Final answer:
A niche refers to the role of a species in its ecosystem, while factors like predator-prey relationships and competition for resources affect populations in the tundra ecosystem.
Step-by-step explanation:
Niche: A niche refers to the role of a species in its ecosystem, including how it interacts with the biotic and abiotic factors of the environment. For example, the niche of a giraffe involves feeding on leaves high in trees and using its long neck to reach them. This allows the giraffe to avoid competition with other herbivores that feed on lower vegetation.
Animal interactions in the tundra ecosystem: In the tundra ecosystem, animal interactions such as predator-prey relationships and competition for resources can affect populations. For instance, predators like arctic foxes and polar bears prey on animals like lemmings and seals, which can impact their population sizes. Additionally, competition for limited food resources, such as plant material or carrion, can influence the populations of different species in the tundra.