A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians have a larval phase of their life cycle; the larva's appearance is very different from the adult form including different unique structures and organs that do not occur in the adult form. Their diet may be different. Larvae are adapted to environments separate from adults. For example, some larvae such as tadpoles live exclusively in aquatic environments, but can live outside water as adult frogs. By living in a distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population. Animals in the larval stage will consume food to fuel their transition into the adult form. In some species like barnacles, adults are immobile but their larvae are mobile, use their mobile larval form to distribute themselves; some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species, the larvae are fed by female workers.
In Ropalidia marginata the males are capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae. The larvae of some species do not develop further into the adult form; this is a type of neoteny. It is a misunderstanding; this could be the case, but the larval stage has evolved secondarily, as in insects. In these cases the larval form may differ more than the adult form from the group's common origin. Within Insects, only Endopterygotes show different types of larvae. Several classifications have been suggested by many entomologists, following classification is based on Antonio Berlese classification in 1913. There are four main types of endopterygote larvae types: Apodous larvae – no legs at all and are poorly sclerotized. Based on sclerotization, three apodous forms are recognized. Eucephalous – with well sclerotized head capsule. Found in Nematocera and Cerambycidae families. Hemicephalus – with a reduced head capsule, retractable in to the thorax.
Found in Tipulidae and Brachycera families. Acephalus – without head capsule. Found in Cyclorrhapha Protopod larvae – larva have many different forms and unlike a normal insect form, they hatch from eggs which contains little yolk. Ex. first instar larvae of parasitic hymenoptera. Polypod larvae – known as eruciform larvae, these larva have abdominal prolegs, in addition to usual thoracic legs, they poorly sclerotized and inactive. They live in close contact with the food. Best example is caterpillars of lepidopterans. Oligopod larvae – have well developed head capsule and mouthparts are similar to the adult, but without compound eyes, they have six legs. No abdominal prolegs. Two types can be seen: Campodeiform – well sclerotized, dorso-ventrally flattened body. Long legged predators with prognathous mouthparts.. Scarabeiform – poorly sclerotized, flat thorax and abdomen. Short legged and inactive burrowing forms.. Crustacean larvae Ichthyoplankton Spawn Non-larval animal juvenile stages and other life cycle stages: In Porifera: olynthus, gemmule In Cnidaria: ephyra, strobila, hydranth, medusa In Mollusca: paralarva, young cephalopods In Platyhelminthes: hydatid cyst In Bryozoa: avicularium In Acanthocephala: cystacanth In Insecta: Nymphs and naiads, immature forms in hemimetabolous insects Subimago, a juvenile that resembles the adult in Ephemeroptera Instar, intermediate between each ecdysis Pupa and chrysalis, intermediate stages between larva and imago Protozoan life cycle stages Apicomplexan life cycle Algal life cycle stages: Codiolum-phase Conchocelis-phase Marine larval ecology Media related to Larvae at Wikimedia Commons The dictionary definition of larva at Wiktionary Arenas-Mena, C.
Indirect development, transdifferentiation and the macroregulatory evolution of metazoans. Philosophical Transactions of the Royal Society B: Biological Sciences. Feb 27, 2010 Vol.365 no.1540 653-669 Brusca, R. C. & Brusca, G. J.. Invertebrates. Sunderland, Mass.: Sinauer Associates. Hall, B. K. & Wake, M. H. eds.. The Origin and Evolution of Larval Forms. San Diego: Academic Press. Leis, J. M. & Carson-Ewart, B. M. eds.. The Larvae of Indo-Pacific Coastal Fishes. An Identification Guide to Marine Fish Larvae. Fauna Malesiana handbooks, vol. 2. Brill, Leiden. Minelli, A.. The larva. In: Perspectives in Animal Phylogeny and Evolution. Oxford University Press. P. 160-170. Link. Shanks, A. L.. An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Oregon State University Press, Corvallis. 256 pp. Smith, D. & Johnson, K. B.. A Guide to Marine Coastal Plankton and Marine Invertebrate Larvae. Kendall/Hunt Plublishing Company. Stanwell-Smith, D. Hood, A. & Peck, L. S.. A field guide to the pelagic invertebrates larvae of the maritime Antarctic.
