The question is asking about an abiotic factor that affects both robins and violets. Here's how to break down the answer:

* Abiotic Factors: These are non-living components of an ecosystem, such as temperature, sunlight, water, and soil.

* Robins: Birds, needing food, shelter, and nesting sites.

* Violets: Plants, requiring sunlight, water, and soil nutrients for growth.

Considering these factors, the most important abiotic factor affecting both robins and violets is temperature.

Here's why:

* Robins: Temperature directly impacts their migration patterns, nesting behavior, and the availability of food (insects).

* Violets: Temperature influences their growth, flowering, and seed production.

Therefore, the answer is temperature.