Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resources in an ecosystem. This can be contrasted with a type of symbiosis. Competition between members of the same species is called intraspecific competition. If a tree species in a dense forest grows taller than surrounding tree species, it is able to absorb more of the incoming sunlight. However, less sunlight is available for the trees that are shaded by the taller tree, thus interspecific competition. Leopards and lions can be in interspecific competition, since both species feed on the same prey, can be negatively impacted by the presence of the other because they will have less food. Competition is only one of many interacting biotic and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, interaction. Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area.
If the resource cannot support both populations lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations and the evolution of interacting species. On an individual organism level, competition can occur as exploitative competition. Direct competition has been observed between individuals and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, between amphibians and mammals. All of the types described here can apply to intraspecific competition, that is, competition among individuals within a species. Any specific example of interspecific competition can be described in terms of both a mechanism and an outcome. Exploitative competition referred to as resource competition, is a form of competition in which one species consumes and either reduces or more efficiently uses a shared limiting resource and therefore depletes the availability of the resource for the other species.
Thus, it is an indirect interaction because the competing species interact via a shared resource. Interference competition is a form of competition in which individuals of one species interacts directly with individuals of another species via antagonistic displays or more aggressive behavior. In a review and synthesis of experimental evidence regarding interspecific competition, Schoener described six specific types of mechanisms by which competition occurs, including consumptive, overgrowth, chemical and encounter. Consumption competition is always resource competition, but the others are cannot always be regarded as exploitative or interference. Separating the effect of resource use from that of interference is not easy. A good example of exploitative competition is found in aphid species competing over the sap in plant phloem; each aphid species that feeds on host plant sap uses some of the resource, leaving less for competing species. In one study, Fordinae geoica was observed to out-compete F. formicaria to the extent that the latter species exhibited a reduction in survival by 84%.
Another example is the one of competition for calling space in amphibians, where the calling activity of a species prevents the other one from calling in an area as wide as it would in allopatry. A last example is driving of bisexual rock lizards of genus Darevskia from their natural habitats by a daughter unisexual form; this type of competition can be observed in forests where large trees dominate the canopy and thus allow little light to reach smaller competitors living below. These interactions have important implications for the population dynamics and distribution of both species. Scramble and contest competition refer to the relative success of competitors. Scramble competition is said to occur when each competitor is equal suppressed, either through reduction in survival or birth rates. Contest competition is said to occur when one or a few competitors are unaffected by competition, but all others suffer either through reduction in survival or birth rates. Sometimes these types of competition are referred to as symmetric vs. asymmetric competition.
Scramble and contest competition are two ends of a spectrum, of equal or unequal effects. Apparent competition is an example of predation that alters the relative abundances of prey on the same trophic level, it occurs when two or more species in a habitat affect shared natural enemies in a higher trophic level. If two species share a common predator, for example, apparent competition can exist between the two prey items in which the presence of each prey species increases the abundance of the shared enemy, thereby suppresses one or both prey species; this mechanism gets its name from experiments in which one prey species is removed and the second prey species increases in abundance. Investigators sometimes mistakenly attribute the increase in abundance in the second species as evidence for resource competition between prey species, it is "apparently" competition, but is in fact due to a shared predator, parasite, or pathogen. Many studies, including those cited have shown major impacts on both individuals and populations from interspecific competition.
Documentation of these impacts has been found in species from every major branch of organism. The effects of interspecific competition can reach communities and can influence the evolution of spec
Hummingbirds are birds native to the Americas and constitute the biological family Trochilidae. They are among the smallest of most species measuring 7.5 -- 13 cm in length. The smallest extant bird species is a hummingbird, the 5 cm bee hummingbird weighing less than 2.0 g. They are known as hummingbirds because of the humming sound created by their beating wings which flap at high frequencies audible to humans, they hover in mid-air at rapid wing-flapping rates, which vary from around 12 beats per second in the largest species, to in excess of 80 in some of the smallest. Of those species that have been measured in wind tunnels, their top speed exceeds 15 m/s and some species can dive at speeds in excess of 22 m/s. Hummingbirds have the greatest mass-specific metabolic rate of any homeothermic animal. To conserve energy when food is scarce, nightly when not foraging, they can go into torpor, a state similar to hibernation, slowing metabolic rate to 1/15th of its normal rate. A map of the hummingbird family tree—reconstructed from analysis of 284 of the world's 338 known species—shows rapid diversification from 22 million years ago.
