Commensalism can be represented as:

Question

Accepted Answer

The correct option is 4: Species A (+) Species B (0)

Commensalism is a type of interspecific interaction where one species derives benefit from the association while the other species is neither benefited nor harmed, remaining neutral to the interaction. In the symbolic notation used in ecology to describe species interactions, the plus sign (+) indicates a positive effect (benefit), the minus sign (-) indicates a negative effect (harm), and zero (0) indicates a neutral effect (neither benefit nor harm). Therefore, the combination Species A (+) Species B (0) accurately represents commensalism, as Species A is gaining an advantage, and Species B is completely unaffected. For instance, in the relationship between an orchid (epiphyte) growing on a mango tree, the orchid benefits (+) by getting support and sunlight without having to reach the ground, while the mango tree (host) is neither helped nor harmed (0).

The incorrect option is 1: Species A (-) Species B (+)

This representation, where Species A is harmed (-) and Species B benefits (+), describes the ecological interaction known as **Parasitism** or **Predation**. In both parasitism and predation, one species gains a substantial benefit from the expense of the other. In a parasitic relationship, the host (A) is negatively affected as the parasite (B) draws nutrients or resources from it. Similarly, in predation, the prey (A) is killed and consumed, and the predator (B) benefits from the meal. Since the core definition of commensalism requires one species to be unaffected (0), a harmful effect on either species means this interaction is not commensalism.

The incorrect option is 2: Species A (-) Species B (0)

This interaction, where Species A is harmed (-) and Species B is unaffected (0), is defined as **Amensalism**. Amensalism is a specific relationship where one species suffers a disadvantage, often due to the release of inhibitory chemicals, while the other species remains entirely neutral. A classic example is the inhibition of bacterial growth (-) by the antibiotic secreted by the *Penicillium* mold, which itself is unaffected (0). The key difference from commensalism is the presence of a negative effect on one species, whereas commensalism involves a positive effect and a neutral effect.

The incorrect option is 3: Species A (+) Species B (+)

This representation, where both Species A (+) and Species B (+) benefit from the association, is known as **Mutualism**. Mutualism is a symbiotic relationship essential for the survival or improved fitness of both participating species. This type of interaction is based on a reciprocal relationship, where the benefits are shared, such as in the relationship between bees and flowering plants, where the bee gets food and the plant achieves pollination. Since the definition of commensalism requires one of the species to be neutral (0), a positive effect on both species explicitly makes this relationship mutualistic, not commensalistic.