Biology: Ecology: Population Growth and Carrying Capacity Worksheet

Question 1

Define population growth and explain why it is important in ecology.

Accepted Answer

Population growth is the change in the number of individuals in a population over time. It is important in ecology because it helps scientists predict resource use, competition, disease spread, species survival, and ecosystem stability.

Question 2

A rabbit population has 120 individuals at the start of spring. During spring, 45 rabbits are born, 18 die, 6 move into the area, and 3 leave the area. What is the population size at the end of spring?

Accepted Answer

The population size is 150 rabbits. The calculation is 120 + 45 - 18 + 6 - 3 = 150.

Question 3

In one year, a population of 500 fish increases to 575 fish. Calculate the percent growth for that year.

Accepted Answer

The population increased by 75 fish, so the percent growth is 75 divided by 500 times 100, which equals 15%.

Question 4

Compare exponential growth and logistic growth. Include the typical shape of each graph and what happens to the population over time.

Accepted Answer

Exponential growth forms a J-shaped curve because the population increases faster and faster when resources are unlimited. Logistic growth forms an S-shaped curve because growth slows as resources become limited and the population approaches carrying capacity.

Question 5

A lake can support about 2,000 adult trout over many years. What term describes this maximum long-term population size, and what does it mean?

Accepted Answer

The term is carrying capacity. It means the largest population size the lake can support over time without using resources faster than they are replaced.

Question 6

The table shows a deer population over time: Year 1: 80, Year 2: 150, Year 3: 275, Year 4: 430, Year 5: 560, Year 6: 615, Year 7: 635, Year 8: 630. Estimate the carrying capacity and explain your reasoning.

Accepted Answer

The carrying capacity is about 630 deer. The population grows quickly at first but then levels off around 630 to 635 deer, which suggests that the environment can support about that many deer.

Question 7

Classify each limiting factor as density-dependent or density-independent: competition for food, drought, disease spread, wildfire.

Accepted Answer

Competition for food and disease spread are density-dependent because their effects usually increase as population density increases. Drought and wildfire are density-independent because they can affect populations regardless of population density.

Question 8

A population of bacteria grows according to the logistic model growth rate = rN(1 - N/K). If r = 0.4, N = 200, and K = 1,000, what is the growth rate?

Accepted Answer

The growth rate is 64 bacteria per time unit. The calculation is 0.4 times 200 times (1 - 200/1000), which equals 80 times 0.8, or 64.

Question 9

Using the logistic growth model, explain why a population grows more slowly when N is close to K.

Accepted Answer

A population grows more slowly when N is close to K because resources such as food, space, and water become limited. In the logistic model, the factor (1 - N/K) becomes very small, which reduces the growth rate.

Question 10

An island has abundant nesting sites and food after a storm removes many competitors. A bird population introduced to the island increases from 10 birds to 20, then 40, then 80 over equal time intervals. What type of growth is shown, and why?

Accepted Answer

The population shows exponential growth because it doubles during each equal time interval. This pattern suggests that resources are abundant and limiting factors are not yet strongly slowing growth.

Question 11

Describe what can happen when a population overshoots its carrying capacity.

Accepted Answer

When a population overshoots carrying capacity, it may use resources faster than they can recover. This can lead to increased competition, starvation, disease, lower birth rates, higher death rates, and a population crash.

Question 12

A graph of a yeast population shows a rapid increase for several hours, then a plateau, then a decline. Explain one likely reason for each part of the pattern.

Accepted Answer

The rapid increase likely occurs because yeast have plenty of sugar and space. The plateau likely occurs because resources become limited and the population reaches carrying capacity. The decline likely occurs because waste builds up or food runs out, causing more yeast to die.

Question 13

How can human activities increase or decrease the carrying capacity of an environment for a species? Give one example of each.

Accepted Answer

Human activities can increase carrying capacity by adding resources, such as planting native vegetation that provides food and shelter for birds. Human activities can decrease carrying capacity by destroying habitat, polluting water, or removing food sources, such as clearing wetlands used by amphibians.

Question 14

Scientists capture and mark 40 turtles in a pond. Later, they capture 50 turtles and find that 10 are marked. Use mark-recapture to estimate the pond's turtle population.

Accepted Answer

The estimated turtle population is 200 turtles. Using the formula total population = marked first sample times total second sample divided by marked recaptured, the estimate is 40 times 50 divided by 10, which equals 200.

Question 15

A wildlife manager sees that a grassland's bison population has been above carrying capacity for two years. The grass is overgrazed, birth rates are falling, and young bison survival is low. Recommend one management action and explain how it could help.

Accepted Answer

One management action is to relocate some bison to another suitable habitat. This could reduce population density, lower competition for grass, allow the grassland to recover, and help the remaining bison have better survival and reproduction.

Biology: Ecology: Population Growth and Carrying Capacity

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