Hummingbirds fall into nine main clades, the Topazes, Mangoes, Coquettes, Mountain Gems and Emeralds, defining their relationship to nectar-bearing flowering plants and the birds' continued spread into new geographic areas. While all hummingbirds depend on flower nectar to fuel their high metabolisms and hovering flight, coordinated changes in flower- and bill shape stimulated the formation of new species of hummingbirds and plants. Due to this exceptional evolutionary pattern, as many as 140 hummingbird species can coexist in a specific region, such as the Andes range; the hummingbird evolutionary tree shows ancestral hummingbirds splitting from insectivorous swifts and treeswifts about 42 million years ago in Eurasia. One key evolutionary factor appears to be an altered taste receptor that enabled hummingbirds to seek nectar. By 22 million years ago the ancestral species of current hummingbirds became established in South America, where environmental conditions stimulated further diversification.
The Andes Mountains appear to be a rich environment for hummingbird evolution because diversification occurred with mountain uplift over the past 10 million years. Hummingbirds remain in dynamic diversification inhabiting ecological regions across South America, North America, the Caribbean, indicating an enlarging evolutionary radiation. Within the same geographic region, hummingbird clades co-evolved with nectar-bearing plant clades, affecting mechanisms of pollination; the same is true for the sword-billed hummingbird, one of the morphologically most extreme species, one of its main food plant clades. Hummingbirds exhibit sexual size dimorphism according to Rensch's rule, in which males are smaller than females in small species, males are larger than females in large-bodied species; the extent of this sexual size difference varies among clades of hummingbirds. For example, the Mellisugini clade exhibits a large size dimorphism, with females being larger than males. Conversely, the Lophomithini clade displays little size dimorphism.
Sexual dimorphisms in bill size and shape are present between male and female hummingbirds, where in many clades, females have longer, more curved bills favored for accessing nectar from tall flowers. For males and females of the same size, females will tend to have larger bills. Sexual size and bill differences evolved due to constraints imposed by courtship because mating displays of male hummingbirds require complex aerial maneuvers. Males tend to be smaller than females, allowing conservation of energy to forage competitively and participate more in courtship. Thus, sexual selection will favor smaller male hummingbirds. Female hummingbirds tend to be larger, requiring more energy, with longer beaks that allow for more effective reach into crevices of tall flowers for nectar, thus females are better at foraging, acquiring flower nectar, supporting the energy demands of their larger body size. Directional selection will thus favor the larger hummingbirds in terms of acquiring food. Another evolutionary cause of this sexual bill dimorphism is that the selective forces from competition for nectar between the sexes of each species are what drive the sexual dimorphism.
Depending on which sex holds territory in the species, it is advantageous for the other sex to have a longer bill and be able to feed on a wide variety of flowers, decreasing intraspecific competition. For example, in species of hummingbirds where males have longer bills, males do not hold a specific territory and have a lek mating system. In species where males have shorter bills than females, males defend their resources and therefore females must have a longer bill in order to feed from a broader range of flower. Hummingbirds are specialized nectarivores and are tied to the ornithophilous flowers upon which they feed; some species those with unusual bill shapes, such as the sword-billed hummingbird and the sicklebills, are co-evolved with a small number of flower species. The bee hummingbird – the world's smallest bird – evolved to dwarfism because it had to compete with long-billed hummingbirds having an advantage for nectar foraging from specialized flowers leading the bee hummingbird to more compete for flower foraging against insects.
Many plants pollinated by hummingbirds produce flowers in shades of red and bright pink, though the birds will take nectar from flowers of other colors
Bats are mammals of the order Chiroptera. Bats are more manoeuvrable than birds, flying with their long spread-out digits covered with a thin membrane or patagium; the smallest bat, arguably the smallest extant mammal, is Kitti's hog-nosed bat, 29–34 mm in length, 15 cm across the wings and 2–2.6 g in mass. The largest bats are the flying foxes and the giant golden-crowned flying fox, Acerodon jubatus, which can weigh 1.6 kg and have a wingspan of 1.7 m. The second largest order of mammals, bats comprise about 20% of all classified mammal species worldwide, with over 1,200 species; these were traditionally divided into two suborders: the fruit-eating megabats, the echolocating microbats. But more recent evidence has supported dividing the order into Yinpterochiroptera and Yangochiroptera, with megabats as members of the former along with several species of microbats. Many bats are insectivores, most of the rest are frugivores. A few species feed on animals other than insects. Most bats are nocturnal, many roost in caves or other refuges.
