Habitat destruction is the process by which natural habitat becomes incapable of supporting its native species. In this process, the organisms that used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity is for the purpose of harvesting natural resources for industrial production and urbanization. Clearing habitats for agriculture is the principal cause of habitat destruction. Other important causes of habitat destruction include mining, logging and urban sprawl. Habitat destruction is ranked as the primary cause of species extinction worldwide, it is a process of natural environmental change that may be caused by habitat fragmentation, geological processes, climate change or by human activities such as the introduction of invasive species, ecosystem nutrient depletion, other human activities. The terms habitat loss and habitat reduction are used in a wider sense, including loss of habitat from other factors, such as water and noise pollution. In the simplest term, when a habitat is destroyed, the plants and other organisms that occupied the habitat have a reduced carrying capacity so that populations decline and extinction becomes more likely.
The greatest threat to organisms and biodiversity is the process of habitat loss. Temple found that 82% of endangered bird species were threatened by habitat loss. Most amphibian species are threatened by habitat loss, some species are now only breeding in modified habitat. Endemic organisms with limited ranges are most affected by habitat destruction because these organisms are not found anywhere else within the world, thus have less chance of recovering. Many endemic organisms have specific requirements for their survival that can only be found within a certain ecosystem, resulting in their extinction. Extinction may take place long after the destruction of habitat, a phenomenon known as extinction debt. Habitat destruction can decrease the range of certain organism populations; this can result in the reduction of genetic diversity and the production of infertile youths, as these organisms would have a higher possibility of mating with related organisms within their population, or different species.
One of the most famous examples is the impact upon China's giant panda, once found across the nation. Now it is only found in fragmented and isolated regions in the southwest of the country, as a result of widespread deforestation in the 20th century. Biodiversity hotspots are chiefly tropical regions that feature high concentrations of endemic species and, when all hotspots are combined, may contain over half of the world’s terrestrial species; these hotspots are suffering from habitat destruction. Most of the natural habitat on islands and in areas of high human population density has been destroyed. Islands suffering extreme habitat destruction include New Zealand, the Philippines, Japan. South and East Asia — China, Malaysia and Japan — and many areas in West Africa have dense human populations that allow little room for natural habitat. Marine areas close to populated coastal cities face degradation of their coral reefs or other marine habitat; these areas include the eastern coasts of Asia and Africa, northern coasts of South America, the Caribbean Sea and its associated islands.
Regions of unsustainable agriculture or unstable governments, which may go hand-in-hand experience high rates of habitat destruction. Central America, Sub-Saharan Africa, the Amazonian tropical rainforest areas of South America are the main regions with unsustainable agricultural practices and/or government mismanagement. Areas of high agricultural output tend to have the highest extent of habitat destruction. In the U. S. less than 25 % of native vegetation remains in many parts of the Midwest. Only 15% of land area remains unmodified by human activities in all of Europe. Tropical rainforests have received most of the attention concerning the destruction of habitat. From the 16 million square kilometers of tropical rainforest habitat that existed worldwide, less than 9 million square kilometers remain today; the current rate of deforestation is 160,000 square kilometers per year, which equates to a loss of 1% of original forest habitat each year. Other forest ecosystems have suffered as more destruction as tropical rainforests.
Farming and logging have disturbed at least 94% of temperate broadleaf forests. Tropical deciduous dry forests are easier to clear and burn and are more suitable for agriculture and cattle ranching than tropical rainforests. Plains and desert areas have been degraded to a lesser extent. Only 10-20% of the world's drylands, which include temperate grasslands and shrublands, deciduous forests, have been somewhat degraded, but included in that 10-20% of land is the 9 million square kilometers of seasonally dry-lands that humans have converted to deserts through the process of desertification. The tallgrass prairies of North America, on the other hand, have less than 3% of natural habitat remaining that has not been converted to farmland. Wetlands and marine areas have endured high levels of habitat destruction. More than 50% of wetlands in the U. S. have been destroyed in just the last 200 years. Between 60% and 70% of European wetlands have been destroyed. In the United Kingdom, there has been an i
Paul R. Ehrlich
Paul Ralph Ehrlich is an American biologist, best known for his warnings about the consequences of population growth and limited resources. He is the Bing Professor of Population Studies of the Department of Biology of Stanford University and president of Stanford's Center for Conservation Biology. Ehrlich became well known for his controversial 1968 book The Population Bomb, which asserted that the world's human population would soon increase to the point where mass starvation ensued. Among the solutions he suggested in that book was population control, to be used in his opinion if voluntary methods were to fail. Ehrlich has been criticized for his opinions. However, Carl Haub observed that Ehrlich's warnings had encouraged governments to change their policies to avert disaster. Ehrlich has acknowledged that some of what he predicted has not occurred, but maintains that his predictions about disease and climate change were correct, that human overpopulation is a major problem. Ehrlich was born in Philadelphia, the son of William Ehrlich and Ruth Ehrlich.
