TOPIC 3.2: ORIGINS OF BIODIVERSITY
Imagine you could scan the earth with a life-detecting probe. You'd be stunned to find millions of living organisms, interacting in the most amazing ways. From leopards, lemurs and lice to ferns and flesh-eating plants, the variety of life forms that populate our planet is mind-boggling. Scientists refer to it as biodiversity. Biodiversity is more than just a lengthy list of the plants, animals, fungi and microorganisms found worldwide. It also encompasses the genes they contain, and the interactions that take place.
3.7 billion years ago, this planet was a tough place for life. Hot lava spewed from the surface of the earth and beneath the sea. Much of the land was dotted with boiling hot springs, and the atmosphere was thick with steam and carbon dioxide. So how did our planet become the hotbed for living creatures that we know today?
In this unit we will see how diversity changes through succession, genetic diversity, limiting factors and human activities. This unit is a minimum of 3 hours.
Evolution is a gradual change in the genetic character of populations over many generations, achieved largely through the mechanism of natural selection.
Environmental change gives new challenges to species, which drives the evolution of diversity.
There have been major mass extinction events in the geological past
How are the issues addressed in this topic of relevance to sustainability or sustainable development
In what ways might the solutions explored in this topic alter your predictions for the state of human societies and the biosphere some decades from now?
Unsustainable development can lead to species extinction. Given the five mass extinctions of the past, is this something that the human race should be concerned about?
What effects could species extinctions have on human societies in years to come?
Knowledge & Understanding:
3.2.U1 Biodiversity arises from evolutionary processes
Biological evolution is the process of change and diversification of living things over time, and it affects all aspects of their lives--morphology, physiology, behavior, and ecology. Underlying these changes are changes in the hereditary materials. Hence, in genetic terms, evolution consists of changes in the organism's hereditary makeup. During the process of evolution - the history of life on earth - both processes speciation and (mas-)extinction were very common.
3.2.U2 Biological variation arises randomly and can either be beneficial to, damaging to, or have no impact on, the survival of the individual
Genetic variation is an important force in evolution as it allows natural selection to increase or decrease frequency of alleles already in the population. Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring). Genetic variation is advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population.
3.2.U3 Natural selection occurs through the following mechanism.
Within a population of one species, there is genetic diversity, which is called variation.
Due to natural variation, some individuals will be fitter than others.
Fitter individuals have an advantage and will reproduce more successfully than individuals who are less fit.
The offspring of fitter individuals may inherit the genes that give that advantage
[Natural selection is an evolutionary driving force, sometimes called “survival of the fittest”. In this context, the meaning of “fittest” is understood to be “best-suited to the niche”.]
Natural Selection is where some species are more adapted to their environment and have an advantage in times of change. Their genes are passed onto future generation.
Environment change gives new changes to the species, those that are suited survive, those that are not will not.
Natural selection is an evolutionary driving force, sometimes called 'survival of the fittest'. (Fittest: the best suited to the niche)Natural selection is one of the main methods in which speciation occurs through the following steps
Within a population of one species there is genetic diversity, which is called variation
Due to the natural variation some individuals will be fitter than others
Fitter individuals have an advantage and will reproduce more successfully
The offspring of fitter individuals may inherit the genes that give the advantage
3.2.U4 This natural selection will contribute to the evolution of biodiversity over time
Natural selection: is the where the organisms that are more adapted to the environment have an advantage over those that are less well adapted, and they survive, flourish and reproduce.
Natural selection refers to the survival of the fittest, with those species containing more favourable traits (strong defence mechanisms, diverse gene pool, can feed on variety of food resources) surviving and those less well suited to their environments not surviving or flourishing
Due to the process of natural selection over generations there is a movement towards fitness in the whole population, the environment constantly selecting for the individuals that are best suited to that niche. Negative changes lead to extinction. Speciation occurs as a result of the isolation (geographical or reproductive) of populations. The concept of fitness should be understood. The history of the development of the modern theory of evolution is not expected, nor is a detailed knowledge of genetics (including allele frequency).
Because of the varying environment both locally as well as globally. Each local environment presents different challenges at different time, if the species migrates to a new place it encounters a much rapid change. Different environmental challenges combined with the time scales involved, results in infinite number of selection criterions, thus leading to diverse selection. Which is repeated for eons. Thus the biodiversity.
3.2.U5 Environmental change gives new challenges to species: those that are suited will survive, and those that are not suited will not survive
Humans are modifying the world in many ways, and not all of them for the better. The changes we cause are often severe challenges to animals, plants and microbes in nature, from the introduction of pathogens or exotic invasive species to adding toxic substance or excessive nutrients, or causing climatic change.
