first enunciated a classical species definition known as the biological species concept (1942)
biological species concept
defines a species as a population or group of populations whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with other species
separation of species or populations so that they cannot interbreed and produce fertile offspring
impede mating between species or hinder the fertilization of ova if members of different species attempt to mate:
1. Habitat isolation
2. Behavioral isolation
3. temporal isolation
4. mechanical isolation
5. gametic isolation
prezygotic barrier between species; the species remain isolated because they breed in different habitats.
prezygotic barrier in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding
prezyogtic barrier in which sperm of one species may not be able to fertilize the eggs of another species
prevent the hybrid zygot from developing into a viable, fertile, adult:
1. Reduced hybrid viability
2. reduced hybrid fertility
3. hybrid breakdown
reduced hybrid viability
Genes of the different parent species may interact and impair the hybrid's development
reduced hybrid fertility
even if hybrids are vigorous they may be sterile; meiosis in hybrids may fail to produce normal gametes
The first-generation hybrids are viable and fertile, but when they mate the offspring are feeble and sterile
ecological species concept
defines a species in terms of its ecological niche, the set of environmental resources a species uses.
pluralistic species concept
the factors that are most important for the cohesion of individuals as a species vary.
morphological species concept
characterizes each species as a set of organisms with a unique genetic history
takes place in populations with geographically separate ranges, likelihood increases when population is small and isolated,
takes place in geographically overlapping populations , requires the emergence of some type of reproductive barrier that isolates the gene pool of a subset of a population without geographic separation from the parent population
A chromosomal alteration in which the organism possesses more than two complete chromosome sets.
An individual that has more than two chromosome sets, all derived from a single species.
A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.
a theory of evolution holding that evolutionary change in the fossil record came in fits and starts rather than in a steady process of slow change
evolution on a large scale extending over geologic era and resulting in the formation of new taxonomic groups
A structure that has evolved in one environmental context and later becomes adapted for a different function in a different environmental context.
The variation in the relative rates of growth of various parts of the body, which helps shape the organism.
The retention in an adult organism of the juvenile features of its evolutionary ancestors.
Any of the genes that control the overall body plan of animals by controlling the developmental fate of groups of cells