Understanding the diversity of parasites relative to their hosts is a central question in ecology and parasitology. Given the following assumptions:

• All known living organisms possess parasites.

• A single host species can harbor more than one type of parasite.

• Parasites are species specific.

What conclusion can we draw about the comparative number of parasite species and host species?

Analyzing the Assumptions

1. All organisms possess parasites: This means every host species has at least one parasite species.

2. A single host can harbor multiple parasite species: This suggests that the number of parasite species per host can be greater than one.

3. Parasites are species specific: Each parasite species infects only one host species, not multiple.

Logical Deduction

Because each host can have several unique, species-specific parasites, and each parasite is tied to a single host species, the number of parasite species must be greater than the number of host species. This is supported by ecological studies, which indicate that if every host has several unique parasite species, then parasites should outnumber their hosts832.

Supporting Evidence

• Scientific literature confirms that host–parasite interactions often show a strong asymmetry, with one host species facing a huge diversity of parasites3.

• Studies in disease ecology and biodiversity consistently find that parasite species richness is typically higher than host species richness, especially when parasites are highly host-specific and multiple parasites infect a single host28.

Conclusion

The correct answer is:

(2) Species of parasites is more than host organisms

This conclusion follows directly from the assumptions and is strongly supported by ecological research: when hosts can be infected by multiple, species-specific parasites, the total number of parasite species will exceed the number of host species