Bats are present throughout the world, with the exception of cold regions. They are important in their ecosystems for dispersing seeds. Bats provide humans at the cost of some threats. Bat dung has been used as fertiliser. Bats consume insect pests, they are sometimes numerous enough to serve as tourist attractions, are used as food across Asia and the Pacific Rim. They are natural reservoirs such as rabies. In many cultures, bats are popularly associated with darkness, witchcraft and death. An older English name for bats is flittermouse, which matches their name in other Germanic languages, related to the fluttering of wings. Middle English had bakke, most cognate with Old Swedish natbakka, which may have undergone a shift from -k- to -t- influenced by Latin blatta, "moth, nocturnal insect"; the word "bat" was first used in the early 1570s. The name "Chiroptera" derives from Ancient Greek: χείρ – cheir, "hand" and πτερόν – pteron, "wing"; the delicate skeletons of bats do not fossilise well, it is estimated that only 12% of bat genera that lived have been found in the fossil record.
Most of the oldest known bat fossils were very similar to modern microbats, such as Archaeopteropus. The extinct bats Palaeochiropteryx tupaiodon and Hassianycteris kumari are the first fossil mammals whose colouration has been discovered: both were reddish-brown. Bats were grouped in the superorder Archonta, along with the treeshrews and primates. Modern genetic evidence now places bats in the superorder Laurasiatheria, with its sister taxon as Fereuungulata, which includes carnivorans, odd-toed ungulates, even-toed ungulates, cetaceans. One study places Chiroptera as a sister taxon to odd-toed ungulates; the phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision into Megachiroptera and Microchiroptera reflected the view that these groups of bats had evolved independently of each other for a long time, from a common ancestor capable of flight; this hypothesis recognised differences between microbats and megabats and acknowledged that flight has only evolved once in mammals.
Most molecular biological evidence supports the view that bats form a monophyletic group. Genetic evidence indicates that megabats originated during the early Eocene, belong within the four major lines of microbats. Two new suborders have been proposed. Yangochiroptera includes the other families of a conclusion supported by a 2005 DNA study. A 2013 phylogenomic study supported the two new proposed suborders. In the 1980s, a hypothesis based on morphological evidence stated the Megachiroptera evolved flight separately from the Microchiroptera; the flying primate hypothesis proposed that, when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features not shared with Microchiroptera. For example, the brains of megabats have advanced characteristics. Although recent genetic studies support the monophyly of bats, debate continues about the meaning of the genetic and morphological evidence; the 2003 discovery of an early fossil bat from the 52 million year old Green River Formation, Onychonycteris finneyi, indicates that flight evolved before echolocative abilities.
Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws on two digits of each hand. It had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches, such as sloths and gibbons; this palm-sized bat had short, broad wings, suggesting that it could not fly as fast or as far as bat species. Instead of flapping its wings continuously while flying, Onychonycteris alternated between flaps and
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, koalas, opossums and Tasmanian devils; some lesser-known marsupials are the dunnarts and cuscuses. Marsupials represent the clade originating from the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they give birth to undeveloped young that reside in a pouch located on their mothers’ abdomen for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent; the remaining 100 are found in the Americas — in South America, but thirteen in Central America, one in North America, north of Mexico. The word marsupial comes from the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and from the ancient Greek μάρσιππος mársippos, meaning "pouch".
