Because it is harder to get the sugars out of complex carbohydrates and easier to get sugars out of simple sugars hence the name.
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.
