Demonstrate understanding of evolutionary processes leading to speciation
Year 12 Recap
Before you start this topic it will be a good thing to recap your Year 12 Biology course in the areas of species/ mutations and gene pools. Link here
Intro to the topic
Biological evolution, simply put, is descent with modification. This definition encompasses small-scale (micro) evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations or macro evolution). Evolution helps us to understand the history of life.
Biological evolution is not simply a matter of change over time. Lots of things change over time: trees lose their leaves, mountain ranges rise and erode, you grow hair in funny places, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance.
The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother.
Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today. Evolution means that we're all distant cousins: humans and kiwis, wetas and sheep.
Key words Link (at the bottom of the page there are also animations linked to the key words)A great podcast explaining how evolution works. And another link from the University of Waikato and their excellent NZ Evolution pages.This standard is all about processes that lead to new species forming (speciation). Before you start be very clear what a species is. Here is a good link and a great video below. The standard goes through all the different processes that could lead to a new species forming and probably most importantly covers how New Zealand provided the conditions and selection pressures to allow some pretty crazy organisms to form such as that flightless bird and the massive carrot eating weta you see on the front page. Just remember this is not the Animal and plant topic! you need to be thinking of why and how the species has formed from an evolution population standpoint and not only the individual behaviours and responses of an organism.
Here is a great link to most of the well known NZ animals at the Waikato University website. Use the following worksheet to guide your thoughts. Hint, New Zealand will be incorporated into the end of year exam. To do well in this standard you will be able to link the terminology to NZ examples. Just as important is how the geology and climate patterns effected the selection pressures of the organisms.
The following documentary is well worth a watch, trust me it will help. Ghosts of Gondwana
Evolution of plants and animals in NZ, a long read but good. Link to Te Awa
You must be able to list and discuss all the agents that contribute to evolution (or changes in the gene pool). Make up your own mnemonic to remember these.Non-random mating, Natural selection, Mutation, Genetic drift (or use Bottleneck and Founder effect), Gene flow (or use Immigration and Emigration). (thanks LAC Biology for this idea).
Lets start thinking about evolution...
•The change in the gene pool of a population from generation to generation.
•It is important to remember that individuals do not evolve, populations evolve.
•All the genes in a population are called the gene pool.
•The ratio of different alleles in that population can change over time.
•As the ratio changes, so evolution occurs.
So what's this standard about. Click on key words to take you to sites to help you understand the concepts. The fist part of the standard covers Evolutionary processes. This is the how part of "speciation" and covers mutation, gene flow, natural selection and genetic drift.
Some key people to at least be familiar with. This probably will not be in the test.
Georges Curvier - Was a French anatomist and is largely responsible for the development of Palaeontology between 1769 - 1832. He recorded the succession of fossils in the Paris Basin. He recognised that the fossils of simpler organisms were in the oldest rock strata, and that there were many extinctions. Cuvier believed that species were fixed. Curvier thought that the boundries between strata were caused by catastrophes like drought, fires and floods. Cuvier thought that the effects of extinctions were probably localised and that after the catastrophe passed, new organisms from the surrounding areas would repopulate the area. This ended up being given the name Catastrophism.Jean Baptist Lamarck - He lived between the years 1774 and 1829. In 1809 Lamarck proposed that organisms could gradually bring about changes in themselves to suit the environment and that these changes could be passed on to their offspring. This was known as the “Inheritance of acquired characteristics”. We now know that this is not possible as changes in somatic cells can not be passed on to offspring.Charles Darwin (who had the best beard in history) lived between the years of 1809 and 1882. Charles Darwin is known as the “Father of Evolution” He thought that there was a unity of life, and that all organisms were related through a common ancestor. He thought similar things could be grouped together, he used Linnaeus’ taxonomy to group his organisms together.Darwin showed that species do not remain unchanged over time which become one of the cornerstones to modern evolutionary thinking.Animations to startAnimation one - Intro to evolution. Covers lightly the main parts or the "big picture".
Animation two - This goes through gene flow. An important idea to understand as you will use this while answering questions.
The concept of Species
Definition to learn: Group of interbreeding or potentially interbreeding individuals that give rise to fertile offspring.
Ring species - A term used when you see two species that are joined by a series of structural and intermediate types but appear different, usually the two species can no longer interbreed. The example you see in all textbooks is the herring gull and black- backed gull (both from europe) but most scientists think this example is wrong. Most NCEA examiners still believe this happens in Gulls so unless they ask about the problems with the use of gulls it does occur!! It definitely happens in a couple of rare examples. Here is a link explaining this. Here is a link to this.
