The primary unit of measure for biological diversity is typically referred to as a species. Species diversity encompasses the variety of different species within a given ecosystem, including the number of species (richness) and their relative abundance (evenness). Various metrics, such as the Shannon index or Simpson's diversity index, are used to quantify diversity and assess the health of ecosystems. High biological diversity generally indicates resilient ecosystems that can better withstand environmental stresses, while low diversity can signal ecological vulnerability and potential collapse.