Final answer:
Longitudinal gradients of species diversity, similar to latitudinal gradients, show higher biodiversity closer to the equator. Tropical butterflies and birds are prime examples of this gradient, influenced by various ecological and evolutionary factors.
Step-by-step explanation:
Longitudinal gradients of species diversity are observed similarly to latitudinal ones, indicating richer biodiversity closer to the equator. This pattern is seen across various ecosystems and taxonomic groups including microbes, plants, invertebrates, and vertebrates. For instance, tropical butterflies and birds display a notable longitudinal gradient, with a peak of diversity often found slightly north of the equator, usually around 20-30°N. The diversity gradient tends to be asymmetric, with a more rapid increase in species richness in the northern hemisphere compared to the southern hemisphere. Different taxonomic groups vary in terms of how steep this gradient is, with some being more tropical than others. Butterflies, for example, are typically more confined to tropical regions compared to birds. Factors such as productive energy, ambient energy, climatic variation, and topographic variation influence speciation and extinction rates, which in turn affect the latitudinal diversity gradient.
In summary, while tropical butterflies and birds are well-known examples of species showing longitudinal gradients in diversity, this concept extends to a multitude of organisms and is a multi-faceted ecological pattern.