Answer:
Plant species diversity drops when fertilizer is added or productivity increases. To explain this, the total competition hypothesis predicts that competition above ground and below ground both become more important, leading to more competitive exclusion, whereas the light competition hypothesis predicts that a shift from below‐ground to above‐ground competition has a similar effect. The density hypothesis predicts that more above‐ground competition leads to mortality of small individuals of all species, and thus a random loss of species from plots.
Explanation:
Fertilizer was added to old field plots to manipulate both below‐ground and above‐ground resources, while shadecloth was used to manipulate above‐ground resources alone in tests of these hypotheses.
