Individuals in different species in the same community fail to encounter each other due to habitat isolation
Breed in different locations
Individuals in different species fail to recognize each other as suitable mates
Structural diffferences prevent mating
Despite mating, gametes of different species don't undergo successful fertilization
Sperm of one species can't fertilize the egg of another species.
Sperm of conspecifics outcompetes sperm of heterospecifics.
Despite mating and fertilization, different species produce less fit hybrids.
Hybrids dont survive well within species offspring.
Hybrids are less fertile than within species offspring so they dont produce functional gametes.
groups of individuals that can interbreed and produce viable and fertile offspring
Cannot accommodate asexual organisms, Cannot elucidate fossil species, Many “good” species hybridize
A group of individuals that look more like each other than like any other individuals.
Can accommodate asexual organisms, Can elucidate fossil species, Morphologically distinct suggests limited gene flow;
Would split up sexually dimorphic species, would combine indistinguishable species, features used to identify species are random.
A monophyletic group of individuals that share uniquely evolved "derived" traits.
Includes an ancestral population and all of its descendants but no others on a phylogenetic tree.
can be applied to any population, logical: groups can only have synapomorphies if they are evolutionary independent
Requires extensive genetic data, may result in many microspecies.
use data from morphology, DNA, reproduction, behavior, geography, ecology, etc
Incorporates multiple factors, making it applicable to various scenarios.
Can be complex to apply, and defining precise criteria may be challenging
supported when reproductive isolation is clear, but its challenged by hybridization in some cases
useful for fossils and visually distinct organisms but may fail with cryptic species
Supported by molecular data, especially in cases where morphology is misleading.
useful in complex situations where multiple criteria is needed, such as cryptic species with both genetic and ecological differences.