Science: Population Ecology and Growth Models
Exploring how populations change over time
Science: Population Ecology and Growth Models
Exploring how populations change over time
Biology - Grade 9-12
- 1
Define population size and population density. Then explain how they are different.
One term is a total count, and the other includes space.
Population size is the total number of individuals in a population. Population density is the number of individuals living in a certain amount of space. They are different because size counts all individuals, while density describes how crowded the population is in an area or volume. - 2
A rabbit population has abundant food and no major predators. It starts with 40 rabbits and grows rapidly each month. Identify the type of growth model that best fits this situation and explain why.
This situation best fits exponential growth. Exponential growth happens when resources are plentiful and the population grows at an increasingly rapid rate because more individuals are reproducing over time. - 3
Describe carrying capacity in an ecosystem. Give one example of a factor that can affect it.
Think about the maximum number of organisms a habitat can support.
Carrying capacity is the largest population size that an environment can support over time without being damaged. One factor that can affect carrying capacity is food availability, because a habitat can only support as many organisms as its resources allow. - 4
A deer population grows quickly for several years, then slows and levels off near 500 deer. What type of growth curve does this describe, and what does the leveling off mean?
This describes logistic growth, which forms an S-shaped curve. The leveling off means the population is reaching carrying capacity, where limiting factors such as food, space, or disease prevent further long-term growth. - 5
List two density-dependent limiting factors and explain how each can slow population growth.
These factors become stronger as a population gets more crowded.
Two density-dependent limiting factors are disease and competition. Disease can spread more easily in crowded populations, increasing death rates. Competition increases when many individuals need the same food, water, or space, which can reduce survival and reproduction. - 6
List two density-independent limiting factors and explain how each can affect a population.
Two density-independent limiting factors are drought and wildfire. Drought can reduce water and food availability for a population regardless of its size. Wildfire can kill organisms and destroy habitat whether the population is large or small. - 7
A bacterial culture doubles every hour. If it begins with 200 cells, how many cells will there be after 3 hours? State the pattern you used.
Multiply by 2 once for each hour.
There will be 1,600 cells after 3 hours. The population doubles each hour, so the pattern is 200, 400, 800, and 1,600. - 8
In a fish population, natality is 120 fish per year, mortality is 80 fish per year, immigration is 25 fish per year, and emigration is 15 fish per year. Calculate the net annual population change.
The net annual population change is an increase of 50 fish per year. This is found by adding natality and immigration, then subtracting mortality and emigration: 120 + 25 - 80 - 15 = 50. - 9
Explain why populations do not usually grow exponentially for long periods in natural ecosystems.
Think about what happens when resources start running out.
Populations do not usually grow exponentially for long periods because resources become limited. As population size increases, competition, disease, predation, and lack of space or food begin to slow growth and keep the population near carrying capacity. - 10
A graph shows a population crashing after overshooting its carrying capacity. Explain what overshoot means and give one possible cause of the crash.
Overshoot means the population temporarily grows beyond the carrying capacity of its environment. One possible cause of the crash is resource depletion, because the population may use food or water faster than the environment can replace it. - 11
Compare r-selected species and K-selected species by describing one characteristic of each.
One strategy focuses on many offspring, and the other focuses on fewer offspring with more investment.
R-selected species usually produce many offspring, reproduce quickly, and provide little parental care. K-selected species usually produce fewer offspring, reproduce more slowly, and invest more energy in parental care and survival. - 12
A scientist introduces a new predator into an area to control an herbivore population that has grown too large. Predict one likely effect on the herbivore population and one possible ecological risk.
One likely effect is that the herbivore population will decrease because more individuals will be eaten. One possible ecological risk is that the introduced predator could also affect non-target species or disrupt the food web in ways that were not intended.