Short Answer 
Zebras migrate to mix genetic material, enhancing genetic diversity which aids adaptability. Competition for resources like sunlight drives natural selection, favoring traits such as height in plants, indirectly impacting dependent animals. Random events, such as grassfires, can selectively influence alleles, altering the genetic landscape of a population.
Step 1: Understanding Zebra Migration
The primary reason zebras migrate to different herds is to introduce and mix new genetic material, resulting in the transfer of new alleles from various populations. This migration helps to increase genetic diversity within herds, which can boost resilience and adaptability in changing environments.
Step 2: Effects of Competition for Resources
In nature, competition for vital resources like sunlight significantly influences which traits are favored through natural selection. For instance, in densely vegetated areas where sunlight is limited, taller trees may have a survival advantage. This competition can lead to the proliferation of alleles that promote greater height among plant species, indirectly affecting the animals that rely on these plants for food.
Step 3: The Role of Random Events in Allele Selection
Random events, such as a grassfire triggered by buffalo movements, can alter the genetic landscape by selectively impacting certain alleles. This event may not intentionally favor any particular trait, but it creates a scenario where the surviving organisms can spread different genetic traits, further influencing the population’s genetic makeup over time.