Campbell Biology Chapter 24

Speciation

The origin of new species

Macroevolution

Broad patterns of evolutionary change above the species level

Biological Species Concept

A group of populations whose members have the potential to interbreed in nature and produce viable,

fertile offspring

Reproductive isolation

Barriers impede two species from producing viable, fertile offspring

Hybrids

Offspring of crosses between different species

Prezygotic Barriers

Before sperm fertilizes egg

Habitat isolation

Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

Temporal isolation

Species that breed at different times of the day, different seasons, or different years cannot mix their gametes

Behavioral isolation

Courtship rituals and other behaviors unique to a species are effective barriers

Mechanical isolation

Morphological differences can prevent successful mating

Gametic Isolation

Sperm of one species may not be able to fertilize eggs of another species

Postzygotic barriers

Inviability of offspring created after fertilization

Reduced hybrid viability

Fertilized eggs fail to develop

Reduced hybrid fertility

Even if hybrids are vigorous, they may be sterile

Hybrid breakdown

Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

Morphological Species Concept

Defines a species by structural features

Ecological Species Concept

Views a species in terms of its ecological niche

Phylogenetic species concept

Defines a species as the smallest group of individuals on a phylogenetic tree

Allopatric Speciation

Physical barrier separates a population; form of speciation

Sympatric Speciation

No barrier separates a population; form of speciation

Polyploidy

Possessing more than 2 sets of chromosomes; occurs most often in plants and decreases gene flow between polyploids and normal individuals

Hybrid Zone

Place where the ranges of two species overlap and they mate to produce hybrids

Reinforcement

Strengthening of barriers

Fusion

Weakening of barriers

Stability

Odd stasis of statis quo; though hybrids aren't healthy, they continue to be created

Punctuated Equilibrium

Periods of apparent stasis interrupted by sudden change; supported by fossil evidence

Gradualism

Slow, steady change of organisms to new species