Final answer:
Among various ecosystems such as grasslands, tropical rainforests, deserts, and wetlands, wetlands are considered the rarest on Earth. This highlights the importance of conservation efforts focused on these critical ecosystems, which support a vast diversity of life. The correct option is d) Wetland.
Step-by-step explanation:
The question of which type of ecosystem is the rarest on Earth requires an understanding of various ecosystems and their global prevalence. Among terrestrial and aquatic ecosystems, such as grasslands, tropical rainforests, deserts, and wetlands, distinguishing the rarest is crucial for conservation efforts. While all these ecosystems are unique and invaluable to the planet's biodiversity, freshwater ecosystems—or wetlands—are considered to be the rarest on Earth. Wetlands cover a relatively small area of the Earth's surface yet play an incredibly vital role in the natural environment and are critical for numerous species.
Exotic species pose significant threats to certain ecosystems, with islands being particularly vulnerable to invasive organisms due to their isolation and distinct ecological niches. Planning a conservation preserve with limited size and highly diversified niches usually centers around models like the tropical rainforest ecosystem, which houses a rich diversity of species, further illustrating the importance of conserving such unique biomes.
It is also important to recognize that while deserts might seem desolate, they too present a great diversity of life that varies significantly across different desert ecosystems, showing the world's natural variety and underscoring the need to preserve the distinctiveness of each ecosystem type.