Which of the following factors would have the least effect on the carrying capacity of an ecosystem?
a.
the total number of organisms
b.
the available water supply
c.
the available food supply
d.
competitive exclusion

Correct D) Competitive exclusion

Carrying capacity of an ecosystem may be defined as the total number of organism it can support. Biotic and abiotic factors such as available space, water, food and shelter  act as a limiting factor, which determine how many organism can live within a ecosystem.

The competitive exclusion principle states that two species that compete for same resources cannot stably coexist.

One among the two competitor will always have slight advantage over the other, it leads to extinction of other competitor or lead to an evolutionary shift of the inferior one to a different ecological niche. Therefore, competitive exclusion have least effect on the carrying capacity of an ecosystem.

if you know your abc's you should be able to get your answer or just use google