Anagenesis is a pattern of descent in which species form within a single, unbranched line with gene flow throughout the entire process.
Evolutionary tree diagrams show a simple way to show lines of descent from a common ancestor.
The gradual model of speciation is represented by tree diagrams with branches at slight angles to each other to show slow change over time. This fits well with evidence from certain lineages in the fossil record.
The punctuation model of speciation is drawn with short, horizontal branches that represent abrupt periods of speciation followed by stable periods. Most changes in morphology are compressed into a brief period near the onset of divergence. This is supported by fossil evidence in some lineages
Adaptive Radiations
An adaptive radiation is a burst of microevolutionary activity that results in the formation of new
species in a wide range of habitats. A single lineage gives rise to many new species. New species
fill a vacant adaptive zone. An adaptive zone is a "way of life". The presence of adaptive zones
presents new ways of life by physical, evolutionary, or ecological access.
Background extinction is the rather inevitable loss of species as local conditions change over periods (usually long) of time.
Mass extinctions are abrupt disappearances due to catastrophic, global events. Species survival is to some extent random. For example, asteroids have repeatedly struck the Earth destroying many lineages. Changes in global temperature favor lineages that are widely distributed.
REVIEW: Allopatric speciation requires
REVIEW: Sympatric speciation occurs
REVIEW: A speciation pattern which exhibits branching of populations is termed
REVIEW: The acquisition of a key evolutionary innovation by a species gives evidence for the
concept of
REVIEW: In an evolutionary tree diagram, a branch point represents a _____, and a branch that ends
represents _____ .
REVIEW: An evolutionary tree diagram with horizontal branches that abruptly become vertical is
consistent with the _____ .
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