4.1 Why are there so many different species?
SPEC- 4.5 ii) Understand that reproductive isolation can lead to accumulation of different
genetic information in populations, potentially leading to the formation of new species.
1. What is species?
Ø A species is a group of organisms with similar morphology, physiology and behaviour,
which can interbreed to produce fertile offspring, and which are reproductively
isolated in place, time or behaviour from other species.
Formation of new species
Ø Caused by reproductive isolation à genetic diversity decreases, size of the gene pool
is smaller, gene flow is reduced, risk of inbreeding depression and genetic drift.
Ø When a part of a population is isolated by means of geographical isolation preventing
a group of individuals from breeding with the rest of the population – they become
less like each other.
Ø They respond to different selection pressures.
Ø As random mutations occur they will not be able to interbreed to produce a fertile
offspring – they become genetically different (mutation results in adaptation).
Ø This process is known as speciation.
Species number may increase due to:
§ Fragmentation of habitat/ geographical/reproductive isolation
§ Different selection pressures acting on populations
§ Evolution leading to formation of new species
§ Different allele frequencies within separate populations
Species number may decrease due to:
§ If the population is critically endangered – may become extinct
§ If there is only one population - vulnerable to inbreeding depression
§ Risk of natural disaster, disease, predation..etc
MAIN POINTS TO REMEMBER FROM MARK SCHEMES
• Successful interbreeding produces an offspring
• If the offspring is fertile – same species
• If the offspring is infertile – different species à infertile due to genetic
incompatibility, different number of chromosomes à species are genetically
different
If two different species interbreed successfully – this leads to two things:
• Increase the genetic diversity / increase size of gene pool.
• This is due to increase in variety of alleles as new/different combination of alleles are
introduced into the population
,Two species DO NOT interbreed due to:
• Different breeding time/season
• Different breeding behaviour
• Reproductive isolation – they become genetically different
• Physically incompatible eg. genitalia
Suggest why two species are so similar in external appearance
- Descending from common ancestor
- Living in similar habitats
- Similar environmental conditions
- Similar selection pressures
- Both well-adapted
- Similar gene pool
Explain what is meant by the term reproductively-isolated populations:
- Populations isolated by means of geographical isolation, preventing a part of the
population from breeding with the rest of the population
- They therefore develop different behaviours, different combinations of alleles
- Different mutations
- Physically Incompatible
- Allotropic speciation: speciation that happens when two populations of the same
species become isolated from one another due to geographical features/changes
- Sub-species are allowed to interbreed, they could produce fertile offspring
SPEC – 4.3 Understand the concept of niche and be able to discuss examples of adaptation
of organisms to their environment (behavioural, physiological and anatomical).
SPEC – 4.1 Know that over time the variety of life has become extensive but is now being
threatened by human activity.
What is a habitat?
Ø A habitat is the place where an organism lives.
Ø Each habitat has a particular set of conditions which support different organisms.
Ø Within a habitat there may be population of organisms.
What is a population?
Ø Group of interbreeding individuals of the same species found in an area.
Ø The various populations in a habitat make up a community.
, o Every species has its own niche
o Niche is the way an organism interacts within its environment / the role of a species
in its environment.
o All the species sharing a habitat have different niches.
o However, if two species have the same role in the environment (food sources, shelter
site) they will compete with one another and the better-adapted organism will out-
compete and exclude the other.
o Predator – controls population of prey
o Prey- provides food for other animals
o Can also provide home / shelter for other animals
Factors that affect the survival chances of species/individuals/population are
o Competition with other species
o Predation – attack/preying of one animal on others.
o Hunters
o Risk of natural disasters , diseases
Types of adaptations
• Behavioural adaptation: any actions by organisms that help them survive/reproduce.
Eg. sheep learn to ignore sounds that have no importance to them.
• Physiological adaptation: features of the internal workings of organisms that help
them survive/reproduction.
Eg. metabolic reactions become less efficient in cold weather so organisms generate
more heat to keep warm.
Eg. Formation of a sun tan when human skin is exposed to sunlight.
Eg. Hearing becoming temporarily less sensitive
Eg. Heart beats faster when hormone adrenaline is released
• Anatomical adaptation: the structures that we can see when we observe an
organism.
Eg. The ears of African elephants are larger than those of Asian elephants, due to
differences in the environment.
