Chapter 24 Flashcards
Speciation
The origin of new species; at the focal point of evolutionary theory
Microevolution
Changes in allele frequency in a population over time
Macroevolution
Broad patterns of evolutionary change above the species level
The Biological species concept
States that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
Reproductive Isolation
the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
Hybrids
the offspring of crosses between different species
Prezygotic barriers
block fertilization from occurring (Habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation)
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 to mating
Mechanical isolation
Morphological differences can prevent the successful completion of mating
Gametic isolation
The sperm of one species may not be able to fertilize eggs from another species
Postzygotic barriers
Prevent the hybrid zygote from developing into a viable, fertile adult (Reduced hybrid viability, Reduced hybrid fertility, hybrid breakdown)
Reduced hybrid viability
genes of the different parent species may interact and impair the hybrid’s development or survival in its environment
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 each other or with either parent species, the offspring of the next generation are feeble or sterile
T/F: The biological species concept cannot be applied to fossils or asexual organisms
True
Morphological species concept
Defines species by structural features (applies to sexual and asexual species but relies on subjective criteria)
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
Speciation can occur in two ways: _________ speciations and ________ speciation
Allopatric; Sympatric
Allopatric speciation
gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
T/F: Regions with less geographic barriers typically have more species than do regions with more barriers
False
Sympatric Speciation
speciation takes place in geographically overlapping populations, but gene flow is inhibited by polyploidy, sexual selection, and habitat differentiation
Polyploidy
the presence of extra sets of chromosomes due to accidents during cell division
Autopolyploid
an individual with more than two chromosome sets, derived from a single species
Allopolyploid
a species with multiple sets of chromosomes derived from different species
Sexual Selection
Drives sympatric speciation
Habitat differentiation
Drives sympatric speciation through new ecological niches; populations become divided into new habitats, leading to speciation
Hybrid zone
A region in which members of different species mate and produce hybrids
Three possible outcomes from hybridization events over time
1) Reinforcement
2) Fusion
3) Stability
Reinforcement
Hybridization barriers become stronger
Fusion
The species comes back together
Stability
