The subarctic is a region in the Northern Hemisphere south of the true Arctic and covering much of Alaska, Iceland, the north of Scandinavia, the Shetland Islands, the Cairngorms. Subarctic regions fall between 50°N and 70°N latitude, depending on local climates. Precipitation is low, vegetation is characteristic of the taiga. Monthly temperatures are at most three months of the year. Precipitation tends to be low due to the low moisture content of the cold air. Precipitation is greater in warmer months, with a summer maximum ranging from moderate in North America to extreme in the Russian Far East. Except in the wettest areas glaciers are not large because of the lack of winter precipitation. Soils of the subarctic are very acidic because of the influence of the vegetation both in the taiga and in peaty bogs, which tends to acidify the soil, as well as the extreme ease with which leaching of nutrients takes place in the most glaciated regions; the dominant soil orders are podsols and further north gelisols.
Subarctic regions are characterized by taiga forest vegetation, though where winters are mild, as in northern Norway, broadleaf forest may occur—though in some cases soils remain too saturated throughout the year to sustain any tree growth and the dominant vegetation is a peaty herbland dominated by grasses and sedges. There are only a few species of large terrestrial mammals in the subarctic regions, the most important being elk, bears and wolves. Agriculture is limited to animal husbandry, though in some areas barley can be grown. Canada and Siberia are rich in minerals, notably nickel, cobalt, lead and uranium, whilst the Grand Banks and Sea of Okhotsk are two of the richest fisheries in the world and provide support for many small towns. Except for those areas adjacent to warm ocean currents, there is always continuous permafrost due to the cold winters; this means that building in most subarctic regions is difficult and expensive: cities are few and small, whilst roads are few. Subarctic rail transport only exists in the Norilsk -- Dudinka line in northern Siberia.
An important consequence is that transportation tends to be restricted to "bush" planes, helicopters and, in summer, riverboats. Except for a few parts of Europe where the winters are mild due to prevailing wind and ocean current patterns, subarctic regions were not explored until the 18th and 19th centuries; the difficulty of transportation ensured that few settlements lasted long—the abandoned, once-thriving cities of the Yukon, Northwest Territories and Siberia illustrate this. The Trans-Siberian Railway, which skirts the edge of the region, provided a major boost to Russian settlement in the subarctic, as did the intensive industrialization under Joseph Stalin that relied on the enormous mineral resources of the Central Siberian Plateau. Today, many towns in subarctic Russia are declining precipitously as mines close. In Canada, after the early minerals ran out, development stalled until hydroelectric development occurred in the 1950s and 1960s. Hydro-Quebec in particular has carried out many engineering works in regions of near-continuous permafrost, but these have never supported a significant population and have served densely populated southern Quebec.
Tourism in recent years has become a major source of revenue for most countries of the subarctic due to the beautiful glacial, landscapes so characteristic of the region. Most areas in the subarctic are among the most expensive places in the world to visit, due to both high costs of living and inaccessibility. Nonetheless, the great opportunities for outdoor recreation lure an ever-increasing number of travelers. At the same time, the older industries of the subarctic are being threatened by both environmental opposition and overfishing leading to depleted stocks of commercially important species. Indigenous peoples of the Subarctic Muskeg Nordicity Northern Canada Subarctic climate "Subarctic climate" in: Ritter, Michael E; the Physical Environment: an Introduction to Physical Geography. 2006
In biology, a hermaphrodite is an organism that has complete or partial reproductive organs and produces gametes associated with both male and female sexes. Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male." For example, the great majority of tunicates, pulmonate snails, opisthobranch snails and slugs are hermaphrodites. Hermaphroditism is found in some fish species and to a lesser degree in other vertebrates. Most plants are hermaphrodites; the term hermaphrodite has been used to describe ambiguous genitalia and gonadal mosaicism in individuals of gonochoristic species human beings. The word intersex has come into preferred usage for humans, since the word hermaphrodite is considered to be misleading and stigmatizing, as well as "scientifically specious and clinically problematic."A rough estimate of the number of hermaphroditic animal species is 65,000.
The percentage of animal species that are hermaphroditic is about 5%.. Most hermaphroditic species exhibit some degree of self-fertilization; the distribution of self-fertilization rates among animals is similar to that of plants, suggesting that similar processes are operating to direct the evolution of selfing in animals and plants. The term derives from the Latin: hermaphroditus, from Ancient Greek: ἑρμαφρόδιτος, translit. Hermaphroditos, which derives from Hermaphroditus, the son of Hermes and Aphrodite in Greek mythology. According to Ovid, he fused with the nymph Salmacis resulting in one individual possessing physical traits of male and female sexes; the word hermaphrodite entered the English lexicon as early as the late fourteenth century. Alexander ab Alexandro stated, using the term hermaphrodite, that the people who bore the sexes of both man and woman were regarded by the Athenians and the Romans as monsters, thrown into the sea at Athens and into the Tiber at Rome. Sequential hermaphrodites occur in species in which the individual is born as one sex, but can change into the opposite sex.
