A biologist tags 50 fish in a pond and releases them. A week later she catches 60 fish, and 10 of them carry tags. Using the mark-recapture method, what is the estimated number of fish in the pond?
300
✓
120
600
3,000
Correct Answer
300
The mark-recapture estimate is the number marked in the first catch times the total in the second catch, divided by the number of marked individuals recaptured: 50 x 60 / 10 = 300. 120 comes from simply adding 50, 60 and 10. 600 comes from multiplying the second catch by the recaptures instead of dividing. 3,000 is 50 x 60 without dividing by the 10 recaptured fish.
Category: Population Measurement
Question 2
Sage plants release chemicals that suppress the growth of nearby plants, so individual sage bushes end up evenly spaced. Which dispersion pattern does this produce?
Clumped
Uniform
✓
Random
Aggregated
Correct Answer
Uniform
A uniform dispersion pattern has individuals spaced at fairly regular distances, often because of chemical inhibition or territorial behavior. Clumped dispersion places individuals in groups, as in herds or schools. Random dispersion occurs when individuals settle unpredictably, as with wind-blown dandelion seeds. Aggregated is another name for clumped, the opposite of even spacing.
Category: Population Measurement
Question 3
Which organism best fits a Type III survivorship curve, with very heavy losses early in life and higher survival among the few that make it past that stage?
Human
Elephant
Oyster
✓
Chimpanzee
Correct Answer
Oyster
Oysters release enormous numbers of eggs and larvae that get no parental care, so most die very young, which is the Type III pattern. Humans have a Type I curve, with most deaths in old age. Elephants also follow a Type I pattern, raising few offspring with heavy care. Chimpanzees are large mammals with few, well-cared-for young and also fit a Type I curve.
Category: Demography
Question 4
In a life table, 500 individuals are alive at the start of an age interval and 25 of them die during that interval. What is the mortality rate per thousand for that interval?
5
20
475
50
✓
Correct Answer
50
Mortality per thousand is the number dying divided by the number alive at the start of the interval, times 1,000: 25 / 500 x 1,000 = 50. 5 is the rate per hundred, not per thousand. 20 comes from dividing 500 by 25 instead of 25 by 500. 475 is the number of survivors, not a rate.
Category: Demography
Question 5
A population of 2,000 has a per capita growth rate, r, of 0.03 per year. Using the exponential growth model (growth = rN), how many individuals are added in one year?
60
✓
6
600
2,060
Correct Answer
60
In the exponential model, the number added per unit time is r times N: 0.03 x 2,000 = 60. 6 results from misplacing the decimal point by a factor of ten. 600 results from treating r as 0.3. 2,060 is the population size after one year, not the number added.
Category: Growth Models
Question 6
A population has r = 0.1 per year, N = 400 and a carrying capacity K = 1,000. Using the logistic model, growth = rN(K - N)/K, how many individuals are added this year?
40
24
✓
16
60
Correct Answer
24
The logistic model multiplies rN by the fraction of carrying capacity still unused: 0.1 x 400 x (600 / 1,000) = 24. 40 is the exponential answer, rN, which ignores the limit set by K. 16 comes from multiplying by N/K (0.4) instead of (K - N)/K (0.6). 60 comes from multiplying r by K - N and leaving out N.
Category: Growth Models
Question 7
According to the logistic growth model, what happens to a population's growth once its size reaches carrying capacity?
Growth reaches its maximum
The population crashes to extinction
Growth drops to zero
✓
Growth becomes exponential
Correct Answer
Growth drops to zero
When N equals K, the term (K - N)/K equals zero, so the model predicts no further net growth and the population levels off. Growth is fastest at intermediate sizes, not at K. The model predicts a plateau, not a crash to extinction. Exponential growth happens at small sizes, when the population is far below its limit.
Category: Growth Models
Question 8
Which factor limits population growth in a density-dependent way?
A wildfire
A sudden hard freeze
An oil spill
Infectious disease
✓
Correct Answer
Infectious disease
Infectious disease spreads more easily when individuals are crowded together, so its effect grows as density rises, making it density dependent. A wildfire kills individuals regardless of how crowded they are. A sudden hard freeze is weather, which acts independently of density. An oil spill is pollution, which also harms individuals whether the population is dense or sparse.
Category: Population Regulation
Question 9
Which set of traits is typical of a K-selected species such as the elephant?
Few large offspring with long parental care
✓
Many small offspring with little parental care
Early maturity and a very short life span
Rapid growth in unstable, changing habitats
Correct Answer
Few large offspring with long parental care
K-selected species live in stable environments near carrying capacity and invest heavily in a small number of large offspring. Many small offspring with little parental care describes r-selected species such as dandelions. Early maturity and a very short life span are r-selected traits. Rapid growth in unstable, changing habitats is also characteristic of r-selected species.
Category: Population Regulation
Question 10
A country's age structure diagram has a very wide base that narrows quickly toward the top. What does this shape indicate about the population?
It is stable in size
It is growing rapidly
✓
It is growing slowly
It is shrinking quickly
Correct Answer
It is growing rapidly
A wide base means a large share of the population is young and will soon reach reproductive age, which signals rapid growth; this shape is common in less developed countries. A stable population has similar numbers across younger age groups, giving a more column-like shape. Slow growth gives a shape whose numbers decrease steadily with age, like that of the United States. A shrinking population has a narrower base than middle layers.
Category: Human Population
Question 11
Which change best explains the sharp acceleration in human population growth during the industrial era?
