A biologist discovers two populations of wolf spiders whose members appear identical. Members of one population are found in the leaf litter deep within the woods. Members of the other population are found in the grass at the edge of the woods. The biologist decides to designate the members of the two populations as two separate species. Which species concept is this biologist most closely utilizing

Ecological species concept is the concept of species where species is a group of organisms adapted to specific resources,called niche in the environment

Every species has a different niche;niche is simply the role played by the organisms in a particular area(environment) in which it is living
Ecological and evolutionary processes controls the resources and divides the species into groups
In the given example members of one population of wolf spiders are found in leaf litter within the woods while the other one is found in the grass at the edge of the woods
Both the members are distanced from each other ecologically and their role to use resources changes
Hence they are designated as two different species by utilizing the ecological species concept