Extinction

The Tasmanian tiger (Thylacinus cynocephalus) is an example of an extinct species.
External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds
The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction.
The passenger pigeon, one of the hundreds of species of extinct birds, was hunted to extinction over the course of a few decades.
Scorched land resulting from slash-and-burn agriculture
The golden toad was last seen on May 15, 1989. Decline in amphibian populations is ongoing worldwide.
The large Haast's eagle and moa from New Zealand
Tyrannosaurus, one of the many extinct dinosaur genera. The cause of the Cretaceous–Paleogene extinction event is a subject of much debate amongst researchers.
Georges Cuvier compared fossil mammoth jaws to those of living elephants, concluding that they were distinct from any known living species.
A great hammerhead caught by a sport fisherman. Human exploitation now threatens the survival of this species. Overfishing is the primary driver of shark population declines, which have fallen over 71% since 1970.

Termination of a kind of organism or of a group of kinds , usually a species.

- Extinction
The Tasmanian tiger (Thylacinus cynocephalus) is an example of an extinct species.

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Alpha

All adult Eurasian blue tits share the same coloration, unmistakably identifying the morphospecies.

Species

Basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity.

Basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity.

All adult Eurasian blue tits share the same coloration, unmistakably identifying the morphospecies.
A region of the gene for the cytochrome c oxidase enzyme is used to distinguish species in the Barcode of Life Data Systems database.
The cladistic or phylogenetic species concept is that a species is the smallest lineage which is distinguished by a unique set of either genetic or morphological traits. No claim is made about reproductive isolation, making the concept useful also in palaeontology where only fossil evidence is available.
A chronospecies is defined in a single lineage (solid line) whose morphology changes with time. At some point, palaeontologists judge that enough change has occurred that two species (A and B), separated in time and anatomy, once existed.
A cougar, mountain lion, panther, or puma, among other common names: its scientific name is Puma concolor.
The type specimen (holotype) of Lacerta plica, described by Linnaeus in 1758
Ernst Mayr proposed the widely used Biological Species Concept of reproductive isolation in 1942.
Palaeontologists are limited to morphological evidence when deciding whether fossil life-forms like these Inoceramus bivalves formed a separate species.
Horizontal gene transfers between widely separated species complicate the phylogeny of bacteria.
John Ray believed that species breed true and do not change, even though variations exist.
Carl Linnaeus created the binomial system for naming species.
Blackberries belong to any of hundreds of microspecies of the Rubus fruticosus species aggregate.
The butterfly genus Heliconius contains many similar species.
The Hypsiboas calcaratus–fasciatus species complex contains at least six species of treefrog.
Carrion crow
Hybrid with dark belly, dark gray nape
Hybrid with dark belly
Hooded crow
Seven "species" of Larus gulls interbreed in a ring around the Arctic.
Opposite ends of the ring: a herring gull (Larus argentatus) (front) and a lesser black-backed gull (Larus fuscus) in Norway
A greenish warbler, Phylloscopus trochiloides
Presumed evolution of five "species" of greenish warblers around the Himalayas

Genes can sometimes be exchanged between species by horizontal gene transfer; new species can arise rapidly through hybridisation and polyploidy; and species may become extinct for a variety of reasons.

Lucretius

Evolution

Change in the heritable characteristics of biological populations over successive generations.

Change in the heritable characteristics of biological populations over successive generations.

Lucretius
Alfred Russel Wallace
Thomas Robert Malthus
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Duplication of part of a chromosome
This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation.
Mutation followed by natural selection results in a population with darker colouration.
Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.
Homologous bones in the limbs of tetrapods. The bones of these animals have the same basic structure, but have been adapted for specific uses.
A baleen whale skeleton. Letters a and b label flipper bones, which were adapted from front leg bones, while c indicates vestigial leg bones, both suggesting an adaptation from land to sea.
Common garter snake (Thamnophis sirtalis sirtalis) has evolved resistance to the defensive substance tetrodotoxin in its amphibian prey.
The four geographic modes of speciation
Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.
Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Paleogene extinction event at the end of the Cretaceous period.
The hominoids are descendants of a common ancestor.
As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.

Existing patterns of biodiversity have been shaped by repeated formations of new species (speciation), changes within species (anagenesis) and loss of species (extinction) throughout the evolutionary history of life on Earth.

Trilobites were highly successful marine animals until the Permian–Triassic extinction event wiped them all out.

Extinction event

Widespread and rapid decrease in the biodiversity on Earth.

Widespread and rapid decrease in the biodiversity on Earth.

Trilobites were highly successful marine animals until the Permian–Triassic extinction event wiped them all out.
Badlands near Drumheller, Alberta, where erosion has exposed the Cretaceous–Paleogene boundary.
An artist's rendering of an asteroid a few kilometers across colliding with the Earth. Such an impact can release the equivalent energy of several million nuclear weapons detonating simultaneously.
Many species of plants and animals are at high risk of extinction due to the destruction of the Amazon rainforest

It occurs when the rate of extinction increases with respect to the rate of speciation.

