bsci160 - exam 3 practice problems

What is the population of cholla cacti in Joshua tree national park?

• census (too difficult)

• subsample

• sample 9 plots that are 10 acres

  • total park size = 800,000 acres

• 14 cacti / 90 acres = 0.1555 cacti/acre

  • 0.1555 × 800,000 = ~124,444 cacti

Imagine that you tag and release 15 birds, and when you collect 15 birds later that year, only one of them is tagged. What is your estimate of the total population size?

Howard county has set up camera traps to estimate the suburban deer population. In the spring, they count a total of 100 adult deer and 50 fawns.

1. What is the per capita birth rate (b)?

Howard county has set up camera traps to estimate the suburban deer population. In the spring, they count a total of 100 adult deer and 50 fawns. During the summer they find 30 adult deer carcasses.

1. What is the per capita (d) death rate for adults?

2. What is the per capita growth rate of the population?

1. b = 50/100 = 0.5 d = 30/100 = 0.3

2. r = b - d → r = 0.5 - 0.3 = 0.2

True/False: A population cannot persist in an environment where per capita growth rate is negativ

TRUE! Population will decline to 0 unless somethings changes r

Which population of squirrels is growing faster?

• start by calculating △N (△ in pop size)

  • 55-50 = 5

  • 76-70 = 6

• need to adjust by population size

  • r= 5/50 = 0.1

  • r = 6/70 = 0.086

• population 1 is growing faster

Suppose there are 100 fish in a pond. The intrinsic rate of growth is -0.3. What is the population size 1 time step later?

• exponential growth

Suppose there are 100 fish in a pond. The intrinsic rate of growth is 0.5.

1. What is the population size 2 time steps later?

2. What is the population size 15 time steps later?

1. picture

2. N(t) = N₀ * (r +1)^t

• N₀ = starting pop size, t = # of time steps

  • N(t) = 100 * (1.50)¹⁵ = 43,789 fish

To determine snail population size, 340 snails were captured, tagged, and released. Later, 420 snails were captured. Of the 420 snails, 16 were already marked. What is the size of the snail population?

• Remember, you can quickly check your work

  • if we recapture (capture a second time) a lot of the individuals we marked, we have a smaller population size closer to our original sample size

150 marlins were captured, tagged, and returned to the deep ocean, where they live. Later, when 140 marlins were captured, 35 of the marlins had tags. What is the size of the marlin population?

• Remember, you can quickly check your work

  • if we recapture (capture a second time) a lot of the individuals we marked, we have a smaller population size closer to our original sample size

In a population of 100 birds, scientists found that in one year, 23 birds died, and 45 eggs were laid.

1. What are the per capita birth and death rates?

2. What is the per capita growth rate?

3. Is the population growing or shrinking?

4. Estimate the size of the population in two years

1. b = 45/100 = 0.45, d = 23/100 = 0.23

2. r = b – d = 0.45 – 0.23 = 0.22

3. Growing! r is positive

4. picture

In a zebra herd, one year there are an estimated 56 individuals, and the next year there are 43. 

1. What is the intrinsic growth rate of this zebra population? 

2. Is the population growing or shrinking?

1. picture

2. Shrinking! The r is negative!

Suppose there are 50 turtles in a pond.  The intrinsic rate of growth is 0.2.  What will the population size in 5 years be?