Species diversity generally tends to increase as one moves from high to low altitudes. This is due to several factors that influence the distribution and abundance of species in different altitudinal zones.

1. Environmental Conditions:
- Altitude is closely associated with changes in environmental conditions such as temperature, precipitation, and oxygen levels. As altitude decreases, these conditions become more favorable for a wider variety of species to thrive.
- Lower altitudes typically have higher temperatures, more consistent precipitation, and higher oxygen levels, which provide a more hospitable environment for a greater diversity of organisms.

2. Habitat Diversity:
- Altitude gradients often lead to changes in habitat types and vegetation. As altitude decreases, there is an increase in the variety of habitats available, such as forests, grasslands, wetlands, and coastal areas. These different habitats support different species, contributing to overall species diversity.
- Lower altitudes also tend to have more complex and diverse vegetation due to factors like richer soils and higher moisture availability. This provides more niches and resources for a greater number of species to occupy.

3. Migration and Dispersal:
- Lower altitudes are often easier to access and traverse for many species. This facilitates migration and dispersal, allowing species to colonize new areas and contribute to species diversity.
- Some species may also have specific altitudinal ranges they prefer. As altitude decreases, more species from higher altitudes may expand their ranges downward, increasing species diversity.

4. Ecological Interactions:
- Species interactions, such as competition, predation, and mutualism, play a crucial role in shaping species diversity. Lower altitudes often support a greater variety of ecological niches and available resources, leading to more complex and diverse interactions among species.
- As species interact and adapt to different ecological conditions, they can evolve into distinct forms or specialize in different ecological roles, further contributing to species diversity.

In summary, species diversity generally increases as one moves from high to low altitudes due to the more favorable environmental conditions, greater habitat diversity, easier migration and dispersal, and the presence of more complex ecological interactions.