British Antarctic Survey, Cambridge. Thyssen, P. J.. Keys for Identification of Immature Insects. In: Amendt, J. et al.. Current Concepts in Forensic Entomology, chapter 2, pp. 25–42. Springer: Dordrecht
Biodiversity refers to the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic and ecosystem level. Terrestrial biodiversity is greater near the equator, the result of the warm climate and high primary productivity. Biodiversity is not distributed evenly on Earth, is richest in the tropics; these tropical forest ecosystems cover less than 10 percent of earth's surface, contain about 90 percent of the world's species. Marine biodiversity is highest along coasts in the Western Pacific, where sea surface temperature is highest, in the mid-latitudinal band in all oceans. There are latitudinal gradients in species diversity. Biodiversity tends to cluster in hotspots, has been increasing through time, but will be to slow in the future. Rapid environmental changes cause mass extinctions. More than 99.9 percent of all species that lived on Earth, amounting to over five billion species, are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.
More in May 2016, scientists reported that 1 trillion species are estimated to be on Earth with only one-thousandth of one percent described. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC. In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor of all organisms living on Earth; the age of the Earth is about 4.54 billion years. The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland. More in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.
According to one of the researchers, "If life arose quickly on Earth.. it could be common in the universe."Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic eon marked a rapid growth in biodiversity via the Cambrian explosion—a period during which the majority of multicellular phyla first appeared; the next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. In the Carboniferous, rainforest collapse led to a great loss of animal life; the Permian–Triassic extinction event, 251 million years ago, was the worst. The most recent, the Cretaceous–Paleogene extinction event, occurred 65 million years ago and has attracted more attention than others because it resulted in the extinction of the dinosaurs; the period since the emergence of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity. Named the Holocene extinction, the reduction is caused by human impacts habitat destruction.
Conversely, biodiversity positively impacts human health in a number of ways, although a few negative effects are studied. The United Nations designated 2011–2020 as the United Nations Decade on Biodiversity. 1916 - The term biological diversity was used first by J. Arthur Harris in "The Variable Desert," Scientific American, JSTOR 6182: "The bare statement that the region contains a flora rich in genera and species and of diverse geographic origin or affinity is inadequate as a description of its real biological diversity." 1975 - The term natural diversity was introduced 1980 - Thomas Lovejoy introduced the term biological diversity to the scientific community in a book.. It became used. 1985 -The contracted form biodiversity was coined by W. G. Rosen 1985 - The term "biodiversity" appears in the article, "A New Plan to Conserve the Earth's Biota" by Laura Tangley. 1988 - The term biodiversity first appeared in a publication. The present - the term has achieved widespread use. "Biodiversity" is most used to replace the more defined and long established terms, species diversity and species richness.
Biologists most define biodiversity as the "totality of genes and ecosystems of a region". An advantage of this definition is that it seems to describe most circumstances and presents a unified view of the traditional types of biological variety identified: taxonomic diversity ecological diversity morphological diversity functional diversity This multilevel construct is consistent with Datman and Lovejoy. An explicit definition consistent with this interpretation was first given in a paper by Bruce A. Wilcox commissioned by the International Union for the Conservation of Nature and Natural Resources for the 1982 World National Parks Conference. Wilcox's definition was "Biological diversity is the variety of life forms...at all levels of biologi
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
In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both biological features. A species' habitat is those places where it can find food, shelter and mates for reproduction; the physical factors are for example soil, range of temperature, light intensity as well as biotic factors such as the availability of food and the presence or absence of predators. Every organism has certain habitat needs for the conditions in which it will thrive, but some are tolerant of wide variations while others are specific in their requirements. A habitat is not a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss, for a parasitic organism it is the body of its host, part of the host's body such as the digestive tract, or a single cell within the host's body. Habitat types include polar, temperate and tropical; the terrestrial vegetation type may be forest, grassland, semi-arid or desert. Fresh water habitats include marshes, rivers and ponds, marine habitats include salt marshes, the coast, the intertidal zone, reefs, the open sea, the sea bed, deep water and submarine vents.
