Venn diagram illustrating differences and similarities between primary and secondary ecological succession.

Final Answer:
Primary Succession: Starts with previously existing soil — ✘
Primary Succession: Pioneer species — ✔
Primary Succession: Happens slowly, takes hundreds of years — ✔
Primary Succession: Comes after a natural disturbance — ✘
Primary Succession: No previous existing life — ✔
Primary Succession: Intermediate species — ✘
Primary Succession: Gradual Community — ✔
Primary Succession: Climax Community — ✔

Secondary Succession: Starts with previously existing soil — ✔
Secondary Succession: Pioneer species — ✔
Secondary Succession: Happens slowly, takes hundreds of years — ✘
Secondary Succession: Comes after a natural disturbance — ✔
Secondary Succession: No previous existing life — ✘
Secondary Succession: Intermediate species — ✔
Secondary Succession: Gradual Community — ✔
Secondary Succession: Climax Community — ✔

Both: Pioneer species — ✔
Both: Comes after a natural disturbance — ✘ (Only secondary)
Both: No previous existing life — ✘ (Only primary)
Both: Intermediate species — ✔
Both: Gradual Community — ✔
Both: Climax Community — ✔

But since the task asks to *use your knowledge* and *fill in the Venn diagram*, and the standard correct classification is:

- Primary Succession:
✓ Pioneer species
✓ Happens slowly, takes hundreds of years
✓ No previous existing life
✓ Gradual Community
✓ Climax Community
✗ Starts with previously existing soil
✗ Comes after a natural disturbance
✗ Intermediate species *(debatable, but intermediate species appear later—technically both have them; however, in many curricula, “intermediate species” is listed under both)*

Actually, looking at standard biology teaching:
- Both include: Pioneer species, Intermediate species, Gradual Community, Climax Community
- Primary only: No previous existing life, starts from bare rock/volcano/glacier, very slow (hundreds–thousands of years)
- Secondary only: Starts with existing soil, comes after disturbance (fire/flood), faster (~50–150 years)

So correct placement:

Primary Succession circle (only):
- No previous existing life
- Starts from bare rock or glacier
- Happens slowly, takes hundreds (or thousands) of years

Secondary Succession circle (only):
- Starts with previously existing soil
- Comes after a natural disturbance
- Happens fast, takes about 50–150 years

Both circle:
- Pioneer species
- Intermediate species
- Gradual Community
- Climax Community

Now matching the checklist in the image:

Left (Primary only):
☐ Starts with previously existing soil → No
☑ Pioneer species → Yes
☑ Happens slowly, takes hundreds of years → Yes
☐ Comes after a natural disturbance → No
☑ No previous existing life → Yes
☐ Intermediate species → Usually Yes for *both*, so not *only* primary
☑ Gradual Community → Yes (both, but often listed in both)
☑ Climax Community → Yes (both)

Right (Secondary only):
☑ Starts with previously existing soil → Yes
☑ Pioneer species → Yes (but also in both)
☐ Happens slowly… → No, it’s fast
☑ Comes after a natural disturbance → Yes
☐ No previous existing life → No
☑ Intermediate species → Yes (both)
☑ Gradual Community → Yes (both)
☑ Climax Community → Yes (both)

The cleanest correct answer — based on standard textbook classification — is:

- Primary Succession only:
• No previous existing life
• Starts from bare rock / glacier / volcanic rock
• Happens slowly (hundreds to thousands of years)

- Secondary Succession only:
• Starts with existing soil
• Comes after disturbance (fire, flood, etc.)
• Happens relatively fast (~50–150 years)

- Both:
• Pioneer species
• Intermediate species
• Gradual community development
• Ends in a climax community

Since the question likely expects checking the correct boxes, and the image shows a list with checkboxes, the final answer should be the list of correct placements.

But per instruction: *Provide only the final correct answer.*

So, as a single concise answer reflecting the correct classification:

Final Answer:
Primary Succession: Pioneer species, No previous existing life, Happens slowly (hundreds+ years), Starts from bare rock/glacier.
Secondary Succession: Starts with existing soil, Comes after disturbance, Happens faster (~50–150 years).
Both: Pioneer species, Intermediate species, Gradual community, Climax community.