Question

Consider this northern site of primary succession following the retreat of a glacier. As we move from left to right, cite evidence we would observe of improvements in the abiotic factors that support plant growth.
Responses
A change in climate over timechange in climate over time
B less competition for water resources due to biodiversityless competition for water resources due to biodiversity
C improved soil quality: increased humus and water retentionimproved soil quality: increased humus and water retention
D increased population density resulting in decreased pathogens

Answer 1

C is correct.

During primary succession after a glacier retreats you first get bare rock, then pioneer species (lichens, mosses) that break down rock and add organic matter as they die. Over time soil depth, humus content, nutrient availability and water‑holding capacity increase, improving the abiotic conditions for plants.

Why the others are wrong:
- A (change in climate): succession changes local soil and microhabitat, but climate does not inherently change as a result of succession.
- B (less competition for water due to biodiversity): this describes a biotic interaction and is inaccurate—greater biodiversity usually increases interactions, not necessarily less competition for water.
- D (increased population density → decreased pathogens): this is about biotic populations and disease dynamics; higher density often increases pathogen transmission rather than decreasing it.