Guided Practice
Learning Objectives
In this guided practice lesson, you will:
- Apply population dynamics concepts to sample problems
- Practice analyzing ecological data and graphs
- Work through biodiversity scenarios
- Develop skills for interpreting ecosystem relationships
Practice Quiz
Apply your ecology knowledge to these questions. Click to reveal each answer.
Question 1: A rabbit population has 500 individuals. The birth rate is 0.3 per year and death rate is 0.1 per year. What is the population growth rate and predicted population after one year?
Answer: Growth rate = 0.3 - 0.1 = 0.2 (or 20%). Population after one year = 500 + (500 x 0.2) = 600 rabbits.
Explanation: Population growth rate = birth rate - death rate. Multiply by current population to find the change.
Question 2: What is the difference between exponential and logistic growth? Which is more realistic for most populations?
Answer: Exponential growth is unlimited, J-shaped curve. Logistic growth levels off at carrying capacity, S-shaped curve. Logistic is more realistic because resources are limited.
Explanation: Exponential growth can only occur temporarily when resources are abundant. Eventually, limiting factors slow growth.
Question 3: In a food web, what happens to energy as it moves from producers to primary consumers to secondary consumers?
Answer: Energy decreases at each level. Only about 10% transfers to the next level; 90% is lost as heat through metabolism.
Explanation: This is the 10% rule. It explains why food chains rarely have more than 4-5 levels and why there are fewer top predators.
Question 4: How do keystone species affect biodiversity in an ecosystem?
Answer: Keystone species have disproportionate effects on their ecosystem relative to their abundance. Their removal causes dramatic changes in community structure and biodiversity.
Explanation: Example: Sea otters eat sea urchins that eat kelp. Without otters, urchins overpopulate and destroy kelp forests, eliminating habitat for many species.
Question 5: Explain competitive exclusion and how species avoid it through resource partitioning.
Answer: Competitive exclusion: Two species competing for identical resources cannot coexist; one will outcompete the other. Resource partitioning: Species divide resources (time, space, food type) to reduce competition.
Explanation: Example: Warblers feeding in different parts of the same tree - one species at the top, another in the middle, another at the bottom.
Question 6: A graph shows a predator population peak following a prey population peak. Explain this pattern.
Answer: When prey is abundant, predators have more food and their population increases. As predators increase, prey decreases. Then predators decline due to less food. This creates cycling.
Explanation: The classic example is the lynx-hare cycle in Canada. There's a time lag because it takes time for populations to respond.
Question 7: What is the difference between a food chain and a food web? Why are food webs more accurate?
Answer: A food chain shows one linear path of energy. A food web shows all interconnected feeding relationships. Food webs are more accurate because most organisms have multiple food sources.
Explanation: A bear doesn't just eat salmon - it also eats berries, insects, and other foods. Food webs capture this complexity.
Question 8: Why do invasive species often outcompete native species?
Answer: Invasive species often lack natural predators, diseases, and competitors in their new environment. They may reproduce faster or use resources more efficiently than natives.
Explanation: Native species evolved with checks on their population. Invasives arrive without those constraints, giving them competitive advantage.
Question 9: How does the nitrogen cycle differ from the carbon cycle in terms of the atmosphere's role?
Answer: Carbon: CO2 easily moves between atmosphere and organisms through photosynthesis and respiration. Nitrogen: N2 in atmosphere cannot be used directly; it requires nitrogen-fixing bacteria to convert it.
Explanation: This is why nitrogen is often a limiting factor for plant growth despite making up 78% of the atmosphere.
Question 10: Explain what carrying capacity (K) means and identify three factors that could change an ecosystem's carrying capacity.
Answer: Carrying capacity is the maximum population an environment can sustain. Factors that change it: 1) Climate change affecting resources, 2) Habitat destruction reducing space, 3) Introduction of new predators or competitors.
Explanation: K is not fixed - it changes as environmental conditions change. Population will fluctuate around K.
Next Steps
- Practice interpreting population graphs
- Review food web diagrams
- Move on to lab analysis when ready