Density dependence

Density-dependent fecundity
Parasite-induced vector mortality
Density-dependence processes (red) in filariasis life cycle

In population ecology, density-dependent processes occur when population growth rates are regulated by the density of a population.

- Density dependence

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Intraspecific competition

Interaction in population ecology, whereby members of the same species compete for limited resources.

Male hartebeest locking horns and fiercely defending their territories. An example of direct competition.
Flamingos competing via interference competition, potentially for territories, mates or food.
Exponential human population growth in the last 1,000 years.
Population growth against time in a population growing logistically. The steepest parts of the graph are where the population growth is most rapid.

As a result, the growth rate of a population slows as intraspecific competition becomes more intense, making it a negatively density dependent process.

Mitosis

Part of the cell cycle in which replicated chromosomes are separated into two new nuclei.

Mitosis in an animal cell (phases ordered counter-clockwise).
Mitosis divides the chromosomes in a cell nucleus.
Label-free live cell imaging of Mesenchymal Stem Cells undergoing mitosis
Onion (Allium) cells in different phases of the cell cycle enlarged 800 diameters.
a. non-dividing cells
b. nuclei preparing for division (spireme-stage)
c. dividing cells showing mitotic figures
e. pair of daughter-cells shortly after division
Stages of early mitosis in a vertebrate cell with micrographs of chromatids
Condensing chromosomes. Interphase nucleus (left), condensing chromosomes (middle) and condensed chromosomes (right).
Prophase during mitosis
A cell in late metaphase. All chromosomes (blue) but one have arrived at the metaphase plate.
Metaphase during Mitosis
Anaphase during Mitosis
Telophase during mitosis
Cytokinesis illustration
Cilliate undergoing cytokinesis, with the cleavage furrow being clearly visible
An abnormal (tripolar) mitosis (12 o'clock position) in a precancerous lesion of the stomach (H&E stain)
Mitosis appearances in breast cancer
Cell shape changes through mitosis for a typical animal cell cultured on a flat surface. The cell undergoes mitotic cell rounding during spindle assembly and then divides via cytokinesis. The actomyosin cortex is depicted in red, DNA/chromosomes purple, microtubules green, and membrane and retraction fibers in black. Rounding also occurs in live tissue, as described in the text.
Some types of cell division in prokaryotes and eukaryotes
closed intranuclear pleuromitosis
closed extranuclear pleuromitosis
closed orthomitosis
semiopen pleuromitosis
semiopen orthomitosis
open orthomitosis
Normal and atypical forms of mitosis in cancer cells. A, normal mitosis; B, chromatin bridge; C, multipolar mitosis; D, ring mitosis; E, dispersed mitosis; F, asymmetrical mitosis; G, lag-type mitosis; and H, micronuclei. H&E stain.

This can occur when cells become overcrowded (density-dependent inhibition) or when they differentiate to carry out specific functions for the organism, as is the case for human heart muscle cells and neurons.

Ornithology

Branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to them."

A marbled godwit being ringed for studies on bird migration
A collection of bird skins, belonging to the family Cotingidae
Geese from a wall panel from the tomb of Nefermaat, Egypt c. 2575–2551 B.C.
Belon's comparison of birds and humans in his Book of Birds, 1555
Cover of Ulisse Aldrovandi's Ornithology, 1599
Antonio Valli da Todi, who wrote on aviculture in 1601, knew the connections between territory and song
An Experiment on a Bird in the Air Pump, Joseph Wright of Derby, 1768
Early bird study focused on collectibles such as eggs and nests.
Kaup's classification of the crow family
Quinarian system of bird classification by Swainson
A mounted specimen of a red-footed falcon
Page from an early field guide by Florence Augusta Merriam Bailey
Bird-preservation techniques
Morphometric measurements of birds are important in systematics.
A bird caught in a mist net
A researcher measures a wild woodpecker. The bird's right leg has a metal identification tag.
A California condor marked with wing tags
An Emlen funnel is used to study the orientation behaviour of migratory birds in a laboratory. Experimenters sometimes place the funnel inside a planetarium to study night migration.
Summer distribution and abundance of Canada goose using data from the North American Breeding Bird Surveys 1994–2003
Red-billed queleas are a major agricultural pest in parts of Africa.

He concluded that population was regulated primarily by density-dependent controls, and also suggested that natural selection produces life-history traits that maximize the fitness of individuals.

On Aggression

On Aggression (Das sogenannte Böse.

Cover of the first edition
The psycho-hydraulic model of Lorenz

He maintains that aggression is a technique used to gain control over necessary resources, and serves as a "density-dependent factor" in population control.

Wildlife

Area without being introduced by humans.

