A population of seed-eating finches on an isolated island experienced a prolonged drought that severely depleted intermediate-sized seeds. Only very small seeds in deep rock crevices and very large, thick-shelled seeds remained. Over several generations, the distribution of beak sizes in the population changed as shown in the graph below:
Which of the following options correctly identifies the type of natural selection operating on this population and its most likely evolutionary outcome?
Type of selection: Directional selectionEvolutionary outcome: Shift in the mean phenotypic value toward a single extreme, leading to a highly specialized monomorphic population.
\begin{aligned} \text{\textbf{Type of selection:}} & \text{ Directional selection} \\ \text{\textbf{Evolutionary outcome:}} & \text{ Shift in the mean phenotypic value toward a single extreme,} \\ & \text{ leading to a highly specialized monomorphic population.} \end{aligned}
Type of selection:Evolutionary outcome: Directional selection Shift in the mean phenotypic value toward a single extreme, leading to a highly specialized monomorphic population.
Type of selection: Disruptive selectionEvolutionary outcome: Selection against the intermediate phenotype, which can lead to sympatric speciation as sub-populations adapt to distinct ecological niches.
\begin{aligned} \text{\textbf{Type of selection:}} & \text{ Disruptive selection} \\ \text{\textbf{Evolutionary outcome:}} & \text{ Selection against the intermediate phenotype, which can} \\ & \text{ lead to sympatric speciation as sub-populations adapt} \\ & \text{ to distinct ecological niches.} \end{aligned}
Type of selection:Evolutionary outcome: Disruptive selection Selection against the intermediate phenotype, which can lead to sympatric speciation as sub-populations adapt to distinct ecological niches.
Type of selection: Stabilising selectionEvolutionary outcome: Maintenance of the intermediate phenotype to preserve genetic stability and reduce phenotypic variation.
\begin{aligned} \text{\textbf{Type of selection:}} & \text{ Stabilising selection} \\ \text{\textbf{Evolutionary outcome:}} & \text{ Maintenance of the intermediate phenotype to preserve} \\ & \text{ genetic stability and reduce phenotypic variation.} \end{aligned}
Type of selection:Evolutionary outcome: Stabilising selection Maintenance of the intermediate phenotype to preserve genetic stability and reduce phenotypic variation.
Type of selection: Disruptive selectionEvolutionary outcome: Selection against extreme phenotypes, leading to a reduced population size and eventual allopatric speciation due to physical barriers.
\begin{aligned} \text{\textbf{Type of selection:}} & \text{ Disruptive selection} \\ \text{\textbf{Evolutionary outcome:}} & \text{ Selection against extreme phenotypes, leading to a} \\ & \text{ reduced population size and eventual allopatric speciation} \\ & \text{ due to physical barriers.} \end{aligned}
Type of selection:Evolutionary outcome: Disruptive selection Selection against extreme phenotypes, leading to a reduced population size and eventual allopatric speciation due to physical barriers.