The correct answer is (D) All the lions in a reserve forest.​

An ecological population consists of individuals of the same species living in a defined geographic area, capable of interbreeding and interacting through shared resources. This GATE Life Sciences question tests the fundamental definition in population ecology.​

Option Analysis

Option A: A pitcher plant and a trapped fly
This represents a predator-prey interaction between two different species—a plant (Nepenthes) and an insect (fly)—not a single-species population.​

Option B: All animals that live near each other in a national park
This describes a community of multiple species coexisting in proximity, lacking the single-species criterion for a population.​

Option C: The leeches and the flatworms that live in a forest
Leeches (Annelida) and flatworms (Platyhelminthes) belong to distinct phyla, forming separate populations rather than one unified population.​

Option D: All the lions in a reserve forest
All lions (Panthera leo) in a reserve forest form a single species group within a specific habitat, meeting the true definition of an ecological population with potential for gene flow.​

Introduction to True Ecological Population

In population ecology, a true ecological population refers to individuals of one species occupying a specific geographic area, interacting via breeding and resources. This concept appears frequently in CSIR NET and GATE Life Sciences exams, distinguishing populations from communities or isolated organisms.​

Why Lions Form a True Ecological Population

Lions in a reserve forest exemplify a classic population: same species (Panthera leo), defined habitat, and interbreeding potential despite dispersal. Conservation data shows Gir Forest lions as a monitored population growing from bottlenecks.​

Common MCQ Traps in Population Ecology

Exams test misconceptions:

• Predator-prey pairs (like pitcher plant-fly) mix species.​

• Multi-species groups (animals in parks or leeches/flatworms) describe communities.​
  Use Britannica’s definition: “individuals of one species… that interbreeds.”​