A changing climate forces plants and animals to migrate in order to survive. However, research has shown that most plant species are able to migrate at only 1/10th of the speed required to keep up with human-induced climate change.
To make matters worse, human settlements and infrastructure have already subdivided ecosystem habitat into isolated patches. Climate change will make many of these patches uninhabitable for the species that live there.
3.2.U6 Speciation is the formation of new species when populations of a species become isolated and evolve differently from other populations.
Speciation is the process through which new species form.Speciation will depended on:
isolation of species:the process by which two populations become separated by
change of environmental
change of gene pool
This leads to the species adapting overtime and thus speciation. For example a giraffe with a slightly longer neck will be able to reach leaves that others can not. This gives it an advantage and means that this giraffe will be more successful and likely to survive and breed, passing on their genes to future generations. Overtime the population will change to incorporate more advantageous traits like these
Speciation can occur gradually via geographic speciation (allopatric) or competitive speciation (sympatric) or abruptly through mechanisms such as polyploidy (sympatric)
3.2.U7 Isolation of populations can be caused by environmental changes forming barriers such as mountain formation, changes in rivers, sea level change, climatic change or plate movements. The surface of the Earth is divided into crustal, tectonic plates that have moved throughout
The surface of the Earth is divided into tectonic plates, which have moved throughout geological time. This has led to the creation of both physical barriers and land bridges with evolutionary consequences.
Isolation of populations, behavioral differences that preclude reproduction and the inability to produce fertile offspring (leading to speciation) should all be examined, with examples.
Isolation factors are:
Geographical factors: island formation, loss of land bridges and mountain ranges
Behavioural factors: reproductive displays, songs, daily activity
Genetic factors: inability to produce fertile offspring due to genetic different
Reproductive factors: anatomical different especially in reproductive organs
All these Lead to speciation
Modes of speciation are often classified according to how much the geographic separation of incipient species (a group of organisms that is about to become a separate species from other) can contribute to reduced gene flow. The demands of a different environment or the characteristics of the members of the new group will differentiate the new species from their ancestors.
There are three basic ideas of speciation:
Allopatric speciation occurs when a species separates into two separate groups which are isolated from one another. A physical barrier, such as a mountain range or a waterway, makes it impossible for them to breed with one another. Each species develops differently based on the demands of their unique habitat or the genetic characteristics of the group that are passed on to offspring.
Sympatric speciation occurs when there are no physical barriers preventing any members of a species from mating with another, and all members are in close proximity to one another. A new species, perhaps based on a different food source or characteristic, seems to develop spontaneously. The theory is that some individuals become dependent on certain aspects of an environment—such as shelter or food sources—while others do not. Some scientist don't believe it exist.
Parapatric speciation occurs when a species is spread out over a large geographic area. Although it is possible for any member of the species to mate with another member, individuals only mate with those in their own geographic region. Like allopatric and peripatric speciation, different habitats influence the development of different species in parapatric speciation. Instead of being separated by a physical barrier, the species are separated by differences in the same environment.
When Arizona's Grand Canyon formed, squirrels and other small mammals that had once been part of a single population could no longer contact and reproduce with each other across this new geographic barrier. They could no longer interbreed. The squirrel population underwent allopatric speciation. Today, two separate squirrel species inhabit the north and south rims of the canyon. On the other hand, birds and other species that could easily cross this barrier continued to interbreed and were not divided into separate populations
The cichlid fish in the lakes of East Africa are one of the largest families of vertebrates. In Lake Victoria there are 170 species of cichlids; in Lake Tanganyika 126 species; and in Lake Malawi 200 species. These populations have probably been isolated for millions of years and have been exposed to different selection pressures because of there slightly different environments. Therefore the fish have adapted to their specific environments. As long as the population is large enough, isolated populations can thrive, if the populations become too small they will die out.
Large flightless birds: e.g. the emu, ostrich, cassowary and rhea. They only occur on those continents that were once part of Gondwana land (Africa, Australia/New Zealand, and South America). However, because Gondwana land split up a very long time ago the species are not closely related.
Australasia (and Antartica) split from Gondwana land a long time ago. At that time, both marsupials and early placental mammals lived in the same area. In South America and Africa placental mammals out-competed marsupials while in Australia the opposite occurred and now marsupials are only found in Australia and Papua New Guinea. The placental mammals present in Australia are rare and came either by sea (seals) or air (bats) or were introduced by humans (cats, dogs, rabbits and rats)
3.2.U8 The distribution of continents has also caused climatic variations and variation in food supply, both contributing to evolution
Life has not evolved on its own; it has evolved on a planet that has experienced changing geology, geography, and climate
The consequences of plate tectonics on speciation should be understood (that is, the separation of gene pools, formation of physical barriers and land bridges) together with the implications these consequences have for evolution.