His father was his mother a Greek and Latin scholar and public school teacher. Ehrlich's mother's Reform-Jewish German ancestors arrived in the United States in the 1840s, his paternal grandparents immigrated there from the Galician and Romanian part of the Austrian Empire. During his childhood his family moved to New Jersey, where he attended high school. Ehrlich earned a bachelor's degree in zoology from the University of Pennsylvania in 1953, an M. A. from the University of Kansas in 1955, a Ph. D. from the University of Kansas in 1957, supervised by the prominent bee researcher Charles Duncan Michener. During his studies he participated with surveys of insects in the areas of the Bering Sea and Canadian Arctic, with a National Institutes of Health fellowship, investigated the genetics and behavior of parasitic mites. In 1959 he joined the faculty at Stanford University, being promoted to professor of biology in 1966. By training he is an entomologist specializing in Lepidoptera, he was appointed to the Bing Professorship in 1977.
He is president of the Center for Conservation Biology at Stanford University. He is a fellow of the American Association for the Advancement of Science, the United States National Academy of Sciences, the American Academy of Arts and Sciences and the American Philosophical Society. A lecture that Ehrlich gave on the topic of overpopulation at the Commonwealth Club of California was broadcast by radio in April 1967; the success of the lecture caused further publicity, the suggestion from David Brower the executive director of the environmentalist Sierra Club, Ian Ballantine of Ballantine Books to write a book concerning the topic. Ehrlich and his wife, Anne Ehrlich, collaborated on the book, The Population Bomb, but the publisher insisted that a single author be credited. Although Ehrlich was not the first to warn about population issues – concern had been widespread during the 1950s and 1960s – his charismatic and media-savvy methods helped publicize the topic; the original edition of The Population Bomb began with this statement: "The battle to feed all of humanity is over.
In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate..." Ehrlich argued that the human population was too great, that while the extent of disaster could be mitigated, humanity could not prevent severe famines, the spread of disease, social unrest, other negative consequences of overpopulation. By the end of the 1970s, this prediction proved to be incorrect. However, he continued to argue that societies must take strong action to decrease population growth in order to mitigate future disasters, both ecological and social. In the book Ehrlich presented a number of "scenarios" detailing possible future events, some of which have been used as examples of errors in the years since. Of these scenarios, Ehrlich has said that although, "we stated that they were not predictions and that'we can be sure that none of them will come true as stated,’ – their failure to occur is cited as a failure of prediction.
In honesty, the scenarios were way off in their timing. But they did deal with future issues that people in 1968 should have been thinking about." Ehrlich further states that he still endorses the main thesis of the book, that its message is as apt now as it was in 1968. Ehrlich's opinions have evolved over time, he has proposed different solutions to the problem of overpopulation. In Population Bomb he wrote, "We must have population control at home through a system of incentives and penalties, but by compulsion if voluntary methods fail. We must use our political power to push other countries into programs which combine agricultural development and population control." Voluntary measures he has endorsed include the easiest possible availability of birth control and abortion. In 1967 he had expressed his belief that aid should only be given to those countries that were not considered to be "hopeless" to feed their own populations. In their sequel to The Population Bomb, the Ehrlichs wrote about how the world's growing population dwarfs the Earth's capacity to sustain current living standards.