Populations of a species that are distinguishable by one or more characteristics much like geographic races in humans.
the region where genetically different populations meet and interbreed a small amount mixing genotypes.
The prevention of gene flow between populations of the same species. This can lead to speciation (new species forming) Examples of this are towards the end of this page. In New Zealand this is usually linked to ice ages and a sea level either rising or sinking but this can be prezygotic or postzygotic which I will cover further down the page.
Looking at a prezygotic example - lacewings animation.
The role of mutation
Mutations are changes in the DNA. A single mutation can have a large effect (punctuated equilibrium (with some stasis thrown in for good measure), but in many cases, evolutionary change is based on the accumulation of many smaller mutations (gradualism).
- The only source of new alleles is mutation.
- These mutations are rare and random.
- Only a mutation in cell lines which lead to the formation of gametes are passed on.
- These are usually harmful and are normally carried in the recessive condition.
- Occasionally a mutation is good for adaptation to an environment – it may be an advantage to offspring.
- The main thing to remember that for a mutation to effect evolution over a long period of time these advantageous mutations may become established in the population.
Excellent Nature magazine article on mutations and evolution link
Types of mutations link
Wiki article covering mutations link
Mutation animation link
Gene flow—also called gene migration—is any movement of genes from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or organisms moving to new niches/ habitats. If genes are carried to a population where those genes previously did not exist, gene flow can be a very important source of genetic variation. If this is stopped mutations may lead after a very long period of time to speciation. This is often the case for New Zealand's example of variations.
How it can be linked to speciation?
Normally populations became separated by mountains/ hills/ geographical barriers. Gene flow between populations stops / do not mate / cannot mate / reproductively isolated / no interbreeding occurs. Due to new niches there will be different selection pressures. New alleles/ phenotypes/ traits/ adaptations selected for. Isolation of populations resulted in no gene flow, leading to eventual speciation.
Animation on Gene flow Gene flow
Gene flow link
Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population.
There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, as greater mobility of an individual tends to give it greater migratory potential. Animals tend to be more mobile than plants, although pollen and seeds may be carried great distances by animals or wind.
Evolution is the process by which modern organisms have descended from ancient ancestors. Evolution is responsible for both the remarkable similarities we see across all life and the amazing diversity of that life—but exactly how does it work?Fundamental to the process is genetic variation upon which selective forces can act in order for evolution to occur. This section examines the mechanisms of evolution focusing on:Descent and the genetic differences that are heritable and passed on to the next generation;Mutation, migration (gene flow), genetic drift, and natural selection as mechanisms of change;The importance of genetic variation;The random nature of genetic drift and the effects of a reduction in genetic variation;How variation, differential reproduction, and heredity result in evolution by natural selection; and
How different species can affect each other’s evolution through coevolution.
The role of Natural selection and Genetic drift
Genetic drift—along with natural selection, mutation, and migration—is one of the basic mechanisms of evolution.
In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. That, in a nutshell, isgenetic drift. It happens to ALL populations—there’s no avoiding the vagaries of chance.
Genetic drift affects the genetic makeup of the population but, unlike natural selection, through an entirely random process. So although genetic drift is a mechanism of evolution, it doesn’t work to produce adaptations.
tldr Through sampling error, genetic drift can cause populations to lose genetic variation.
You must learn a definition and apply it to the example.
Here is an example using Darwins Finches.
There is genetic variation within the species, individuals with longer beaks can gain more food and be reproductively successful. Individuals best adapted to each the seeds of the balloon vine tend to leave more offspring.
Adding comparison to adaptive advantage
Longer mouth parts as a means to access a new and increasing food source over that of the short beaked bugs. There is a change in the population with an increasing prevalence of balloon vine as an invasive weed.
Definition from an exam.
Natural selection is where the best suited individuals have a greater chance of reproductive success.The survival of the species is promoted.
individuals with more suited / better adapted phenotypes will compete more favourably than others that are less suited and are more likely to reproduce, passing on their favourable alleles.
Favourable alleles will increase in frequency within the population.
Mitochondrial genes have come up in previous questions
Mitochondrial DNA is used to investigate speciation because it is only passed on via one parent and is not subject to recombination, like nuclear DNA. It also gathers mutations, which can be used to estimate how long two populations have been separated.
A great starter animation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or "cladogenesis," as opposed to "anagenesis" or "phyletic evolution" occurring within lineages. Whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion.