A lion (Panthera leo)
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A Douglas squirrel (Tamiasciurus douglasii)
Map of early human migrations, according to mitochondrial population genetics. Numbers are millennia before the present.
Deforestation and increased road-building in the Amazon Rainforest are a significant concern because of increased human encroachment upon wild areas, increased resource extraction and further threats to biodiversity.

Initially when a portion of a wild population is hunted, an increased availability of resources (food, etc.) is experienced increasing growth and reproduction as density dependent inhibition is lowered.

Soay sheep

Breed of domestic sheep descended from a population of feral sheep on the 100 ha island of Soay in the St Kilda Archipelago, about 65 km from the Western Isles of Scotland.

Soay sheep of varied colours
A Soay lamb

The sheep exhibit a phenomenon known as overcompensatory density dependence, in which their population never reaches equilibrium.

Culling

Process of segregating organisms from a group according to desired or undesired characteristics.

Drafting out culled sheep
Double-crested cormorant
New Zealand fur seal
Great white shark
White-tailed deer buck

Diseases are density dependent factors and decreases in the density of the deer populations through culling causes diseases, such as chronic wasting disease and Lyme disease, to spread less quickly and effectively.

Quaternary extinction event

The Quaternary period (from 2.588 ± 0.005 million years ago to the present) has seen the extinctions of numerous predominantly megafaunal species, which have resulted in a collapse in faunal density and diversity and the extinction of key ecological strata across the globe.