The book calls for action to confront population growth and the ensuing crisis: When is
The Aral Sea was an endorheic lake lying between Kazakhstan in the north and Uzbekistan in the south. The name translates as "Sea of Islands", referring to over 1,100 islands that had dotted its waters; the Aral Sea drainage basin encompasses Uzbekistan and parts of Tajikistan, Kyrgyzstan, Kazakhstan and Iran. The fourth largest lake in the world with an area of 68,000 km2, the Aral Sea has been shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects. By 1997, it had declined to 10% of its original size, splitting into four lakes: the North Aral Sea, the eastern and western basins of the once far larger South Aral Sea, one smaller intermediate lake. By 2009, the southeastern lake had disappeared and the southwestern lake had retreated to a thin strip at the western edge of the former southern sea. Satellite images taken by NASA in August 2014 revealed that for the first time in modern history the eastern basin of the Aral Sea had dried up; the eastern basin is now called the Aralkum Desert.
In an ongoing effort in Kazakhstan to save and replenish the North Aral Sea, a dam project was completed in 2005. Salinity has dropped, fish are again found in sufficient numbers for some fishing to be viable; the maximum depth of the North Aral Sea is 42 m. The shrinking of the Aral Sea has been called "one of the planet's worst environmental disasters"; the region's once-prosperous fishing industry has been decimated, bringing unemployment and economic hardship. The water from the diverted Syr Darya river is used to irrigate about two million hectares of farmland in the Ferghana Valley; the Aral Sea region is heavily polluted, with consequential serious public health problems. UNESCO added the historical documents concerning the development of the Aral Sea to its Memory of the World Register as a unique resource to study this "environmental tragedy". Geographer Nick Middleton believes that the Amu Darya did not flow into the shallow depression that now forms the Aral Sea until the beginning of the Holocene, it is known that the Amu Darya flowed into the Caspian Sea via the Uzboy channel until the Holocene.
The Syr Darya formed a large lake in the Kyzyl Kum during the Pliocene known as the Mynbulak depression. Most of the area around the Aral Sea was inhabited by desert nomads who left few written records. However, the Oxus delta to the south has a long history under the name of Khwarezm, it was once the westernmost border of Tang dynasty China. Russian naval presence on the Aral Sea started in 1847, with the founding of Raimsk, soon renamed Fort Aralsk, near the mouth of the Syr Darya. Soon, the Imperial Russian Navy started deploying its vessels on the sea. Owing to the Aral Sea basin not being connected to other bodies of water, the vessels had to be disassembled in Orenburg on the Ural River, shipped overland to Aralsk, reassembled; the first two ships, assembled in 1847, were the two-masted schooners named Mikhail. The former was a warship. In 1848, these two vessels surveyed the northern part of the sea. In the same year, a larger warship, the Constantine, was assembled. Commanded by Lt. Alexey Butakov, the Constantine completed the survey of the entire Aral Sea over the next two years.
The exiled Ukrainian poet and painter Taras Shevchenko participated in the expedition, painted a number of sketches of the Aral Sea coast. For the navigation season of 1851, two newly built steamers arrived from Sweden, again by caravan from Orenburg; as the geological surveys had found no coal deposits in the area, the Military Governor-General of Orenburg Vasily Perovsky ordered "as large as possible supply" of saxaul to be collected in Aralsk for use by the new steamers. Saxaul wood did not turn out a suitable fuel, in the years, the Aral Flotilla was provisioned, at substantial cost, by coal from the Donbass. In the early 1960s, the Soviet government decided the two rivers that fed the Aral Sea, the Amu Darya in the south and the Syr Darya in the east, would be diverted to irrigate the desert, in an attempt to grow rice, melons and cotton; this was part of "white gold", to become a major export. This temporarily succeeded, in 1988, Uzbekistan was the world's largest exporter of cotton. Cotton production in Uzbekistan is still important to the national economy of the country.