Marsupials are taxonomically identified as members of the mammalian infraclass Marsupialia, first described as a family under the order Pollicata by German zoologist Johann Karl Wilhelm Illiger in his 1811 work Prodromus Systematis Mammalium et Avium. However, James Rennie, author of The Natural History of Monkeys and Lemurs, pointed out that the placement of five different groups of mammals - monkeys, tarsiers, aye-ayes and marsupials - under a single order did not appear to have a strong justification. In 1816, French zoologist George Cuvier classified all marsupials under the order Marsupialia. In 1997, researcher J. A. W. Kirsch and others accorded infraclass rank to Marsupialia. There are two primary divisions: Australian marsupials. Marsupialia is further divided as follows:† - Extinct Superorder Ameridelphia Order Didelphimorphia Family Didelphidae: opossums Order Paucituberculata Family Caenolestidae: shrew opossums Superorder Australidelphia Order Microbiotheria Family Microbiotheriidae: monito del monte Order †Yalkaparidontia Order Dasyuromorphia Family †Thylacinidae: thylacine Family Dasyuridae: antechinuses, dunnarts, Tasmanian devil, relatives Family Myrmecobiidae: numbat Order Notoryctemorphia Family Notoryctidae: marsupial moles Order Peramelemorphia Family Thylacomyidae: bilbies Family †Chaeropodidae: pig-footed bandicoots Family Peramelidae: bandicoots and allies Order Diprotodontia Suborder Vombatiformes Family Vombatidae: wombats Family Phascolarctidae: koalas Family †Diprotodontidae: Giant wombats Family †Palorchestidae: Marsupial tapirs Family †Thylacoleonidae: marsupial lions Suborder Phalangeriformes Family Acrobatidae: feathertail glider and feather-tailed possum Family Burramyidae: pygmy possums Family †Ektopodontidae: sprite possums Family Petauridae: striped possum, Leadbeater's possum, yellow-bellied glider, sugar glider, mahogany glider, squirrel glider Family Phalangeridae: brushtail possums and cuscuses Family Pseudocheiridae: ringtailed possums and relatives Family Tarsipedidae: honey possum Suborder Macropodiformes Family Macropodidae: kangaroos and relatives Family Potoroidae: potoroos, rat kangaroos, bettongs Family Hypsiprymnodontidae: musky rat-kangaroo Comprising over 300 extant species, several attempts have been made to interpret the phylogenetic relationships among the different marsupial orders.
Studies differ on whether Didelphimorphia or Paucituberculata is the sister group to all other marsupials. Though the order Microbiotheria is found in South America, morphological similarities suggest it is related to Australian marsupials. Molecular analyses in 2010 and 2011 identified Microbiotheria as the sister group to all Australian marsupials. However, the relations among the four Australidelphid orders are not as well understood; the cladogram below, depicting the relationships among the various marsupial orders, is based on a 2015 phylogenetic study. DNA evidence supports a South American origin for marsupials, with Australian marsupials arising from a single Gondwanan migration of marsupials from South America to Australia. There are many small arboreal species in each group; the term "opossum" is used to refer to American species, while similar Australian species are properly called "possums". Marsupials have the typical characteristics of mammals—e.g. Mammary glands, three middle ear bones, true hair.
There are, striking differences as well as a number of anatomical features that separate them from Eutherians. In addition to the front pouch, which contains multiple nipples for the protection and sustenance of their young, marsupials have other common structural features. Ossified patellae are absent in most modern marsupials and epipubic bones are present. Marsupials lack a gross communication between the right and left brain hemispheres; the skull has peculiarities in comparison to placental mammals. In general, the skull is small and tight. Holes are located in the front of the orbit; the cheekbone extends further to the rear. The angular extension of the lower jaw is bent toward the center. Another feature is the hard palate which, in contrast to the placental mammals' foramina, always have more openings. The
Eutheria is one of two mammalian clades with extant members that diverged in the Early Cretaceous or the Late Jurassic. Except for the Virginia opossum, from North America, a metatherian, all post-Miocene mammals indigenous to Europe, Africa and North America north of Mexico are eutherians. Extant eutherians, their last common ancestor, all extinct descendants of that ancestor are members of Placentalia. Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles and teeth. All extant eutherians lack epipubic bones; this allows for expansion of the abdomen during pregnancy. The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the Jurassic in China. Eutheria was named in 1872 by Theodore Gill. Distinguishing features are: an enlarged malleolus at the bottom of the tibia, the larger of the two shin bones the joint between the first metatarsal bone and the entocuneiform bone in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones—in metatherians these joints are level with each other various features of jaws and teeth Eutheria contains several extinct genera as well as larger groups, many with complicated taxonomic histories still not understood.
