A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position; when released, the restoring force acting on the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period; the period depends on the length of the pendulum and to a slight degree on the amplitude, the width of the pendulum's swing. From the first scientific investigations of the pendulum around 1602 by Galileo Galilei, the regular motion of pendulums was used for timekeeping, was the world's most accurate timekeeping technology until the 1930s; the pendulum clock invented by Christian Huygens in 1658 became the world's standard timekeeper, used in homes and offices for 270 years, achieved accuracy of about one second per year before it was superseded as a time standard by the quartz clock in the 1930s.
Pendulums are used in scientific instruments such as accelerometers and seismometers. They were used as gravimeters to measure the acceleration of gravity in geophysical surveys, as a standard of length; the word "pendulum" is new Latin, from the Latin pendulus, meaning'hanging'. The simple gravity pendulum is an idealized mathematical model of a pendulum; this is a weight on the end of a massless cord suspended without friction. When given an initial push, it will swing forth at a constant amplitude. Real pendulums are subject to friction and air drag, so the amplitude of their swings declines; the period of swing of a simple gravity pendulum depends on its length, the local strength of gravity, to a small extent on the maximum angle that the pendulum swings away from vertical, θ0, called the amplitude. It is independent of the mass of the bob. If the amplitude is limited to small swings, the period T of a simple pendulum, the time taken for a complete cycle, is: T ≈ 2 π L g θ 0 ≪ 1 r a d i a n where L is the length of the pendulum and g is the local acceleration of gravity.
For small swings the period of swing is the same for different size swings: that is, the period is independent of amplitude. This property, called isochronism, is the reason. Successive swings of the pendulum if changing in amplitude, take the same amount of time. For larger amplitudes, the period increases with amplitude so it is longer than given by equation. For example, at an amplitude of θ0 = 23 ° it is 1 % larger; the period increases asymptotically as θ0 approaches 180°, because the value θ0 = 180° is an unstable equilibrium point for the pendulum. The true period of an ideal simple gravity pendulum can be written in several different forms, one example being the infinite series: T = 2 π L g where θ 0 is in radians; the difference between this true period and the period for small swings above is called the circular error. In the case of a typical grandfather clock whose pendulum has a swing of 6° and thus an amplitude of 3°, the difference between the true period and the small angle approximation amounts to about 15 seconds per day.
For small swings the pendulum approximates a harmonic oscillator, its motion as a function of time, t, is simple harmonic motion: θ = θ 0 cos where φ is a constant value, dependent on initial conditions. For real pendulums, the period varies with factors such as the buoyancy and viscous resistance of the air, the mass of the string or rod, the size and shape of the bob and how it is attached to the string, flexibility and stretching of the string. In precision applications, corrections for these factors may need to be applied to eq. to give the period accurately. Any swinging rigid body free to rotate about a fixed horizontal axis is called a compound pendulum or physical pendulum; the appropriate equivalent length L for calculating the period of any such pendulum is the distance from the pivot to the center of oscillation. This point is located under the center of mass at a distance from the pivot traditionally called the radius of oscillation, which depends on the mass distribution of the pendulum.
If most of the mass is concentrated in a small bob compared to the pendulum length, the center of oscillation is close to the center of mass. The radiu
Diurnality is a form of plant or animal behavior characterized by activity during daytime, with a period of sleeping or other inactivity at night. The common adjective used for daytime activity is "diurnal"; the timing of activity by an animal depends on a variety of environmental factors such as the temperature, the ability to gather food by sight, the risk of predation, the time of year. Diurnality is a cycle of activity within a 24-hour period. Animals active during twilight are crepuscular, those active during the night are nocturnal, animals active at sporadic times during both night and day are cathemeral. Plants that open their flowers during the daytime are described as diurnal, while those that bloom during nighttime are nocturnal; the timing of flower opening is related to the time at which preferred pollinators are foraging. For example, sunflowers open during the day to attract bees, whereas the night-blooming cereus opens at night to attract large sphinx moths. Many types of animals are classified as being diurnal, meaning they are active during the day time and inactive or have periods of rest during the night time.