Eg. People living in a cold climate have a shorter neck
SPEC- 4.5 ii) Understand that reproductive isolation can lead to accumulation of different
genetic information in populations, potentially leading to the formation of new species.
1. What is species?
Ø A species is a group of organisms with similar morphology, physiology and behaviour,
which can interbreed to produce fertile offspring, and which are reproductively
isolated in place, time or behaviour from other species.
Formation of new species
Ø Caused by reproductive isolation à genetic diversity decreases, size of the gene pool
is smaller, gene flow is reduced, risk of inbreeding depression and genetic drift.
Ø When a part of a population is isolated by means of geographical isolation preventing
a group of individuals from breeding with the rest of the population – they become
less like each other.
Ø They respond to different selection pressures.
Ø As random mutations occur they will not be able to interbreed to produce a fertile
offspring – they become genetically different (mutation results in adaptation).
Ø This process is known as speciation.
Species number may increase due to:
§ Fragmentation of habitat/ geographical/reproductive isolation
§ Different selection pressures acting on populations
§ Evolution leading to formation of new species
§ Different allele frequencies within separate populations
Species number may decrease due to:
§ If the population is critically endangered – may become extinct
§ If there is only one population - vulnerable to inbreeding depression
§ Risk of natural disaster, disease, predation..etc
MAIN POINTS TO REMEMBER FROM MARK SCHEMES
• Successful interbreeding produces an offspring
• If the offspring is fertile – same species
• If the offspring is infertile – different species à infertile due to genetic
incompatibility, different number of chromosomes à species are genetically
different
If two different species interbreed successfully – this leads to two things:
• Increase the genetic diversity / increase size of gene pool.
• This is due to increase in variety of alleles as new/different combination of alleles are
introduced into the population
,Two species DO NOT interbreed due to:
• Different breeding time/season
• Different breeding behaviour
• Reproductive isolation – they become genetically different
• Physically incompatible eg. genitalia
Suggest why two species are so similar in external appearance
- Descending from common ancestor
- Living in similar habitats
- Similar environmental conditions
- Similar selection pressures
- Both well-adapted
- Similar gene pool
Explain what is meant by the term reproductively-isolated populations:
- Populations isolated by means of geographical isolation, preventing a part of the
population from breeding with the rest of the population
- They therefore develop different behaviours, different combinations of alleles
- Different mutations
- Physically Incompatible
- Allotropic speciation: speciation that happens when two populations of the same
species become isolated from one another due to geographical features/changes
- Sub-species are allowed to interbreed, they could produce fertile offspring
SPEC – 4.3 Understand the concept of niche and be able to discuss examples of adaptation
of organisms to their environment (behavioural, physiological and anatomical).
SPEC – 4.1 Know that over time the variety of life has become extensive but is now being
threatened by human activity.
What is a habitat?
Ø A habitat is the place where an organism lives.
Ø Each habitat has a particular set of conditions which support different organisms.
Ø Within a habitat there may be population of organisms.
What is a population?
Ø Group of interbreeding individuals of the same species found in an area.
Ø The various populations in a habitat make up a community.
, o Every species has its own niche
o Niche is the way an organism interacts within its environment / the role of a species
in its environment.
o All the species sharing a habitat have different niches.
o However, if two species have the same role in the environment (food sources, shelter
site) they will compete with one another and the better-adapted organism will out-
compete and exclude the other.
o Predator – controls population of prey
o Prey- provides food for other animals
o Can also provide home / shelter for other animals
Factors that affect the survival chances of species/individuals/population are
o Competition with other species
o Predation – attack/preying of one animal on others.
o Hunters
o Risk of natural disasters , diseases
Types of adaptations
• Behavioural adaptation: any actions by organisms that help them survive/reproduce.
Eg. sheep learn to ignore sounds that have no importance to them.
• Physiological adaptation: features of the internal workings of organisms that help
them survive/reproduction.
Eg. metabolic reactions become less efficient in cold weather so organisms generate
more heat to keep warm.
Eg. Formation of a sun tan when human skin is exposed to sunlight.
Eg. Hearing becoming temporarily less sensitive
Eg. Heart beats faster when hormone adrenaline is released
• Anatomical adaptation: the structures that we can see when we observe an
organism.
Eg. The ears of African elephants are larger than those of Asian elephants, due to
differences in the environment.
Eg. People living in a cold climate have a shorter neck
