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Define biodiversity.
A4.2.1: Biodiversity as the variety of life in all its forms, levels and combinations
Biodiversity is the variety of life found in an area.
Outline how biodiversity is quantified at different levels of biological organization.
A4.2.1: Biodiversity as the variety of life in all its forms, levels and combinations
Ecosystem diversity considers diversity from the largest overall viewpoint (like the Great Barrier Reef as a whole).
Species diversity (or species richness) is the number of different species in a community. Species evenness measures the relative abundance of each of the species in a community (and is often more important than species biodiversity).
Genetic diversity refers to the size of the gene pool (all the alleles found in the population). Populations with greater genetic diversity (bigger gene pool) can better withstand environmental pressures because at least some of the population is likely to survive, which makes the population more stable. If the population of an organism falls to low levels, the gene pool becomes very small, and any genetic diseases in the population are more likely to be expressed.
Compare the number of species on earth today with past levels of biodiversity.
A4.2.2: Comparisons between current number of species on Earth and past levels of biodiversity
The current rate of extinction is very high, and the number of species alive today is lower than it was a few hundred years ago.
Most loss of diversity is due to human activities (that cause extinctions)
However, the fossil record shows that there are more species alive today than at any other geological time period. This is because there have been many long periods when the speciation rate was higher than the extinction rate (which results in a higher total number of species).
At the same time, the number of species alive today & in the past are estimates because the fossil record is incomplete & biologists are always discovering new species.
Define extinction.
A4.2.2: Comparisons between current number of species on Earth and past levels of biodiversity
Extinction is the complete disappearance of a species from Earth.
State the number of mass extinction events that have occurred on Earth.
A4.2.2: Comparisons between current number of species on Earth and past levels of biodiversity
There have been 5 mass extinction events on Earth.
Outline the cause and effect of mass extinctions that have occurred on Earth.
A4.2.2: Comparisons between current number of species on Earth and past levels of biodiversity
Causes of mass extinction include extreme temperature changes, rising/falling of sea levels, and catastrophic events (huge volcanic eruptions or an asteroid hitting Earth).
The effects of mass extinction are reduced competition for resources and vacant niches that surviving lineages can evolve into.
Define anthropogenic.
A4.2.3: Causes of anthropogenic species extinction
Anthropogenic refers to environmental change caused/influenced by humans (directly or indirectly).
Anthropogenic species extinction is the extinction of a species caused by human activity.
Outline anthropogenic causes of species extinction.
A4.2.3: Causes of anthropogenic species extinction
Human population growth is the overarching cause of species extinction
Hunting and other forms of over-exploitation have killed off species or destroyed their habitat. Urbanization, Deforestation, and clearance of land for agriculture resulted in loss of natural habitat. Humans have also increased pollution, spread pests, spread diseases, and introduced alien invasive species (through global transport).
Outline the extinction of the Moas.
A4.2.3: Causes of anthropogenic species extinction
The North Island Giant Moa (Dinornis novaezealandiae) lived in New Zealand until 1300 BCE.
They were large herbivorous birds that swallowed & retained stones in gizzards to grind plants in their diet & extract more nutrients. They didn’t have wings, but were covered by long feathers (up to 18 cm in length). Females (about 3m tall) were much larger than males.
New Zealand was first populated by Polynesian people around 1200-1300 BCE. The North Island giant moa was hunted to extinction within (about) 100 years of human arrival on the island.
Outline the extinction of the Caribbean monk seal.
A4.2.3: Causes of anthropogenic species extinction
Caribbean monk seals (Neomonachus tropicalis) were declared extinct in 2008 by US National Marine Fisheries (although they could’ve actually gone extinct decades earlier). They were docile marine mammals that lived in the waters around the Gulf of Mexico & Caribbean islands. They likely existed in at least 13 major colonies and had an overall population of about ¼ million.
European colonists killed the monk seal for its oil (for lamps) & food. The seals went on beaches & rocks and showed little fear of humans, so they were easy targets for humans. Some of the last Caribbean monk seals were killed to provide scientific specimens.
List direct and indirect anthropogenic causes of ecosystem loss.
A4.2.4: Causes of ecosystem loss
Human population growth
Hunting & other forms of over-exploitation
Urbanization
Deforestation & clearance of land for agriculture → loss of natural habitat
Pollution
Spread of pests
Diseases
Global transport → Alien invasive species
Outline the cause of the loss of mixed dipterocarp forest ecosystem in Southeast Asia.
