Practice question

Species interactions are major drivers of succession because organisms change both the physical environment and one another’s probability of establishment and survival. Pioneer plants may facilitate successors by building soil, adding nitrogen, or providing shade. Residents may instead inhibit newcomers through competition, allelopathy, or occupation of space. In tolerance pathways, later species establish independently but ultimately prevail because they survive low light or resources better. Herbivory, predation, mutualism, and decomposition also redirect trajectories. The keyed choice highlights this biotic mechanism, but succession is not driven by interactions alone. Disturbance creates or resets sites, dispersal determines which species arrive, and abiotic conditions filter which can persist; the workbook itself later recognizes this fuller combination. Mutation and evolution can influence traits over longer periods, while “migration only” omits establishment filters and local dynamics. Therefore, species interactions are the best offered driver, provided they are understood as operating with disturbance, dispersal, and environmental constraints rather than as an exclusive cause.