Week 9 - iClicker & TPCS Questions

Clicker Question • Some time after the Eurasian species cheatgrass first invades a new prairie in the western U.S., its population enters what is known as a "naturalization" phase. Increased plant density and resource utilization mean that the population enters a period of *logistic*, rather than geometric, growth. Assuming a value of λ of 1.6 as before and a carrying capacity of 2000, what is the *per capita growth rate* when the population is at 1200 plants? r = ln(λ) dN/dt = rN (1-N/K) per capita growth rate--->dN/dt N • (A) 0.19 • (B) 0.25 • (C) 0.32 • (D) 0.50

(A) 0.19

Clicker Question Cheatgrass is an annual grass plant native to Eurasia that was unintentionally introduced into the Great Basin area of Utah and Wyoming. During the colonization phase of cheatgrass invasions, this exotic species often exhibits *geometric growth.* If there are *150 cheatgrass plants in a single plot of land at year 6* and the population is growing with a finite rate of increase *(λ) of 1.6,* approximately *how many plants were in the initial invasion at time zero?* • (A) 4 • (B) 9 • (C) 12 • (D) 25 N(t+1) = Ntλ Nt = N0λ^t

(B) 9?

CLICKER Question When N = (1/2)K under logistic growth: (A) the population size has reached its equilibrium (B) the ratio of births to deaths has become constant over time (C) the number of births equals the number of deaths (D) the population is increasing in size at its maximum rate (E) the population is growing the slowest

(D) the population is increasing in size at its maximum rate

Clickers! Age structure pyramids • Broad base (many young people) • Is this growing, declining or stable? - i.e., what is going to happen in 20 years? A. Growing B. Declining C. Stable

A. Growing

Clickers! What kind of life history do humans have? A. Iteroparous and slow B. Semelprous and slow C. Iteroparous and fast D. Semelparous and fast

A. Iteroparous and slow

Which of the following is *not* an assumption of the geometric growth equation? A. Reproduction can (and does) occur continuously. B. Population growth is discrete. C. The growth rate is constant. D. Age structure of the population can be ignored

A. Reproduction can (and does) occur continuously.

T-P-C-S Can natural selection shape life history traits (fecundity, parity, time to sexual maturity, parental investment, parity, longevity)? A. Yes B. No C. Unsure Why or why not? Think about the three assumptions for natural selection to occur

A. Yes By tracking genotype frequencies with microsatellite DNA markers over the subsequent three years (up to three generations, ≈5,000 genotyped plants), *we show rapid and consistent *evolution* of two heritable plant life-history traits (shorter life span and later flowering time).*

Clickers! Age structure pyramids • Narrow base and wide middle. • Is this population A. Growing B. Declining C. Stable

B. Declining

Clickers! Age structure pyramids • Straight sides. • Is this population A. Growing B. Declining C. Stable

C. Stable

Bacteria are capable of rapid growth under ideal conditions Assume: 1. Staphylococcus grow exponentially 2. r = 1.386 h^-1 3. Initial inoculation = 2 cells *How many cells will there be after 12 hours?* N(t) = N(0)ert A. ~ 90 cells B. ~ 96 cells C. ~ 451,000 cells D. ~ 33,400,000 cells E. ~ 8.57 x 1016 cells

D. ~ 33,400,000 cells

T-P-S • Think about a 2 populations: - one is mostly composed of old people (>50 yrs) - one is mostly composed of young people (<50 yrs) • Do you think that they will grow at different rates? • Why or why not?

These two populations differ in their *Age Distribution*: the distribution of individuals among age classes within a population