What factor contributes significantly to massive, detrimental populations in non-native regions compared to their native range?

Answer

Lack of evolved specialized predators

In non-native regions, the lack of evolved specialized predators, combined with milder climates, has led to population densities that far surpass those seen in their native European habitats.

What factor contributes significantly to massive, detrimental populations in non-native regions compared to their native range?
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