1. Temperature: This refers to the average heat of the environment. Temperature can vary greatly depending on the location (latitude, altitude), time of day, and season. Temperature directly influences the types of plants and animals that can survive in an ecosystem.

2. Sunlight: The amount of sunlight an ecosystem receives is crucial. This determines how much photosynthesis can occur, which is the basis for the food chain. Sunlight intensity also affects the temperature and humidity of the environment.

3. Water: Water is essential for all life. Its availability, quality (salt content, pH), and flow patterns (rain, rivers, lakes) strongly influence the types of organisms that inhabit an ecosystem.