Classified diurnal animals include mammals and reptiles. Most primates are diurnal. Scientifically classifying diurnality within animals can be a challenge, apart from the obvious increased activity levels during the day time light. Most animals were diurnal, but adaptations that allowed some animals to become nocturnal is what helped contribute to the success of many mammals; this evolutionary movement to nocturnality allowed them to better avoid predators and gain resources with less competition from other animals. This did come with some adaptations. Vision has been one of the most affected senses from switching back and forth from diurnality to nocturnality, this can be seen using biological and physiological analysis of rod nuclei from primate eyes; this includes losing two of four cone opsins that assists in colour vision, making many mammals dichromats. When early primates converted back to diurnality, better vision that included trichromatic colour vision became advantageous, making diurnality and colour vision adaptive traits of simiiformes, which includes humans.
Studies using chromatin distribution analysis of rod nuclei from different simian eyes found that transitions between diurnality and nocturnality occurred several times within primate lineages, with switching to diurnality being the most common transitions. Still today, diurnality seems to be reappearing in many lineages of other animals, including small rodent mammals like the Nile grass rat and golden mantle squirrel and reptiles. More geckos, which have thought to be nocturnal have shown many transitions to diurnality, with about 430 species of geckos now showing diurnal activity. With so many diurnal species recorded, comparative analysis studies using newer lineages of gecko species have been done to study the evolution of diurnality. With about 20 transitions counted for the gecko lineages, it shows the significance of diurnality. Strong environmental influences like climate change, predation risk, competition for resources are all contributing factors. Using the example of geckos, it is thought that species like Mediodactylus amictopholis that live at higher altitudes have switched to diurnality to help gain more heat through the day, therefore conserve more energy when colder seasonal temperatures hit.
Light is one of the most defining environmental factors that determines an animal’s activity pattern. Photoperiod or a light dark cycle is determined by the geographical location, with day time being associated with lots of ambient light, night time being associated with little ambient light. Light is one of the strongest influences of the suprachiasmatic nucleus, part of the hypothalamus in the brain that controls the circadian rhythm in most animals; this is. The SCN uses visual information like light to start a cascade of hormones that are released and work on many physiological and behavioural functions. Light can produce powerful masking effects on an animal’s circadian rhythm, meaning that it can “mask” or influence the internal clock, changing the activity patterns of an animal, either temporarily or over the long term if exposed to enough light over a long period of time. Masking can be referred to either as positive masking or negative masking, with it either increasing an diurnal animals activity or decreasing a nocturnal animal's activity, respectively.
This can be depicted. When a diurnal Nile grass rat and nocturnal mouse are exposed to the same photoperiod and light intensity, increased activity occurred within the grass rat, decreased activity within the mouse. Small amounts of environmental light change have shown to have an effect on the activity of mammals. An observational study done on the activity of nocturnal owl monkeys in the Gran Chaco in South America showed that increased amounts of moonlight at night increased their activity levels through the night, which led to a decrease of daytime activity. Meaning that for this species, ambient moonlight is negatively correlated with diurnal activity; this is connected with the foraging behaviours of the monkeys, as when there were nights of little to no moonlight, it affected the monkey’s ability to forage efficiently, so they were forced to be more active in the day to find food. Diurnality has shown to be an evolutionary trait in many animal species, with diurnality re
Christiaan Huygens was a Dutch physicist, mathematician and inventor, regarded as one of the greatest scientists of all time and a major figure in the scientific revolution. In physics, Huygens made groundbreaking contributions in optics and mechanics, while as an astronomer he is chiefly known for his studies of the rings of Saturn and the discovery of its moon Titan; as an inventor, he improved the design of the telescope with the invention of the Huygenian eyepiece. His most famous invention, was the invention of the pendulum clock in 1656, a breakthrough in timekeeping and became the most accurate timekeeper for 300 years; because he was the first to use mathematical formulae to describe the laws of physics, Huygens has been called the first theoretical physicist and the founder of mathematical physics. In 1659, Huygens was the first to derive the now standard formula for the centripetal force in his work De vi centrifuga; the formula played a central role in classical mechanics and became known as the second of Newton's laws of motion.