The role of plate activity in generating new and diverse habitats, thus promoting biodiversity, should also be considered. Detailed understanding of the mechanism of plate tectonics is not required.
The earths crust is split into sections called tectonic plates. Convection currents in the mantle (the molten layer under the crust) drag these plates slowly in different directions. In some places the edges of the plates crash into each other (destructive and collision boundaries) and in other places the plates edges move apart (constructive boundaries).
Plate tectonics have created the major mountain ranges of the world and their movement has changed the locations of landmasses and some of the links between landmasses. This has had a significant impact on species diversity:
Mountain ranges form a physical barrier that many species do not cross, this allows isolation of gene pools and subsequently uniques species of plants and animals living on the same land masses.
Plate seperation such as the African and South American plates moving apart also allow isolation of gene pools. The movement of land masses has also meant that many continents have travelled through different climate zones (over millions of years) which has led to species adaptation and evolution.
Plate Tectonics therefore lead to the development of physical barriers, and land bridges (e.g. between North and South America, which allows movement of organisms, e.g. Bears from North to South America.) Land bridges may be formed by continental drift or lowered sea levels (e.g. between North America and Asia, the Bering Straits).
Another example of how plate tectonics has affected the evolution of species is the Llamas and camels, which are both domesticated animals fulfilling similar roles and they are distant cousins. Kangaroos fulfil and similar ecological role to cattle in Australia. Both are large herbivores (eat grass and convert it into meat). Kangaroos are marsupial mammals. All mammals suckle their young with milk produced by their mothers.
Placental mammals have a placenta, which provides food for the embryo in the uterus and are the most successful in evolutionary terms. Marsupials have a pouch in which the embryo develops. The monotremes lay eggs (duck-billed platypus) are the third group of mammals. Marsupials and monotremes are mostly confined to Australasia and placental mammals have out-competed them in all other regions.
3.2.U9 Mass extinctions of the past have been caused by various factors, such as tectonic plate movements, super-volcanic eruption, climatic changes (including drought and ice ages), and meteorite impact—all of which resulted in new directions in evolution and therefore increased biodiversity.
A mass extinction is defined as a period in which at least 75 % of the total number of species on the Earth at the time are wiped out.. There have been five major mass extinction events in Earth's history. These are shown in the table given, along with the major events that characterized each.
We are currently living through the 'sixth' mass extinction according to many scientists. The present rate of extinction of species is thought to be 140 000 species per year since approximately 10 000 BC and has continued into the 21st century. The extinction includes disappearance of large mammals such as the woolly mammoth.
The sixth extinction event is thought to be occurring at a rapidly increasing rate. The two major causes for the sixth extinction are thought to be human hunting and the rapid rise in human population.
Application & Skills
3.2.A1 Explain how plate activity has influenced evolution and biodiversity.
The movement of the major and minor plates in relation to one another is called plate tectonics.
Movement of tectonic plates can produce barriers such as mountain ranges, oceans and rift valleys that can lead to isolation of gene pools and then speciation
Land bridges can form from previously unconnected plates allowing species to spread.
The movement of plates through different climatic zones allows new habitats to present themselves, and allow for different adaptations.
3.2.A2 Discuss the causes of mass extinctions.
There is still a lot of debate among scientists as to what caused the mass extinctions. To be a valid theory to explain what
caused mass extinctions, the theory must:
explain all the losses of species at a particular mass extinction event (not just specific losses e.g. dinosaurs).
explain why some organisms died and others survived.
be based on natural events and processes that are shown to have occurred around the time of extinction.
Two of the hypotheses put forward are:
the impact theory of extinction
massive volcanic activity
Between 1.4 and 1.8 million species have been described and named. The number of species alive on Earth is ever changing. Some become extinct, while others evolve into new species. Extinction is a natural process, eventually all species become extinct. The average lifespan for a species varies. The rates at which extinctions occur are not constant and depend on the background extinction rate as well as mass extinctions (when a sudden loss of species occurs in a relatively short period of time).
Background extinction rate: is the natural extinction rate of all species. Rates are estimated by using fossil records. There are about 5000 mammal species alive today and there background extinction rate is estimated at 1 per 200 years but the past 400 years has seen 89 mammalian extinctions.
Another 169 mammalian species are listed as critically endangered. E.O. Wilson, a well-known biologist, thinks that the current rate of extinction is 1000 times the background rate and that is caused by human activities. The rate is estimated to be at 3 species per hour. The rate is not equally spread but is worse in certain areas (hotspots).
Mass extinctions have occurred over geological time and there have been five major ones. We know this from fossil records. These could have been caused by a natural disaster such as a volcanic eruption, which results in many species dying out as they can not adapt to the changed environment.
