Only a small percentage of all consumers are specialists. what danger does a specialists face that's generalist does not?

Generalist species are adapt to live in a wider range of environment conditions. Specialist species are adapt to live in a narrow range of environment conditions. Thus, specialists are in a greater danger if some of the conditions in the environment change. For example, species A and B live in a river with an average temperature of 17°C. Species A is the generalist species and it can survive water temperature of 5-35°C. Species B is the specialist species and can survive water temperature of 15-20°C. If the temperature of the river decrease to 10°C, specialist species B will not survive but generalist species a will survive.