Amensalism is a type of interspecific interaction where one species is inhibited or harmed, while the other species is unaffected. This '0/-' interaction, where one organism suffers and the other experiences no benefit or harm, can indeed act as a significant biotic factor influencing the geographic limits of species.

Here's how amensalism can determine geographic limits:

1. Competitive Exclusion (Indirectly): While not direct competition, amensalism can lead to a form of competitive exclusion. If one species produces a substance or modifies the environment in a way that is detrimental to another species, the affected species may be unable to thrive or even survive in that area. This effectively creates a 'no-go' zone for the harmed species, limiting its distribution.

2. Allelopathy in Plants: A classic example of amensalism is allelopathy, particularly common in plants. Some plants release biochemicals (allelochemicals) into the soil or air that inhibit the growth, germination, or survival of other plant species. For instance, the Black Walnut tree (Juglans nigra) produces juglone, a chemical that is toxic to many other plants, preventing them from growing in its vicinity. This creates a clear boundary around the walnut tree where other susceptible species cannot establish, thus defining their local geographic limit.

3. Antibiosis in Microorganisms: Similar to allelopathy, some microorganisms produce antibiotics or other inhibitory substances that harm or kill competing microbial species. This allows the producing microorganism to dominate a particular niche, excluding others and setting their boundaries.

4. Habitat Modification: Amensalism can also occur through physical modification of the environment. For example, a large, dominant tree species might cast a dense shade that prevents the growth of shade-intolerant understory plants. While the tree itself isn't directly harmed or benefited by the absence of these plants, the understory species are negatively impacted, and their distribution is limited to areas with more light.

In essence, amensalism creates environmental conditions that are unfavorable for certain species, preventing them from expanding their range into areas where the amensalist species is present and active. This interaction can be a powerful force in shaping community structure and defining the realized niche and geographic distribution of species, especially when the inhibitory effect is strong and widespread.