In seedcracker finches from cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. if long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?

The type of selection that will operate on the finch population is DIRECTIONAL SELECTION. Directional selection is a type of selection in which an extreme phenotype is favoured over other phenotype which make the allele frequency  to shift over time in the direction of the favoured phenotype. Directional selection is one of the three types of natural selection.