Late Pleistocene landscape of northern Spain, by Mauricio Antón (left to right: Equus ferus, Mammuthus primigenius, Rangifer tarandus, Panthera spelaea, Coelodonta antiquitatis)
A reconstruction of normative vegetation cover at the Last Glacial Maximum, circa 18,000 years ago, based on fossil pollen samples recovered from lake and bog sediments.
Speculative life restoration of an Indian aurochs (Bos (primigenius) namadicus)
Several species of the giant long-horned buffalo (Pelorovis): P. antiquus, P. turkanensis & P. oldowayensis (from left to right)
Hippopotamus lemerlei skull
Giant tapir (Tapirus augustus) restoration
Life-sized models of Stegodon
Palaeoloxodon namadicus fossil at Indian Museum, Kolkata, India
Archaeolemur edwardsi life restoration
Archaeoindris fontoynontii life restoration
Comparison of the aepyornithids Mullerornis (front), Vorombe titan (largest), and Aepyornis (back)
Fossil jaw (Xiahe mandible) of a denisovan
Saiga antelope (Saiga spp.) inhabited a range from England and France to Yukon in the Late Pleistocene, diversifying into two species. S. borealis is now extinct and the critically endangered S. tatarica is now limited to the steppe in Kazakhstan and Mongolia
Hippopotamuses (Hippopotamus spp.) inhabited Great Britain until 80,000 BCE, whence due to glacial shifts, hippopotamuses were restricted to southeastern Europe, Mediterranean islands and finally western Asia until 1,000 BCE
Reconstruction of the five phenotypes of Pleistocene wild horse. The coat colours and dimensions are based on genetic evidence and historic descriptions
Elasmotherium sibiricum reconstruction
Cave paintings of the wooly rhinoceros (Coelodonta antiquitatis) in Chauvet-Pont-d'Arc Cave, France
Modern cheetah (Acinonyx jubatus) replaced giant cheetah (Acinonyx pardinensis) in Eurasia after the Middle Pleistocene and inhabited a range from eastern Europe and the Balkans to China. Today, the critically endangered Eurasian cheetah are now restricted to Iran
The 'Gallery of Lions', representations of the Eurasian cave lion in Chauvet-Pont-d'Arc Cave, France
The leopard (Panthera pardus) inhabited the entire expanse of Afro-Eurasia below the 54th parallel north, from modern day Spain and the UK in the west, to South Africa in the south, and Siberia, Japan and Sundaland in the east during the Late Pleistocene
Cave bear (Ursus spelaeus) reconstruction
The woolly mammoth became extinct around 10,000 BCE – except for diminutive relict populations on St. Paul Island and Wrangel Island, which humans did not colonise until 3,600 BCE and 2,000 BCE respectively
Models of the straight-tusked elephant (Paleoloxodon antiquus)
Majorcan giant dormouse (Hypnomys morpheus) life restoration
Long-horned/Giant bison (Bos latifrons), fossil bison skeleton (public display, Cincinnati Museum of Natural History & Science, Cincinnati, Ohio, United States)
Mounted skeleton of a shrub-ox (Euceratherium collinum)
Life restoration of Cervalces scotti
Tetrameryx shuleri restoration
A Chacoan peccary (Catagonus wagneri), believed to be the closest surviving relative of the extinct Platygonus
Western camel (Camelops hesternus) reconstruction
Life restoration of the Yukon horse (Equus lambei)
Mixotoxodon larenis reconstruction
Saber-toothed cat (Smilodon fatalis) reconstruction
Scimitar cat (Homotherium serum) reconstruction
American lion (Panthera atrox) reconstruction
The dhole (Cuon alpinus), now restricted to the southern portions of Asia, was present from Iberia to Mexico during the Late Pleistocene
Short-faced bear (Arctodus simus) reconstruction
American mastodon (Mammut americanum) reconstruction
Columbian mammoth (Mammuthus columbi) reconstruction
Giant beaver (Castoroides ohioensis) skeleton displayed at the Field Museum of Natural History, Chicago, Illinois, United States
Skull of Paralouatta marianae, one of the two Cuban members of the extinct Antilles monkeys (Xenotrichini)
Eremotherium laurillardi skeleton displayed at the Houston Museum of Natural Science
Life restoration of Nothrotheriops texanus
Glyptotherium reconstruction
Californian flightless sea duck (Chendytes lawi)
Californian turkey (Meleagris californica) and megafaunal Californian condor (Gymnogyps amplus) fossil displays at La Brea Tar Pits
Teratornis merriami skeleton from the La Brea Tar Pits in flight pose
Reconstruction of the Cuban giant owl (Ornimegalonyx oteroi), of Pleistocene Cuba, with the carcass of a large solenodon
Fossil skull of Hippidion, a genus of horse native to South America which went extinct in the early Holocene (6,000 BCE).
Reconstruction of a Macrauchenia mother and calf, from Pleistocene South America.
A Toxodon skull in an exhibition commemorating the 200th anniversary of Charles Darwin's birth, Esplanada dos Ministérios, Brasília
Reconstruction of the Dire wolf (Aenocyon dirus)
Life restoration of Arctotherium bonariense.
Cuvieronius reconstruction
An illustration of Megatherium.
Doedicurus clavicaudatus reconstruction, distributed in the temperate savannah and woodland of South America.
Fossil reconstruction of Panochthus frenzelianus with metal model.
The disputed Late Pleistocene remains of a phorusrhacid in Uruguay are similar in size to the above Pliocene age Procariama simplex.
Thylacoleo carnifex rock art
Procoptodon goliath reconstruction
The American flamingo (Phoenicopterus ruber) was one of four species of flamingo present in Australia in the Quaternary, all of which are now either extinct or extirpated. Australia is now the only inhabited continent in the world without flamingoes.
Megalania skeleton, Melbourne Museum
Reconstruction of the extinct Giant Fijian Iguana, Lapitiguana impensa, and two Viti Levu Giant Pigeons, Natunaornis gigoura, from prehistoric Fiji.
Reconstruction of the Late Pleistocene mekosuchine crocodile, Mekosuchus inexpectans, of prehistoric Fiji.
A woolly mammoth hunt
The earliest finds of Homo sapiens point to an emergence during the Middle Pleistocene of Africa. However, there is evidence of extinction waves, particularly of megafaunal carnivores, coinciding with both cranial and technological developments within ancestral Homo during the Early Pleistocene of Africa. This has suggested a human role in these ecological cascades. H. sapiens skull described from Jebel Irhoud, Morocco, dated to 315,000 BCE.
Despeciation within the genus Homo.
Known H. sapiens migration routes in the Pleistocene.
The timing of extinctions follows the "March of Man"
multiple
advances and withdrawals
Combination Hypotheses: Climate Change, Overkill + Climate Change, Second-Order Predation + Climate Change
Overkill Hypothesis and Second-Order Predation

This led to a region wide extinction vortex, resulting in cyclically diminishing bio-productivity and defaunation.

Russell Lande

American evolutionary biologist and ecologist, and an International Chair Professor at Centre for Biodiversity Dynamics at the Norwegian University of Science and Technology (NTNU).

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

He is a specialist of stochastic population dynamics, on which he co-authored a book with Steinar Engen and Bernt-Erik Sæther, and of methods for estimating density dependence from time series of population density.

Simarouba amara

Species of tree in the family Simaroubaceae, found in the rainforests and savannahs of South and Central America and the Caribbean.

Illustration of S. amara (as Quassia simarouba) drawn by Adolphus Ypey and published in 1813. Note that the flowers are incorrectly coloured and should be yellow.
The range of Simarouba amara in green
A mantled howler, one animal that disperses the seeds of S. amara
saplings
The lantern bug, Enchophora sanguinea is found preferentially on the trunks of S. amara

Density-dependent inhibition occurs between seedlings: they are more likely to survive in areas where fewer seedlings of S. amara are growing.