In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word тӯндар meaning "uplands", "treeless mountain tract". Tundra vegetation is composed of dwarf shrubs and grasses, lichens. Scattered trees grow in some tundra regions; the ecotone between the tundra and the forest is known as timberline. There are three regions and associated types of tundra: Arctic tundra, alpine tundra, Antarctic tundra. Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt; the word "tundra" refers only to the areas where the subsoil is permafrost, or permanently frozen soil. Permafrost tundra includes vast areas of northern Canada; the polar tundra is home to several peoples who are nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area. Arctic tundra is frozen for much of the year; the soil there is frozen from 25 to 90 cm down. Instead and sometimes rocky land can only support certain kinds of Arctic vegetation, low growing plants such as moss and lichen.
There are two main seasons and summer, in the polar tundra areas. During the winter it is cold and dark, with the average temperature around −28 °C, sometimes dipping as low as −50 °C. However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south. During the summer, temperatures rise somewhat, the top layer of seasonally-frozen soil melts, leaving the ground soggy; the tundra is covered in marshes, lakes and streams during the warm months. Daytime temperatures during the summer rise to about 12 °C but can drop to 3 °C or below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national Biodiversity Action Plan. Tundra tends to be windy, with winds blowing upwards of 50–100 km/h. However, in terms of precipitation, it is desert-like, with only about 15–25 cm falling per year. Although precipitation is light, evaporation is relatively minimal. During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, so the water forms the lakes and marshes found during the summer months.
There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals that vary from 150 to 200 years, with dryer lowland areas burning more than wetter highland areas; the biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. There are a few fish species. There are few species with large populations. Notable animals in the Arctic tundra include reindeer, musk ox, Arctic hare, Arctic fox, snowy owl and polar bears near the ocean. Tundra is devoid of poikilotherms such as frogs or lizards. Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity though they are sometimes rich in natural resources such as petroleum, natural gas and uranium. In recent times this has begun to change in Alaska and some other parts of the world: for example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.
A severe threat to tundra is global warming. The melting of the permafrost in a given area on human time scales could radically change which species can survive there. Another concern is that about one third of the world's soil-bound carbon is in taiga and tundra areas; when the permafrost melts, it releases carbon in the form of carbon dioxide and methane, both of which are greenhouse gases. The effect has been observed in Alaska. In the 1970s the tundra was a carbon sink. Methane is produced when vegetation decays in wetlands; the amount of greenhouse gases which will be released under projected scenarios for global warming have not been reliably quantified by scientific studies, although a few studies were reported to be underway in 2011. It is uncertain whether the impact of increased greenhouse gases from this source will be minimal or massive. In locations where dead vegetation and peat has accumulated, there is a risk of wildfire, such as the 1,039 km2 of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.
Such events may both contribute to global warming. Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, most of the continent is covered by ice fields. However, some portions of the continent the Antarctic Peninsula, have areas of rocky soil that support plant life; the flora presently consists of around 300–400 lichens, 100 mosses, 25 liverworts, aro
Arabis, or rockcress, is a genus of flowering plants, within the family Brassicaceae, subfamily Brassicoideae. The species are herbaceous, annual or perennial plants, growing to 10–80 cm tall densely hairy, with simple entire to lobed leaves 1–6 cm long, small white four-petaled flowers; the fruit is a slender capsule containing 10-20 or more seeds. Natural habitat for Arabis species is rocky mountain/cliff sides or dry sites Cultivation of Arabis is best suited for rock gardens or container gardens; this genus is pollinated by members of Lepidoptera. Though traditionally recognized as a large genus with many Old World and New World members, more recent evaluations of the relationships among these species using genetic data suggest there are two major groups within the old genus Arabis; these two groups are not each other's closest relatives, so have been split into two separate genera. Most of the Old World members remain in the genus Arabis, whereas most of the New World members have been moved into the genus Boechera, with only a few remaining in Arabis.