Most biologists think we are now in the sixth mass extinction, called the Holocene extinction event. This extinction event started 10 000 years ago when large mammals such as the woolly mammoth and sabre-tooth tiger became extinct. But the extinction rate has accelerated in the last 100 years. This is mostly due to climate change, which is caused by one species, humans.
Humans alter the landscape on an unprecedented scale. Some organisms thrive in the environments that we create (e.g. urban rats, and domesticated animals), while most do not. It has taken 5-10 million years for the planets biodiversity to recover after past mass extinctions.
The previous mass extinctions were due to physical (abiotic) causes over long timespans. The current mass extinction has a biotic cause, humans. Humans are the direct cause of ecosystem stress because we:
Transform the environment: with roads, cities, and agriculture.
Overexploit other species: fishing, hunting, harvesting.
Introduce alien species: which may not have natural predators and therefore make the environment unstable.
Pollute the environment: which may kill species directly or indirectly.
Natural Selection Virtual Lab - Gene frequency
pHet Natural Selection Simulation
Peppered Moth Simulation
pHet Simulation: Plate Tectonics
Science Sauce Topic 3.2 Natural Selection and Evolution
Science Sauce Topic 3.2 Isolation of Populations
Science Sauce Topic 3.2 Mass Extensions
Natural History Museum site
Darwin's full works - Darwin Online
Charles Darwin and evolution - Natural Selection animation for CSU
Natural Selection - Charles Darwin and Evolution
Evolution 101 on natural selection and speciation - Berkeley
Important Dates and Cool Creatures In Earths History - University of Kentucky
Plate tectonic - PBS
Island Biogeography from Stanford University, USA
Another good island biogeography animation showing the physical migration, real-time data, and a graph.
Millennium seed bank
In The News
Mechanics of speciation: Model examines factors that contribute to emergence of new species - Science Daily June 27, 2011
The Looming Mass Extinction by Humans - BBC News 1 Nov 2013
The theory of evolution by natural selection tells us that change in populations is achieved through the process of natural selection-is there a difference between a convincing theory and a correct one?
Within the human population, distinct characteristics have evolved within different populations through natural selection and exposure to the environmental conditions that were unique to the regions of those populations. How has globalization altered some of the environmental factors that were formerly unique to different human populations?
Human impact has increased the rate at which some mass extinctions have occurred on a global scale.
The Habitable Planet: Biodiversity Decline Video
The theory of evolution explains how the enormous variety of life could come into existence. How it is possible for primitive life forms to spawn the millions of different creatures, that exist today. Unfortunately, evolution is often misunderstood, because it's mechanisms seem counter intuitive
The Socotra archipelago in the Arabian Sea supports so many diverse and unique species that it has been described as the most alien place on Earth. Hank takes you on a tour of this weird place in this episode of SciShow.
Genetic technologies can be helpful conservation tools, particularly when they help us better monitor the species we are trying to preserve, but they are no substitute for protecting habitats
Paul Andersen explains the importance of genetic variation within a population.
Hank guides us through the process of natural selection, the key mechanism of evolution
Hank explains specification - the evolutionary process by which new biological species arise - in terms of finches, ligers, mules, and dogs.
Mr. Andersen describes how plate tectonics shapes our planet. Continental and oceanic platers are contrasted and major plate boundaries are discussed
Visualization of asteroid impact that killed dinosaurs 65 million years ago, based on accurate research and scientific fact. Created by Radek Michalik (email@example.com) at the Science Institute of Columbia College Chicago
According to the United Nations, we are losing about 200 species per day--a thousand times the normal background rate of extinction. How does this stack up to previous mass extinctions?
Hank takes us on a trip through time to revisit the 5 major mass extinction events that have impacted species over the Earth's history, and leaves us with some thoughts about what could possibly be the sixth event - the one caused by human activities.
"Medea Hypothesis" author Peter Ward argues that most of Earth's mass extinctions were caused by lowly bacteria. The culprit, a poison called hydrogen sulfide, may have an interesting application in medicine.
Topic 3.2: Origins of Biodiversity
Natural Selection Simulation
Natural Selection vs Selective Breeding
Examples of Natural Selection
Peppered Moth Simulation --- Peppered Moth video (melanistic insects)
Natural Selection of Pocket mice
The Beak of the Finch -- Darwin's Finches
Antibiotic Resistance -- Antibiotic Resistance video
Gene Pools (genetic connections)
Speciation video- ted.ed
Modes of Speciation
Causes of Speciation
Continental Drift and Plate Tectonics
Continental Drift explained- video
Plate Tectonics Computer Simulation- plate movement
Plate Tectonics Map