Beavers from North America constitute an invasive species in Tierra del Fuego, where they have a substantial impact on landscape and local ecology through their dams.

Invasive species

Introduced organism that becomes overpopulated and harms its new environment.

Introduced organism that becomes overpopulated and harms its new environment.

Beavers from North America constitute an invasive species in Tierra del Fuego, where they have a substantial impact on landscape and local ecology through their dams.
Kudzu, a Japanese vine species invasive in the southeast United States, growing in Atlanta, Georgia
Vinca spreading in a garden
The brown tree snake (Boiga irregularis)
Lantana growing in abandoned citrus plantation; Moshav Sdei Hemed, Israel
Chinese mitten crab (Eriocheir sinensis)
Cargo ship de-ballasting
An American alligator attacking a Burmese python in Florida; the Burmese python is an invasive species which is posing a threat to many indigenous species, including the alligator
Alien invasive species Parthenium hysterophorus smothering native flora in Achanakmar Tiger Reserve, Bilaspur, Chhattisgarh, India

Native species can be threatened with extinction through the process of genetic pollution.

2016 conservation indicator which includes the following indicators: marine protected areas, terrestrial biome protection (global and national), and species protection (global and national).

Conservation biology

2016 conservation indicator which includes the following indicators: marine protected areas, terrestrial biome protection (global and national), and species protection (global and national).
Efforts are made to preserve the natural characteristics of Hopetoun Falls, Australia, without affecting visitors' access.
White gyrfalcons drawn by John James Audubon
More conservation research is needed for understanding ecology and behaviour of asiatic wild dog in central China.
Roosevelt and Muir on Glacier Point in Yosemite National Park
A pie chart image showing the relative biomass representation in a rain forest through a summary of children's perceptions from drawings and artwork (left), through a scientific estimate of actual biomass (middle), and by a measure of biodiversity (right). Notice that the biomass of social insects (middle) far outweighs the number of species (right).
Tadrart Acacus desert in western Libya, part of the Sahara
An art scape image showing the relative importance of animals in a rain forest through a summary of (a) child's perception compared with (b) a scientific estimate of the importance. The size of the animal represents its importance. The child's mental image places importance on big cats, birds, butterflies, and then reptiles versus the actual dominance of social insects (such as ants).

Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.

Summary of major biodiversity-related environmental-change categories expressed as a percentage of human-driven change (in red) relative to baseline (blue)

Biodiversity loss

Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity.

Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity.

Summary of major biodiversity-related environmental-change categories expressed as a percentage of human-driven change (in red) relative to baseline (blue)
Demonstrator against biodiversity loss, at Extinction Rebellion (2018).
The Forest Landscape Integrity Index measures global anthropogenic modification on remaining forests annually. 0 = Most modification; 10= Least.
Industrial processes contributing to air pollution though the emission of carbon dioxide, sulfur dioxide, and nitrous oxide.
Mass fishing of Pacific jack mackerel (with possible bycatch) with a Chilean purse seiner.
DPSIR: drivers, pressures, state, impact and response model of intervention
An infographic describing the relationship between biodiversity and food.
Earth's 25 terrestrial hot spots of biodiversity. These regions contain a number of plant and animal species and have been subjected to high levels of habitat destruction by human activity.

Even though permanent global species loss is a more dramatic and tragic phenomenon than regional changes in species composition, even minor changes from a healthy stable state can have dramatic influence on the food web and the food chain insofar as reductions in only one species can adversely affect the entire chain (coextinction), leading to an overall reduction in biodiversity, possible alternative stable states of an ecosystem notwithstanding.

African pygmy kingfisher, showing coloration shared by all adults of that species to a high degree of fidelity.

Speciation

Evolutionary process by which populations evolve to become distinct species.

Evolutionary process by which populations evolve to become distinct species.

African pygmy kingfisher, showing coloration shared by all adults of that species to a high degree of fidelity.
Comparison of allopatric, peripatric, parapatric and sympatric speciation
Cichlids such as Haplochromis nyererei diversified by sympatric speciation in the Rift Valley lakes.
Rhagoletis pomonella, the hawthorn fly, appears to be in the process of sympatric speciation.
Reinforcement assists speciation by selecting against hybrids.
Gaur (Indian bison) can interbreed with domestic cattle.
Male Drosophila pseudoobscura
Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote. In plants, this can effectively be a new species, reproductively isolated from its parents, and able to reproduce.
Phyletic gradualism, above, consists of relatively slow change over geological time. Punctuated equilibrium, bottom, consists of morphological stability and rare, relatively rapid bursts of evolutionary change.

This has a snowball effect, with large species growing at the expense of the smaller, rarer species, eventually driving them to extinction.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

Biology

Scientific study of life.

