Practice question

Ecosystem services are most reliably sustained when multiple species make substantial contributions rather than when function is concentrated in one dominant species. Even contribution raises functional evenness: different taxa participate in production, decomposition, pollination, nutrient retention, or trophic regulation, reducing dependence on a single vulnerable contributor. It can also strengthen the “insurance effect,” because species respond differently to drought, disease, or disturbance; decline of one contributor may be offset by another. This does not mean every species performs an identical role or contributes exactly the same amount. Complementarity among distinct functional traits may be more important than numerical equality, and some keystone species have disproportionate effects. Functional redundancy can buffer loss, but redundancy alone does not guarantee maximum service if redundant species all respond similarly to stress. Communities composed entirely of predators or mutualists are trophically unrealistic and omit processes needed for complete ecosystem functioning. Among the alternatives, even contribution best captures broad participation and low dominance. The general principle is that service delivery depends on abundance distribution, functional identity, and complementarity together, so evenness supports stability without implying that species are ecologically interchangeable.