Rising birth rates
Increased emigration
Falling death rates
✓
Longer generation times
Correct Answer
Falling death rates
Public health, sanitation, medicine and a more reliable food supply lowered death rates, so births outpaced deaths by a widening margin. Birth rates did not rise to cause the surge; in many countries they later fell. Emigration moves people between regions but does not add to the global total. Longer generation times would slow growth, not speed it up.
Category: Human Population
Question 12
Records of snowshoe hare and lynx populations in Canada show linked cycles. How do lynx numbers change relative to hare numbers?
Lynx peaks come a year or two before hare peaks
Lynx numbers stay constant as hares cycle
Lynx peaks occur only when hares are at their lowest
Lynx peaks lag a year or two behind hare peaks
✓
Correct Answer
Lynx peaks lag a year or two behind hare peaks
As hares become plentiful, lynx have more food and their numbers rise, but this response trails the hare increase by one to two years. Lynx cannot peak first, because their growth depends on abundant prey. Lynx numbers do not stay constant; they cycle along with hares. Lynx do not peak at the hare low point; they decline once their prey becomes scarce.
Category: Species Interactions
Question 13
Several species of foul-tasting Heliconius butterflies share the same bright wing pattern, so predators that learn to avoid one avoid them all. What is this called?
Müllerian mimicry
✓
Batesian mimicry
Camouflage
Competitive exclusion
Correct Answer
Müllerian mimicry
In Müllerian mimicry, several defended species share one warning pattern, so predators learn the lesson faster and every species benefits. Batesian mimicry involves a harmless species copying a harmful one. Camouflage helps an organism blend in, while these butterflies are conspicuous. Competitive exclusion describes competition for resources, not appearance.
Category: Species Interactions
Question 14
When Paramecium aurelia and Paramecium caudatum are grown together on the same limited food supply, P. caudatum eventually dies out. Which idea does this demonstrate?
Logistic growth model
Competitive exclusion principle
✓
Keystone species concept
Resource partitioning
Correct Answer
Competitive exclusion principle
The competitive exclusion principle states that two species competing for exactly the same limited resources cannot coexist indefinitely; the better competitor eliminates the other. The logistic growth model describes how a single population levels off at carrying capacity. The keystone species concept concerns one species with an outsized effect on community structure. Resource partitioning is the opposite outcome, in which species divide resources and coexist.
Category: Species Interactions
Question 15
A bird builds its nest in the branches of a large tree. The bird gains shelter, and the tree is neither helped nor harmed. What kind of relationship is this?
Mutualism
Parasitism
Commensalism
✓
Predation
Correct Answer
Commensalism
Commensalism is a relationship in which one species benefits and the other is unaffected, as with a bird nesting in a tree. In mutualism, both species benefit. In parasitism, one species benefits at the host's expense. Predation involves one organism killing and eating another.
Category: Species Interactions
Question 16
Kelp in California's coastal forests is an abundant producer whose tall fronds create the physical habitat for many other species. What role does kelp play in this community?
Keystone species
Invasive species
Pioneer species
Foundation species
✓
Correct Answer
Foundation species
A foundation species is usually an abundant producer that forms the structure and base of its community, as kelp and reef-building corals do. A keystone species has an influence out of proportion to its abundance, like the sea star Pisaster. An invasive species is a nonnative organism that disrupts the community it enters. A pioneer species is among the first to colonize bare or disturbed ground.
Category: Community Structure
Question 17
Two forests each contain 10 tree species. In the first, one species makes up 90 percent of the trees; in the second, all 10 species are about equally common. In what do the forests differ?
Relative abundance
✓
Species richness
Carrying capacity
Dispersion pattern
Correct Answer
Relative abundance
Relative abundance describes how individuals are distributed among the species present, and here it is very uneven in the first forest and even in the second. Species richness is the number of species, which is 10 in both forests. Carrying capacity is the maximum population size a habitat can support, which is not described. Dispersion pattern refers to the spacing of individuals in one population, not the mix of species.
Category: Community Structure
Question 18
Which event begins primary succession?
A forest regrowing after a wildfire
A new island forming from cooled lava
✓
An abandoned farm field returning to forest
A meadow recovering after a flood
Correct Answer
A new island forming from cooled lava
Primary succession begins on newly formed or exposed land that has no soil, such as fresh lava rock, so pioneers must build soil from scratch. A forest regrowing after a wildfire is secondary succession, because soil remains. An abandoned farm field also keeps its soil, so its recovery is secondary succession. A flooded meadow retains its soil as well, making its recovery secondary succession.
Category: Community Structure
Question 19
Which statement describes an invasive species such as the zebra mussel in North America?
A native species with an outsized effect on community structure
The first species to colonize newly exposed bare rock
A nonnative species that spreads and disrupts its new community
✓
An abundant native producer that forms a habitat's physical structure
Correct Answer
A nonnative species that spreads and disrupts its new community
Invasive species are organisms introduced outside their native range that spread and alter the communities they enter, as zebra mussels have done in North American waters. A native species with an outsized effect on community structure is a keystone species. The first species to colonize bare rock is a pioneer species. An abundant producer that forms habitat structure is a foundation species.
Category: Community Structure
Question 20
Which sampling method is best suited to estimating the population of a small, mobile mammal such as a field mouse?
Quadrat sampling
Counting every individual
Life table analysis
Mark and recapture
✓
Correct Answer
Mark and recapture
Mark and recapture works well for animals that move around, because marked individuals mix back into the population before the second sample. Quadrat sampling suits plants and slow-moving organisms that stay in place within a frame. Counting every individual is rarely practical for small, hidden, mobile animals. Life table analysis tracks survival by age; it does not estimate population size.
Category: Population Measurement