General Biology 2: Exam 2

Biological Species Concept

Biological Species Concept

Mechanisms that stop gene flow between populations

Types of reproductive isolation

Prezygotic, Postzygotic

Prezygotic isolation

Individuals of different species are prevented from mating successfully

Postzygotic isolation

The hybrid offspring do not survive or reproduce

Example of prezygotic isolation

Two bird species live in the same area and, though similar in plumage, engage in dramatically different courtship dances

Example of postzygotic isolation

Two frog species meet and mate with each other, but the hybrid offspring are infertile

Limitations to the biological species concept

Not related to fossil species, asexually reproducing organisms, or sexual organisms with open mating systems

Morphospecies concept

Uses physical attributes to define species

Example of morphological species concept

An African fish eagle is similar in appearance to the bald eagle, but the two birds are members of different species

Limitations to the morphological species concept

Species can be indistinguishable even if separation in lineage is clear

Phylogenetic species concept

Species are descendants of a common ancestor, and they all have certain defining or derived traits

Example of phylogenetic species concept

Three monophyletic groups of elephants will be apparent in a phylogenetic tree but they will have unique DNA sequences that make them distinguishable

Limitations to phylogenetic species concept

Information on certain species may not be readily available, and closely related species may accidentally be grouped together

Allopatric speciation

Populations live in different areas

Dispersal

Movement of individuals from one place to another

Vicariance

Physical splitting of a habitat splits the population into subgroups that are isolated

Genetic Isolation

Happens when populations become geographically separated

Biogeography

The study of the geographic distribution of living things and the abiotic factors that affect their distribution

Can inform allopatric speciation

Biogeography

Sympatry

Speciation that occurs among populations within the same geographical area

How sympatric speciation occurs

Often by disruptive/diversifying selection

Types of secondary contact

Fusion, reinforcement of divergence, and stability

Fusion

Separate groups interbreed

Reinforcement of divergence

traits that prevent interbreeding

Stability

A geographic area where interbreeding occurs, and hybrids are common

Phylogenetic tree

A simplified diagram of the branching evolutionary history of a group of organisms

Branches

Show transfer of genetic information from one generation to the next

Node

A point where an ancestral lineage splits to give rise to two or more descendant lineages

Data Matrix

Contains a character or trait, with two possible states, present (1) or absent (0), and an out group

Character/trait

Any genetic, morphological, physiological, developmental, or behavioral characteristic to be studied

Out group

A taxon that diverged before that taxa that are the focus of the study; helps to root the tree

Monophyletic group

Any group that forms any evolutionary unit including an ancestral population and all of its descendants but no others

Non-monophyletic groups

A group that includes an ancestral population and some descendants but not all, or a group that shares similar traits but does not include the most recent ancestor

Complications

Convergent evolution, reversal of character trait, and different types of data showing different group patterns

Convergent evolution

Independent evolution of similar traits in distantly related organisms, occurs when there are adaptations to similar environmental pressures

Example of convergent evolution

The white winter coat of the arctic fox and the ptarmigan’s plumage (bird)

Homology

A common evolutionary past is shared

Example of homology

Bat and bird wings

Taxonomy

A hierarchical model used to organize living organisms into increasingly specific categories (levels and scientific names)

Example of taxonomy

Domain: Eukarya; Kingdom: Animalia; Phylum: Chordata; Class: Mammalia; etc…

Macroevolution

Large scale changes in life’s patterns

Adaptive radiation

Increase in species diversity (extrinsic and intrinsic factors)

Extrinsic factors

Ecological opportunity

Intrinsic factors

Evolution of morphological traits

Examples of intrinsic factors

Hawaiian islands, Cambrian time period, Lake Victoria

Types of extinction

Mass and background

Mass extinction

The rapid extinction of a large number of diverse species around the world (opposite of adaptive radiation)

What mass extinctions are caused by

catastrophic events

Background extinction

The lower average rate of extinction (1 out of 100 million species per year)

The sixth mass extinction

Caused by human impacts

Examples of human impacts

Habitat loss, pollution, overfishing, invasive species, climate change