Assertion: During an ecological succession, the number of species increases, the community biomass increases and the community's ratio of respiration to photosynthesis also increases.

Answer

### Step-by-Step Solution:

1. **Understanding Ecological Succession**:
- Ecological succession is defined as a series of progressive changes in the species composition of a community over time. It can occur in two forms: primary succession and secondary succession.

2. **Types of Ecological Succession**:
- **Primary Succession**: This occurs in lifeless areas where there has been no previous colonization, such as newly cooled lava, areas left bare by glacier retreat, or landslides.
- **Secondary Succession**: This occurs in areas where a disturbance has destroyed an existing community but left the soil intact.

3. **Role of Pioneer Species**:
- During primary succession, the first organisms to colonize the area are known as pioneer species. These are typically hardy species such as lichens and bacteria that can survive in harsh conditions.
- Pioneer species contribute to the weathering of rocks, which leads to soil formation.

4. **Increase in Biodiversity**:
- As soil is formed, it allows for the establishment of other plant species. This process increases the number of species in the community, enhancing biodiversity.
- The presence of more species leads to a more complex community structure.

5. **Community Biomass**:
- With the increase in the number of species, the biomass of the community also increases. Biomass refers to the total mass of living matter in a given area, and as more plants and animals establish themselves, the overall biomass rises.

6. **Ratio of Respiration to Photosynthesis**:
- In a developing ecosystem, as more plants (which perform photosynthesis) grow, the community's ratio of respiration (the process by which organisms convert oxygen and glucose into energy) to photosynthesis changes.
- Initially, during early succession, respiration may exceed photosynthesis, but as the community matures and more plants grow, photosynthesis increases, often leading to a higher ratio of photosynthesis to respiration.

7. **Conclusion**:
- Therefore, the assertion that during ecological succession, the number of species increases, community biomass increases, and the community's ratio of respiration to photosynthesis also increases is correct.