This contrasts simultaneous hermaphrodites, in which an individual may possess functional male and female genitalia. Sequential hermaphroditism is common in fish and many gastropods, some flowering plants. Sequential hermaphrodites can only change sex once. Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage mode first proposed by Michael T. Ghiselin which states that if an individual of a certain sex could increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex. Sequential hermaphrodites can be divided into three broad categories: Protandry: Where an organism is born as a male, changes sex to a female. Example: The clownfish are colorful reef fish found living in symbiosis with sea anemones. One anemone contains a'harem', consisting of a large female, a smaller reproductive male, smaller non-reproductive males. If the female is removed, the reproductive male will change sex and the largest of the non-reproductive males will mature and become reproductive.
It has been shown that fishing pressure can change when the switch from male to female occurs, since fishermen prefer to catch the larger fish. The populations are changing sex at a smaller size, due to natural selection. Protogyny: Where the organism is born as a female, changes sex to a male. Example: wrasses are a group of reef fish in which protogyny is common. Wrasses have an uncommon life history strategy, termed diandry. In these species, two male morphs exists: a terminal phase male. Initial phase males do not spawn in groups with other females, they are not territorial. They are female mimics. Terminal phase males have a distinctively bright coloration. Individuals are born as males or females, but if they are born males, they are not born as terminal phase males. Females and initial phase males can become terminal phase males; the most dominant female or initial phase male replaces any terminal phase male when those males die or abandon the group. Bidirectional Sex Changers: where an organism has female and male reproductive organs, but act as either female or male during different stages in life.
Example: Lythrypnus dalli are a group of coral reef fish in which bidirectional sex change occurs. Once a social hierarchy is established a fish changes sex according to its social status, regardless of the initial sex, based on a simple principle: if the fish expresses subordinate behavior it changes its sex to female, if the fish expresses dominant or not subordinate behavior the fish changes its sex to male. Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance, groupers are favoured fish for eating in many Asian countries and are aquacultured. Since the adults take several
The eudicots, Eudicotidae or eudicotyledons are a clade of flowering plants, called tricolpates or non-magnoliid dicots by previous authors. The botanical terms were introduced in 1991 by evolutionary botanist James A. Doyle and paleobotanist Carol L. Hotton to emphasize the evolutionary divergence of tricolpate dicots from earlier, less specialized, dicots; the close relationships among flowering plants with tricolpate pollen grains was seen in morphological studies of shared derived characters. These plants have a distinct trait in their pollen grains of exhibiting three colpi or grooves paralleling the polar axis. Molecular evidence confirmed the genetic basis for the evolutionary relationships among flowering plants with tricolpate pollen grains and dicotyledonous traits; the term means "true dicotyledons", as it contains the majority of plants that have been considered dicots and have characteristics of the dicots. The term "eudicots" has subsequently been adopted in botany to refer to one of the two largest clades of angiosperms, monocots being the other.
The remaining angiosperms include magnoliids and what are sometimes referred to as basal angiosperms or paleodicots, but these terms have not been or adopted, as they do not refer to a monophyletic group. The other name for the eudicots is tricolpates, a name which refers to the grooved structure of the pollen. Members of the group have tricolpate pollen; these pollens have three or more pores set in furrows called colpi. In contrast, most of the other seed plants produce monosulcate pollen, with a single pore set in a differently oriented groove called the sulcus; the name "tricolpates" is preferred by some botanists to avoid confusion with the dicots, a nonmonophyletic group. Numerous familiar plants are eudicots, including many common food plants and ornamentals; some common and familiar eudicots include members of the sunflower family such as the common dandelion, the forget-me-not and other members of its family, buttercup and macadamia. Most leafy trees of midlatitudes belong to eudicots, with notable exceptions being magnolias and tulip trees which belong to magnoliids, Ginkgo biloba, not an angiosperm.
The name "eudicots" is used in the APG system, of 1998, APG II system, of 2003, for classification of angiosperms. It is applied to a monophyletic group, which includes most of the dicots. "Tricolpate" is a synonym for the "Eudicot" monophyletic group, the "true dicotyledons". The number of pollen grain furrows or pores helps classify the flowering plants, with eudicots having three colpi, other groups having one sulcus. Pollen apertures are any modification of the wall of the pollen grain; these modifications include thinning and pores, they serve as an exit for the pollen contents and allow shrinking and swelling of the grain caused by changes in moisture content. The elongated apertures/ furrows in the pollen grain are called colpi, along with pores, are a chief criterion for identifying the pollen classes; the eudicots can be divided into two groups: the basal eudicots and the core eudicots. Basal eudicot is an informal name for a paraphyletic group; the core eudicots are a monophyletic group.
