Orginis Of Species Flashcards
What is speciation ?
Process by which one species splits into two species
Speciation produced…
The diversity of life
Factors to consider when defining a species
Morphology, ecology, physiology and genetics
What is the biology species concept (BSC)?
A group of populations whose members have the potential to interbreed and produce viable, fertile offspring
BSC has an emphasis on…
Reproductive isolation
Species do not produce viable, fertile offspring with…
Other groups
What is reproductive isolation?
Biological factors (barriers) impede members of two species from interbreeding and producing viable, fertile offspring
In reproductive isolation, barriers block…
Gene flow
In reproductive isolation, it limits…
The formation of hybrids
What are hybrids?
Offspring that result from inter specific mating (mating between two different species)
What are the limitations of the BSC?
Cannot apply to fossils
Does not apply to asexual organisms
Cannot apply to geographically isolated populations
Designated by “absence of gene flow”
But there are morphologically and ecologically distinct species that can, mate and produce viable/fertile offspring
What is the morphological species concept (MSC)?
Distinguishes a species by body shape and other structural features
MSC applies to…
Asexual and sexual organisms
Limitations of the MSC
Disagreement on what features are most important in distinguishing a species
Intra-species (within species) morphological variation often greater that inter-species variation
What is the Ecological Species Concept(ESC)?
Defines a species in terms of its ecological niche or the sum of how species interact with biotic and abiotic parts of their environment
ESC accommodates…
Sexual and asexual species
ESC emphasizes…
The role of disruptive natural selection
Limitations if ESC
Might separate species that still have gene flow
Required specific understanding of species ecological niche
Two main types of barriers
Pre-zygotic barriers
Post-zygotic barriers
What is Perozygotic barriers?
Before zygote, anything that prevents mating and/or fertilization from occurring
What is habitat isolation?
Two species occupy different habitats within same area but may meet each other (even without physical barriers)
What is temporal isolation?
Two species have timing differences in breeding
What is behavioral isolation?
Courtship rituals unique to a species can be effective reproductive barriers
What is mechanical isolation?
Mating is attempted but morphological differences prevent successful completion
What is gametic isolation?
Sperm of one species may not be able to fertilize the eggs of another species (may not survive, may not get through a biochemical barrier)
What is postzygotic barriers?
After zygote, reproductive isolation after hybrid zygote is formed, usually, hybrid offspring do not survive or are sterile
What is reduced hybrid viability?
Genes of different parent species may interact to impair hybrids development or survival, most do not survive the embryonic phase
What is reduced hybrid fertility?
Hybrids maybe sterile, often result in differences in number or structure of parental chromosomes so meiosis in hybrids fail to produce normal gametes
What is allopathic speciation?
Occurs between physically or geographically isolated populations
What is Sympathetic speciation?
Occurs without physical or geographic isolation
Vicariance (type 1): Allopatric Speciation
Large population split into two or more sub-popukations
Usually due to emerging geographic barriers
New populations isolated genetically —> no gene flow
Subpopulations diverge genetically
Dispersal/ Colonization (type 2): Allopatric Speciation
Small # of individuals disperse to a new habitat
Founder effect increases likelihood of genetic drift
If environment is different, selective pressure will be different
Ex. Commonly found in species on islands
What is the importance of Allopatric speciation?
Regions that are isolated typically have more species than other regions
-Island endemics (local species)
-areas broken up by mountain ranges/ water features
What is sympathetic speciation?
Occurs without physical isolation
Natural selection overwhelms gene flow
What are the three main mechanisms of sympathetic speciation?
Polyploidy
Sexual selection
Habitat differentiation
What is polyploidy?
Species may originate from accident during cell division that results in an extra set of chromosomes
Botanists estimate that…
> 80% of plant species today are descended from ancestors that formed by polyploidy speciation
What is habitat differentiation?
In the same area, but there is a niche that is specific to a certain species
What happens when there is incomplete reproductive isolation?
Hybrid zones can form
What is a hybrid zone?
Region in which members of what are considered different species meet and mate producing at least some offspring of mixed ancestry
