Practice question

Autogenic change is environmental modification caused by organisms within the community, and it can drive succession. Plants create shade, roots alter soil structure, litter adds organic matter, nitrogen-fixing microbes enrich nutrient supply, and sphagnum can acidify wetland water. These changes modify the establishment and competitive success of later species. Allogenic change originates outside the community, such as volcanic deposition, flooding, erosion, climate shifts, or altered fire regimes. “Catagenic” and “progenetic” are not the standard contrasting terms for organism-driven succession in this context. Autogenic processes can facilitate successors, as when pioneers build soil, or inhibit them, as when a closed canopy excludes light-demanding seedlings. Thus, the term identifies the source of the environmental change, not whether its ecological effect is positive or negative. Feedback is central: organisms respond to conditions and then alter those same conditions, changing future community composition. This causal loop explains why modification by organisms is described as autogenic.