- This is the formation of a new species from an existing species. It is not gradual change over time as a definition.
- a species is a group of organisms that can interbreed to produce fertile offspring.
- Members of a species belong to the same gene pool.
- For a new species to form there must be separation of the gene pool of the species from the gene pool of the parent population.
Definition from exam
Speciation isthe process of forming new biological species. Speciation
involves the loss of ability to interbreed to produce fertile offspring
Modes of Speciation
Sympatric - Click the word for animations looking at this
Sympatric speciation is the process through which new species are formed from one common ancestor while in the same geographic region. Sympatric speciation does not require large geographical distance to reduce gene flow in the population. An example of sympatric speciation is the three spined stickleback, a freshwater fish found in Canada. The three spined stickleback with larger mouths feed on prey in the depth at the waters edge while the smaller mouth spined stickleback feed on plankton near the surface of the water. This variation in phenotype is due to non random mating (ie large fish only mated with other large fish) and due to selection pressures in competition for food. Source:Erena
Sympatric speciation is where species don’t interbreed due to niche differences.
For instance, they may breed at different times, which means that there is limited gene flow. Eventually, genetic changes will mean they cannot interbreed.
Allopatric Click the words for animations explaining these concepts.
Almost certainly most speciation occurs allopatrically (that is, when the forms occur in different places). The main driving forces appear to be drift and/or mutation drive the divergence between the forms, although sometimes very different selection pressures (natural selection) may be the dominant force. Reduced gene flow (lack of "migration" in the population genetics sense) is also important. For example, the rise of the Andes appears to have been very important in producing patterns of genetic differentiation in neotropical plants and animals. The best-worked examples of sympatric speciation in animals used to be for Rhagoletis flies. More recently, it has become a very active area for fish and brood parasitic birds. A major driving force here may be specialization on different host plants or different habitats and resources (in the case of fish or birds). As the host plants diverge in phenology, secondary compounds or other ecological features, it becomes more and more disadvantageous to fall "somewhere in the middle". The eventual result may be the evolution of reproductive isolating mechanisms that reduce or prevent successful offspring production across forms. Some of the spectacular radiation of African cichlid fishes is probably also a result of sympatric speciation, perhaps driven by a combination of ecological and sexual selection. Recent work on the cichlids also suggests that water level lowering created separated lakes that further promoted speciation processes (i.e., more traditional allopatric speciation). Sympatric speciation can occur more readily in plants because plants can change their chrosome number (polyploidy) and persist or spread by asexual reproduction. Parapatric speciation occurs where the ranges of two forms abut but do not overlap extensively. In such cases, lower fitness of hybrids drives increased differentiation, eventually resulting in premating isolation.
•Usually populations of organisms get geographically separated (eg by river) and Gene flow stops --> Genetic isolation occurs.
•Differences in natural selection can cause differences in allele frequencies between the populations over time.
•Differences may accumulate, when the populations come back together they now no may longer interbreed and are now defined as seperate species.
New Zealands isolation and island formation have led to many examples of allopatric speciation.
Snares and Rockhopper is an example of allopatric speciation, as they live on different islands. Because they now have different crests, the Rockhopper and Snares penguins don’t recognise each other as a mate, which is good, as if they did, the offspring may be infertile, so they have wasted time and energy.
Reproductive Isolating Mechanisms
Whats an isolating mechanism?
A reproductive isolating mechanism is a barrier that prevents two organisms from differing species from mating and producing fertile offspring / prevents successful interbreeding / prevents gene flow
This works to preserve the uniqueness of gene pools, prevent hybridisation thus reinforcing separateness of species.
Because species are finely tuned to their niche adding genes from another species suited to another niche will cause a reduction in fitness.
Prezygotic Mechanisms (Factors acting before a zygote forms)
· Geographical (spatial) – physical barriers preventing gene exchange. example being different robin species in NZ can’t breed together as they are on different islands.
· Temporal (time/season) – breeding doesn’t occur because reproductive activities (mating, flowering) occurs at different times, seasons, years between species.
· Ecological (habitat) – no breeding b/c organisms occupy different niches in same habitat. Eg ground dwelling monkey doesn’t breed with tree dwelling monkey.
· Gamete Mortality – Sperm and egg fail to fuse. Eg sperm of one species may die inside female of another species or sperm may not recognise chemical attractant from another species’ egg.
· Behavioural (ethological) – If an organism can’t carry out the courtship rituals of another species then mating won’t occur (b/c male female aggression isn’t reduced, physiological changes not synchronised (eg ovulation at time of mating)
· Structural (morphological ) – shape of copulatory organs (insect lock and key reproductive parts) and mating pheromones (moths) are species specific.
