In population ecology, __________ is defined as the number of individuals of a population that leave their original habitat and move out to other areas during a given time period.

Introduction / Context:
Population ecology studies how the number of individuals in a population changes over time due to births, deaths and movements. Two important processes are immigration, when individuals enter a population from elsewhere, and emigration, when individuals leave a population. This question focuses on the correct term for the number of individuals that leave their original habitat and move to other areas during a specified time period.

Given Data / Assumptions:

• The definition mentions individuals leaving a habitat and going elsewhere.
• The time period is clearly specified, which is standard for demographic rates.
• Key population parameters include natality, mortality, immigration and emigration.
• We assume basic textbook definitions used in ecology and environmental science.

Concept / Approach:
Natality refers to the birth rate, or the number of new individuals added to a population through reproduction. Mortality refers to the death rate, or the number of individuals removed from a population by death. Immigration describes the number of individuals that enter a population from outside, increasing its size. Emigration describes the number of individuals that leave a population and move to other areas, decreasing the original population size. Because the definition in the question explicitly mentions individuals leaving the habitat and going elsewhere, emigration is the correct term.

Step-by-Step Solution:
Step 1: Identify the key phrase in the question: individuals of the population who left the habitat and gone elsewhere. Step 2: Recall that natality is related to births, which add individuals to a population internally, not by movement. Step 3: Recall that mortality is related to deaths, which remove individuals from the population because they die, not because they move. Step 4: Distinguish between immigration and emigration: immigration is entry into a population, emigration is exit from a population. Step 5: Match the idea of leaving the habitat with the term emigration and choose it as the correct answer.

Verification / Alternative check:
Ecology textbooks and population biology notes define four main parameters affecting population size: natality, mortality, immigration and emigration. Diagrams often show arrows indicating movement into and out of a population. The arrow pointing outwards from the population is labelled emigration, while the inward arrow is labelled immigration. Numerically, population size at a given time is often expressed in terms of these parameters. These consistent definitions confirm that the movement described in the question, leaving the habitat and going elsewhere, is emigration rather than immigration or any other term.

Why Other Options Are Wrong:
Option a, natality, refers to the birth rate inside the population and does not involve movement between habitats.

Option b, mortality, refers to the death rate and deals with individuals removed from the population through death, not through movement.

Option c, immigration, refers to individuals entering a population from outside, which is the opposite direction of movement described in the question.

Common Pitfalls:
Learners sometimes confuse immigration and emigration because the words sound similar and both involve movement. A useful memory aid is to associate immigration with coming in and emigration with exiting out. Another pitfall is to treat any decrease in population size as mortality, forgetting that individuals can also leave while still alive. By carefully analysing whether the change is due to births, deaths or movement, you can correctly identify emigration as the term for individuals leaving the habitat.

Final Answer:
The process described is Emigration, the movement of individuals out of a population and habitat.