Population Dynamics

The pyramid shown represents a (D) Declining population.

Expanding: Expanding populations have a wide base (lots of births) and progressively narrower tiers. This represents a high birth rate and lower life expectancy.

Stable: Stable populations have relatively even tiers, with only a slight tapering towards the top. Birth and death rates are relatively balanced. This is what the image depicts.

Declining: Declining populations have a narrow base (few births) and wider tiers in the older age groups. This represents a low birth rate and a higher life expectancy.

The size of a population (the number of individuals of a species in a given area) is dynamic and fluctuates over time. These changes are influenced by various environmental factors that affect birth rates, death rates, immigration, and emigration.

Let's consider the factors listed:

• Food availability: The amount of available food resources directly impacts the carrying capacity of the environment.
  • Abundant food can lead to higher birth rates (better nutrition for reproduction) and lower death rates (less starvation), potentially increasing population size.
  • Scarcity of food can lead to lower birth rates, higher death rates, and potentially increased emigration, causing a decrease in population size.
• Predation pressure: The presence and activity of predators affect the mortality rate of the prey population.
  • High predation pressure increases the death rate, leading to a decrease in population size.
  • Low predation pressure allows for higher survival rates, potentially allowing the population to grow (if other factors are favorable).
• Adverse weather: Environmental conditions like extreme temperatures, droughts, floods, storms, etc., can significantly impact populations.
  • Severe weather events can directly cause mortality (increasing death rates) and reduce reproductive success (decreasing birth rates), leading to a decline in population size.
  • Favorable weather conditions can support population growth.

Since population size keeps changing depending on food availability, predation pressure, and adverse weather conditions (among other factors like disease and competition), all the listed factors contribute to fluctuations in population size.

Therefore, the correct answer is All of the above.

Given the values provided:

Natality = 25

Mortality = 24

Immigration = 2

Emigration = 3

The net increase in population (M) can be calculated as follows:
M=Natality−Mortality+Immigration−Emigration
M=25−24+2−3
M=1+2−3
M=3−3
M=0

Based on the given values, the net increase in the population (M) is 0. Therefore, the correct option is (B) 0.