Members of the Adapisoriculidae and Leptictida have been placed within the out-dated placental group Insectivora, while Zhelestids have been considered primitive ungulates. However, more recent studies have suggested these enigmatic taxa represent stem group eutherians, more basal to Placentalia; the weakly favoured cladogram favours Boreoeuthearia as a basal Eutherian clade as sister to the Atlantogenata
A hibernaculum plural form: hibernacula is a place in which a creature seeks refuge, such as a bear using a cave to overwinter. The word can be used to describe a variety of shelters used by many kinds of animals, including insects, lizards, bats and primates of various species. Insects range in their size and general appearance but most use hibernacula. All insects are exothermic. For this reason cold temperatures, such as those experienced in the winter season, outside of tropical locations, cause their metabolic systems to shut down. Insects survive colder winters through the process of overwintering, which occurs at all stages of development and may include migration or hibernation for different insects, the latter of which must be done in hibernacula. Insects that do not migrate must halt their growth to avoid freezing to death, in a process called diapause. Insects prepare to overwinter through a variety of mechanisms, such as using anti-freeze proteins or cryoprotectants in freeze-avoidant insects, like Soybean aphids.
Cryoprotectants are toxic, with high concentrations only tolerated at low temperatures. Thus, hibernacula are used to avoid sporadic warming and the risk of death due high concentrations of cryoprotectants at warmer temperatures. Freeze-tolerant insects, like second-generation corn-borers, can survive being frozen and therefore, undergo inoculative freezing. Hibernacula range in structure depending on the insects using them. However, insect hibernacula are required to be: Well-insulated from extreme temperature changes Protected from weather Dry Some insects, like convergent lady beetles, reuse the same hibernacula, year after year, they migrate to hibernacula used by prior generations. They are able to find old hibernacula due to hydrocarbons released by lady beetle feet which create a lasting path; this allows lady beetles to retrace their footsteps to used hibernacula. Their tendency to aggregate and overwinter in groups is due to their attraction to similar environments and conspecifics. Beetles use rock crevices as hibernacula clumping in them, in groups.
These rock crevices are found in rock fields the beetle are attracted to for high levels of vegetation and greenery. Other types of insect hibernacula include self-spun silk hibernacula, such as those made and used by spruce budworms as they moult and overwinter in their second instars. An example is the eastern spruce budworm which creates hibernacula after dispersing during its first instar overwinter before emerging from the hibernacula in early May. Woolly bear caterpillars overwinter as caterpillars and grow to be Isabella tiger moths, they use plant debris as makeshift hibernacula. Some butterflies, like the White admiral butterfly only mature halfway as a caterpillar before hibernating for the winter. For freeze-avoidant insects, ideal hibernacula are dry, as freeze-avoidant insects are less to dampen and freeze in them, however moist hibernacula promote inoculative freezing for freeze-tolerant insects. Amphibians that hibernate include several species of frogs and salamanders from the northern continental climates of North America and Eurasia and from extreme southern hemisphere climates.
These amphibians slow their metabolism during winter to avoid unsuitable conditions, such as freezing. Most freeze avoidance strategies include overwintering in aquatic situations or burrowing in the soil to depths below the frostline. A hibernaculum for amphibians should provide the following: Optimum temperatures; some species will not survive hibernation at temperatures that exceed 4 °C. For amphibians that hibernate under ice, it is necessary for the animal to be submerged in water, 10 to 15 cm deep and to maintain the temperature between 2 and 3 °C and not above 4 °C. Water should be well aerated, with maintained low-intensity light levels and minimal disturbance of the amphibians. Like other amphibians, frogs show minimal capacities for freezing tolerance and survive winter by using terrestrial hibernacula where they avoid freezing. However, frogs may exhibit greater freeze-tolerance capacity at high latitude range limits, where winter climate is more severe. For example, data suggests that while cricket frogs in South Dakota survive winter by locating hibernacula that prevent freezing, their toleration of short freezing bouts may expand the range of suitable hibernacula.
