Predator-Prey Population Graphs worksheet with a line graph illustrating the cyclical relationship between fox and rabbit populations over 40 years.

Problem Analysis:

The image contains a graph showing the population cycles of rabbits (prey) and foxes (predators) over time. The task involves analyzing the graph to answer specific questions about the populations and their interactions. Additionally, there is a section at the bottom asking for an explanation of how seasons affect animal populations in food chains.

Graph Description:

- X-axis: Time (years)
- Y-axis: Population (thousands)
- Blue Line: Rabbit population
- Green Line: Fox population

Step-by-Step Solution:

#### 1. What is happening to the rabbit population at 25 years?
- At 25 years, the rabbit population is decreasing. This can be observed by the downward slope of the blue line at that point.

#### 2. Why is the population doing this?
- The rabbit population is decreasing because the fox population (predators) is increasing. As the number of foxes rises, they prey on more rabbits, leading to a decline in the rabbit population.

#### 3. Show on the graph (with a ruler) where the maximum population of foxes was. What was it?
- Using a ruler, locate the peak of the green line (fox population). The maximum population of foxes occurs around 18 years.
- The population value at this peak is approximately 1.5 thousand.

#### 4. Show on the graph (with a ruler) where the maximum population of rabbits was. What was it?
- Using a ruler, locate the peak of the blue line (rabbit population). The maximum population of rabbits occurs around 10 years.
- The population value at this peak is approximately 4.5 thousand.

#### 5. At 20 years, was the fox population increasing or decreasing?
- At 20 years, the fox population is increasing. This can be seen from the upward slope of the green line at that point.

#### 6. Why was the fox population doing this?
- The fox population is increasing because the rabbit population (their prey) is still relatively high. With abundant food (rabbits), the fox population grows.

#### 7. How often in the 40 years are the populations the same?
- To determine when the populations are the same, look for points where the blue line (rabbits) intersects the green line (foxes).
- From the graph, the populations appear to be the same at approximately 5 years, 25 years, and 35 years.
- Therefore, the populations are the same three times in the 40-year period.

Explanation of Seasonal Effects on Populations:

#### Seasons Affecting Animal Populations in Food Chains:
1. Winter:
- Decrease in Prey Populations: In winter, many prey animals (e.g., rabbits) face harsh conditions such as scarcity of food, cold temperatures, and limited shelter. These factors lead to higher mortality rates among prey, causing their populations to decline.
- Impact on Predators: With fewer prey available, predators (e.g., foxes) also struggle to find food. This leads to a decrease in predator populations due to starvation or reduced reproductive success.

2. Spring:
- Increase in Prey Populations: As spring arrives, the environment becomes more favorable. Food sources (plants, insects) become abundant, and prey animals have better access to resources. This leads to increased survival and reproduction among prey, causing their populations to rise.
- Impact on Predators: With more prey available, predators have easier access to food. This improves their chances of survival and allows them to reproduce more successfully, leading to an increase in predator populations.

3. Knock-On Effects Through the Food Chain:
- The fluctuations in prey populations directly influence predator populations. When prey populations are high, predator populations tend to increase. Conversely, when prey populations are low, predator populations decline.
- This cyclical relationship is evident in the graph, where peaks in the rabbit population (prey) precede peaks in the fox population (predators), and vice versa.

Final Answers:

1. The rabbit population is decreasing at 25 years.
2. The rabbit population is decreasing because the fox population is increasing, leading to more predation.
3. The maximum population of foxes was approximately 1.5 thousand at around 18 years.
4. The maximum population of rabbits was approximately 4.5 thousand at around 10 years.
5. The fox population was increasing at 20 years.
6. The fox population was increasing because the rabbit population (their prey) was still relatively high, providing ample food.
7. The populations are the same three times in the 40 years (at approximately 5 years, 25 years, and 35 years).

Boxed Final Answer:

\[
\boxed{
\begin{array}{l}
1. \text{Decreasing} \\
2. \text{Due to increasing fox population (predation)} \\
3. \text{1.5 thousand at 18 years} \\
4. \text{4.5 thousand at 10 years} \\
5. \text{Increasing} \\
6. \text{Due to abundant rabbit prey} \\
7. \text{Three times (5 years, 25 years, 35 years)}
\end{array}
}
\]