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99-470: Mozabites mainly live in five oases ; namely, Ghardaïa , Beni Isguen , El Atteuf , Melika and Bounoura , as well as two other isolated oases farther north: Berriane and El Guerrara . Ghardaïa is the capital of the confederation, followed in importance by Beni Isguen , the chief commercial centre. In 767, a refugee Persian Ibadi leader founded the Rustamid Kingdom , leading to most of

198-475: A "central pool of open water surrounded by a ring of water-dependent shrubs and trees…which are in turn encircled by an outlying transition zone to desert plants." Rain showers provide subterranean water to sustain natural oases, such as the Tuat . Substrata of impermeable rock and stone can trap water and retain it in pockets, or on long faulting subsurface ridges or volcanic dikes water can collect and percolate to

297-465: A dramatic effect on community structure. Hunting of sea otters, for example, is thought to have led indirectly to the extinction of the Steller's sea cow ( Hydrodamalis gigas ). While the keystone species concept has been used extensively as a conservation tool, it has been criticized for being poorly defined from an operational stance. It is difficult to experimentally determine what species may hold

396-428: A dramatic impact on the ecology of individual species or whole ecosystems. For instance, the replacement of an ant species by another (invasive) ant species has been shown to affect how elephants reduce tree cover and thus the predation of lions on zebras . A trophic level (from Greek troph , τροφή, trophē, meaning "food" or "feeding") is "a group of organisms acquiring a considerable majority of its energy from

495-412: A flattened body relative to the main populations that live in open savanna. The population that lives in an isolated rock outcrop hides in crevasses where its flattened body offers a selective advantage. Habitat shifts also occur in the developmental life history of amphibians, and in insects that transition from aquatic to terrestrial habitats. Biotope and habitat are sometimes used interchangeably, but

594-612: A higher one." Small scale patterns do not necessarily explain large scale phenomena, otherwise captured in the expression (coined by Aristotle) 'the sum is greater than the parts'. "Complexity in ecology is of at least six distinct types: spatial, temporal, structural, process, behavioral, and geometric." From these principles, ecologists have identified emergent and self-organizing phenomena that operate at different environmental scales of influence, ranging from molecular to planetary, and these require different explanations at each integrative level . Ecological complexity relates to

693-444: A keystone role in each ecosystem. Furthermore, food web theory suggests that keystone species may not be common, so it is unclear how generally the keystone species model can be applied. Complexity is understood as a large computational effort needed to piece together numerous interacting parts exceeding the iterative memory capacity of the human mind. Global patterns of biological diversity are complex. This biocomplexity stems from

792-408: A keystone species can result in a community collapse just as the removal of the keystone in an arch can result in the arch's loss of stability. Sea otters ( Enhydra lutris ) are commonly cited as an example of a keystone species because they limit the density of sea urchins that feed on kelp . If sea otters are removed from the system, the urchins graze until the kelp beds disappear, and this has

891-741: A legacy niche that was constructed before their time. Biomes are larger units of organization that categorize regions of the Earth's ecosystems, mainly according to the structure and composition of vegetation. There are different methods to define the continental boundaries of biomes dominated by different functional types of vegetative communities that are limited in distribution by climate, precipitation, weather, and other environmental variables. Biomes include tropical rainforest , temperate broadleaf and mixed forest , temperate deciduous forest , taiga , tundra , hot desert , and polar desert . Other researchers have recently categorized other biomes, such as

990-439: A linear successional route, changes might occur quickly or slowly over thousands of years before specific forest successional stages are brought about by biological processes. An ecosystem's area can vary greatly, from tiny to vast. A single tree is of little consequence to the classification of a forest ecosystem, but is critically relevant to organisms living in and on it. Several generations of an aphid population can exist over

1089-439: A macroscopic view of the system. While the notion of trophic levels provides insight into energy flow and top-down control within food webs, it is troubled by the prevalence of omnivory in real ecosystems. This has led some ecologists to "reiterate that the notion that species clearly aggregate into discrete, homogeneous trophic levels is fiction." Nonetheless, recent studies have shown that real trophic levels do exist, but "above

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1188-599: A merchant trade route. They continued as a merchant community, with subsequent waves of immigration during times of anti-Semitism across the Sahara, Europe, and the Middle East. In 1881, one year before the French annexed the M'zab, there were estimated 3,000 Mozabite Jews out of the 30,000 Algerian Jews. By 1921, the latter number would grow to 74,000, a result of a spike in anti-Semitism in the later 1800s and early 1900s, but

1287-516: A mix of herbivores and predators). Omnivores do not fit neatly into a functional category because they eat both plant and animal tissues. It has been suggested that omnivores have a greater functional influence as predators because compared to herbivores, they are relatively inefficient at grazing. Trophic levels are part of the holistic or complex systems view of ecosystems. Each trophic level contains unrelated species that are grouped together because they share common ecological functions, giving

1386-419: A natural condition, such as the presence of water that may be stored in reservoirs and used for irrigation, most oases, as we know them, are artificial. The word oasis came into English from Latin : oasis , from Ancient Greek : ὄασις , óasis , which in turn is a direct borrowing from Demotic Egyptian . The word for oasis in the latter-attested Coptic language (the descendant of Demotic Egyptian)

