Final answer:
In the absence of a keystone species, there is typically a decrease in biodiversity within an ecosystem due to their pivotal role in maintaining ecological balance. The loss of such species can lead to negative consequences for the variety of species present and the overall health of the environment.
Step-by-step explanation:
When a keystone species is removed from an ecosystem, the consequences are typically a decrease in biodiversity. Keystone species, like the intertidal sea star Pisaster ochraceus in the northwestern United States or the banded tetra in tropical streams, play critical roles in maintaining the structure of ecological communities. Without these species, the ecological balance can be disrupted, leading to an increase in populations of their natural prey, which in turn can completely alter the species composition and reduce biodiversity. An example is when Pisaster ochraceus is absent, mussel populations surge, negatively impacting the variety of species in the area.In conclusion, the absence of a keystone species commonly results in a reduction of the variety of life in the affected ecosystem, which can lead to ecological collapse and affect the well-being of human populations, who rely on biodiversity for ecosystem services.