SBI4U · Unit 5 test review

Population Dynamics: Test Review

Everything for the Unit 5 test on one page: the key facts from all 5 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

Population Characteristics and Sampling

Density: $D = \frac{N}{A}$ (or $\frac{N}{V}$ in water); quadrat estimate $N \approx \frac{total count}{total area sampled} \times total area .$
Lincoln–Petersen mark–recapture: $N = \frac{M n}{m}$ , assuming a closed population, no lost marks, random mixing and equal catchability.
Dispersion: clumped (patchy resources, social groups), uniform (territoriality, competition, allelopathy), random (uniform resources, no interaction).
Survivorship: Type I dies mostly old (humans), Type II constant rate (songbirds), Type III dies mostly young (oysters, cod).
Fecundity is potential reproductive output; natality is the actual birth rate; mortality is the death rate.
Minimum viable population: the smallest size that can survive demographic, environmental and genetic chance events over a set time.

Population Growth Models

$Δ N = (B + I) - (D + E)$ ; per-capita growth rate $cgr = \frac{Δ N}{N}$ . Closed populations have no $I$ or $E$ .
Geometric (discrete breeding): $N_{t} = N_{0} λ^{t}$ with $λ = \frac{N _{t + 1}}{N _{t}}$ . Exponential (continuous): $N_{t} = N_{0} e^{r t}$ .
Doubling time: $t_{d} = \frac{ln 2}{r} \approx \frac{70}{growth rate in %}$ (rule of 70).
Logistic: $\frac{d N}{d t} = r_{ma x} N \frac{K - N}{K}$ ; growth is fastest at $N = \frac{K}{2}$ and zero at $N = K$ .
Density-dependent factors (competition, predation, disease, waste) regulate near $K$ ; density-independent factors (weather, fire, pollution) do not.
r-selected: many offspring, little care, unstable habitats. K-selected: few offspring, much care, stable habitats near $K$ .

Species Interactions and Population Cycles

Competition is $- / -$ ; predation and parasitism are $+ / -$ ; mutualism is $+ / +$ ; commensalism is $+ /0$ .
Competitive exclusion principle (Gause): two species cannot coexist indefinitely on exactly the same limited resources; resource partitioning (MacArthur's warblers) allows coexistence.
In predator–prey cycles the predator peak lags behind the prey peak because predators need time to reproduce in response to abundant prey.
Batesian mimicry: a harmless species copies a harmful one. Müllerian mimicry: harmful species resemble each other.
A keystone species (sea otter) has an effect out of proportion to its numbers; removing it triggers a trophic cascade.

Human Population Growth and the Ecological Footprint

Demographic transition: death rate falls first (stage 2, rapid growth), birth rate follows (stage 3), then both are low (stage 4); stage 5 is natural decrease.
Pyramids: expanding (wide base, rapid growth), stable (straight sides, little growth), contracting (narrow base, decline).
About 10% of energy passes to the next trophic level, so eating plants directly feeds roughly ten times as many people as feeding the plants to livestock first.
Ecological footprint is measured in global hectares; overshoot occurs when footprint exceeds biocapacity.
Doubling time $\approx \frac{70}{growth rate in %}$ ; world growth fell from about 2% per year (late 1960s) to under 1% per year.

Environmental Contaminants and Human Health

Endocrine disruptors (EE2, BPA, phthalates, PFAS) mimic, block or interfere with hormones and can act at nanogram-per-litre levels.
Experimental Lakes Area, Lake 260: about 5–6 ng/L of EE2 feminized male fathead minnows and collapsed the population; it recovered after additions stopped.
Bioaccumulation: build-up within one organism. Biomagnification: concentration rises at each trophic level, so top predators carry the most.
Biomagnifying substances are persistent, retained in fat or bound to protein, and slowly excreted. Biomagnification factor $= \frac{C _{predator}}{C _{food}}$ .
Grassy Narrows: mercury released at Dryden (1962–1970) became methylmercury, biomagnified in fish and caused Minamata disease symptoms.
Dose-response: threshold, NOAEL and LD₅₀; tolerable intakes are set by dividing the NOAEL by safety factors.

