The graphs below depict the number of individuals of two organisms, named P and Q, when grown independently, and together. Based on these growth patterns, which one of the following statements is correct?
Show Hint
In ecological interaction graphs:
If one species dies out completely in the presence of another while both can live fine alone, it indicates either competitive exclusion or intense predation.
Since "competition" is not in the options, "Q is a predator of P" is the most logical answer as the predator eats up the entire prey population in a closed system.
Step 1: Understanding the Question:
This question tests our ability to interpret population growth curves of two species under separate (independent) and mixed (together) culture conditions to determine the nature of their ecological interaction. Step 2: Key Formula or Approach:
Evaluate the population dynamics shown in the three graphs:
1. Growth of P independently: P shows a typical sigmoidal (logistic) growth curve, reaching a stable carrying capacity.
2. Growth of Q independently: Q also shows a sigmoidal growth curve, reaching its own carrying capacity.
3. Growth of P and Q together: Q's population grows successfully to a high carrying capacity. In contrast, P's population initially rises slightly and then crashes rapidly to zero (extinction). Step 3: Detailed Explanation:
Let's analyze the ecological options based on these observations:
• Why Mutualism is incorrect: In a mutualistic relationship, both species benefit ($+/+$). When grown together, both P and Q should show enhanced growth or at least survive together. Here, P is driven to extinction, which contradicts mutualism.
• Why Commensalism is incorrect: In commensalism, one species benefits while the other is unaffected ($+/0$). Since P is completely eliminated, it is highly affected, ruling out commensalism.
• Why Parasitism is incorrect: If P were a parasite of Q, P would depend on host Q for survival. A parasite does not typically drive its host to extinction while thriving independently. Furthermore, if P is the parasite, it should do better when Q is present, but here P goes extinct when grown with Q.
• Why Predation is correct: When a predator (Q) and prey (P) are grown together in a confined space without refuges, the predator Q consumes the prey P. This intense predation leads to the rapid decline and eventual local extinction of the prey population (P).
Since Q can also grow independently (perhaps using an alternative food source provided in the medium), it continues to survive and reach its carrying capacity after consuming all of P. Step 4: Final Answer:
The sharp decline of P to zero and the robust growth of Q when cultured together indicates that Q acts as a predator that eliminates its prey P.