Cotton is Uzbekistan's main cash crop, accounting for 17% of its exports in 2006. The construction of irrigation canals began on a large scale in the 1940s. Many of the canals were poorly built, allowing water to evaporate. From the Qaraqum Canal, the largest in Central Asia 30 to 75% of the water went to waste. Today, only 12% of Uzbekistan's irrigation canal length is waterproofed. Of the 47,750 km of interfarm irrigation channels in the basin, only 28% have anti-infiltration linings. Only 77% of farm intakes have flow gauges, of the 268,500 km of onfarm channels, only 21% have anti-infiltration linings, which retain on average 15% more water than unlined channels. By 1960, between 20 and 60 km3 of water eac
Ecology is the branch of biology which studies the interactions among organisms and their environment. Objects of study include interactions of organisms that include biotic and abiotic components of their environment. Topics of interest include the biodiversity, distribution and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, the non-living components of their environment. Ecosystem processes, such as primary production, nutrient cycling, niche construction, regulate the flux of energy and matter through an environment; these processes are sustained by organisms with specific life history traits. Biodiversity means the varieties of species and ecosystems, enhances certain ecosystem services. Ecology is not synonymous with natural history, or environmental science, it overlaps with the related sciences of evolutionary biology and ethology. An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function.
Ecologists seek to explain: Life processes and adaptations The movement of materials and energy through living communities The successional development of ecosystems The abundance and distribution of organisms and biodiversity in the context of the environment. Ecology has practical applications in conservation biology, wetland management, natural resource management, city planning, community health, economics and applied science, human social interaction. For example, the Circles of Sustainability approach treats ecology as more than the environment'out there', it is not treated as separate from humans. Organisms and resources compose ecosystems which, in turn, maintain biophysical feedback mechanisms that moderate processes acting on living and non-living components of the planet. Ecosystems sustain life-supporting functions and produce natural capital like biomass production, the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, many other natural features of scientific, economic, or intrinsic value.
The word "ecology" was coined in 1866 by the German scientist Ernst Haeckel. Ecological thought is derivative of established currents in philosophy from ethics and politics. Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology became a much more rigorous science in the late 19th century. Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory; the scope of ecology contains a wide array of interacting levels of organization spanning micro-level to a planetary scale phenomena. Ecosystems, for example, contain interacting life forms. Ecosystems are dynamic, they do not always follow a linear successional path, but they are always changing and sometimes so that it can take thousands of years for ecological processes to bring about certain successional stages of a forest. An ecosystem's area can vary from tiny to vast. A single tree is of little consequence to the classification of a forest ecosystem, but critically relevant to organisms living in and on it.
Several generations of an aphid population can exist over the lifespan of a single leaf. Each of those aphids, in turn, support diverse bacterial communities; the nature of connections in ecological communities cannot be explained by knowing the details of each species in isolation, because the emergent pattern is neither revealed nor predicted until the ecosystem is studied as an integrated whole. Some ecological principles, however, do exhibit collective properties where the sum of the components explain the properties of the whole, such as birth rates of a population being equal to the sum of individual births over a designated time frame; the main subdisciplines of ecology, population ecology and ecosystem ecology, exhibit a difference not only of scale, but of two contrasting paradigms in the field. The former focus on organisms distribution and abundance, while the focus on materials and energy fluxes; the scale of ecological dynamics can operate like a closed system, such as aphids migrating on a single tree, while at the same time remain open with regard to broader scale influences, such as atmosphere or climate.
Hence, ecologists classify ecosystems hierarchically by analyzing data collected from finer scale units, such as vegetation associations and soil types, integrate this information to identify emergent patterns of uniform organization and processes that operate on local to regional and chronological scales. To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a nested hierarchy, ranging in scale from genes, to cells, to tissues, to organs, to organisms, to species, to populations, to communities, to ecosystems, to biomes, up to the level of the biosphere; this framework exhibits non-linear behaviors.
The wolf known as the grey/gray wolf or timber wolf, is a canine native to the wilderness and remote areas of Eurasia and North America. It is the largest extant member of its family, with males averaging 43 -- females 36 -- 38.5 kg. It is distinguished from other Canis species by its larger size and less pointed features on the ears and muzzle, its winter fur is long and bushy and predominantly a mottled gray in color, although nearly pure white and brown to black occur. Mammal Species of the World, a standard reference work in zoology, recognises 38 subspecies of C. lupus. The gray wolf is the second most specialized member of the genus Canis, after the Ethiopian wolf, as demonstrated by its morphological adaptations to hunting large prey, its more gregarious nature, its advanced expressive behavior, it is nonetheless related enough to smaller Canis species, such as the coyote, golden jackal, to produce fertile hybrids. It is the only species of Canis to have a range encompassing both Eurasia and North America, originated in Eurasia during the Pleistocene, colonizing North America on at least three separate occasions during the Rancholabrean.