Habitats change over time. This may be due to a violent event such as the eruption of a volcano, an earthquake, a tsunami, a wildfire or a change in oceanic currents. Other changes come as a direct result of human activities; the introduction of alien species can have a devastating effect on native wildlife, through increased predation, through competition for resources or through the introduction of pests and diseases to which the native species have no immunity. The word "habitat" has been in use since about 1755 and derives from the Latin habitāre, to inhabit, from habēre, to have or to hold. Habitat can be defined as the natural environment of an organism, the type of place in which it is natural for it to live and grow, it is similar in meaning to a biotope. The chief environmental factors affecting the distribution of living organisms are temperature, climate, soil type and light intensity, the presence or absence of all the requirements that the organism needs to sustain it. Speaking, animal communities are reliant on specific types of plant communities.
Some plants and animals are generalists, their habitat requirements are met in a wide range of locations. The small white butterfly for example is found on all the continents of the world apart from Antarctica, its larvae feed on a wide range of Brassicas and various other plant species, it thrives in any open location with diverse plant associations. The large blue butterfly is much more specific in its requirements. Disturbance is important in the creation of biodiverse habitats. In the absence of disturbance, a climax vegetation cover develops that prevents the establishment of other species. Wildflower meadows are sometimes created by conservationists but most of the flowering plants used are either annuals or biennials and disappear after a few years in the absence of patches of bare ground on which their seedlings can grow. Lightning strikes and toppled trees in tropical forests allow species richness to be maintained as pioneering species move in to fill the gaps created. Coastal habitats can become dominated by kelp until the seabed is disturbed by a storm and the algae swept away, or shifting sediment exposes new areas for colonisation.
Another cause of disturbance is when an area may be overwhelmed by an invasive introduced species, not kept under control by natural enemies in its new habitat. Terrestrial habitat types include forests, grasslands and deserts. Within these broad biomes are more specific habitats with varying climate types, temperature regimes, soils and vegetation types. Many of these habitats grade into each other and each one has its own typical communities of plants and animals. A habitat may suit a particular species well, but its presence or absence at any particular location depends to some extent on chance, on its dispersal abilities and its efficiency as a coloniser. Freshwater habitats include rivers, lakes, ponds and bogs. Although some organisms are found across most of these habitats, the majority have more specific requirements; the water velocity, its temperature and oxygen saturation are important factors, but in river systems, there are fast and slow sections, pools and backwaters which provide a range of habitats.
Aquatic plants can be floating, semi-submerged, submerged or grow in permanently or temporarily saturated soils besides bodies of water. Marginal plants provide important habitat for both invertebrates and vertebrates, submerged plants provide oxygenation of the water, absorb nutrients and play a part in the reduction of pollution. Marine habitats include brackish water, bays, the open sea, the intertidal zone, the sea bed and deep / shallow water zones. Further variations include rock pools, sand banks, brackish lagoons and pebbly beaches, seagrass beds, all supporting their own flora and fauna; the benth
Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not closely related, is thus polyphyletic. Including organisms ranging from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata and phloem, which are found in land plants; the largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example and the stoneworts. No definition of algae is accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.
Algae constitute a polyphyletic group since they do not include a common ancestor, although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, the roots and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy; some unicellular species of green algae, many golden algae, euglenids and other algae have become heterotrophs, sometimes parasitic, relying on external energy sources and have limited or no photosynthetic apparatus.
Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. The singular alga retains that meaning in English; the etymology is obscure. Although some speculate that it is related to Latin algēre, "be cold", no reason is known to associate seaweed with temperature. A more source is alliga, "binding, entwining"; the Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it. The Latinization, fūcus, meant the cosmetic rouge; the etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך, "paint", a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean.
It could be any color: black, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used; the name Fucus appears in a number of taxa. The algae contain chloroplasts. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events; the table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members; some retain plastids, but not chloroplasts. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum, the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are considered among algae.