A 2010 study suggested the core eudicots can be divided into two clades, Gunnerales and a clade called "Pentapetalae", comprising all the remaining core eudicots. The Pentapetalae can be divided into three clades: Dilleniales superrosids consisting of Saxifragales and rosids superasterids consisting of Santalales, Berberidopsidales and asteridsThis division of the eudicots is shown in the following cladogram: The following is a more detailed breakdown according to APG IV, showing within each clade and orders: clade Eudicots order Ranunculales order Proteales order Trochodendrales order Buxales clade Core eudicots order Gunnerales order Dilleniales clade Superrosids order Saxifragales clade Rosids order Vitales clade Fabids order Fabales order Rosales order Fagales order Cucurbitales order Oxalidales order Malpighiales order Celastrales order Zygophyllales clade Malvids order Geraniales order Myrtales order Crossosomatales order Picramniales order Malvales order Brassicales order Huerteales order Sapindales clade Superasterids order Berberidopsidales order Santalales order Caryophyllales clade Asterids order Cornales order Ericales clade Campanulids order Aquifoliales order Asterales order Escalloniales order Bruniales order Apiales order Dipsacales order Paracryphiales clade Lamiids order Solanales order Lamiales order Vahliales order Gentianales order Boraginales order Garryales order Metteniusales order Icacinales Eudicots at the Encyclopedia of Life Eudicots, Tree of Life Web Project Dicots Plant Life Forms
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks and cnidarians; the majority of animal species are invertebrates. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata; some of the so-called invertebrates, such as the Tunicata and Cephalochordata are more related to the vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy; the word "invertebrate" comes from the Latin word vertebra, which means a joint in general, sometimes a joint from the spinal column of a vertebrate. The jointed aspect of vertebra is derived from the concept of turning, expressed in the root verto or vorto, to turn; the prefix in- means "not" or "without". The term invertebrates is not always precise among non-biologists since it does not describe a taxon in the same way that Arthropoda, Vertebrata or Manidae do.
Each of these terms describes a valid taxon, subphylum or family. "Invertebrata" is a term of convenience, not a taxon. The Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of "Vertebrata" and "Invertebrata" has limited practicality. In the more formal taxonomy of Animalia other attributes that logically should precede the presence or absence of the vertebral column in constructing a cladogram, for example, the presence of a notochord; that would at least circumscribe the Chordata. However the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or bauplan. Despite this, the concept of invertebrates as a taxon of animals has persisted for over a century among the laity, within the zoological community and in its literature it remains in use as a term of convenience for animals that are not members of the Vertebrata; the following text reflects earlier scientific understanding of the term and of those animals which have constituted it.
According to this understanding, invertebrates do not possess a skeleton of bone, either internal or external. They include hugely varied body plans. Many have like jellyfish or worms. Others have outer shells like those of insects and crustaceans; the most familiar invertebrates include the Protozoa, Coelenterata, Nematoda, Echinodermata and Arthropoda. Arthropoda include insects and arachnids. By far the largest number of described invertebrate species are insects; the following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species, 2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, which means that over 95% of the described animal species in the world are invertebrates; the trait, common to all invertebrates is the absence of a vertebral column: this creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only. Being animals, invertebrates are heterotrophs, require sustenance in the form of the consumption of other organisms.
With a few exceptions, such as the Porifera, invertebrates have bodies composed of differentiated tissues. There is typically a digestive chamber with one or two openings to the exterior; the body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A minority, exhibit no symmetry. One example of asymmetric invertebrates includes all gastropod species; this is seen in snails and sea snails, which have helical shells. Slugs appear externally symmetrical. Other gastropods develop external asymmetry, such as Glaucus atlanticus that develops asymmetrical cerata as they mature; the origin of gastropod asymmetry is a subject of scientific debate. Other examples of asymmetry are found in hermit crabs, they have one claw much larger than the other. If a male fiddler loses its large claw, it will grow another on the opposite side after moulting. Sessile animals such as sponges are asymmetrical alongside coral colonies. Neurons differ in invertebrates from mammalian cells.
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. Learning and memory using nociceptors in the sea hare, Aplysia has been described. Mollusk neurons are able to detect tissue trauma. Neurons have been identified in a wide range of invertebrate species, including annelids, molluscs and arthropods. One type of invertebrate respi
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
The Holarctic is the name for the biogeographic realm that encompasses the majority of habitats found throughout the northern continents of the world, combining Wallace's Palearctic zoogeographical region, consisting of North Africa and all of Eurasia, the Nearctic zoogeographical region, consisting of North America, north of Mexico. These regions are further subdivided into a variety of ecoregions. Many ecosystems, the animal and plant communities that depend on them, are found across multiple continents in large portions of this realm; the continuity of these ecosystems results from the shared glacial history of the realm. The floristic Boreal Kingdom corresponds to the Holarctic realm. Within the Holarctic realm, there are a variety of ecosystems; the type of ecosystem found in an area depends on local geography. In the far north, a band of arctic tundra circles the shore of the Arctic Ocean; the ground beneath this land is frozen year-round. In these difficult growing conditions, few plants can survive.
