In a combined population, higher percentage of herbivorous animals would affect the vegetation, depending on the climate and consumption, the vegetation may not keep up with the demand. In evolution, feeding habits of animals change based on the availability of food resources. For instance, a certain species may prefer a certain diet of say lichen but its absence may prompt that group of species to find other source of nutrition.
Pollination is accomplished by natural means (wind) as well as by insects. If insect population declines and the climate is humid with no strong winds then pollination frequency is likely to decline changing the population demographics.
Winds, especially strong winds help in seed-dispersal increasing the plants to grow far and wide. Withlimited seed dispersal the plant come under pressure to grow in confined area growth conditions might be inadequate thereby affecting the population.
Hope this helps.