Selected speciesArabis aculeolata Arabis alpina Arabis armena Arabis blepharophylla Arabis caucasica Willd. Arabis cypria Arabis glabra Arabis hirsuta Arabis kazbegi Arabis kennedyae Arabis lemmonii Arabis macdonaldiana Arabis procurrens Arabis pycnocarpa Arabis serotina Some species, notably A. alpina, are cultivated as ornamental plants in gardens. Many others are regarded as weeds. Natural History Museum
The reindeer known as the caribou in North America, is a species of deer with circumpolar distribution, native to Arctic, sub-Arctic, tundra and mountainous regions of northern Europe and North America. This includes both migratory populations. Rangifer herd size varies in different geographic regions; the Taimyr herd of migrating Siberian tundra reindeer in Russia is the largest wild reindeer herd in the world, varying between 400,000 and 1,000,000. What was once the second largest herd is the migratory boreal woodland caribou George River herd in Canada, with former variations between 28,000 and 385,000; as of January 2018, there are fewer than 9,000 animals estimated to be left in the George River herd, as reported by the Canadian Broadcasting Corporation. The New York Times reported in April 2018 of the disappearance of the only herd of southern mountain caribou in the lower 48 states, with an expert calling it "functionally extinct" after the herd's size dwindled to a mere three animals.
Rangifer varies in size and colour from the smallest, the Svalbard reindeer, to the largest, the boreal woodland caribou. The North American range of caribou extends from Alaska through Yukon, the Northwest Territories and Nunavut into the boreal forest and south through the Canadian Rockies and the Columbia and Selkirk Mountains; the Barren-ground caribou, Porcupine caribou, Peary caribou live in the tundra, while the shy boreal woodland caribou prefer the boreal forest. The Porcupine caribou and the barren-ground caribou form large herds and undertake lengthy seasonal migrations from birthing grounds to summer and winter feeding grounds in the tundra and taiga; the migrations of Porcupine caribou herds are among the longest of any mammal. Barren-ground caribou are found in Kitaa in Greenland, but the larger herds are in Alaska, the Northwest Territories, Nunavut; some subspecies are rare and at least one has become extinct: the Queen Charlotte Islands caribou of Canada. The range of the sedentary boreal woodland caribou covered more than half of Canada and into the northern States in the U.
S. Woodland caribou have disappeared from most of their original southern range and were designated as threatened in 2002 by the Committee on the Status of Endangered Wildlife in Canada. Environment Canada reported in 2011 that there were 34,000 boreal woodland caribou in 51 ranges remaining in Canada.. Siberian tundra reindeer herds are in decline, Rangifer tarandus is considered to be vulnerable by the IUCN. Arctic peoples have depended on caribou for food and shelter, such as the Caribou Inuit, the inland-dwelling Inuit of the Kivalliq Region in northern Canada, the Caribou Clan in Yukon, the Inupiat, the Inuvialuit, the Hän, the Northern Tutchone, the Gwich'in. Hunting wild reindeer and herding of semi-domesticated reindeer are important to several Arctic and sub-Arctic peoples such as the Duhalar for meat, antlers and transportation; the Sami people have depended on reindeer herding and fishing for centuries. In Lapland, reindeer pull pulks. Male and female reindeer can grow antlers annually, although the proportion of females that grow antlers varies between population and season.
Antlers are larger on males. In traditional festive legend, Santa Claus's reindeer pull a sleigh through the night sky to help Santa Claus deliver gifts to good children on Christmas Eve. Carl Linnaeus chose the name Rangifer for the reindeer genus, which Albertus Magnus used in his De animalibus, fol. Liber 22, Cap. 268: "Dicitur Rangyfer quasi ramifer". This word may go back to the Saami word raingo. Linnaeus chose the word tarandus as the specific epithet, making reference to Ulisse Aldrovandi's Quadrupedum omnium bisulcorum historia fol. 859–863, Cap. 30: De Tarando. However and Konrad Gesner – thought that rangifer and tarandus were two separate animals. In any case, the tarandos name goes back to Theophrastus; the use of the terms Reindeer and caribou for the same animal can cause confusion, but the IUCN delineates the issue: "The world's Caribou and Reindeer are classified as a single species Rangifer tarandus. Reindeer is the European name for the species while in North America, the species is known as Caribou."
