Practice question

Species diversity often increases during ecological succession as habitat structure becomes more complex and additional niches develop. Pioneer communities contain relatively few stress-tolerant colonists. Their growth modifies light, temperature, soil, moisture, and organic matter, allowing new plants, decomposers, herbivores, predators, and mutualists to establish. Diversity may later level off or even decline if strong competitors exclude earlier species, so the trend is not universally monotonic. Biomass also usually increases as vegetation accumulates, which makes this item ambiguous because both species diversity and biomass can rise through much of succession. Gross productivity often increases initially as leaf area develops, whereas net ecosystem production tends to peak earlier and decline as maintenance respiration grows. The keyed emphasis on species diversity reflects a standard textbook generalization, but biomass is also scientifically defensible among the provided choices. A precise question would specify which ecosystem attribute, successional interval, or single-best convention is intended. The mechanistic basis for the diversity trend is progressive habitat modification and greater structural and trophic complexity.