Final answer:
The number of species of swallowtail butterflies, as well as biodiversity in general, tends to increase at lower latitudes, which are closer to the equator. Option b.
Step-by-step explanation:
The number of species of swallowtail butterflies tends to increase at low latitudes(B). This pattern correlates with a well-documented ecological observation that biodiversity in many taxonomic groups increases nearer the equator. This phenomenon is attributable to a variety of factors, including warmer temperatures, higher primary productivity, and more stable climates. Notably, while certain species like Edith's checkerspot butterfly have shifted their ranges northward or to higher altitudes in response to climate change, the general pattern still holds that biodiversity is greater at lower latitudes.