ORIGIN OF SPECIES Chapter 24 Biological Species Concept

ORIGIN OF SPECIES Chapter 24

Biological Species Concept Evolution leads to potential speciation One species becoming two or more species Speciation leads to macroevolution Broad changes beyond the species level Speciation occurring

Biological Species Concept � Members of a species in a population have the potential to interbreed and produce viable offspring � Species can remain distinct if they can not interbreed Ex. Humans vs. Chimps � However, gene flow between species in a population can hold the population together genetically

Biological Species Concept � Reproductive Isolation � Biological factors that impede two members of a species from mating � This blocks gene flow between species � Limits the production of hybrids Prezygotic vs. Postzygotic barriers

Biological Species Concept Behavioral Isolation Two populations will not breed because of differences in courtship Fireflies

Biological Species Concept �Geographical Isolation Rivers, mountains, or bodies of water separate two populations � Snapping Shrimp and placental vs. marsupial mammals

Biological Species Concept � Temporal Isolation � Different species mate at different times Times of day Times of year � Trees and plants

Biological Species Concept Mechanical Isolation Mating is attempted by morphological differences prevent completion Ex. Ophrys orchids and bees

Biological Species Concept Gametic Isolation Sperm from one species may not be able to fertilize the egg of another Sperm may not survive reproductive tract Biochemical mechanisms may prevent sperm entry into an egg

Biological Species Concept � Reduced Hybrid Viability � Genes of different parent species may interact in ways that impair hybrid’s survival or development Ex. Salamanders of genus Enstania occasionally hybridize but the offspring often don’t develop or are very frail

Biological Species Concept Reduced Hybrid Fertility Hybrids are born sterile Often due to differing chromosome numbers between species

Biological Species Concept Hybrid Breakdown Initial offspring may be fertile but after mating with one another or parents the hybrid produced is sterile

Other Species Definitions Morphological Species Concept Characterizes species based on shape and various features In practice, most scientists use this concept Ecological Species Concept Views species in regards to their ecological niche Two species may resemble one another, but have differ in diets or mating habits Phylogenic Species Concept The smallest group of species that share a common ancestor Difficulty is determining the degree of difference between different species

Process of Speciation Can take place with or without geographic separation Types of speciation Allopatric Sympatric