In population ecology, which term refers specifically to the number of births that occur in a population during a given period and are added to the initial population density?

Introduction / Context:
Population ecology uses specific terms to describe changes in the size and composition of populations. Understanding the meaning of natality, mortality, immigration and emigration is fundamental for answering biology questions related to population growth and regulation. This question focuses on the term that describes the number of births added to the population during a given time period.

Given Data / Assumptions:

• The definition mentions the number of births in a population during a given period.
• These births are said to be added to the initial population density.
• Options include natality, mortality, immigration, emigration and carrying capacity.

Concept / Approach:
Natality is defined as the birth rate or the number of new individuals born per unit time in a population. It contributes positively to population growth. In contrast, mortality refers to deaths, immigration refers to individuals entering a population from outside, and emigration refers to individuals leaving the population. Carrying capacity is the maximum population size that an environment can support, not a birth related term.

Step-by-Step Solution:
Step 1: Identify the key component of the definition, which is the number of births during a given period.Step 2: Recall that natality is the term used in ecology for birth rate and addition of individuals through reproduction.Step 3: Understand that mortality is the opposite process, involving removal of individuals through death.Step 4: Check that immigration and emigration describe movement into or out of the population, not birth within it.Step 5: Therefore, the correct term that matches the given definition is natality.

Verification / Alternative check:
You can verify by recalling that many textbooks define population growth rate roughly as birth plus immigration minus death minus emigration. In that expression, natality is the component representing births. This confirms that natality is the correct term when the question explicitly mentions births that add to the initial population density.

Why Other Options Are Wrong:
Mortality: This refers to the number of deaths in the population during a given period, which reduces population size instead of adding to it.
Immigration: This is the arrival of individuals from other populations or regions, not birth within the population.
Emigration: This is the departure of individuals from the population to other areas, which decreases population size.
Carrying capacity: This term denotes the maximum number of individuals that the environment can support sustainably, and is not a birth related rate.

Common Pitfalls:
Students sometimes confuse natality with immigration because both increase the number of individuals. To avoid this, remember that natality is always about births, while immigration is about movement from outside. A helpful memory aid is to link natality with the word "natal", which relates to birth. Keeping these distinctions clear will help when solving numerical or conceptual problems in population ecology.

Final Answer:
The term that refers to the number of births added to the population is natality.