Postzygotic Isolating Mechanisms (Factors acting after a zygote forms)
· Hybrid sterility – offspring of two different species (eg mule from donkey and horse) is often sterile. Usually because offspring has an odd chromosome number (eg 53) – pairing of chromosomes at meiosis to create gametes can’t occur with an odd number.
· Hybrid Inviability (zygote mortality) – genetic incompatibility means that even if a zygote forms from two different species it won’t divide properly because of unmatched chromosome numbers
· Hybrid breakdown – because of conflict between genes is often infertile or inviable. Even if the first generation is fertile (usually with reduced viability & fertility)
Gradualism vs Punctuated Equilibrium
Gradualism is thought to occur when species slowly and steadily diverge from one another over time.
Punctuated equilibrium is thought to occur when there are long periods of little change in species and then short bursts of speciation when there is rapid change in the environment or selection pressures.
Sexual selection and speciation
Some good animations
Polyploidy is due to nondisjunction / failure of chromosomes to separate during meiosis resulting in an extra set of chromosomes in the offspring. This leads to instant speciation / no gene flow / new species.. The offspring cannot reproduce with is parent species/ can only reproduce vegetatively / asexually and so gene flow does not occur.
Hermaphrodite animals usually are polyploidy, such as flatworms, and earthworms. Polyploid humans usually abort spontaneously.
Polyploidy = when an organism contains 3 or more times the haploid (1N) number of chromosomes.
E.g. Normal for 2N (homologous pairs), polyploidy = 3N or more)
Allopolyploidy = type of polyploidy, results from mating between TWO different SPECIES.
Amphiploidy = The name given to the step when there is an error in meiosis (non disjunction) resulting in double the number of chromosomes in the hybrid.
Autopolyploidy = form of polyploidy, results from mating between SAME SPECIES
Non-disjunction – this is the process that leads to these mutations and how species can go from producing infertile hybrids to fertile new species.
Visualising Polyploidy (basic) - https://www.youtube.com/watch?v=nQ3Rjh661X8&index=22&list=PLmjJBIXLVmpBAaTppoD3F5V6OeP14w8UG
Tragopogon: Understanding the evolution of Polyploidy
Sympatric Speciation via Polyploidy
NOTES from No Brain too Small - Polyploidy
(thanks to D McKenzie from NGHS for the links above)
Example of what you will usually have to cover in a polyploidy question
· describes polyploidy as a doubling / multiple of chromosome sets
· describes effect of polyploidy on phenotype, e.g. hybrid vigour
· explain why species must be closely related
· explains why hybrids are infertile
· explains the role of meiotic error/ double chrom #/ non-disjunction/ amphiploidy in polyploidy
· explains the role of self fertilisation in polyploidy
· links the changes in genotype to the changes in phenotype in modern wheat development
· explains instant speciation or sympatric in terms of reproductive isolation
species evolving in response to each other.
As the slowest penguins are predated on, the more agile penguins pass on their alleles, so penguins become more agile overall. As a result, the most successful seals will be the ones that can catch these more agile penguins, and so the more successful seals will pass on their alleles, so both species become more agile.
From the 2014 Exam
The evolutionary relationship between the monarch butterfly and the milkweed plant is an example of co-evolution, where the species have exerted selection pressures on each other over time. The monarch butterfly is adapted to survive the toxicity of the milkweed, which normally poisons most other animal species. The milkweed is adapting to the damage caused by the monarch caterpillar feeding on its leaves by undergoing rapid regrowth of damaged tissue.
A co-evolution relationship develops where over time two species develop specific adaptations to enable their existence in the presence of the other organism. This might be, for example, predator-prey, parasitic, mutualistic or herbivory relationships, so that both are able to survive the impact of one upon the other.
In the case of the monarch butterfly and the milkweed plant, the monarch caterpillar has developed immunity to the milkweed’s poisonous alkaloids. This gives the monarch a virtual monopoly over milkweed both as a food supply for its larvae and a safe place for laying its eggs, as the poisonous nature of the plant keeps other animals from eating it. Potential predators of the monarch butterfly when they, in turn, become poisonous to many animals, will be reduced. The milkweed, in response to the caterpillar herbivory, have developed the ability to rapidly regenerate and replace damaged tissues. There would be pressure for this to happen where monarch caterpillar populations are high and the resulting damage to milkweed plants due to caterpillar feeding is also high. The high levels of herbivory could threaten the co-evolutionary relationship if plants became too heavily grazed and the monarchs lost their food and egg-laying preference and the protection it offers.
