How does genetic diversity increase the chances that a population will survive a change in their environment?
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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. Significant Ideas
Big questions:
Knowledge & Understanding: 3.2.U1 Biodiversity arises from evolutionary processes image from www.lycaenid.org 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. Evolution, the development of new species over very long periods of geological Evidence is found by examination of the fossil record: older rocks contain fossils of simpler forms of life, more recent rocks contain fossils of more complex life forms.
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.
image from https://authortomharper.com/2019/03/21/a-primer-on-evolution-pt-2/ 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. Beneficial change to the gene pool of a species can lead to increased chances of survival and the ability to pass on the same genetic advantage to the next generation. Survival has a genetic basis – nature selects the individuals possessing what it takes to survive. This means successful genes are selected and passed on to the next generation. Over time, a change in the species’ gene pool takes place, and such changes ultimately lead to new species. Changes to the genetic code can also lead to non-beneficial effects, such as the development of a genetic disease, the affected genes can still be passed down through the generations but offer no adaptive advantage. Should such genes be distinctly harmful, individuals with them may die before they can reproduce. Some variation has no effect on the survival of a species (it is said to be neutral). 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.
[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”.] image from www.tutorvista.com Natural Selection is the gradual evolutionary change that results from genetic variation in each 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
3.2.U4 This natural selection will contribute to the evolution of biodiversity over time image from www.tes.com 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.
image from www.lternet.edu 3.2.U6 Speciation is the formation of new species when populations of a species become isolated and evolve differently from other populations. image from evolution.berkeley.edu Speciation is the process through which new species form. Speciation will depended on:
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 image from tutorvista.com 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 factors are:
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 onto 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.
3.2.U8 The distribution of continents has also caused climatic variations and variation in food supply, both contributing to evolution image from www.wonderwhizkids.com 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:
image from from-beginning-to-infinity.tumblr.com
image from www.terrapsych.com 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 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:
Two of the hypotheses put forward are:
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:
image from https://www.nationalgeographic.org/media/mass-extinctions/ Key Terms
Powerpoint and Notes Adapted from Brad Kremer, P Brooks and Ms. McCrindle Correct use of terminology is a key skill in ESS. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary. International-mindedness:
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
Biologists teach that all living things on Earth are related. Is there any solid evidence to back this claim?
Discover natural selection as a mechanism of evolution with the Amoeba Sisters. This video also uncovers the relationship of natural selection and antibiotic resistance in bacteria and emphasizes biological fitness.
There is a dizzying diversity of species on our planet. From genetic evidence we know that all of those species evolved from a single ancient ancestor. But how does one species split in to many? Through the evolutionary process of speciation — which begins when populations become isolated by changes in geography or by shifts in behavior so that they no longer interbreed. This video illustrates the speciation process in birds to help you understand the basis of earth's biodiversity.
In this video you will learn how weird and wonderful animals are formed in the process of speciation and the formation of new species
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 () 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.
Why is a genetically diverse population more likely to survive a change to the environment?A genetically diverse population of individuals is more likely to survive than a population of individuals with similar genetic makeup. Variation allows some individuals within a population to adapt to the changing environment and natural selection allows the expression of those beneficial traits to persist.
How does genetic diversity affect a population change of survival?Genetic diversity is important because it gives species a better chance of survival. However, genetic diversity can be lost when populations get smaller and isolated, which decreases a species' ability to adapt and survive.
Why is genetic diversity important for survival of populations?Genetic diversity is important because it helps maintain the health of a population, by including alleles that may be valuable in resisting diseases, pests and other stresses. Maintaining diversity gives the population a buffer against change, providing the flexibility to adapt.
How does genetic diversity affect a population?Genetic diversity is required for populations to evolve and its loss is related to inbreeding in random mating populations, and thus to reduced population fitness and increased extinction risk. Neutral theory is widely used to predict levels of genetic diversity.
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