The correct answer is option 'C': increase in food availability.

Explanation:
Population pressure refers to the strain on resources and living conditions caused by an increase in the number of individuals within a particular area. In this case, population pressure is said to have increased due to an increase in food availability.

1. Introduction:
Population pressure occurs when the number of individuals in a given area exceeds the available resources and living space. It can result in competition for resources, overcrowding, and other negative consequences.

2. Factors affecting population pressure:
a) End of ice age: The end of the ice age may have led to the expansion of habitable areas, but it would not directly contribute to population pressure.
b) Change in climate: While a change in climate can impact the availability of resources, it does not necessarily lead to an increase in population pressure.
c) Increase in food availability: When there is an increase in food availability, populations tend to grow as individuals have access to more resources and are better able to survive and reproduce. This can lead to population pressure as more individuals compete for limited resources.
d) Domestication: Domestication refers to the process of taming and breeding animals and cultivating plants for human use. While domestication can lead to an increase in food availability, it is not the cause of population pressure itself.

3. Explanation of the correct answer:
The increase in food availability is the most plausible reason for an increase in population pressure. When food becomes more abundant, individuals are better nourished and can produce more offspring. As a result, the population increases, and more individuals compete for limited resources, leading to population pressure.

4. Conclusion:
Population pressure can be influenced by various factors, but an increase in food availability is a significant contributor. When food resources are plentiful, populations tend to grow, leading to an increased strain on resources and living conditions.