Huygens was the first to formulate the correct laws of elastic collision in his work De motu corporum ex percussione, but his findings were not published until 1703, after his death. In the field of optics, he is best known for his wave theory of light, which he proposed in 1678 and described in 1690 in his Treatise on Light, regarded as the first mathematical theory of light, his theory was rejected in favor of Isaac Newton's corpuscular theory of light, until Augustin-Jean Fresnel adopted Huygens' principle in 1818 and showed that it could explain the rectilinear propagation and diffraction effects of light. Today this principle is known as the Huygens–Fresnel principle. Huygens invented the pendulum clock in 1656. In addition to this invention, his research in horology resulted in an extensive analysis of the pendulum in his 1673 book Horologium Oscillatorium, regarded as one of the most important 17th-century works in mechanics. While the first part of the book contains descriptions of clock designs, most of the book is an analysis of pendulum motion and a theory of curves.
In 1655, Huygens began grinding lenses with his brother Constantijn in order to build telescopes to conduct astronomical research. He designed a 50-power refracting telescope with which he discovered that the ring of Saturn was "a thin, flat ring, nowhere touching, inclined to the ecliptic." It was with this telescope that he discovered the first of Saturn's moons, Titan. He developed in 1662 what is now called the Huygenian eyepiece, a telescope with two lenses, which diminished the amount of dispersion; as a mathematician, Huygens was a pioneer on probability and wrote his first treatise on probability theory in 1657 with the work Van Rekeningh in Spelen van Gluck. Frans van Schooten, the private tutor of Huygens, translated the work as De ratiociniis in ludo aleae; the work is a systematic treatise on probability and deals with games of chance and in particular the problem of points. The modern concept of probability grew out of the use of expectation values by Huygens and Blaise Pascal; the last years of Huygens, who never married, were characterized by loneliness and depression.
As a rationalist, he refused to believe in an immanent supreme being, could not accept the Christian faith of his upbringing. Although Huygens did not believe in such a supernatural being, he did hypothesize on the possibility of extraterrestrial life in his Cosmotheoros, published shortly before his death in 1695, he speculated that extraterrestrial life was possible on planets similar to Earth and wrote that the availability of water in liquid form was a necessity for life. Christiaan Huygens was born on 14 April 1629 in The Hague, into a rich and influential Dutch family, the second son of Constantijn Huygens. Christiaan was named after his paternal grandfather, his mother was Suzanna van Baerle. She died in 1637, shortly after the birth of Huygens' sister; the couple had five children: Constantijn, Lodewijk and Suzanna. Constantijn Huygens was a diplomat and advisor to the House of Orange, a poet and musician, his friends included Marin Mersenne and René Descartes. Huygens was educated at home until turning sixteen years old.
He liked to play with miniatures of other machines. His father gave him a liberal education: he studied languages and music and geography, mathematics and rhetoric, but dancing and horse riding. In 1644 Huygens had as his mathematical tutor Jan Jansz de Jonge Stampioen, who set the 15-year-old a demanding reading list on contemporary science. Descartes was impressed by his skills in geometry, his father sent Huygens to study law and mathematics at the University of Leiden, where he studied from May 1645 to March 1647. Frans van Schooten was an academic at Leiden from 1646, a private tutor to Huygens and his elder brother, replacing Stampioen on the advice of Descartes. Van Schooten brought his mathematical education up to date, in particular introducing him to the work of Fermat on differential geometry. After two years, from March 1647, Huygens continued his studies at the newly founded Orange College, in Breda, where his father was a curator: the change occurred because of a duel between his brother Lodewijk and another student.
