Final answer:
c. Animal species present are not used to determine the outer boundaries of a wetland area; instead, hydrology, soil type, and plant species present are the main characteristics considered.
Step-by-step explanation:
The factor that is NOT used to determine the outer boundaries of a wetland area is C) Animal species present. When defining wetlands, experts look at three main characteristics: hydrology (the water presence or flow), soil type (typically hydric soils that are saturated with water), and plant species present (hydrophytic vegetation adapted to wet soil conditions).
While the presence of certain animal species can be an indicator of a wetland environment, they are not a defining characteristic for the boundaries as animals can migrate and are not as permanently fixed to an area as soil and plants.