Convergent and divergent evolution
convergent evolution is where similar selection pressures result in similar adaptations in species from different ancestors.
Species arising from different evolutionary lines/ without a common ancestor (must indicate no relation in the past) similar phenotypes/ adaptations/ traits/ structures/ analogous structures have evolved due to occupation of similar niches/ having similar selection pressures/ similar habitats/ similar environmental conditions
when conditions change very slowly, the selection pressure is not very intense. This means that while some individuals will have a greater chance of reproductive success, any change in allele frequency will occur over a long period. This results in gradual change of the species
Sudden changes in niche availability or environmental changes after a long period of stasis (no change) can lead to periods of rapid evolutionary change -punctuated evolution.
Example of how this usually happens in NZ
New / empty niches are available / mountain building glaciations/ ice ages/ sea level changes.
Populations of (insert species here) spread into different areas due to competition for resources (food, nesting sites, mates).
Excellence example - Comparing the two
when conditions change very slowly, the selection pressure is not very intense. This means that while some individuals will have a greater chance of reproductive success, any change in allele frequency will occur over a long period. This results in gradual change of the species, such as in milliganii. This is gradualism. Whereas with the introduction of a species to a new place, such as Dracophyllum to New Zealand, the one species has a number of new niches, each with its own selection pressures – causing sudden speciation, which is punctuated equilibrium.
Scientific evidence for evolution
which may include examples from New Zealand’s flora and fauna, will be selected from fossils, comparative anatomy, molecular biology and biography. The section below will cover this.
Paleontology - a quick intro can be found here
fossil evidence - Yip all the information is here, thanks Waikato Uni! Link
comparative anatomy (homologous and analogous structures)
Meet Shashana, love these videos!
Molecular biology (proteins and DNA analysis) Wikipedia article
Molecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure and function of nucleic acids and protein. Some of the key topics that spurred development of the field have been the evolution of enzyme function, the use of nucleic acid divergence as a "molecular clock" to study species divergence, and the origin of noncoding DNA.
Mitochondrial DNA Evidence
mtDNA analysis provides evidence for how closely related the organisms / groups are and their times of divergence mtDNA is found only in the mitochondria of cells (and not the nucleus of cells). Therefore, it is not subject to the processes of meiosis and crossing over.
Mitochondria remain in the cytoplasm of egg cells so are passed on when the egg is fertilized. They are therefore passed down the female / maternal lineage from generation to generation.
Changes in mtDNA result from mutation only and these are not subject to natural selection. Mutations in mtDNA typically occur at a steady rate and this typically is more rapid than in nuclear DNA, this allows scientists to use mtDNA as a molecular clock.
Therefore, by comparing presence of mutations in mtDNA from different individuals / groups, scientists can determine not only how closely related they are but the likely times of divergence of individuals / groups. These comparisons are now the main source of evidence used by scientists to produce phylogenetic trees.
Biogeography is a branch of geography that studies the past and present distribution of the world's many species. It is usually considered to be a part of physical geography as it often relates to the examination of the physical environment and how it affects species and shaped their distribution across space. As such it studies the world's biomes and taxonomy - the naming of species. In addition, biogeography has strong ties to biology, ecology, evolution studies, climatology, and soil science.
Types of Biogeography
The distribution of many groups of NZ animals only makes sense if we accept that they are all from a common ancestor, a good example being the ratites (The kiwi's cuzzy's). Another example are those sneaky marsupials that are distributed across the southern continents, as they arose during the Mesozoic period when a single landmass broke away. Ask your teacher to show you the land of the kiwi dvd (the new one, not the boring old one).
Geographical isolation can happen when populations become geographically separated due to environmental events such as mountain uplift / tectonic plate movement / sea level changes/ ice ages so gene flow cannot happen between populations so becomes reproductively isolated.Physical barriers may change the environment / habitat / niche, which alters the selection pressures. New phenotypes/ adaptations lead to new species.
Today, biogeography is broken into three main fields of study. The three fields are historical biogeography, ecological biogeography, and conservation biogeography. Each field, however, looks at phytogeography (the past and present distribution of plants) and zoogeography (the past and present distribution of animals).
Historical biogeography is called paleobiogeography and studies the past distributions of species. It looks at their evolutionary history and things like past climate change to determine why a certain species may have developed in a particular area. For example, the historical approach would say there are more species in the tropics than at high latitudes because the tropics experienced less severe climate change during glacial periods. This led to fewer extinctions and more stable populations over time.
