In a population of field mice living in a grassland with dark soil and patches of white sand, individuals with very light fur are camouflaged on the sand, while individuals with very dark fur are camouflaged against the soil. Mice with intermediate, medium-brown fur are easily spotted by hawks in both environments. Over several generations, the frequency of light and dark mice increases, while medium-brown mice become rare. Which type of natural selection does this scenario describe?

A biologist is studying a population of birds where the average clutch size (the number of eggs laid) is five. Birds that lay fewer than five eggs have lower fitness because they produce fewer offspring, while birds that lay more than five eggs have lower fitness because they struggle to provide enough food for all the chicks, leading to higher mortality. If the population's average remains at five eggs and the variance decreases over time, which mode of selection is occurring?

Over several decades, a population of finches on a remote island experienced a shift in beak depth. Following a severe drought that left only large, hard-shelled seeds as a food source, birds with thicker, stronger beaks survived and reproduced more successfully than those with thin or intermediate beaks. As a result, the average beak depth of the population increased significantly. This shift in the population's phenotype is an example of which process?

Suppose a population of insects is exposed to a new chemical pesticide. Initially, most insects are killed, but a few individuals possess a mutation that allows them to detoxify the chemical. Over the next ten generations, the average resistance level of the population increases significantly as the allele for the detoxifying enzyme becomes more common. This shift in the population's mean trait value represents which type of selection?

In a hypothetical population of flowering plants, pollinators show a strong preference for either very small flowers that fit their narrow proboscis or very large flowers that provide a wide landing platform. Plants with medium-sized flowers are rarely visited, resulting in lower reproductive success. If this preference persists, how will the phenotypic distribution of flower size change, and what is the name of this selection type?

In human birth weight, infants who are significantly smaller than the average are more likely to experience health complications, while infants who are significantly larger than the average may cause complications during delivery for both the mother and the baby. Consequently, infants with an intermediate birth weight have the highest survival rates. This pattern of natural selection is known as:

A population of snails exhibits a wide range of shell thicknesses. A new predator is introduced to the environment that can easily crush thin shells but is unable to break the thickest ones. At the same time, a parasitic wasp that selectively targets and lays eggs inside snails with very thick shells becomes more prevalent. If the mortality rates from both the predator and the parasite result in the highest survival for snails with shells of intermediate thickness, which type of selection is operating?

In a specific species of salmon, large males are able to successfully defend nesting territories and attract mates through physical dominance. Simultaneously, very small 'jack' males are able to sneak into the territories undetected to fertilize eggs. Males of intermediate size are too small to win fights against the large males and too large to remain unnoticed like the small males, resulting in the lowest reproductive success. This scenario describes which type of selection?

In a population of woodland plants, leaf size varies significantly. A prolonged period of drought occurs where plants with large leaves lose too much water through transpiration and die. Simultaneously, a new species of herbivorous insect is introduced that prefers to eat plants with small leaves because they are easier to manipulate. If plants with medium-sized leaves have the highest survival and reproductive success under these dual pressures, which type of selection is the population experiencing?