The word rein is of Norse origin. The word deer was broader in meaning, but became more specific over time. In Middle English, der meant a wild animal of any kind, in contrast to cattle; the word caribou comes through French, from the Mi'kmaq qalipu, meaning "snow shoveler", referring to its habit of pawing through the snow for food. Because of its importance to many cultures, Rangifer tarandus and some of its subspecies have names in many languages. Inuktitut is spoken in the eastern Arctic, the caribou is known by the name tuktu; the Gwich’in people have over two dozen distinct caribou-related words. The species' taxonomic name, Rangifer tarandus, was defined by Carl Linnaeus in 1758; the woodland caribou subspecies' taxonomic name Rangifer tarandus caribou was defined by Gmelin in 1788. Based on Banfield's often-cited A Revision of the Reindeer and Caribou, Genus Rangifer, R. t. caboti, R. t. osborni and R. t. terraenovae were considered invalid and included in R. t. caribou. Some recent authorities have considered them all valid suggesting that they are quite distinct.
In their book entitled Mammal Species of the World, American zoologist Don E. Wilson and DeeAnn Reeder agree with Valerius Geist, specialist on large North American mammals, that
Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them. Conversely, it can be seen as an approach to the study of evolution that incorporates an understanding of the interactions between the species under consideration; the main subfields of evolutionary ecology are life history evolution, the evolution of inter specific relations and the evolution of biodiversity and of communities. Evolutionary ecology considers two things: how interactions shape species through selection and adaptation, the consequences of the resulting evolutionary change. A large part of evolutionary ecology is about finding empirical data as proof. Examples include the Lack clutch size model devised by David Lack and his study of Darwin's finches on the Galapagos Islands. Lack's study of Darwin's finches was important in analyzing the role of different ecological factors in speciation.
Lack suggested that differences in species were adaptive and produced by natural selection, based on the assertion by G. F. Gause that two species cannot occupy the same niche. Richard Levins introduced his model of the specialization of species in 1968, which investigated how habitat specialization evolved within heterogeneous environments using the fitness sets an organism or species possesses; this model developed the concept of spatial scales in specific environments, defining fine-grained spatial scales and coarse-grained spatial scales. The implications of this model include a rapid increase in environmental ecologists' understanding of how spatial scales impact species diversity in a certain environment. Another model is Law and Diekmann's 1996 models on mutualism, defined as a relationship between two organisms that benefits both individuals. Law and Diekmann developed a framework called adaptive dynamics, which assumes that changes in plant or animal populations in response to a disturbance or lack thereof occurs at a faster rate than mutations occur.
It is aimed to simplify other models addressing the relationships within communities. The tangled nature model provides different methods for demonstrating and predicting trends in evolutionary ecology; the model analyzes an individual prone to mutation within a population as well as other factors such as extinction rate. The model was developed by Simon Laird, Daniel Lawson, Henrik Jeldtoft Jensen of the Imperial College London in 2002; the purpose of the model is to create a logical ecological model based on observation. The model is designed such that ecological effects can be accounted for when determining form, fitness of a population. Ecological genetics tie into evolutionary ecology through the study of how traits evolve in natural populations. Ecologists are concerned with how the timeframe leads to genes becoming dominant. Organisms must continually adapt. Genes define which will die out; when organisms develop different genetic variations though they stem from the same species, it is known as polymorphism.
Organisms that pass on beneficial genes continue to evolve their species to have an advantage inside of their niche. The basis of the central principles of evolutionary ecology can be attributed to Charles Darwin in referencing his theory of natural selection and population dynamics, which discusses how populations of a species change over time. According to Ernst Mayr, professor of Zoology at Harvard University, Darwin’s most distinct contributions to evolutionary biology and ecology are as follows: “The first is the non-constancy of species, or the modern conception of evolution itself; the second is the notion of branching evolution, implying the common descent of all species of living things on earth from a single unique origin.” Additionally, “Darwin further noted that evolution must be gradual, with no major breaks or discontinuities. He reasoned that the mechanism of evolution was natural selection.” George Evelyn Hutchinson’s contributions to the field of ecology spanned over 60 years, in which he had significant influence in systems ecology, radiation ecology and entomology.
