Final answer:
A region's size and age since initial colonization affect species richness, with larger areas supporting more species and offering a diverse array of habitats and niches. Smaller regions tend to have fewer species and higher extinction risks, and as regions age, the rate of species addition generally declines.
Step-by-step explanation:
The student's question pertains to how a region's size and age since initial colonization affect the region's species richness. The concept that needs to be understood is the species-area relationship, where larger habitats tend to support a greater number of species due to factors such as a higher diversity of habitats, larger populations that span viable spatial ranges, and the capacity to accommodate more niche environments. Contrastingly, smaller regions are prone to higher extinction risks for species due to smaller habitat sizes, decreased number of niches, and the probability that smaller regions contain fewer species to begin with.
Moreover, as regions age post-colonization, the rate of new species colonizing typically slows, while the established species either sustain or reach a carrying capacity. The assumption that species continuously increase over time is fallacious; ecological saturation may occur, or extinctions can balance or exceed colonizations.
Lastly, regions with a mosaic of land uses might offer a heterogeneous landscape that supports higher species richness, but this largely depends on how much original habitat remains and the spatial arrangement of these habitats. In summary, while larger habitats and long-established ecosystems have the potential for higher species diversity, numerous ecological dynamics govern the actual species richness observed in a given region.