Constantijn Huygens was involved in the new College, which lasted only to 1669. Christiaan Huygens lived at the home of the jurist Johann Henryk Dauber, and
A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. These 24-hour rhythms are driven by a circadian clock, they have been observed in plants, animals and cyanobacteria; the term circadian comes from the Latin circa, meaning "around", diēm, meaning "day". The formal study of biological temporal rhythms, such as daily, weekly and annual rhythms, is called chronobiology. Processes with 24-hour oscillations are more called diurnal rhythms. Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called zeitgebers, which include light and redox cycles. In medical science, an abnormal circadian rhythm in humans is known as circadian rhythm disorder. In 2017, the Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young "for their discoveries of molecular mechanisms controlling the circadian rhythm" in fruit flies; the earliest recorded account of a circadian process dates from the 4th century BC, when Androsthenes, a ship captain serving under Alexander the Great, described diurnal leaf movements of the tamarind tree.
The observation of a circadian or diurnal process in humans is mentioned in Chinese medical texts dated to around the 13th century, including the Noon and Midnight Manual and the Mnemonic Rhyme to Aid in the Selection of Acu-points According to the Diurnal Cycle, the Day of the Month and the Season of the Year. The first recorded observation of an endogenous circadian oscillation was by the French scientist Jean-Jacques d'Ortous de Mairan in 1729, he noted that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica continued when the plants were kept in constant darkness, in the first experiment to attempt to distinguish an endogenous clock from responses to daily stimuli. In 1896, Patrick and Gilbert observed that during a prolonged period of sleep deprivation, sleepiness increases and decreases with a period of 24 hours. In 1918, J. S. Szymanski showed that animals are capable of maintaining 24-hour activity patterns in the absence of external cues such as light and changes in temperature.
In the early 20th century, circadian rhythms were noticed in the rhythmic feeding times of bees. Extensive experiments were done by Auguste Forel, Ingeborg Beling, Oskar Wahl to see whether this rhythm was due to an endogenous clock; the existence of circadian rhythm was independently discovered in the fruit fly Drosophila melanogaster in 1935 by two German zoologists, Hans Kalmus and Erwin Bünning. In 1954, an important experiment was reported by Colin Pittendrigh who showed that eclosion in D. pseudoobscura was a circadian behaviour. He demonstrated that while temperature played a vital role in eclosion rhythm, the period of eclosion was delayed but not stopped when temperature was decreased, it was an indication. The term circadian was coined by Franz Halberg in 1959. According to Halberg's original definition: The term "circadian" dies. Herein, "circadian" might be applied to all "24-hour" rhythms, whether or not their periods, individually or on the average, are different from 24 hours, longer or shorter, by a few minutes or hours.
In 1977, the International Committee on Nomenclature of the International Society for Chronobiology formally adopted the definition, which states: Circadian: relating to biologic variations or rhythms with a frequency of 1 cycle in 24 ± 4 h. Note: term describes rhythms with an about 24-h cycle length, whether they are frequency-synchronized with or are desynchronized or free-running from the local environmental time scale, with periods of yet different from 24-h. Ron Konopka and Seymour Benzer identified the first clock mutant in Drosophila in 1971 and called it "period" gene, the first discovered genetic determinant of behavioral rhythmicity. Per gene was isolated in 1984 by two teams of researchers. Konopka, Jeffrey Hall, Michael Roshbash and their team showed that per locus is the centre of the circadian rhythm, that loss of per stops circadian activity. At the same time, Michael W. Young's team reported similar effects of per, that the gene covers 7.1-kilobase interval on the X chromosome and encodes a 4.5-kb poly+ RNA.