It is a social animal, travelling in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring. The gray wolf is an apex predator throughout its range, with only humans and tigers posing a serious threat to it, it feeds on large ungulates, though it eats smaller animals, livestock and garbage. A seven-year-old wolf is considered to be old, the maximum lifespan is about 16 years; the global gray wolf population is estimated to be 300,000. The gray wolf is one of the world's best-known and most-researched animals, with more books written about it than any other wildlife species, it has a long history of association with humans, having been despised and hunted in most pastoral communities because of its attacks on livestock, while conversely being respected in some agrarian and hunter-gatherer societies. Although the fear of wolves is pervasive in many human societies, the majority of recorded attacks on people have been attributed to animals suffering from rabies. Non-rabid wolves have attacked and killed people children, but this is rare, as wolves are few, live away from people, have developed a fear of humans from hunters and shepherds.
The English'wolf' stems from the Old English wulf, itself thought to be derived from the Proto-Germanic *wulfaz. The Latin lupus is a Sabine loanword. Both derive from the Proto-Indo-European root * lukwos; the species Canis lupus was first recorded by Carl Linnaeus in his publication Systema Naturae in 1758, with the Latin classification translating into the English words "dog wolf". The 37 subspecies of Canis lupus are listed under the designated common name of "wolf" in Mammal Species of the World, published in 2005; the nominate subspecies is the Eurasian wolf known as the common wolf. The subspecies includes the domestic dog, eastern wolf and red wolf, but lists C. l. italicus as a synonym of C. l. lupus. However, the classification of several as either species or subspecies has been challenged; the evolution of the wolf occurred over a geologic time scale of at least 300,000 years. The gray wolf Canis lupus is a adaptable species, able to exist in a range of environments and which possesses a wide distribution across the Holarctic.
Studies of modern gray wolves have identified distinct sub-populations that live in close proximity to each other. This variation in sub-populations is linked to differences in habitat – precipitation, temperature and prey specialization – which affect cranio-dental plasticity; the archaeological and paleontological records show gray wolf continuous presence for at least the last 300,000 years. This continuous presence contrasts with genomic analyses, which suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as as 20,000 years ago; these analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. However, the geographic origin of this radiation is not known. In 2018, whole genome sequencing was used to compare members of the genus Canis, along with the dhole and the African hunting dog. There is evidence of gene flow between African golden wolves, golden jackals, gray wolves.
One African golden wolf from the Egyptian Sinai Peninsula showed high admixture with the Middle Eastern gray wolves and dogs, highlighting the role of the land bridge between the African and Eurasian continents in canid evolution. There was evidence of gene flow between golden jackals and Middle Eastern wolves, less so with European and Asian wolves, least with North American wolves; the study proposes that the golden jackal ancestry found in North American wolves may have occurred before the divergence of the Eurasian and North American gray wolves. The study indicates that the common ancestor of the coyote and gray wolf has genetically admixed with a ghost population of an extinct unidentified canid; the canid is genetically close to the dhole and has evolved after the divergence of the African hunting dog from the other canid species. The basal position of the coyote compared to the wolf is proposed to be due to the coyote retaining more of the mitochondrial genome of this unknown canid.
In 2013, a genetic study found that the wolf population in Europe was divided along a north-south axis and formed five major clusters. Three clusters were identified occupying southern and
The Mexican wolf known as the lobo, is a subspecies of gray wolf once native to southeastern Arizona, southern New Mexico, western Texas and northern Mexico. It is the smallest of North America's gray wolves, is similar to C. l. nubilus, though it is distinguished by its smaller, narrower skull and its darker pelt, yellowish-gray and clouded with black over the back and tail. Its ancestors were the first gray wolves to enter North America after the extinction of the Beringian wolf, as indicated by its southern range and basal physical and genetic characteristics. Though once held in high regard in Pre-Columbian Mexico, it is the most endangered gray wolf in North America, having been extirpated in the wild during the mid-1900s through a combination of hunting, trapping and digging pups from dens. After being listed under the Endangered Species Act in 1976, the United States and Mexico collaborated to capture all lobos remaining in the wild; this extreme measure prevented the lobos' extinction.
