Final answer:
Wallace's Line is a biogeographical division in Southeast Asia based on ecological differences in species between the mainland and insular regions, reflecting their distinct biodiversity.
Explanation:
The criteria for the division created by Wallace's Line are based on biogeographical differences. This line delineates the distinct biospheres of the Asian and Australasian regions by separating the ecological biodiversity and species. The division reflects the natural distribution and variety of plant and animal life found on either side, which is significantly different due to a long history of geographic and evolutionary separation. The mainland region of Southeast Asia comprises countries that border China and India, featuring extensive river systems, like the Mekong and the Red River. In contrast, the insular region includes numerous islands and peninsulas that lie between Asia and Australia.
Wallace's Line was established to account for the striking differences in flora and fauna between the two realms. This biogeographical boundary affects many aspects of life in the region, including agriculture, settlement patterns, and even the spread of culture and trade through maritime routes. The division has been significant in shaping the historical colonization and cultural development of Southeast Asia.