South of the tundra, the boreal forest stretches across North Eurasia. This land is characterized by coniferous trees. South of here, the ecosystems become more diverse; some areas are covered in temperate grassland, while others are covered in temperate forest, dominated by deciduous trees. The southern extent of the Holarctic reaches into the desert, dominated by plants and animals adapted to the dry conditions. A variety of animal species are distributed across continents, throughout much of the Holarctic realm; some of these included the brown bear, grey wolf, red fox, moose, golden eagle and the common raven. The brown bear is found in semi-open areas distributed throughout the Holarctic, it once occupied much larger areas, but has been driven out by human development and the resulting habitat fragmentation. Today it is only found in remaining wilderness areas; the grey wolf is found in a wide variety of habitats from tundra to desert, with different populations adapted for each. Its historical distribution encompasses the vast majority of the Holarctic realm, though human activities such as development and active extermination have extirpated the species from much of this range.
The red fox is a adaptable predator. It has the widest distribution of any terrestrial carnivore, is adapted to a wide range of habitats, including areas of intense human development. Like the wolf, it is distributed throughout the majority of the Holarctic, but it has avoided extirpation; the wolverine is a large member of the weasel family found in the arctic and in boreal forests, ranging south in mountainous regions. It is distributed in such areas throughout North America; the moose is the largest member of the deer family. It is found throughout most of the boreal forest through continental Eurasia into Scandinavia, eastern North America, boreal and montane regions of western North America. In some areas it ranges south into the deciduous forest; the caribou, or reindeer is found in boreal forest and tundra in the northern parts of the Holarctic. In Eurasia it has been domesticated, it is divided into several subspecies, which are adapted to geographic areas. The golden eagle is one of the best-known birds of prey in the Northern Hemisphere.
It is the most distributed species of eagle. Golden eagles use their agility and speed combined with powerful feet and massive, sharp talons to snatch up a variety of prey; the common raven is the most widespread of the corvids, one of the largest. It is found in a variety of habitats, but wooded northern areas, it has been known to adapt well to areas of human activity. Their distribution makes up most of the Holarctic realm. Leptothorax acervorum is a small red holarctic ant distributed across Eurasia, ranging from central Spain and Italy to the northernmost parts of Scandinavia and Siberia; the continuity of the northern parts of the holarctic results from their shared glacial history. During the Pleistocene, these areas were subjected to repeated glaciations. Icecaps expanded, reshaping its topography. During glacial periods, species survived in refugia, small areas that maintained a suitable climate due to local geography; these areas are believed to have been in southern regions, but some genetic and paleontological evidence points to additional refugia in the sheltered areas of the north.
Wherever these areas were found, they became source populations during interglacial periods. When the glaciers receded and animals spread into the newly opened areas. Different taxa responded to these changing conditions in different ways. Tree species spread outward from refugia during interglacial periods, but in varied patterns, with different trees dominating in different periods. Insects, on the other hand, shifted their ranges with the climate, maintaining consistency in species for the most part throughout the period, their high degree of mobility allowed them to move as the glaciers advanced or retreated, maintaining a constant habitat despite the climatic oscillations. Despite their apparent lack of mobility, plants managed to colonize new areas as well. Studies of fossil pollen indicate. Mammals recolonized at varying rat
Saxifragaceae is a plant family with about 640 known species in 33 accepted genera. The flowers are actinomorphic, they have 5 or 10 stamens. Well known species include: Bergenia cordifolia Saxifraga stellaris Saxifraga oppositifolia Saxifraga paniculataParnassiaceae have sometimes been treated as part of this family, although they are only distantly genetically related and are now placed in Celastraceae; the family does not include the genus Sassafras, despite the related Latin etymology of the names. Saxifragaceae are found in the Northern Hemisphere, with centers of diversity in the Himalayas, East Asia, Western North America; the greatest diversity is in the Pacific Northwest region of North America. The family is divided into two main lineages – the saxifragoids, which includes genera Saxifraga and Saxifragella, the heucheroids, which includes all the other genera; the heucheroids are composed of eight tribes: Darmera, Peltoboykinia, Boykinia, Leptarrhena and Cascadia. Media related to Saxifragaceae at Wikimedia Commons "Saxifragaceae".
Encyclopædia Britannica. 24. 1911. Saxifragaceae in Topwalks