Described as the “father of modern ecology” by Stephen Jay Gould, Hutchinson was one of the first scientists to link the subjects of ecology and mathematics. According to Hutchinson, he constructed “mathematical models of populations, the changing proportions of individuals of various ages, the ecological niche, population interaction in this technical introduction to population ecology.” He had a vast interest in limnology, due to his belief that lakes could be studied as a microcosmthat provides insight into system behavior. Hutchinson is known for his work Circular Casual Systems in Ecology, in which he states that “groups of organisms may be acted upon by their environment, they may react upon it. If a set of properties in either system changes in such a way that the action of the first system on the second changes, this may cause changes in properties of the second system which alter the mode of action of the second system on the first.” Robert MacArthur is best known in the field of Evolutionary Ecology for his work The Theory of Island Biogeography, in which he and his co-author propose “that the number of species on any island reflects a balance between the rate at which new species colonize it and the rate at which populations of established species become extinct.”
According to the
The tucuxi, alternatively in Peru bufeo gris or bufeo negro, is a species of freshwater dolphin found in the rivers of the Amazon Basin. The word tucuxi is derived from the Tupi language word tuchuchi-ana, has now been adopted as the species' common name. Despite being found in geographic locations similar to those of'true' river dolphins such as the boto, the tucuxi is not related to them genetically. Instead, it is classed in the oceanic dolphin family. Physically, the species resembles the bottlenose dolphin but differs sufficiently to be placed in a separate genus, Sotalia; the costero, related dolphins present in coastal and estuarine environments and grouped together with the tucuxi, have been recognized as a distinct species. The tucuxi is described as looking similar to the bottlenose dolphin, but it is smaller at around 1.5 m. The dolphin is colored light to bluish grey on its back and sides; the ventral region is much lighter pinkish. It is theorized that this pinkish color may be intensified by increased blood flow.
The dorsal fluke is slightly hooked. The beak is well-defined and of moderate length. There are 26 to 36 pairs of teeth in lower jaws; the tucuxi Sotalia fluviatilis was described by Gervais and Deville in 1853, the costero Sotalia guianensis by Pierre-Joseph van Bénéden in 1864. These two species were subsequently synonymized, with the two species being treated as subspecies of marine and freshwater varieties; the first to reassert differences between these two species was a three-dimensional morphometric study of Monteiro-Filho and colleagues. Subsequently, a molecular analysis by Cunha and colleagues unambiguously demonstrated that Sotalia guianensis was genetically differentiated from Sotalia fluviatilis; this finding was reiterated by colleagues with a larger number of genes. The existence of two species has been accepted by the scientific community; the tucuxi exists along much the length of the Amazon River and many of its tributaries, is found in Venezuela, Peru, southeastern Colombia. Numerous individuals have been seen in the Orinoco River further north, though it is not clear whether these are tucuxi or costero.
This species occurs in freshwater habitats only. Tucuxis forage in tight groups chasing fish in rapid dashes just below the water surface, with fish jumping out of their way. Thirty species of fish are known to be prey, some living in protected lakes and channels, while others occur in fast-flowing rivers; the tucuxi exists in small groups of about 10-15 individuals, swim in tight-knit groups, suggesting a developed social structure. Tucuxis are quite active and may jump clear of the water, spy-hop or tail-splash, they are unlikely, however, to approach boats. Tucuxis have been observed to feed with other river dolphins, they feed on a wide variety of fish. Studies of growth layers suggest; the oldest known animal was 36 years of age. The tucuxi is endemic to the regions described above. A significant human problem is fishing nets. Deliberate hunting in the Amazon Basin for food has been reported. Pollution, in particular, mercury poisoning of water due to gold mining, is a particular concern for this species.
