A drought hits the habitat of a semi-aquatic bird population. All ponds dry up, and fish populations decline. There are two groups of birds in the population that differ in leg length and diet. Long-legged birds eat fish, while short-legged birds eat insects. The drought has little effect on insect populations.
What is the main selective pressure in this scenario?
The main selective pressure in this scenario would be the availability of food resources, specifically fish. During the drought, the ponds dry up, causing a decline in fish populations. As a result, the availability of fish as a food source decreases for the long-legged birds that primarily eat fish. With fewer fish available, the long-legged birds may struggle to find enough food to survive and reproduce.
On the other hand, the short-legged birds, which primarily eat insects, are less affected by the drought since the insect populations remain relatively stable. This gives the short-legged birds an advantage over the long-legged birds in terms of food availability. As a result, the main selective pressure in this scenario is the availability of fish as a food resource, favoring the short-legged birds.