They went on to discover the key genes and neurones in Drosophila circadian system, for which Hall and Young received the Nobel Prize in Physiology or Medicine 2017. Joseph Takahashi discovered the first mammalian circadian clock mutation using mice in 1994. However, recent studies show that deletion of clock does not lead to a behavioral phenotype, which questions its importance in rhythm generation. To be called circadian, a biological rhythm must meet these three general criteria: The rhythm has an endogenous free-running period that lasts 24 hours; the rhythm persists with a period of about 24 hours. The period of the rhythm in constant conditions is called the free-running period and is denoted by the Greek letter τ; the rationale for this criterion is to distinguish circadian rhythms from simple responses to daily external cues. A rhythm cannot be said to be endogenous unless it ha
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Phase response curve
A phase response curve illustrates the transient change in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received. PRCs are used in various fields. In humans and animals, there is a regulatory system that governs the phase relationship of an organism's internal circadian clock to a regular periodicity in the external environment. In most organisms, a stable phase relationship is desired, though in some cases the desired phase will vary by season among mammals with seasonal mating habits. In circadian rhythm research, a PRC illustrates the relationship between a chronobiotic's time of administration and the magnitude of the treatment's effect on circadian phase. A PRC is a graph showing, by convention, time of the subject's endogenous day along the x-axis and the amount of the phase shift along the y-axis; the curve has one nadir in each 24-hour cycle. Relative circadian time is plotted vs. phase shift magnitude. The treatment is narrowly specified as a set intensity and colour and duration of light exposure to the retina and skin, or a set dose and formulation of melatonin.
These curves are consulted in the therapeutic setting. The body's various physiological rhythms will be synchronized within an individual organism with respect to a master biological clock. Of particular importance is the sleep–wake cycle. Various sleep disorders and externals stresses can interfere with this. People with non-24-hour sleep–wake disorder experience an inability to maintain a consistent internal clock. Extreme chronotypes maintain a consistent clock, but find that their natural clock does not align with the expectations of their social environment. PRC curves provide a starting point for therapeutic intervention; the two common treatments used to shift the timing of sleep are light therapy, directed at the eyes, administration of the hormone melatonin taken orally. Either or both can be used daily; the phase adjustment is cumulative with consecutive daily administrations, and—at least partially—additive with concurrent administrations of distinct treatments. If the underlying disturbance is stable in nature, ongoing daily intervention is required.
For jet lag, the intervention serves to accelerate natural alignment, ceases once desired alignment is achieved. Note that PRC curves from the experimental setting are aggregates of the test population, that there can be mild or significant variation within the test population, that individuals with sleep disorders respond atypically, that the formulation of the chronobiotic might be specific to the experimental setting and not available in clinical practice; the discussions below are restricted to the PRCs for the melatonin in humans. Starting about two hours before an individual's regular bedtime, exposure of the eyes to light will delay the circadian phase, causing wake-up time and sleep onset; the delaying effect gets stronger. The effect is small in dim indoor lighting. About five hours after usual bedtime, coinciding with the body temperature nadir the PRC peaks and the effect changes abruptly from phase delay to phase advance. After this peak, light exposure has its greatest phase-advancing effect, causing earlier wake-up and sleep onset.
Again, illuminance affects results. The effect diminishes until about two hours after spontaneous wake-up time, when it reaches zero. During the period between two hours after usual wake-up time and two hours before usual bedtime, light exposure has little or no effect on circadian phase. Another image of the PRC for light is here. Within that image, the explanatory text is Delay region: evening light shifts sleepiness and Advance region: morning light shifts sleepiness earlier. Light therapy with a light box producing 10,000 lux at a prescribed distance, can be used in the evening to delay or in the morning to advance a person's sleep timing; because losing sleep to obtain bright light exposure is considered undesirable by most people, because it is difficult to estimate when the greatest effect will occur in an individual, the treatment is applied daily just prior to bedtime, or just after spontaneous awakening. In addition to its use in the adjustment of circadian rhythms, light therapy is used as treatment for several affective disorders including seasonal affective disorder.
In 2002 Brown University researchers led by David Berson announced the discovery of special cells in the human eye, ipRGCs, which many researchers now believe control the light entrainment effect of the phase response curve. In the human eye, the ipRGCs have the greatest response to light in the 460–480 nm range. In one experiment, 400 lux of blue light produced the same effects as 10,000 lux of white l
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures have developed senses of hearing and specially adapted eyesight; such traits can help animals such as the Helicoverpa zea moths avoid predators. Some animals, such as cats and ferrets, have eyes that can adapt to both low-level and bright day levels of illumination. Others, such as bushbabies and bats, can function only at night. Many nocturnal creatures including tarsiers and some owls have large eyes in comparison with their body size to compensate for the lower light levels at night. More they have been found to have a larger cornea relative to their eye size than diurnal creatures to increase their visual sensitivity: in the low-light conditions. Nocturnality helps wasps, such as avoid hunting in intense sunlight. Diurnal animals, including squirrels and songbirds, are active during the daytime.
