Macroevolution Flashcards
the origin and extinction of new taxonomic groups.
It can happen gradually, or slowly.
Macroevolution
The two major processes of macroevolution
Speciation
Extinction
A modern understanding of speciation begins 100 years after Darwin, when Ernst Mayr, and others, developed a scientific theory of speciation based upon
Extinction took even longer
Genetic and Ecological Processes
Species are groups of actually or potentially interbreeding individuals that can mate and produce fertile offspring
A species is the smallest set of organisms that share a common ancestor, and can be distinguished from other such sets
Biological Species Concept
Phylogenetic Species Concept
Species are collections of living organisms that have certain morphological and biochemical traits in common.
Morphological Species Concept
This idea was promoted by Ernst Mayr, an evolutionary biologist who worked on birds.
It is excellent, conceptually, because it defines species objectively, based upon the capabilities of the organisms in question.
BIiological Species Concept
In principle, this applies to most species, but in many cases, it is simply impossible to test whether two species have the potential to interbreed.
Fossil species, species which do not reproduce in the lab or zoo (the vast majority), and asexual species are sticky issues.
Biological species concept
This is what most taxonomists actually use to classify specimens and describe species.
It is expedient-it can be applied to dead specimens, and even to fossils.
Morphological Species Concept
It has many disadvantages.
It is subjective.
Cryptic species, which look identical to humans but are in fact reproductively isolated, are problematic.
Species with morphological variation, and complex life histories, pose problems.
Morphological Species Concept
This concept emphasizes the species as a lineage on the tree of life.
It is, at least in theory, objective, because it defines lineages as the smallest set of organisms that share a common ancestor-though in practice, that common ancestor is always dead, and its existence must be inferred.
Phylogenetic Species Concept
the origin of new species. With extinction, it is one of two keystone processes of macroevolution
It is one of two cornerstone processes of macroevolution.
It takes _____ for species to originate
Speciation
Reproductive Isolation
If this reproductive isolation continues long enough, speciation occurs. One, or several, new species originate from isolated populations of the parent species.
As we shall see, this is frequently the result of a geographic barrier, although it may be the result of a chromosomal change or habitat preference.
This type of species live in the same place. Without some mechanism preventing allele and gene exchange among sympatric species, distinct species would be impossible.
Sympatric Species
Instead, we would see a continuum of variation from one form of life to another, and many forms of life would not be possible, because interbreeding with different forms would produce non-viable combinations of traits
Barriers to allele flow are called …
They allow sympatric species to exist and to maintain distinct sets of characters and adaptations.
Isolation Mechanisms
Without isolation mechanisms, closely related species would hybridize: allele flow and recombination would eventually transform them into a single, polymorphic species.
Isolation mechanisms are responsible for the origin of species, and they maintain the integrity of species
Isolation mechanisms prevent mating, so that gametes of sympatric species never form hybrid zygotes.
Prezygotic Isolation mechanisms
Isolation mechanisms that act after a mating has occurred, to prevent fertilization or to prevent potential hybrids from passing on their genes.
Postzygotic Isolation Mechanisms
The 5 prezygotic isolation mechanisms
Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametes Die
occurs because sympatric species never meet due to differences in their habitat preference.
Habitat Isolation
What type of isolation?
Sympatric species of spadefoot toads (Scaphiopus) seldom meet because they prefer different soil types.
Habitat Isolation
Type of isolation?
Many species of closely-related parasites, such as bird lice, never meet because they live and mate on different hosts.
Habitat Isolation
Isolation that occurs because species mate at different times
Temporal Isolation
Type of isolation
The American Toad (Bufo americanus) and the Fowler’s Toad (Bufo fowleri) have been mated in laboratory settings, but mating does not happen in the wild because the American Toad mates early in the summer, and the Fowler’s Toad mates in late summer.
Temporal Isolation
isolation mechanisms that include differences in courtship behavior, differences in chemical signals or vocalizations, and differences in color or morphology that allow individuals to recognize their own species.
They are a very common mechanism keeping closely-related sympatric animals from interbreeding
Behavioral/Ethological Isolation