Scientific study of life.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
In the Bohr model of an atom, electrons (blue dot) orbit around an atomic nucleus (red-filled circle) in specific atomic orbitals (grey empty circles).
Model of hydrogen bonds (1) between molecules of water
Organic compounds such as glucose are vital to organisms.
A phospholipid bilayer consists of two adjacent sheets of phospholipids, with the hydrophilic tails facing inwards and the hydrophobic heads facing outwards.
The (a) primary, (b) secondary, (c) tertiary, and (d) quaternary structures of a hemoglobin protein
Structure of an animal cell depicting various organelles
Structure of a plant cell
Example of an enzyme-catalysed exothermic reaction
Respiration in a eukaryotic cell
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
In meiosis, the chromosomes duplicate and the homologous chromosomes exchange genetic information during meiosis I. The daughter cells divide again in meiosis II to form haploid gametes.
Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
Bases lie between two spiraling DNA strands.
The extended central dogma of molecular biology includes all the processes involved in the flow of genetic information.
Regulation of various stages of gene expression
Composition of the human genome
Construction of recombinant DNA, in which a foreign DNA fragment is inserted into a plasmid vector
Model of concentration gradient building up; fine yellow-orange outlines are cell boundaries.
Natural selection for darker traits
Comparison of allopatric, peripatric, parapatric and sympatric speciation
Bacteria – Gemmatimonas aurantiaca (-=1 Micrometer)
Archaea – Halobacteria
Diversity of protists
Diversity of plants
Diversity of fungi. Clockwise from top left: Amanita muscaria, a basidiomycete; Sarcoscypha coccinea, an ascomycete; bread covered in mold; chytrid; Aspergillus conidiophore.
Bacteriophages attached to a bacterial cell wall
Root and shoot systems in a eudicot
The xylem (blue) transports water and minerals from the roots upwards whereas the phloem (orange) transports carbohydrates between organs.
Reproduction and development in sporophytes
Negative feedback is necessary for maintaining homeostasis such as keeping body temperature constant.
Diffusion of water and ions in and out of a freshwater fish
Different digestive systems in marine fishes
Respiratory system in a bird
Circulatory systems in arthropods, fish, reptiles, and birds/mammals
Asynchronous muscles power flight in most insects. a: Wings b: Wing joint c: Dorsoventral muscles power upstrokes d: Dorsolongitudinal muscles power downstrokes.
Mouse pyramidal neurons (green) and GABAergic neurons (red)
Sexual reproduction in dragonflies
Cleavage in zebrafish embryo
Processes in the primary immune response
Brood parasites, such as the cuckoo, provide a supernormal stimulus to the parenting species.
Terrestrial biomes are shaped by temperature and precipitation.
Reaching carrying capacity through a logistic growth curve
A (a) trophic pyramid and a (b) simplified food web. The trophic pyramid represents the biomass at each level.
Fast carbon cycle showing the movement of carbon between land, atmosphere, and oceans in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. Effects of the slow carbon cycle, such as volcanic and tectonic activity, are not included.
Efforts are made to preserve the natural characteristics of Hopetoun Falls, Australia, without affecting visitors' access.

Conservation biology is the study of the conservation of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.

Rainforest ecosystems are rich in biodiversity. This is the Gambia River in Senegal's Niokolo-Koba National Park.

Ecosystem

An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact.

An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact.

Rainforest ecosystems are rich in biodiversity. This is the Gambia River in Senegal's Niokolo-Koba National Park.
Flora of Baja California Desert, Cataviña region, Mexico
Global oceanic and terrestrial phototroph abundance, from September 1997 to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential and not an actual estimate of it.
Sequence of a decomposing pig carcass over time
Biological nitrogen cycling
Loch Lomond in Scotland forms a relatively isolated ecosystem. The fish community of this lake has remained stable over a long period until a number of introductions in the 1970s restructured its food web.
Spiny forest at Ifaty, Madagascar, featuring various Adansonia (baobab) species, Alluaudia procera (Madagascar ocotillo) and other vegetation
A hydrothermal vent is an ecosystem on the ocean floor. (The scale bar is 1 m.)
The High Peaks Wilderness Area in the 6000000 acre Adirondack Park is an example of a diverse ecosystem.
The Forest Landscape Integrity Index measures global anthropogenic modification on remaining forests annually. 0 = Most modification; 10= Least.

Ecosystem collapse could be reversible and in this way differs from species extinction.

Life

Characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased or because they never had such functions and are classified as inanimate.

Characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased or because they never had such functions and are classified as inanimate.

Adenovirus as seen under an electron microscope
Definition of cellular life according to Budisa, Kubyshkin and Schmidt.
The structure of the souls of plants, animals, and humans, according to Aristotle
Cyanobacteria dramatically changed the composition of life forms on Earth by leading to the near-extinction of oxygen-intolerant organisms.
Deinococcus radiodurans is an extremophile that can resist extremes of cold, dehydration, vacuum, acid, and radiation exposure.
Animal corpses, like this African buffalo, are recycled by the ecosystem, providing energy and nutrients for living creatures

Extinction is the term describing the dying-out of a group or taxon, usually a species.