Which of the following is a direct consequence of decreased pollinator populations?

Decreased pollinator populations directly lead to a decline in flowering plant reproduction because many plants rely specifically on pollinators for the process of fertilization. Pollinators, such as bees, butterflies, and birds, facilitate the transfer of pollen from the male parts of a flower to the female parts, enabling the plants to produce seeds and fruit. When pollinator populations decline, the efficiency and effectiveness of this reproduction process are diminished, resulting in lower seed set and diversity of flowering plants. This has broader implications for ecosystems, as flowering plants are vital for providing food and habitat for various organisms and maintaining ecological balance.

In contrast, other options such as improved crop diversity, increased pest resistance, and better air quality do not directly stem from a decrease in pollinator populations and are influenced by different ecological processes and factors. For instance, improved crop diversity typically requires effective pollination to produce a wide range of plant varieties.