I. Typological Species Concept

- by Charles Darwin
- categorized by look

II. Biological Species Concept

- if two similar organisms will breed, they are the same species
- in some cases of breeding a hybrid is produced
- some species can mate to create intergrades
- problem with the concept is asexual organisms and when females reproduce when no males are present

III. Ecological Species Concept

- separated by niche
- depends on interactions within the environment and eating habits
- environmental preference between organisms can make a difference

IV. Evolutionary History Species Concept

- structured according to evolution
- refers to genetic trees
- caused by geographic separation
- ex: species A evolves into species A and B. later species A creates another offshoot to create species C.

V. Phylogenetic Species Concept

- says that one species evolves in to two completely new species leaving the old species extinct
- ex: species A evolves into species B and C and A no longer exists