A drought hits a habitat of semi-aquatic bird population. All the ponds dry up and the fish population declines. There are two groups of birds in the population that differ in length and diet. Long-legged birds eat fish, well short-legged birds eat insects. The drought has little effect on the insect population. What is the main selective pressure in this scenario? Drought, fish population, length of the legs or the insect population?

Answer 1

The main selective pressure in this scenario would likely be the decline in the fish population. This decline in the availability of fish as a food source would put selective pressure on the long-legged birds that rely on fish for their diet. The short-legged birds, on the other hand, would have less competition for their food source of insects, meaning that they may be better equipped to survive and reproduce in this new environmental condition. Ultimately, the availability of food (in this case, fish) is a key factor driving the selective pressure in this scenario.