Crepuscular species, such as rabbits, skunks and hyenas, are erroneously referred to as nocturnal. Cathemeral species, such as fossas and lions, are active both at night. While it is difficult to say which came first, nocturnality or diurnality, there is a leading hypothesis out in the evolutionary biology community. Known as the "bottleneck theory", it postulates that millions of years ago in the Mesozoic era, many ancestors of modern-day mammals evolved nocturnal characteristics in order to avoid contact with the numerous diurnal predators. A recent study attempts to answer the question as to why so many modern day mammals retain these nocturnal characteristics though they are not active at night; the leading answer is that the high visual acuity that comes with diurnal characteristics isn't needed anymore due to the evolution of compensatory sensory systems, such as a heightened sense of smell and more astute auditory systems. In a recent study extinct elephant birds and modern day nocturnal kiwi bird skulls were examined to recreate their brain and skull formation.
They indicated that olfactory bulbs were much larger in comparison to their optic lobes, indicating they both have a common ancestor who evolved to function as a nocturnal species, decreasing their eyesight in favor of a better sense of smell. The anomaly to this theory were anthropoids, who appeared to have the most divergence from nocturnality than all organisms examined. While most mammals didn't exhibit the morphological characteristics expected of a nocturnal creature and birds fit in perfectly. A larger cornea and pupil correlated well with whether these two classes of organisms were nocturnal or not. Being active at night is a form of niche differentiation, where a species' niche is partitioned not by the amount of resources but by the amount of time. Hawks and owls can hunt the same field or meadow for the same rodents without conflict because hawks are diurnal and owls are nocturnal; this means. Nocturnality is a form of an adaptation to avoid or enhance predation. One of the reasons that lions prefer to hunt at night is that many of their prey species have poor night vision.
Many species of small rodents, such as the Large Japanese Field Mouse, are active at night because most of the dozen or so birds of prey that hunt them are diurnal. There are many diurnal species. For example, many seabirds and sea turtles only gather at breeding sites or colonies at night to reduce the risk of predation to themselves and/or their offspring. Nocturnal species take advantage of the night time to prey on species that are used to avoiding diurnal predators; some nocturnal fish species will use the moonlight to prey on zooplankton species that come to the surface at night. Some species have developed unique adaptations. Bats are famous for using echolocation to hunt down their prey, using sonar sounds to capture them in the dark. Another reason for nocturnality is avoiding the heat of the day; this is true in arid biomes like deserts, where nocturnal behavior prevents creatures from losing precious water during the hot, dry daytime. This is an adaptation. One of the reasons that lions prefer to hunt at night is to conserve water.
Many plant species native to arid biomes have adapted so that their flowers only open at night when the sun's intense heat cannot wither and destroy their moist, delicate blossoms. These flowers are pollinated by another creature of the night. Climate-change and the change in global temperatures has led to an increasing amount of diurnal species to push their activity patterns closer towards crepuscular or nocturnal behavior; this adaptive measure allows species to avoid the heat of the day, without having to leave that particular habitat. The exponential increase in human expansion and technological advances in the last few centuries has had a major effect on nocturnal animals, as well as diurnal species; the causes of these can be traced to distinct, sometimes overlapping areas: light pollution and spatial disturbance. Light pollution is a major issue for nocturnal species, the impact continues to increase as electricity reaches parts of the world that had no access. Species in the tropics are more affected by this due to the change in their constant light patterns, but temperate species relying on day-night triggers for behavioral patterns are affected as well.
Many diurnal species see the benefit of a "longer day", allowin