Answer
(a) Dispersal - Bringing livestock or pet animals to new areas where those animals did not already live.
(b) Biotic interactions - Changing the landscape of an area (for example, by logging), creating a larger habitat for a species. In the logging example, this might be a tall grass that cannot live in shade.
Work Step by Step
(a) Humans have brought many animals with them as they've expanded their own range, intentionally or not. For example, the shipping industry introduced rats into areas that previously did not have them. Animals and plants are also often transported by traveling humans inadvertently.
(b) Humans make many dramatic changes to their environments which impact the species that live around them. For example, the elimination of the buffalo from the grassy plains in North America has caused a spike in the amount and range of scrubby juniper trees that grow in this region.