However, overwinter mortality may be high at the northern range boundary due to colder temperatures and might limit cricket frogs from expanding their range northward. The microclimate refers to the climate of a small or restricted area, like the hibernaculum when this differs from the climate of the surrounding area. Overwinter survival in these cricket frogs among other frogs is dependent on using hibernacula with appropriate physical microclimate characteristics, such as moist soil, that buffer frogs from temperatures that drop below the freezing point of the body fluids for extended periods. Although, determining if frogs can identify sites with appropriate microclimates to support overwinter survival and what factors might inform such choices are still unknown and will require further study. Therefore, it is still not known to what extent various types of prospective hibernacula for frogs might be suitable in the years to come factoring in climate change; as part the Highways Agency Biodiversity Action Plan
Sleep in non-human animals
Sleep in non-human animals refers to a behavioral and physiological state characterized by altered consciousness, reduced responsiveness to external stimuli, homeostatic regulation. Sleep is observed in mammals, reptiles and some fish, and, in some form, in insects and in simpler animals such as nematodes; the internal circadian clock promotes sleep at night for diurnal organisms and in the day for nocturnal organisms. Sleep patterns vary among species, it appears to be a requirement for most other animals. Sleep can follow behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone, a compensatory increase following deprivation of the state. In the behavioral sense, sleep is characterized by minimal movement, non-responsiveness to external stimuli, the adoption of a typical posture, the occupation of a sheltered site, all of, repeated on a 24-hour basis; the physiological definition applies well to birds and mammals, but in other animals, the behavioral definition is more used.
In simple animals, behavioral definitions of sleep are the only ones possible, then the behavioral repertoire of the animal may not be extensive enough to allow distinction between sleep and wakefulness. Sleep is reversible, as opposed to hibernation or coma, sleep deprivation is followed by longer or deeper rebound sleep. If sleep were not essential, one would expect to find: Animal species that do not sleep at all Animals that do not need recovery sleep after staying awake longer than usual Animals that suffer no serious consequences as a result of lack of sleepOutside of a few basal animals that have no brain or a simple one, no animals have been found to date that satisfy any of these criteria. While some varieties of shark, such as great whites and hammerheads, must remain in motion at all times to move oxygenated water over their gills, it is possible they still sleep one cerebral hemisphere at a time as marine mammals do; however it remains to be shown definitively. Sleep as a phenomenon appears to have old evolutionary roots.
Unicellular organisms do not "sleep", although many of them have pronounced circadian rhythms. The jellyfish Cassiopea is the most primitive organism in which sleep-like states have been observed; the nematode C. elegans is another primitive organism. Here, a lethargus phase occurs in short periods preceding each moult, a fact which may indicate that sleep primitively is connected to developmental processes. Raizen et al.'s results furthermore suggest that sleep is necessary for changes in the neural system. The electrophysiological study of sleep in small invertebrates is complicated. Insects go through circadian rhythms of activity and passivity but some do not seem to have a homeostatic sleep need. Insects do not seem to exhibit REM sleep. However, fruit flies appear to sleep, systematic disturbance of that state leads to cognitive disabilities. There are several methods of measuring cognitive functions in fruit flies. A common method is to let the flies choose whether they want to fly through a tunnel that leads to a light source, or through a dark tunnel.
Flies are attracted to light. But if sugar is placed in the end of the dark tunnel, something the flies dislike is placed in the end of the light tunnel, the flies will learn to fly towards darkness rather than light. Flies deprived of sleep require a longer time to learn this and forget it more quickly. If an arthropod is experimentally kept awake longer than it is used to its coming rest period will be prolonged. In cockroaches that rest period is characterized by the antennae being folded down and by a decreased sensitivity to external stimuli. Sleep has been described in crayfish, characterized by passivity and increased thresholds for sensory stimuli as well as changes in the EEG pattern, markedly differing from the patterns found in crayfish when they are awake. In honeybees, it has been suggested. Sleep in fish is subject of current scientific research. Fish exhibit periods of inactivity but show no significant reactions to deprivation of this condition; some species that always live in shoals or that swim continuously are suspected never to sleep.
There is doubt about certain blind species that live in caves. Other fish seem to sleep, however. For example, tilapia, brown bullhead, swell shark become motionless and unresponsive at night. A 1961 observational study of 200 species in European public aquaria reported many cases of apparent sleep. On the other hand, sleep patterns are disrupted and may disappear during periods of migration and parental care. Mammals and reptiles evolved from amniotic ancestors, the first vertebrates with life cycles independent of water; the fact that birds and mammals are the only known animals to exhibit REM and NREM sleep indicates a common trait before divergence. Reptiles are therefore the most logical group to investigate the origins of sleep. Daytime activity in reptiles alternates between basking and short bouts of active behavior, which has significant neurologica