A4.2.4: Causes of ecosystem loss
Dipterocarps are a family (Dipterocarpacae) of hardwood, tropical trees with about 500 species.
Dipterocarp forests once were all over islands nations of Southwest Asia. Ecosystems provided by dipterocarp tree species were rich & varied
However, Southeast Asia is losing about 1% of its rainforests each year. In some individual areas, this percentage is much higher. Some regions have lost over 50% of their dipterocarp forested area
The forested land is often completely stripped of its trees (clear-cutting), resulting in total loss of the ecosystem. Sometimes less damaging alternatives for timber removal are used, but clear-cutting is the least expensive option.
The land is then used for agricultural purposes, particularly for planting palm oil trees, whose fruits are used to make oil used in hundreds of products.
List the types of evidence that can be monitored to assess the status of a biodiversity crisis.
A4.2.5: Evidence for a biodiversity crisis
Intergovernmental Science-Policy Platform on Biodiversity
Ecosystem Services reports
Results from reliable surveys of biodiversity in a wide a range of habitats around the world are required
Surveys need to be repeated
Evidence usually has to be from a published source
Peer-reviewed & checked methodology
List the types of evidence that can be monitored to assess the status of a biodiversity crisis.
A4.2.5: Evidence for a biodiversity crisis
Species Population Trends: The abundance & distribution of species over time to identify declines or increases in population size
Habitat Loss & Degradation: Monitoring changes in the extent & quality of natural habitats (deforestation, wetland destruction, urbanization)
Endangered & Threatened Species List
Biodiversity Hotspots: Regions with exceptionally high levels of biodversity, so may require extra conservation attention
Invasive Species Monitoring
Climate Change Indicators
Genetic Diversity
Explain the use of species richness and evenness measures in the tracking of biodiversity over time.
A4.2.5: Evidence for a biodiversity crisis
Species richness measures how many different species there are in an area. Monitoring species richness allows scientists to assess changes in the number of species. An increase indicates that new species have been added, and a decrease indicates extinctions or decline of certain species.
Species evenness measures the abundance of different species in an ecosystem (how well-distributed the populations are). Monitoring species evenness allows scientists to assess how well-distributed resources and ecological niches are. High evenness means species have similar abundance (balanced ecosystem). Low evenness means there is a dominant species, which may suggest a loss of biodiversity.
State the role of “citizen scientists” in monitoring a biodiversity crisis.
A4.2.5: Evidence for a biodiversity crisis
Local individuals (citizen scientists) are an important source of information about populations.
However, they may not be sampling populations in a scientific manner, so data gathered from the local population must be collated by a reliable scientific organization (which can provide established methods of collecting data that can then be published in peer-reviewed research papers).
Discuss the impact of human population growth on the causes of the current biodiversity crisis.
A4.2.6: Causes of the current biodiversity crisis
Human population growth means more resources are necessary to support the population and more pollution is produced. Resources (food, minerals, water) must be sourced from ecosystems.
Examples of human population growth effects on biodiversity:
Over-exploitation of resources: commercial fishing
Hunting: African elephant (Loxodanta africana) populations decrease drastically because animals are often illegally hunted for tusks
Deforestation: forests reduced to extract minerals, hardwoods, or to clear land so it can be used for agriculture
Crops planted are often monocultures → reduced biodiversity
Monoculture agriculture practices: palm oil plantations
Pollution: microparticles of plastics are in almost all parts of the ocean
Increased pest species: Spruce bark beetle (Ips typographus) first found in the UK in 1982, entered from untreated wood from either Europe or Asia
Invasive species: Burmese python (Python bivittatus) accidentally introduced into the Florida Everglades, no natural predators → risk to native wildlife → decreases biodiversity
Urbanization: growing population → houses & services needed, uses land previously unused or used for agriculture
Spread of disease in both humans & other organisms
Compare in situ to ex situ approaches to conservation.
A4.2.7: Need for several approaches to conservation of biodiversity
In situ and ex situ approaches both have the goal of improving biodiversity.
In situ conservation efforts are in natural habitats (such as reclaiming degraded ecosystems, rewilding, and managing nature reserves or natural parks). Ex situ conservation manages species outside their natural area (such as breeding programs by zoos, botanic gardens, seed and animal tissue banks).
