Summary:
Process-based species concepts (the Biological Species Concept and the Evolutionary Species Concept) don’t work because they are circular and not universal (there are many different speciation processes)
Pattern-based concepts (the Phylogenetic Species Concept and the Monophyletic Species Concept) are more objective
The Monophyletic Species Concept cannot be applied to reticulating systems of relationship
The Phylogenetic Species Concept is the one most often used in systematics.