Final answer:
Species biodiversity decreases with increasing latitude, meaning that as one moves away from the equator towards the poles, there is a general decline in the number of species.
Step-by-step explanation:
The question pertains to the pattern of species biodiversity in relation to latitude. One of the oldest and most consistent patterns in ecology is that biodiversity tends to decrease with increasing latitude. This means that as you move away from the equator and toward the poles, the number of species typically declines. Thus, having understood this concept, the correct answer to the question “Species diversity decreases by what?” is b) Latitude. As latitude increases (moving away from the equator), species diversity tends to decrease. This pattern is evident in most taxonomic groups across the globe, with the highest biodiversity typically found in tropical regions, which are near the equator where the latitude is lower.