Short Answer 
Zebras migrate to enhance genetic diversity, which improves adaptability and resilience in changing environments. Competition for resources drives natural selection, favoring traits that promote survival, while environmental pressures lead to genetic adaptations in response to threats from other species.
Step 1: Understand Zebra Migration
Zebras migrate to different herds primarily to enhance their genetic diversity. This migration allows zebras to interact and breed with different populations, thereby introducing new alleles into their gene pool. The advantages of mixing alleles include increased adaptability and resilience, which are crucial for survival in changing environments.
Step 2: Competition for Resources
Within their habitats, zebras face competition for essential resources such as sunlight. This competition can lead to natural selection where specific traits are favored. For instance, the growth of taller grasses and trees due to this competition may result in alleles that support better survival rates becoming more prevalent. These adaptations are key for thriving in environments where resources are limited.
Step 3: Genetic Changes and Environmental Impact
In response to environmental pressures, such as those imposed by other species like snakes or buffalo, genetic adaptations occur. For example, some snakes develop venomous traits due to changes in their DNA, which can introduce new alleles. These genetic variations enhance their chances of survival, while events like grassfires affect which traits are retained or selected for in populations such as buffalo or zebras.