The IUCN cites habitat fragmentation by dam construction as a threat, though more detailed study is necessary. Tucuxis are observed not to maintain good attitude in captive environments. A few tucuxis remained in captivity in European aquaria, but the last one died in 2009 in the Zoo of Münster, Germany; the tucuxi is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals. It is listed on Appendix II as it has an unfavourable conservation status or would benefit from international co-operation organised by tailored agreements. List of whale and dolphin species Environmental issues in Brazil National Audubon Society Guide to Marine Mammals of the World ISBN 0-375-41141-0 Encyclopedia of Marine Mammals ISBN 0-12-551340-2 Whales and Porpoises, Mark Carwardine, ISBN 0-7513-2781-6 Whale and Dolphin Conservation Society
Physiology is the scientific study of the functions and mechanisms which work within a living system. As a sub-discipline of biology, the focus of physiology is on how organisms, organ systems, organs and biomolecules carry out the chemical and physical functions that exist in a living system. Central to an understanding of physiological functioning is the investigation of the fundamental biophysical and biochemical phenomena, the coordinated homeostatic control mechanisms, the continuous communication between cells; the physiologic state is the condition occurring from normal body function, while the pathological state is centered on the abnormalities that occur in animal diseases, including humans. According to the type of investigated organisms, the field can be divided into, animal physiology, plant physiology, cellular physiology and microbial physiology; the Nobel Prize in Physiology or Medicine is awarded to those who make significant achievements in this discipline by the Royal Swedish Academy of Sciences.
Human physiology seeks to understand the mechanisms that work to keep the human body alive and functioning, through scientific enquiry into the nature of mechanical and biochemical functions of humans, their organs, the cells of which they are composed. The principal level of focus of physiology is at the level of systems within systems; the endocrine and nervous systems play major roles in the reception and transmission of signals that integrate function in animals. Homeostasis is a major aspect with regard to such interactions within plants as well as animals; the biological basis of the study of physiology, integration refers to the overlap of many functions of the systems of the human body, as well as its accompanied form. It is achieved through communication that occurs in a variety of both electrical and chemical. Changes in physiology can impact the mental functions of individuals. Examples of this would be toxic levels of substances. Change in behavior as a result of these substances is used to assess the health of individuals.
Much of the foundation of knowledge in human physiology was provided by animal experimentation. Due to the frequent connection between form and function and anatomy are intrinsically linked and are studied in tandem as part of a medical curriculum. Plant physiology is a subdiscipline of botany concerned with the functioning of plants. Related fields include plant morphology, plant ecology, cell biology, genetics and molecular biology. Fundamental processes of plant physiology include photosynthesis, plant nutrition, nastic movements, photomorphogenesis, circadian rhythms, seed germination and stomata function and transpiration. Absorption of water by roots, production of food in the leaves, growth of shoots towards light are examples of plant physiology. Although there are differences between animal and microbial cells, the basic physiological functions of cells can be divided into the processes of cell division, cell signaling, cell growth, cell metabolism. Microorganisms can be found everywhere on Earth.
Types of microorganisms include archaea, eukaryotes, protists and micro-plants. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel and other bioactive compounds, they are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora, they are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. Most microorganisms can reproduce and bacteria are able to exchange genes through conjugation and transduction between divergent species; the study of human physiology as a medical field originates in classical Greece, at the time of Hippocrates. Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time in China and elsewhere.
Hippocrates incorporated his belief system called the theory of humours, which consisted of four basic substance: earth, water and fire. Each substance is known for having a corresponding humour: black bile, phlegm and yellow bile, respectively. Hippocrates noted some emotional connections to the four humours, which Claudius Galenus would expand on; the critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece. Like Hippocrates, Aristotle took to the humoral theory of disease, which consisted of four primary qualities in life: hot, cold and dry. Claudius Galenus, known as Galen of Pergamum, was the first to use experiments to probe the functions of the body. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, including the entire body, his modification of this theory better equipped doctors to make more precise diagnoses. Galen played off of Hippocrates idea that emotions were tied to the humours, added the notion of temperaments: sanguine corresponds with blood.
Galen saw the human body consisting of three connected systems: the brain and nerves, which are responsible for thoughts and sensations.