definition of a species and speciation reproductive barriers between species different forms of...
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SPECIATION
AGENDA Definition of a Species and Speciation
Reproductive barriers between species
Different forms of Speciation Adaptive radiation Convergent Evolution Co-evolution
Rates of speciation
WHAT IS A SPECIES
A species is a population or group of populations whose members have the ability to breed with one another in nature and produce fertile offspring.
Hybrids can also exist, however they produce offspring with reduced or no capabilities of producing fertile offspring. Only occur in species close in evolutionary
history
HYBRIDS – TIGON (TIGER – LION)
GROLAR/PIZZLY BEAR (GRIZZLY – POLAR)
MULE (HORSE – DONKEY)
EXCEPTIONS TO THE SPECIES DEFINITION
Fossils: Cannot be assessed on whether extinct species were able to breed with other species
Organisms that reproduce asexually
Binary Fission
SPECIATION
The production of a new species is referred to as speciation.
A new species only occurs when two species can no longer breed with one another.
This means that each species must be reproductively isolated from one another This means that two species may look exactly
alike but if their reproductive system is different, then they are two distinct species.
EXAMPLE: WESTERN/EASTERN SPOTTED SKUNK
Reproductive Barriers Between
Species
REPRODUCTIVE BARRIERS
Reproductive barriers are barriers that exist preventing species from breeding with one another. Often facilitates evolution
There are several types of reproductive barriers: Geographic Isolation Habitat Isolation Other barriers
GEOGRAPHIC ISOLATION
Geographical isolation occurs when a population of species becomes geographically isolated.
The same species will have two populations separated by a geographical barrier (e.g. river, mountain, canyon)
While separated, one of the individual populations may change allele frequencies.
I.e. undergo speciation
Both species will be unableto breed
HABITAT ISOLATION
Habitat isolation occurs when similar species adapt to different habitats in the same general location.
E.g. Two similar species of garter snake (land and water habitat)
OTHER REPRODUCTIVE BARRIERS
Temporal Isolation: Species have different breeding seasons (e.g. Eastern/Western spotted skunks)
Behavioural Isolation: Species have different mating behaviours (courtships) (e.g. Blue footed booby)
Mechanical isolation: Incompatible reproductive structures
OTHER REPRODUCTIVE BARRIERS Gametic Isolation: Sperm and
eggs from different species do not recognize one another
Hybrid inviability: Hybrid offspring does not live a full expected life
Hybrid infertility: Hybrid offspring matures into adulthood but cannot reproduce (e.g. horse + donkey = mule)
DIFFERENT FORMS OF
SPECIATION
ADAPTIVE RADIATION Occurs when a small population(s) migrates to a new island
This population may undergo evolutionary change (new gene pool)
Some of these individuals may then migrate to another island in the chain where they may undergo an evolutionary change
This process, known as adaptive radiation, may repeat itself
ADAPTIVE RADIATION AND THE GALAPAGOS ISLANDS
The Galapagos islands have a diverse and unique amount of species due to adaptive radiation
Adaptive radiation explains why there are various Galapagos finches on the different islands.
CONVERGENT EVOLUTION
In convergent evolution, distantly related species that live in similar environments develop similar adaptations.
Recall the Rhea, Emu, and Ostrich
CO-EVOLUTION
Co-evolution is the process in which one species evolves in response to the evolutionary changes of another species
Occurs most often in predator-prey relations E.g. The preys will evolve ways of avoiding the
predator and the predator will evolve ways of capturing the prey
CO-EVOLUTION – ZEBRA AND LION
The zebra is constantly evolving to become quicker, more camouflaged, more agile, a good sense of smell and sight.
The lion will likewise evolve to become quicker, more agile, more stealthy, and also possess a strong sense of smell and sight.
CO-EVOLUTION – GARDER SNAKES AND POISONOUS NEWT
Newts are heavily preyed upon by garder snakes
Newts evolved to be poisonous in order to reduce attacks by garder snakes.
Meanwhile, garder snakes co-evolved to be resistant to newt toxins
CO-EVOLUTION - MIMICRY
In mimicry, one species (“the mimic”), resembles another species (“the model”), in order to gain a survival advantage.
E.g. The hoverfly (“the mimic”) and the wasp (“the model)
Wasp has a poisonous sting while hoverfly does not
MIMICRY E.G. 2 - MONARCH AND VICEROY
MIMICRY (VIDEO)
RATES OF SPECIATION Darwin proposed the
gradualism model Species diverge and accumulate
small changes over time creating two distinct species
Niles Eldredge and Stephen Gould developed the punctuated equilibrium model to explain species development. Species diverge in spurts of
relatively rapid evolutionary change