Final answer:
Soil composition, while important, is not the direct cause of changes in biomes observed by an ecologist climbing a mountain; changes in temperature, altitude, and humidity are the primary factors.
Step-by-step explanation:
An ecologist hiking up a mountain observes different biomes influenced by various abiotic factors. Factors like elevation, which impacts temperature, and rainfall, which impacts humidity, are critical in determining biome types. However, the question asks which one does not cause a change in biomes: Temperature, Altitude, Soil composition, or Humidity. Soil composition, while influenced by abiotic factors and affecting plant life, is not the direct cause of the change in biomes; the other factors listed (temperature, altitude, and humidity) are directly related to the definition and characteristics of different biomes.