In Systema Naturae, Linnaeus described the genera Volvox and Corallina, a species of Acetabularia, among the animals. In 1768, Samuel Gottlieb Gmelin published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus, it included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey and Lamouroux were the first to divide macroscopic algae into four divisions based on their pigmentation; this is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae, brown algae, green algae, Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers studying the Infusoria. Unlike macroalgae, which were viewed as plants, microalgae were considered animals because they are motile; the nonmotile microalgae were sometimes seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-D
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds. Kelp forests occur worldwide throughout temperate and polar coastal oceans. In 2007, kelp forests were discovered in tropical waters near Ecuador. Physically formed by brown macroalgae, kelp forests provide a unique, three-dimensional habitat for marine organisms and are a source for understanding many ecological processes. Over the last century, they have been the focus of extensive research in trophic ecology, continue to provoke important ideas that are relevant beyond this unique ecosystem. For example, kelp forests can influence coastal oceanographic patterns and provide many ecosystem services. However, the influence of humans has contributed to kelp forest degradation. Of particular concern are the effects of overfishing nearshore ecosystems, which can release herbivores from their normal population regulation and result in the overgrazing of kelp and other algae.
This can result in transitions to barren landscapes where few species persist. The implementation of marine protected areas is one management strategy useful for addressing such issues, since it may limit the impacts of fishing and buffer the ecosystem from additive effects of other environmental stressors; the term kelp refers to marine algae belonging to the order Laminariales. Though not considered a taxonomically diverse order, kelps are diverse structurally and functionally; the most recognized species are the giant kelps, although numerous other genera such as Laminaria, Lessonia and Eisenia are described. A wide range of sea life uses kelp forests including fish. In the North Pacific kelp forests rockfish, many invertebrates, such as amphipods, marine snails, bristle worms, brittle stars. Many marine mammals and birds are found, including seals, sea lions, sea otters, terns, snowy egrets, great blue herons, cormorants, as well as some shore birds. Considered an ecosystem engineer, kelp provides a physical substrate and habitat for kelp forest communities.
In algae, the body of an individual organism is known as a thallus rather than as a plant. The morphological structure of a kelp thallus is defined by three basic structural units: The holdfast is a root-like mass that anchors the thallus to the sea floor, though unlike true roots it is not responsible for absorbing and delivering nutrients to the rest of the thallus; the stipe is analogous to a plant stalk, extending vertically from the holdfast and providing a support framework for other morphological features. The fronds are leaf- or blade-like attachments extending from the stipe, sometimes along its full length, are the sites of nutrient uptake and photosynthetic activity. In addition, many kelp species have pneumatocysts, or gas-filled bladders located at the base of fronds near the stipe; these structures provide the necessary buoyancy for kelp to maintain an upright position in the water column. The environmental factors necessary for kelp to survive include hard substrate, high nutrients, light.
Productive kelp forests tend to be associated with areas of significant oceanographic upwelling, a process that delivers cool, nutrient-rich water from depth to the ocean’s mixed surface layer. Water flow and turbulence facilitate nutrient assimilation across kelp fronds throughout the water column. Water clarity affects the depth. In ideal conditions, giant kelp can grow as much as 30–60 cm vertically per day; some species, such as Nereocystis, are annuals, while others such as Eisenia are perennials, living for more than 20 years. In perennial kelp forests, maximum growth rates occur during upwelling months and die-backs correspond to reduced nutrient availability, shorter photoperiods, increased storm frequency. Kelps are associated with temperate and arctic waters worldwide. Of the more dominant genera, Laminaria is associated with both sides of the Atlantic Ocean and the coasts of China and Japan; the region with the greatest diversity of kelps is the northeastern Pacific, from north of San Francisco, California, to the Aleutian Islands, Alaska.
Although kelp forests are unknown in tropical surface waters, a few species of Laminaria have been known to occur in tropical deep waters. This general absence of kelp from the tropics is believed to be due to insufficient nutrient levels associated with warm, oligotrophic waters. One recent study spatially overlaid the requisite physical parameters for kelp with mean oceanographic conditions has produced a model predicting the existence of subsurface kelps throughout the tropics worldwide to depths of 200 m. For a hotspot in the Galapagos Islands, the local model was improved with fine-scale data and tested; this suggests that their global model might be accurate, if so, kelp forests would be prolific in tropical subsurface waters worldwide. The importance of this contribution has been ack