Outline the advantages of an in situ approach to conservation.
A4.2.7: Need for several approaches to conservation of biodiversity
In situ approaches to conservation preserves recovering populations in their natural surroundings and help create and maintain conditions for evolution and adaptation within their own environments. Thus, it helps preserve diverse genetic material, preserve natural habitats and species relationships, and protects the land from being exploited by humans.
Define “rewilding.”
A4.2.7: Need for several approaches to conservation of biodiversity
Rewilding is the process of restoring an area of land to its natural uncultivated state. The aim is to let nature take better care of an area than people have done, undo previous damage by removing things, and reduce active management of wildlife populations.
List examples of ex situ conservation programs.
A4.2.7: Need for several approaches to conservation of biodiversity
Breeding Programs by Zoos
Animal husbandry facilities to promote the continuation of species that are threatened & endangered
Artificial insemination: A common technique used by zoos (becuase they usually have very small populations of captive animals); facilitates the production of offspring from animals in 2 different zoos
Promotes genetic diversity within the captive population
Careful pedigrees of animals are kept to choose breeding pairs that will increase genetic diversity
Botanic Gardens: Provide a living store of plant material to promote biodiversity & help conservation efforts
Some plant species only exist in artificial garden facilities
Plants provide a reservoir or genetic material for restoration efforts
Source of material for scientific research of a species
Botanic gardens often exchange seeds or pollen in order to help reserve rare, threatened, or endangered species
Seed Banks: A place to safely store living seeds
Over 1,000 seed banks scattered around the world
Seeds can be used to repopulate a species of plant if necessary
Ideally kept in cool, dark, dry conditions
Ex: Svalbard International Seed Vault in Norway
Animal Tissue Banks:
2 types of tissue stored in animal tissue banks: germplasm (sperm, eggs, embryos) & somatic tissue (non-reproductive tissue samples for DNA research & possible cloning)
Aim: collect & store reproductive cells of various threatened species
Challenge: collect germplasm from wild populations of animals to have reproductive cells to use for captive breeding programs
Tissue usually stored cryogenically & can be kept for a nearly indefinite period of time before use
Outline the rationale used for conservation by the EDGE of Existence program.
A4.2.7: Need for several approaches to conservation of biodiversity
Conservation is rationalized by selecting evolutionary distinct and globally endangered species so that they can be promoted to priority status in conservation programs.
First, the IUCN Red List rating on a species is consulted. A score is generated from this list to show how endangered a species is. Then the species is evaluated for its unique evolutionary history (using DNA sequencing information). Finally, the species that are most endangered and most evolutionarily distinct are given a high EDGE score, meaning they should be prioritized.
Define evolution.
Evolution is the process by which populations of organisms change over time through variations in traits, which are passed on to future generations. This process is driven by mechanisms such as natural selection, genetic drift, mutation, and gene flow, leading to the adaptation of species to their environments and, eventually, the formation of new species.
Distinguish between heritable and acquired characteristics.
Lamarckism: Jean-Baptiste Lamarck proposed that organisms evolve through the inheritance of acquired characteristics. In this theory, traits developed during an organism's lifetime (e.g., a giraffe stretching its neck) are passed on to its offspring.
Darwinian Evolution: Charles Darwin’s theory of evolution by natural selection states that individuals with traits best suited to their environment are more likely to survive and reproduce, passing on these advantageous traits to their offspring. This process leads to gradual changes in the species over time.
State that similarities and differences between DNA, RNA and amino acids sequences can be evidence for evolution.
Natural selection represents a shift from earlier, supernatural explanations of species change to a scientific, evidence-based understanding. Before Darwin, it was widely believed that species were fixed. Darwin's theory proposed that species evolved due to natural selection, a process where organisms better adapted to their environment survive and reproduce, leading to gradual changes in species over generations.
Discuss sequence data showing evidence for evolution within a species
Sequence data (such as DNA, RNA, or protein sequences) provides molecular evidence for evolution. Similarities and differences in genetic sequences can reveal how species are related. For example, DNA sequence comparisons between different populations of a species can show genetic divergence over time, providing evidence of microevolution and speciation within a species.
Outline the relationship between time, evolutionary relationships and biological sequence (nitrogenous base or amino acid) similarities between species.
