### Immediate Effects (First few weeks to months):

1. **Plants**: 
   - **Effect**: Reduced photosynthesis due to 50% less sunlight. Plant growth slows down, and some plants may begin to wither or die, especially those sensitive to reduced light.
   - **Reasoning**: Sunlight is essential for photosynthesis, the process by which plants convert light energy into chemical energy. A 50% reduction in sunlight directly impacts their ability to produce food and grow.

2. **Rabbits**: 
   - **Effect**: Limited food availability as plant biomass decreases. Rabbits may experience reduced foraging success, leading to lower energy intake, weight loss, and increased competition for remaining food.
   - **Reasoning**: The rabbits' primary food source is the plants. As plant populations decline, the rabbits' food supply is directly impacted, leading to nutritional stress and potential starvation.

3. **Foxes**: 
   - **Effect**: Slight or no immediate change, but foxes may begin to notice fewer rabbits during hunting. However, the effect is delayed because rabbits can survive for some time on reduced food.
   - **Reasoning**: Foxes rely on rabbits as their main food source, but the impact on foxes is lagged compared to rabbits because the rabbit population can decline over time before significantly affecting foxes.

### Medium-Term Effects (First 1-3 years):

1. **Plants**: 
   - **Effect**: Significant reduction in plant populations. Only the most resilient species may survive, leading to a shift in the plant community composition. Some plants may adapt by growing deeper roots or becoming more efficient at low-light conditions.
   - **Reasoning**: Prolonged reduced sunlight weakens plant populations, allowing only the hardiest species to persist. This leads to a restructuring of the plant community over time.

2. **Rabbits**: 
   - **Effect**: Population decline due to starvation and malnutrition. Rabbit reproduction rates may drop as fewer offspring survive due to insufficient food. Some rabbits may migrate to areas with more food if possible.
   - **Reasoning**: With limited food, the rabbit population cannot sustain its numbers. Reduced food availability leads to higher mortality rates and lower birth rates, causing the population to shrink.

3. **Foxes**: 
   - **Effect**: Population decline as rabbit numbers drop. Foxes may struggle to find enough food, leading to starvation, reduced reproductive success, and increased competition among foxes. Some foxes may also migrate to find alternative food sources.
   - **Reasoning**: Foxes are directly dependent on rabbits. As the rabbit population declines, foxes face food scarcity, which leads to population reduction and potential behavioral changes like migration.

### Long-Term Effects (After several years to decades):

1. **Plants**: 
   - **Effect**: A new equilibrium may be reached where only the most shade-tolerant or resilient plant species dominate. If sunlight levels eventually return to normal, plants may slowly recover, but some species may not return to their original abundance.
   - **Reasoning**: If the volcanic ash settles and sunlight levels improve, plants may recover over time. However, the prolonged stress may have caused irreversible changes to the ecosystem, such as the loss of some plant species.

2. **Rabbits**: 
   - **Effect**: Population recovery if plant populations rebound, but the rabbit community may be smaller or composed of different species adapted to the new plant community. If sunlight does not return to normal, the rabbit population may stabilize at a lower level.
   - **Reasoning**: Rabbits depend on plants for food. If plants recover, rabbits can recover, but the prolonged absence of food may have led to a permanent reduction in their population or shifts in species composition.

3. **Foxes**: 
   - **Effect**: Population may recover if rabbit populations rebound, but like rabbits, foxes may face a new equilibrium with fewer individuals. If sunlight does not return to normal, foxes may need to adapt by hunting alternative prey or migrating.
   - **Reasoning**: Foxes are at the top of this food chain and depend on rabbits. Their long-term fate is tied to the recovery of rabbit populations. If the environment changes permanently, foxes may need to adapt or face sustained population declines.

### Summary of the Causal Chain:
1. The supervolcano eruption reduces sunlight by 50%, directly impacting plants' ability to photosynthesize.
2. Reduced plant growth leads to less food for rabbits, causing their population to decline.
3. As rabbit populations decline, foxes face food shortages, leading to a decline in their population as well.
4. Over time, the ecosystem may reach a new equilibrium with fewer plants, rabbits, and foxes, or it may recover if sunlight levels return to normal. The exact outcome depends on the duration of the reduced sunlight and the adaptability of the species involved.