Topic 3- Biodiversity and conservation KEY DEFINITONS
Isolation- The process by which two populations become separated by geographical,
3.2 Origins of biodiversity behavioural, genetic or reproductive factors. If gene flow between the two subpopulations
is prevented, new species may evolve.
Speciation- The formation of new species when populations of species become isolated and
SIGNIFICANT IDEAS
evolve differently from other populations.
-Evolution is gradual change in the genetic character of populations over
many generations, achieved largely through the mechanism of natural PLATE ACTIVITY
selection. The outer crust and upper mantle (the lithosphere) of the Earth are divided into many plates
Environmental change gives new challenges to specie, which drive the that move over the molten part of the mantle (magma).
evolution of diversity. Plates move apart, slide against each other or collide.
-There have been major extinction events in the geological past. Plates move apart at constructive plate margins
Plates move together as destructive plate margins
EVOLUTION Plates collide at collision plate margins
Biodiversity arises from evolutionary processes.
The separation of continental plates leads to isolation of populations. This separates
KEY DEFINITION organisms with a common ancestor. Separation of gene pool results in divergent
Evolution- The cumulative, gradual change in the genetic characteristics of evolution, for example within the ratites (flightless birds): emu in Australia, ostrich in
successive generations of a species or race of an organism, ultimately giving Africa, rhea in South America.
rise to species or races different from the common ancestor. Evolution Collision of plates can lead to uplift and mountain formation. The mountains form a
reflects changes in the genetic composition of a population over time.
physical barrier, which isolates populations. The uplift also creates new habitats,
promoting biodiversity. Adaptation to new habitats then occurs through natural
Natural selection: selection.
Collision of plates also cause the spread of species through the creation of land bridges.
Charles Darwin developed the theory of evolution by natural selection This leads to a mixing of gene pools and possible hybridisation.
Plate activity can create new islands, usually through volcanic activity. This can lead to
Populations show variation (i.e. not all individuals are the same) adaptations to fill new habitats/ niches.
Populations always over- reproduce to produce excess offspring The movement of plates to new climate regions leads to evolutionary change to adapt
Resources, such as food and space, are limited and there are not to new conditions, for example the northwards movement of the Australian plate.
enough for all offspring
There is competition for resources
Due to variation within the species, some individuals will be fitter
than others.
Fitter individuals have an advantage and will reproduce more
successfully than individuals who are less fit.
The individuals that survive contain genes that give them adaptive
advantage.
These genes are inherited by offspring and passes on to the next
generation.
Over time there is a change in the gene pool, which can lead to CASE STUDY
the formation of new species. Galapagos finches
The Galapagos islands were created by rising magma from breaks in the crust (‘hot
Charles Darwin published The Origins of Species in 1859; the book explained spots’)
and provided evidence for the theory of evolution by natural selection. Volcanic islands were formed as a plate moved over the hot spots.
An ancestral finch colonised the islands from mainland South America
Speciation is the process by which new species from. Natural selection works Different populations of the finch became isolated on different islands.
with isolating mechanisms to produce new species. They adapted to the different conditions found on each island
Natural selection contributes to the evolution of biodiversity over time Galapagos finches have undergone speciation to fill many of the niches on these
Biological variation arises randomly and can either be beneficial to, damaging volcanic islands and they now are very different from the original mainland South
to, or have no impact on, the survival of the individual. American finch.
QUICK CHECK QUESTIONS QUICH CHECK QUESTIONS
-Define the term evolution -Outline how geographical isolation leads to speciation
-Outline the theory of evolution by natural selection -Explain the role of reproductive isolation in the formation of new species
-Outline the role of plate activity in speciation
THYE ROLE OF ISOLATION IN FORMING NEW SPECIES Environmental change gives new challenges to species those that are suited will survive, and
those that are not suited will not survive.
Geographical isolation:
Geographical isolation is caused by a physical barrier that leads to populations
becoming separated, eventually leadi8ng to speciation. Causes of geographical PAST AND PRESENT RATES OF SPECIES EXTINCTION
isolation include plate activity, and the formation of mountains, seas, lakes, The fossil record shows that there have been five periods of mass extinction in the past. Mass
rivers and deserts. extinctions include events in which 75% of the species on Earth disappear within a
geologically short time period, usually between a few hundred thousand to a few million
The process of speciation: years.
1. Original population
2. Geographical isolation divides the population into two separate Pass mass extinctions have been caused by natural, physical (abiotic) causes. Scientists
groups consider that the Earth is currently undergoing a sixth mass extinction, caused by human
3. Populations become adapted to different local conditions and activities (i.e. biotic causes). The current mass extinction can be divided into two phases:
become genetically different from each other - Modern humans dispersed to different parts of the world, around 100000 years ago.
4. Reproductive isolation occurs and the species cannot interbreed - Humans started to grow food using agriculture, around 10 000 years ago.
to produce fertile offspring if they meet - Scientists predict that at current rates of extinction the Earth will enter its sixth mass
Reproductive isolation: extinction within the next 300-2000 years.
Environmental isolation- the geographic ranges of two species
overlap, but their niches differ enough to cause reproductive
KEY DEFINITION
isolation
Mass extinction- events in which 75% of the species on Earth disappear within a
Temporal isolation- two species whose ranges overlap have
geologically short time period, usually between a few hundred thousand to a few million
different times of activity years.
Behavioural isolation- courtship rituals (breeding calls, mating
dances etc.) between two species vary, such as birds of paradise
Mechanical isolation- physical differences in, for example, QUICK CHECK QUESTIONS
-Define the term mass extinction
reproductive organs, prevent mating or pollination
-What is the difference between past mass extinctions and the predicted sixth mass
Genetic isolation- sperm and ova are incompatible, and will not
extinction?
allow fertilisation to take place.
EXAM QUESTIONS
-Define the term species diversity (1m)
KEY DEFINITIONS -Explain how natural selection can produce new species (2m)
Plate tectonics- The movement of the eight major and several minor internally ridged
plates of the Earth’s; lithosphere in relation to each other and the partially mobile
-State, giving examples, two ways in which an understanding of plate tectonics has helped
asthenosphere below. to explain patterns of biodiversity. (4m)