As species evolve over time, their genetic material (DNA or protein sequences) undergoes changes. The more closely related two species are, the more similar their sequences will be. Over time, mutations accumulate in the genetic code, and the number of differences between species increases. Molecular clock techniques use these genetic differences to estimate evolutionary relationships and the timing of divergence between species.
Define selective breeding and artificial selection.
Artificial selection is the process by which humans selectively breed organisms with desirable traits, manipulating the reproductive process to enhance those traits in future generations. This is different from natural selection, where environmental pressures determine which traits are advantageous.
List reasons why humans have selectively bred domesticated animals and crop plants.
To enhance desirable traits such as size, yield, or resistance to diseases.
To improve aesthetic qualities (e.g., flower color or pet behavior).
To adapt crops and animals to specific climates or environmental conditions.
To increase food production and efficiency.
Outline how selective breeding can lead to rapid evolutionary change.
Selective breeding accelerates evolutionary changes by promoting certain traits in successive generations. By controlling which individuals mate, humans can rapidly increase the frequency of beneficial traits within a population, leading to observable evolutionary changes in a short time span (e.g., dogs of different breeds or faster-growing crops).
Explain an example of artificial selection in a crop plant.
An example is the breeding of corn (maize) for larger ears and higher yields. Through selective breeding, farmers have chosen plants with these desirable traits, leading to significant changes in the size and productivity of corn crops over just a few generations.
Explain an example of artificial selection in a domestic animal.
The domestication of dogs is a prime example. Selective breeding has produced a wide variety of dog breeds with specific traits, such as size, temperament, and behavior. For instance, breeding for smaller size and docile behavior has resulted in breeds like Chihuahuas.
Define homologous structure.
Homologous structures are anatomical features in different species that have a common evolutionary origin, despite having different functions. These structures arise from shared ancestry.
List examples of different types of homologous structures at different levels of biological organization.
Molecular level: DNA sequences, proteins.
Anatomical level: Limbs of vertebrates (e.g., human arm, bat wing, and whale flipper).
Embryological level: Similarities in early development of species like vertebrates
Define pentadactyl limb.
A pentadactyl limb is a limb with five digits, found in most vertebrates (e.g., humans, whales, and birds). The pentadactyl structure is a homologous feature, indicating common ancestry.
List the bone structures present in the pentadactyl limb (specific names of bones are not required).
The pentadactyl limb typically contains:
A single bone in the upper limb (humerus in the arm, femur in the leg).
Two bones in the lower limb (radius and ulna, tibia and fibula).
Multiple smaller bones in the hand or foot (carpals, metacarpals, phalanges).
Identify pentadactyl limb structures in diagrams of amphibians, reptiles, birds and mammals.
In diagrams, you can see that all these groups share a similar basic limb structure (e.g., a single upper bone, two lower bones, and digits). However, the structure may vary depending on function (e.g., wings in birds, flippers in whales).
Relate differences in pentadactyl limb structures to differences in limb function.
The pentadactyl limb’s basic structure is modified to suit different functions:
In humans, it is adapted for grasping.
In birds, it is modified into wings for flight.
In whales, it is modified into flippers for swimming.
In frogs, it is adapted for jumping.
Define divergent evolution.
Divergent evolution occurs when two related species evolve different traits due to different environmental pressures or habitats, leading to speciation.
Describe how divergent evolution explains the pattern found in pentadactyl limb structure yet allows for the specialization of different limb functions.
Divergent evolution explains how the pentadactyl limb, which is homologous across vertebrates, has evolved into different forms to serve distinct functions. Despite sharing a common ancestor, species in different environments adapt their limbs for specific purposes like flight, swimming, or walking.
Define analogous structure.
Analogous structures are body parts in different species that perform similar functions but have different evolutionary origins. These structures are the result of convergent evolution, not shared ancestry.
State an example of an analogous structure found in two species.
The wings of bats (mammals) and insects (arthropods) are analogous structures. While they both serve the function of flight, they evolved independently.
Outline how convergent evolution results in analogous structures.
Convergent evolution occurs when species from different evolutionary backgrounds independently evolve similar traits due to similar environmental pressures or ecological niches. This results in analogous structures, such as wings in bats and birds, which evolved for flight but come from different anatomical origins.
