The species concept works better when classifying asexual species

Phylogenetic species concept 

Phylogenetic species concept is when a member of irreducible group descended from a common ancestor and they have combination of certain trait. Also, this concept of species share a unique evolutionary history but focuses on their physiology, morphology and behaviour. However, Phylogenetic species concept works better when classifying asexual species.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.