Populations I guess
In a prairie dog colony, each breeding pair aggressively defends its own burrow entrance from neighbors, so entrances end up almost perfectly evenly spaced across the field.
Uniform dispersion — even spacing typically caused by territoriality or competition for space.
A remora fish rides along attached to a shark, eating leftover scraps from the shark's kills. The shark experiences no measurable benefit or harm from carrying the remora.
Commensalism — one species benefits while the other is unaffected.
Algae in a pond contain 200,000 kcal of energy. Using the standard 10% rule, how much energy is available to the primary consumers (zooplankton)?
20,000 kcal — 200,000 × 0.10 = 20,000 kcal.
A biologist records the heart rate, body temperature, and hibernation behavior of one individual bear over a winter.
Organismal ecology — the study focuses on a single organism's physiology and behavior.
A geologist notes that a fossil sits below one rock layer and above another, and concludes it must be older than the layer above and younger than the layer below — without calculating a number of years.
Relative dating — age is inferred from position in rock strata, not a calculated numerical age.
Researchers tag and release 80 turtles in a wetland (n1). Three weeks later they capture 120 turtles (n2), and 24 of them are already tagged (m2). Using the Lincoln-Petersen estimate, what is the total population size?
400 — N = (n1 × n2) / m2 = (80 × 120) / 24 = 400.
A harmless hoverfly has evolved bold yellow-and-black stripes that closely resemble a stinging wasp's pattern, causing predators to avoid it even though it cannot sting.
Batesian mimicry — a harmless species mimics a dangerous one to gain protection.
In a grassland chain — grass (1,000,000 kcal) → grasshoppers → shrews → owls — how much energy reaches the owls (the tertiary consumer level) after three successive 10% transfers?
1,000 kcal — 1,000,000 → 100,000 → 10,000 → 1,000 kcal.
Two grasslands each have 5 plant species and 200 total plants. Grassland X has one species with 160 individuals and four rare ones; Grassland Y splits its 200 individuals almost evenly across all five species. Which grassland has the higher Shannon Index, and why?
Grassland Y — for the same richness, greater evenness among species increases H′.
Under early-Earth-like conditions, fatty acid molecules spontaneously assemble into hollow spherical membranes, enclosing a small pool of organic molecules and separating them from the surrounding environment.
Formation of a protocell membrane — a key step toward a self-contained, cell-like structure in the origin of life.
A songbird population of 800 experiences 210 births, 130 deaths, 55 immigrants, and 20 emigrants over one year. What is the population size at year's end?
915 — ΔN = (210−130) + (55−20) = 80 + 35 = 115; 800 + 115 =
915.
Two toxic butterfly species that are unrelated to each other independently evolve nearly identical bold warning color patterns; both are genuinely unpalatable to predators.
Müllerian mimicry — two or more harmful species converge on a similar warning signal, reinforcing predator avoidance.
Prairie dogs dig extensive burrow networks that aerate soil and change water infiltration across a grassland, physically reshaping the habitat for many other species independent of any feeding relationship.
Ecosystem engineer — a species that physically modifies the habitat, creating structure other species depend on.
A wetland community has three species with proportions 0.5, 0.3, and 0.2. Calculate H'
1.03 — H′ = −[(0.5×−0.693)+(0.3×−1.204)+(0.2×−1.609)] = −(−0.347−0.361−0.322) = 1.03.
Which came first, the Cambrian explosion or the Permian-Triassic extinction, and what do the two events bracket together?
The Cambrian explosion came first — it marks the start of the Paleozoic, while the Permian-Triassic extinction marks its end; together they bracket the entire era.
True or false
Top-down control by predators causes prey population size to follow a constrained, oscillating (or S-shaped/logistic) curve.
True
Aphids continuously feed on the sap of a single host plant, weakening it gradually without killing it. If the aphid population becomes dense enough to eventually kill the plant after prolonged feeding, this interaction begins to resemble which other type of exploitation?
Parasitism — prolonged harm without immediate death is the hallmark of parasitism, which sustained herbivory starts to resemble here.
A predator makes up just 2% of a community's biomass, but its removal causes local extinction of 60% of other species. What ecological role does this describe?
Keystone species — an extreme mismatch between low biomass share and outsized community-wide impact.
Researchers study nutrient exchange between a river and its adjoining floodplain wetland as one linked system spanning several kilometers. Ecosystem or landscape ecology?
Landscape ecology — multiple connected ecosystems exchanging matter across a broader region, not one self-contained system.
A ribozyme both stores genetic information and catalyzes its own replication, while a nearby DNA molecule cannot self-replicate without protein enzymes. What does this contrast support?
The RNA World hypothesis — RNA's dual role as both genetic material and catalyst makes it a more plausible first self-replicator than DNA.
A K-selected species with a Type I survivorship curve is introduced to a habitat with abundant resources and no predators. Over several generations, individuals begin reproducing earlier, producing more offspring per litter, and investing less in parental care per offspring — even though K-selected traits like large body size are retained. What does this shift suggest about the relationship between r/K selection and environment, and how might the survivorship curve begin to change?
It shows r/K selection is a response to environmental conditions, not a fixed trait of a species — with resources abundant and mortality pressure removed, selection favors higher reproductive output even in an otherwise K-selected lineage. The survivorship curve would likely shift somewhat toward Type II or Type III at the youngest ages (more offspring, less individual investment), while probably retaining better-than-Type-III survival at older ages due to the species' underlying K-selected traits (size, longevity) — a partial, not total, shift.
Two lizard species could both technically forage anywhere from the forest floor to the high canopy, but one is regularly driven off the high branches by the more aggressive species and ends up foraging mostly on the ground. What does this show about their niches?
Their fundamental niche is broader than their realized niche, due to interspecific competition.
A drought cuts river nutrients, shrinking algae, which reduces herbivorous fish, which reduces predatory fish, which lets a suppressed competitor fish species increase. What control type is this, and where does it originate?
Bottom-up control — the disruption starts at the abiotic nutrient base and propagates upward through the food web.
Permafrost thaw alters methane release from tundra across northern Russia, Canada, and Alaska simultaneously. Landscape or biosphere ecology?
Biosphere ecology — spans multiple continents, exceeding a single connected regional landscape.
A eukaryotic cell has two organelles with their own circular DNA: one metabolizes oxygen, the other photosynthesizes. Name both organelles and their bacterial ancestor types.
Mitochondria (from aerobic alphaproteobacteria) and chloroplasts (from photosynthetic cyanobacteria) — acquired through separate endosymbiotic events.