Where marks get lost

Mixing up the letters in Lincoln–Petersen. $M$ and $n$ go on top and the recaptured marked count $m$ goes on the bottom; writing $\frac{M m}{n}$ gives a number smaller than the number you marked, which is impossible. (Population Characteristics and Sampling)
Dividing the quadrat total by the number of quadrats instead of the total area sampled. Five 0.25 m² quadrats cover 1.25 m², not 5 m², so the density is the count divided by 1.25 m². (Population Characteristics and Sampling)
Confusing density with dispersion. Two populations can have the same density (individuals per m²) but very different spacing (clumped versus uniform). (Population Characteristics and Sampling)
Treating fecundity and natality as the same thing. Fecundity is the maximum possible output; natality is the actual birth rate, which is usually far lower. (Population Characteristics and Sampling)
Reading a straight survivorship line as a constant number dying each year. On the usual logarithmic axis, a straight line (Type II) means a constant proportion dies each interval. (Population Characteristics and Sampling)
Using immigration and emigration for a closed population. If the question says the population is closed (an island, a sealed flask), $Δ N = B - D$ only. (Population Growth Models)
Putting a percentage into $e^{r t}$ . A 5% growth rate is $r = 0.05$ ; $e^{5 t}$ would predict absurd growth. (Population Growth Models)
Using the decimal form in the rule of 70. At 5% per year, $t_{d} \approx \frac{70}{5} = 14$ years, not $\frac{70}{0.05} = 1400$ years. (Population Growth Models)
Saying a logistic population grows fastest near carrying capacity. At $N = K$ growth is zero; the maximum rate is at $N = \frac{K}{2}$ . (Population Growth Models)
Calling a factor density-dependent just because it kills many individuals. A severe ice storm may kill thousands of birds, but if it kills the same proportion at any density it is density-independent. (Population Growth Models)
Drawing predator and prey peaks at the same time. The predator peak lags behind the prey peak because predators respond through reproduction, which takes time. (Species Interactions and Population Cycles)
Assuming predators alone drive the hare–lynx cycle. Food supply matters too; the Kluane experiments showed the cycle depends on predation and food acting together. (Species Interactions and Population Cycles)
Swapping Batesian and Müllerian mimicry. Batesian: a harmless mimic of a harmful model. Müllerian: several harmful species share one warning pattern. (Species Interactions and Population Cycles)
Thinking competitive exclusion means competing species can never live together. It applies only to species with identical niches; partitioning resources lets competitors coexist. (Species Interactions and Population Cycles)
Calling any close relationship mutualism. Check who benefits: if one species is unaffected it is commensalism; if one is harmed it is parasitism. (Species Interactions and Population Cycles)
Saying stage 2 growth happens because birth rates rise. Birth rates stay about the same; growth accelerates because death rates fall. (Human Population Growth and the Ecological Footprint)
Assuming a population stops growing the moment birth rates reach replacement level. A wide-based pyramid keeps growing for decades because of population momentum. (Human Population Growth and the Ecological Footprint)
Reading a 73% Living Planet Index decline as 73% of all animals lost. It is the average change across monitored vertebrate populations. (Human Population Growth and the Ecological Footprint)
Thinking the energy not passed up a food chain is destroyed. It is converted to heat through respiration or left in uneaten and undigested material; energy is conserved but not available to the next level. (Human Population Growth and the Ecological Footprint)
Comparing footprints in ordinary hectares. Footprints use global hectares so that land and water of different productivity can be added and compared with biocapacity. (Human Population Growth and the Ecological Footprint)
Using bioaccumulation and biomagnification as synonyms. Bioaccumulation happens within one organism over time; biomagnification is the increase from one trophic level to the next. (Environmental Contaminants and Human Health)
Assuming a chemical is safe because its concentration in the water is tiny. Biomagnification can multiply it millions of times by the top of the food chain, and endocrine disruptors act at nanogram levels. (Environmental Contaminants and Human Health)
Thinking every toxic metal biomagnifies. Methylmercury does strongly; lead bioaccumulates in bone but does not magnify much through food webs. (Environmental Contaminants and Human Health)
Treating the LD₅₀ as a safe dose. It is the dose that kills half the test animals; safe intakes are set far lower, from the NOAEL divided by safety factors. (Environmental Contaminants and Human Health)
Describing the Grassy Narrows case as only a health problem. The contamination also destroyed a fishery, jobs and a traditional food source, which is why social and economic impacts are part of the case. (Environmental Contaminants and Human Health)

Practice test

25 questions from across the unit. Each one shows the lesson it comes from.