Five wild Mexican wolves were captured alive in Mexico from 1977 to 1980 and used to start a captive breeding program. From this program, captive-bred Mexican wolves were released into recovery areas in Arizona and New Mexico beginning in 1998 in order to assist the animals' recolonization of their former historical range; as of 2017, there are 143 240 in captive breeding programs. The Mexican wolf was first described as a distinct subspecies in 1929 by Edward Nelson and Edward Goldman on account of its small size, narrow skull and dark pelt; this wolf is recognized as a subspecies of Canis lupus in the taxonomic authority Mammal Species of the World. Gray wolves migrated from Eurasia into North America 70,000–23,000 years ago and gave rise to at least two morphologically and genetically distinct groups. One group is represented by the other by the modern populations. One author proposes that the Mexican wolf's ancestors were the first gray wolves to cross the Bering Land Bridge into North America during the Late Pleistocene after the extinction of the Beringian wolf, colonizing most of the continent until pushed southwards by the newly arrived ancestors of C. l. nubilus.
A haplotype is a group of genes found in an organism that are inherited together from one of their parents. Mitochondrial DNA can date back thousands of years. A 2005 study compared the mitochondrial DNA sequences of modern wolves with those from thirty-four specimens dated between 1856 and 1915; the historic population was found to possess twice the genetic diversity of modern wolves, which suggests that the mDNA diversity of the wolves eradicated from the western US was more than twice that of the modern population. Some haplotypes possessed by the Mexican wolf, the extinct Great Plains wolf, the extinct Southern Rocky Mountain wolf were found to form a unique "southern clade". All North American wolves group together with those from Eurasia, except for the southern clade which form a group exclusive to North America; the wide distribution area of the southern clade indicates that gene flow was extensive across the recognized limits of its subspecies. In 2016, a study of mitochondrial DNA sequences of both modern and ancient wolves generated a phylogenetic tree which indicated that the two most basal North American haplotypes included the Mexican wolf and the Vancouver Island wolf.
In 2018, a study looked at the limb morphology of modern and fossil North American wolves. The major limb bones of the dire wolf, Beringian wolf, most modern North American gray wolves can be distinguished from one another. Late Pleistocene wolves on both sides of the Laurentide Ice Sheet — Cordilleran Ice Sheet possessed shorter legs when compared with most modern wolves; the Late Pleistocene wolves from the Natural Trap Cave and Rancho La Brea, southern California were similar in limb morphology to the Beringian wolves of Alaska. Modern wolves in the Midwestern USA and northwestern North America possess longer legs that evolved during the Holocene driven by the loss of slower prey. However, shorter legs survived well into the Holocene after the extinction of much of the Pleistocene megafauna, including the Beringian wolf. Holocene wolves from Middle Butte Cave and Moonshiner Cave in Bingham County, Idaho were similar to the Beringian wolves; the Mexican wolf and pre-1900 samples of the Great Plains wolf resembled the Late Pleistocene and Holocene fossil gray wolves due to their shorter legs.
