a resource (five warblers in five parts of a spruce). Character displacement is the evolutionary process that produced it — selection driving divergence, detected by comparing sympatric with allopatric populations (finch beak depths). Pattern vs process.
Individualistic viewvsHolistic view
Individualistic: species respond independently, so composition changes gradually and communities form a continuum — this is what the Santa Catalina data and the 20,000-year fossil record support. Holistic: species function as one integrated unit that moves together. An abrupt change at an ecotone is not evidence for holism; it just means the physical environment changed abruptly.
Keystone speciesvsMerely abundant species
A keystone species has an effect out of proportion to its abundance — Pisaster is not the most abundant intertidal animal, yet removing it costs seven species. An abundant dominant like Mytilus has a big effect because there is a lot of it. Keystones need not be predators: beavers and alligators qualify as habitat engineers.
Direct effectvsIndirect effect
Direct = the two species interact themselves, as rodents and ants eating the same seeds (negative). Indirect = the effect travels through a third species: rodents suppress large-seeded plants, which frees small-seeded plants, which feed ants (positive). The rodent-removal result — ants up, then down — is exactly the two effects fighting each other.