A chiropractor. you might've heard about them 'cracking your back' professionally
Oxygen is a vital element within cellular respiration. An intrinsic part of the cellular respiration cycle is the transfer or electrons through the electron transport chain, and at the end of it exists the mitochondria, in which electrons are donated to the Oxygen and combine with hydrogen ions to form water.
The correct answer is - increased competition.
If an ecosystem experiences an increase in its biodiversity, than the result of it would be increased competition. The increased competition will be for food sources, water sources, territory. The reason why increased competition will occur is that there are only limited mounts of food sources, water sources, and territory in the ecosystem. There's also certain amount of niches in the ecosystem, and once all of them are occupied by some species, any other that is specialized for that niche will be competitor plus. This increased competition will lead to high evolutionary pressure, which will result in relatively quick adaptations and specialization in order to survive.