Population Characteristics and Sampling
1
Northern gannets nest on cliff ledges with each nest just beyond pecking distance of its neighbours. What dispersion pattern is this, and what causes it?
Population Characteristics and Sampling
2
An aerial survey counts 240 white-tailed deer in a 12 km² conservation area. What is the population density?
deer/km²
Population Characteristics and Sampling
3
Which organism is most likely to show a Type III survivorship curve?
Population Characteristics and Sampling
4
Put the steps of a mark–recapture study in order.
1. 1Calculate N = Mn/m
2. 2Capture a second sample and count the total (n) and the marked animals (m)
3. 3Release the marked animals and allow them to mix with the population
4. 4Capture a first sample of animals
5. 5Mark each animal harmlessly and record the number marked (M)
Population Characteristics and Sampling
5
What is the term for the smallest population size that is likely to persist for a set period despite random genetic, demographic and environmental events? (Give the full term or its abbreviation.)
Population Growth Models
6
An open population of 800 beavers has 120 births, 70 deaths, 15 immigrants and 25 emigrants in one year. What is the per-capita growth rate, as a percentage? Give one decimal place.
%
Population Growth Models
7
A logistic population has $r_{ma x} = 0.80$ per year and $K = 500$ . What is its growth rate $\frac{d N}{d t}$ when $N = 100$ ?
individuals/year
Population Growth Models
8
In logistic growth, at what population size does the population add the most individuals per unit time?
Population Growth Models
9
Match each growth pattern with its description.
Exponential (J-shaped)
Sigmoid (S-shaped)
Sinusoidal
Overshoot and dieback
Population Growth Models
10
What term describes the maximum population size that a particular environment can sustain indefinitely?
Species Interactions and Population Cycles
11
A harmless hoverfly has yellow and black bands like a stinging wasp, and birds avoid it. This is an example of
Species Interactions and Population Cycles
12
Name the principle stating that two species competing for exactly the same limited resources cannot coexist indefinitely.
Species Interactions and Population Cycles
13
Five warbler species feed on insects in the same spruce trees but in different zones of the tree. MacArthur's explanation for their coexistence was
Species Interactions and Population Cycles
14
A fur-record data set shows snowshoe hare population peaks in 1857, 1866, 1876 and 1886. What is the average length of the cycle? Give one decimal place.
years
Species Interactions and Population Cycles
15
What is the term for a symbiotic relationship in which one species benefits and the other is neither helped nor harmed?
Human Population Growth and the Ecological Footprint
16
In which stage of the demographic transition is the death rate falling rapidly while the birth rate remains high?
Human Population Growth and the Ecological Footprint
17
A population pyramid has a very wide base that narrows steadily toward the top. What does this predict?
Human Population Growth and the Ecological Footprint
18
Put the stages of the demographic transition in order.
1. 1Birth rate below death rate; natural decrease
2. 2Low birth rate and low death rate; stable population
3. 3Birth rate falls; growth slows
4. 4High birth rate and high death rate; slow growth
5. 5Death rate falls while birth rate stays high; rapid growth
Human Population Growth and the Ecological Footprint
19
What term describes the capacity of ecosystems to regenerate resources and absorb wastes, measured in global hectares?
Human Population Growth and the Ecological Footprint
20
What term describes designing products so that they fail or become outdated quickly, encouraging replacement?
Environmental Contaminants and Human Health
21
Order these organisms from the lowest to the highest expected concentration of methylmercury in a northern Ontario lake.
1. 1People who eat walleye as a staple food
2. 2Walleye
3. 3Small fish such as minnows
4. 4Algae (phytoplankton)
5. 5Zooplankton
Environmental Contaminants and Human Health
22
A tap-water sample contains 0.012 mg/L of lead. Canada's maximum acceptable concentration is 0.005 mg/L. How many times the limit is this? (1 decimal place)
times
Environmental Contaminants and Human Health
23
Which property makes a contaminant most likely to biomagnify?
Environmental Contaminants and Human Health
24
What happened to the fathead minnow population in Lake 260 after the additions of synthetic estrogen stopped?
Environmental Contaminants and Human Health
25
Bacteria in river sediments convert inorganic mercury into what more dangerous form that biomagnifies in fish?

Endless drill

Fresh numbers every time, for the calculation questions in this unit.

Endless drillnew numbers every time

Generating a problem…