Complex sentence: By training he is an entomologist specializing in Lepidoptera (butterflies), but he is known better as an ecologist and a demographer, specifically for his incorrect predictions about population growth and limited resources.
Split into simpler sentences: By training he is an entomologist specializing in Lepidoptera (butterflies), but he also a prominent ecologist and demographer. Erlich is best known for for his incorrect predictions about population growth and limited resources.