Final answer:
Commensal organisms are generally harmless and may be beneficial. However, they can become harmful if the immune system is weakened or environmental changes occur. Commensal relationships include examples like mites on insects and cattle egrets with livestock.
Step-by-step explanation:
Interactions between different species, including commensalism, do not always result in harm. Commensal organisms, such as commensal bacteria on human skin, are often harmless and can even be beneficial. However, these organisms may cause harm under certain conditions, such as when a person's immune system is compromised.
In such cases, what is normally a harmless commensal can become opportunistic and potentially pathogenic, leading to infections or other health issues. Similarly, changes in the environment or the introduction of invasive species can alter the nature of commensal relationships.
Examples of Commensalism
Commensalism is characterized by one species benefitting while the other is unaffected. Examples include mites hitching a ride on larger insects or cattle egrets feeding on insects disturbed by livestock. Microorganisms on the human body, such as those that make up the Human Microbiome Project, typically participate in commensal relationships, aiding in digestion and nutrition without harming us.