Unlike eastern wolves and red wolves, the gray wolf species interbreeds with coyotes in the wild. Direct hybridizations between coyotes and gray wolves was never explicitly observed. In a study that analyzed the molecular genetics of the coyotes as well as samples of historical red wolves and Mexican wolves from Texas, a few coyote genetic markers have been found in the historical samples of some isolated individual Mexican wolves. Gray wolf Y-chromosomes have been found in a few individual male Texan coyotes; this study suggested that although the Mexican gray wolf is less prone to hybridizations with coyotes compared to the red wolf, there may have been exceptional genetic exchanges with the Texan coyotes among a few individual gray wolves from historical remnants before the population was extirpated in Texas. However, the same study countered that theory with an alternative possibility that it may have been the red wolves, who in turn once overlapped with both species in the central Texas region, who were involved in circuiting the gene-flows between the coyote
In paleontology, a fern spike is the occurrence of unusually high spore abundance of ferns in the fossil record immediately after an extinction event. The spikes are believed to represent a large, temporary increase in the number of ferns relative to other terrestrial plants after the extinction or thinning of the latter. Fern spikes are associated with the Cretaceous–Paleogene extinction event, although they have been found in other points of time and space such as at the Triassic-Jurassic boundary. Outside the fossil record, fern spikes have been observed to occur in response to local extinction events, such as the 1980 Mount St. Helens eruption. Extinction events have been caused by massive environmental disturbances, such as meteor strikes. Volcanic eruptions can wipe out local ecosystems through pyroclastic flows and landslides, leaving the ground bare for new colonization. For a population to recover and thrive after such an event, it must be able to tolerate the conditions of the disturbed environment.
Ferns have multiple characteristics. Plants reproduce with spores or seeds, meaning those will be what germinates in a disaster's aftermath, but spores have advantages over seeds in the environmental conditions produced by a disaster. They're produced in higher numbers than seeds, are smaller, aiding wind dispersal. While many wind-dispersed pollens of seed plants are smaller and farther dispersed than spores, pollen cannot germinate into a plant and must land in a receptive flower; some seed plants require animals to disperse their seeds, which may not be present after a disaster. These characteristics allow ferns to colonize an area with their spores. Fern spores require light to germinate. Following major disturbances that clear or reduce plant life, the ground would receive ample sunlight that may promote spore germination; some species' spores contain chlorophyll, which hastens germination and may aid rapid colonization of clear ground. After the eruption of El Chichón, the fern Pityrogramma calomelanos was observed to regenerate from rhizomes buried by ash though the plants' leaves were destroyed.
The rhizomes tolerated exposure to sulfur from the volcanic matter. Their survival suggests resilience of ferns to the harsh environmental conditions imposed by certain kinds of disasters, rhizome regeneration may have been a factor in fern recovery after other events. Fern spikes follow the pattern of ecological succession. In the past and in modern times, ferns have been observed to act as pioneer species, their abundance at a site decreases as other plants such as gymnosperms begin to grow. Fern spikes cannot not occur without ferns existing in the area, so spikes occur in regions where ferns are a prominent part of the ecosystem. At the Cretaceous-Paleogene extinction event, a fern spike occurred in the New Zealand area, where ferns made up 25% of plant abundance pre-extinction. After the event, fern abundance increased to 90%. Prehistoric fern spikes can be detected by sampling sediment. Sources include sediment, accumulating in a lake since the event of interest and sedimentary rocks such as sandstone.
Because sediment accumulates over time and thus shows superposition, layers can be assigned to certain times. Spore concentration in a layer can be compared to the concentration at different times, concentration of other particles such a pollen grains. A fern spike is characterized by a higher abundance of fern spores following a disaster accompanied by a decrease in other plant species as indicated by their pollen. Fern abundance will decrease, hence the term "spike" describing the pattern. Modern fern spikes can be directly observed, allow for observation of factors contributing to the spike that may not be detectable otherwise, such as rhizomes persisting in ash; because fern spikes coincide with certain disasters such as meteorite strikes and volcanic eruptions, their presence in the fossil record can indicate those events. A fern spike is believed to support a meteorite impact as cause of the Triassic-Jurassic extinction event, similar to the one causing extinction at the end of the Cretaceous period.
A fern spike followed a fungal spike after the Permian-Triassic extinction event. It has been observed in Australia. After the Triassic-Jurassic extinction event, ferns drastically increased in abundance while seed plants became scarce; the spike has been detected in eastern North Europe. A widespread fern spike occurred after the Cretaceous–Paleogene extinction event; the spike has been predominantly observed in North America, with just one observance outside the continent in Japan. Fern spikes today are observed after volcanic eruptions; the areas affected by the eruptions of Mount St. Helens and El Chichón exhibited such a pattern. Ecological succession Extinction event Fern Paleoecology