Define speciation.
Speciation is the process through which new species arise from a common ancestor, typically due to reproductive isolation and accumulated genetic differences over time.
Compare the process of speciation with that of gradual evolutionary change in an existing species.
Speciation involves the formation of new species from a population that becomes reproductively isolated from the parent species. In contrast, gradual evolutionary change in an existing species occurs when populations evolve in response to environmental pressures without splitting into new species.
State the impact of speciation and extinction on the total number of species on Earth.
Speciation increases the number of species, adding diversity.
Extinction decreases the number of species, reducing biodiversity
List two processes required for speciation to occur.
Reproductive isolation (mechanisms that prevent interbreeding).
Genetic divergence (differences in allele frequencies).
Define reproductive isolation.
Reproductive isolation occurs when two populations of the same species can no longer interbreed and produce fertile offspring due to genetic or behavioral differences.
Outline how reproductive isolation and differential survival lead to speciation.
Reproductive isolation prevents gene flow between populations, and differential survival (natural selection) leads to changes in allele frequencies. Over time, these processes lead to genetic divergence and the formation of new species.
Outline the speciation between chimpanzees and bonobos.
Chimpanzees and bonobos are two species that arose from a common ancestor. They were geographically separated by the Congo River, leading to reproductive isolation. Different selection pressures on each side of the river caused divergence in behavior and social structures, leading to speciation.
Compare allopatric and sympatric speciation.
Allopatric speciation occurs when populations are geographically isolated, preventing gene flow.
Sympatric speciation occurs when populations are not geographically isolated but become reproductively isolated due to other factors like behavioral changes or temporal differences.
Explain temporal, behavioral and geographic isolation as mechanisms of reproductive isolation.
Temporal isolation: Different mating times prevent interbreeding.
Behavioral isolation: Differences in courtship or mating behaviors prevent mating.
Geographic isolation: Physical barriers (mountains, rivers) prevent gene flow.
Describe an example of temporal, behavioral and geographic reproductive isolation.
Temporal isolation: Different species of frogs may breed at different times of year.
Behavioral isolation: Different species of birds have different courtship rituals.
Geographic isolation: A population of squirrels is split by the Grand Canyon, preventing gene flow.
Outline the cause and consequence of adaptive radiation.
Adaptive radiation occurs when a single ancestral species rapidly diversifies into many different species, each adapted to different ecological niches. This process increases biodiversity.
Outline an example of adaptive radiation as a source of biodiversity.
The Darwin's finches in the Galápagos Islands are an example of adaptive radiation. They evolved from a common ancestor into multiple species, each adapted to different types of food sources on the islands.
Define interspecies hybrid.
An interspecies hybrid is the offspring of two different species, often with mixed traits from both parents. Hybrids are typically infertile, as seen in mules (offspring of a horse and a donkey).
Describe the example of a mule as an infertile interspecies hybrid.
A mule is a hybrid resulting from the mating of a horse (2n) and a donkey (2n). Mules are infertile because they have an intermediate number of chromosomes (63), which prevents proper chromosome pairing during meiosis.
State why organisms have evolved barriers to prevent interspecies hybridization.
Barriers to hybridization prevent the mixing of species and ensure reproductive success. Hybridization can produce sterile offspring, preventing gene flow between species and maintaining the integrity of each species.
Outline pre- and post-zygotic mechanisms to prevent interspecies hybridization.
Pre-zygotic barriers: Prevent mating (e.g., temporal, behavioral, and geographic isolation).
Post-zygotic barriers: Occur after fertilization and include hybrid sterility or inviability.
Define polyploidy.
Polyploidy is a condition where an organism has more than two sets of chromosomes, often due to errors during cell division. It is common in plants.
Outline the cause of polyploidy.
Polyploidy can result from errors during meiosis (e.g., nondisjunction) or hybridization between species, leading to a mismatch in chromosome number.
Explain how allopolyploidy can lead to abrupt speciation.
Polyploid individuals are reproductively isolated from the parent species because their chromosome numbers are incompatible with the parent’s. This isolation can result in the formation of a new species.
Compare autopolyploidy to allopolyploidy.
Autopolyploidy: Polyploidy that arises within a single species.
Allopolyploidy: Polyploidy that arises from hybridization between two different species.
Outline how polyploidy has led to many species of Persicaria.