The branch of historical biogeography is called paleobiogeography because it often includes paleogeographic ideas- most notably plate tectonics. This type of research uses fossils to show the movement of species across space via moving continental plates. Paleobiogeography also takes varying climate as a result of the physical land being in different places into account for the presence of different plants and animals.
Ecological biogeography looks at the current factors responsible for the distribution of plants and animals. The most common fields of research within ecological biogeography are climatic equability, primary productivity, and habitat heterogeneity.
Climatic equability looks at the variation between daily and annual temperatures. It is harder to survive in areas with high variation between day and night and seasonal temperatures. Because of this, there are fewer species at high latitudes because more adaptations are needed to be able to survive there. In contrast, the tropics have a steadier climate with fewer variations in temperature. This means plants do not need to spend their energy on being dormant and then regenerating their leaves and/or flowers, they don’t need a flowering season, and they do not need to adapt to extreme hot or cold conditions.
Primary productivity looks at the evapotranspiration rates of plants. Where evapotranspiration is high, so is plant growth. Therefore, areas like the tropics that are warm and moist foster plant transpiration allowing more plants to grow there. In high latitudes, it is simply too cold for the atmosphere to hold enough water vapor to produce high rates of evapotranspiration and there are fewer plants present.
Finally, habitat heterogeneity leads to the presence of more biodiversity (a greater number of species present).
New Zealand's Geology
NZ Mountains are very young when compared with many mountains around the world. The main ranges are still being formed by collisions between the Pacific and Australian plates. Mountain barriers tend to isolate animals populations from each other. This produces selection pressures for new species to evolve.
Volcanoes have a large effect on the species present both before and after an eruption. Many species may be completely wiped out and may not re-colonise an effected area again. Plants may re-colonise areas buried in ash and new species evolve to occupy the barren lands. This can be linked to the bottleneck and founder effects.
Changing Sea Levels
Several times in the past few million years, ices ages have caused sea level changes. Each time the polar ice caps increase in size and the sea level drops 80-100 metres. Shallow sea floors become dry land and some islands become joined. During interglacial periods sea levels rise again and some mountains become islands. These islands cause isolation and new species evolve. E.g. Kaka and Kea and the Weta species.
Ice ages also have a more direct effect on life – It gets colder. 20 000 years ago NZ was covered mostly by snowfields and cold-climate grasslands. The climate caused forests to shrink to a few coastal areas in the north containing mostly Totara and Rimu.
All this changed when the Earth’s climate began to warm up again 15 000 years ago. Forest spread and many warm climate species arrived and new species evolved.
Phylogeny and Cladistics
Cladistics is a particular method of hypothesizing relationships among organisms.
There are three basic assumptions in cladistics:
- Any group of organisms are related by descent from a common ancestor.
- There is a bifurcating pattern of cladogenesis.
- Change in characteristics occurs in lineages over time.
There is always the classic animations from McGrawHillhttp://highered.mheducation.com/.../PhylogeneticTrees.swf
and probably better http://www.auburn.edu/.../23_ani_phylogenetic_trees.swf
Key words - Click the word for a link to notes/ websites discussing the idea
When a large number of species form to occupy different ecological niches.
Speciation as a result of geographical isolation.
convergent evolution is where similar selection pressures result in similar adaptations in species from different ancestors.
When different species living in the same environment come to look similar
A group of individuals of a species that have many features in common. Another word used is ‘race’.
When one extreme is selected for.
Disruptive (diversifying) selection
Where both extremes are selected for against the middle range. This ultimately produces two new species.
When one species branches to form two or three species.
All the genes in a reproducing population.
Random changes in allele frequencies because of small population size.
The genetic make-up of an individual.
Slow changes between populations that occur as a result of different selection pressures.
Any mechanism that prevents interbreeding of hybrids.
When cells have more than 2n chromosomes. Polyploidy is common in plants.
Where evolution consists of long periods of stability, followed by short rapid changes as a result of critical selection pressures.
The environmental factors that favour certain phenotypes.
A mechanism by which new species are formed.
A group of individuals with common features and ancestry, that will interbreed.
Selection for the middle range against the extremes.
Groups that are very different from each other, but can still interbreed. Subspecies develop from races, but the differences are more extreme.
Speciation within the same area by natural selection. There are a number of niches and groups move into the niches best suited to them.
And finally. This covers most of the points of this topic.