1485-420: A new appreciation for the influence that organisms have on the ecosystem and evolutionary process. The term "niche construction" is more often used in reference to the under-appreciated feedback mechanisms of natural selection imparting forces on the abiotic niche. An example of natural selection through ecosystem engineering occurs in the nests of social insects , including ants, bees, wasps, and termites. There

1584-836: A particular route. For example, the oases of Awjila , Ghadames and Kufra , situated in modern-day Libya , have at various times been vital to both north–south and east–west trade in the Sahara Desert . The location of oases also informed the Darb El Arba'īn trade route from Sudan to Egypt, as well as the caravan route from the Niger River to Tangier , Morocco. The Silk Road "traced its course from water hole to water hole, relying on oasis communities such as Turpan in China and Samarkand in Uzbekistan." According to

1683-435: A population-level phenomenon, as with the migration routes followed by plants as they occupied northern post-glacial environments. Plant ecologists use pollen records that accumulate and stratify in wetlands to reconstruct the timing of plant migration and dispersal relative to historic and contemporary climates. These migration routes involved an expansion of the range as plant populations expanded from one area to another. There

1782-401: A region), and sites are classed either as sources or sinks. A site is a generic term that refers to places where ecologists sample populations, such as ponds or defined sampling areas in a forest. Source patches are productive sites that generate a seasonal supply of juveniles that migrate to other patch locations. Sink patches are unproductive sites that only receive migrants; the population at

1881-517: A seasonal influx of new immigrants. A dynamic metapopulation structure evolves from year to year, where some patches are sinks in dry years and are sources when conditions are more favorable. Ecologists use a mixture of computer models and field studies to explain metapopulation structure. Community ecology examines how interactions among species and their environment affect the abundance, distribution and diversity of species within communities. Johnson & Stinchcomb (2007) Community ecology

1980-411: A shovel is needed. Wells may or may not be equipped with pumps. Frequently the pumps are broken and useless, and a rope and bucket are then necessary to obtain water. Most of the wells in this region are less than 100 feet deep, but some are deeper, and 100 feet of rope is not too much to provide. As a rule the rope and bucket at a well, if they were ever provided, soon disappear, and one should never trust

2079-456: A species describes the environment over which a species is known to occur and the type of community that is formed as a result. More specifically, "habitats can be defined as regions in environmental space that are composed of multiple dimensions, each representing a biotic or abiotic environmental variable; that is, any component or characteristic of the environment related directly (e.g. forage biomass and quality) or indirectly (e.g. elevation) to

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2178-402: A specific habitat, such as a cave or a pond, and principles gleaned from small-scale studies are extrapolated to larger systems. Feeding relations require extensive investigations, e.g. into the gut contents of organisms, which can be difficult to decipher, or stable isotopes can be used to trace the flow of nutrient diets and energy through a food web. Despite these limitations, food webs remain

2277-446: A valuable tool in understanding community ecosystems. Food webs illustrate important principles of ecology : some species have many weak feeding links (e.g., omnivores ) while some are more specialized with fewer stronger feeding links (e.g., primary predators ). Such linkages explain how ecological communities remain stable over time and eventually can illustrate a "complete" web of life. The disruption of food webs may have

2376-399: A wide array of interacting levels of organization spanning micro-level (e.g., cells ) to a planetary scale (e.g., biosphere ) phenomena . Ecosystems, for example, contain abiotic resources and interacting life forms (i.e., individual organisms that aggregate into populations which aggregate into distinct ecological communities). Because ecosystems are dynamic and do not necessarily follow

2475-463: Is wahe or ouahe which means a "dwelling place". Oasis in Arabic is wāḥa ( Arabic : واحة ). Oases develop in " hydrologically favored" locations that have attributes such as a high water table , seasonal lakes, or blockaded wadis . Oases are made when sources of freshwater, such as underground rivers or aquifers , irrigate the surface naturally or via man-made wells. The presence of water on

2574-485: Is a central concept in the ecology of organisms and is sub-divided into the fundamental and the realized niche. The fundamental niche is the set of environmental conditions under which a species is able to persist. The realized niche is the set of environmental plus ecological conditions under which a species persists. The Hutchinsonian niche is defined more technically as a " Euclidean hyperspace whose dimensions are defined as environmental variables and whose size

2673-480: Is a fertile area of a desert or semi-desert environment that sustains plant life and provides habitat for animals. Surface water may be present, or water may only be accessible from wells or underground channels created by humans. In geography, an oasis may be a current or past rest stop on a transportation route, or less-than-verdant location that nonetheless provides access to underground water through deep wells created and maintained by humans. Although they depend on

2772-504: Is a function of the number of values that the environmental values may assume for which an organism has positive fitness ." Biogeographical patterns and range distributions are explained or predicted through knowledge of a species' traits and niche requirements. Species have functional traits that are uniquely adapted to the ecological niche. A trait is a measurable property, phenotype , or characteristic of an organism that may influence its survival. Genes play an important role in

2871-414: Is a larger taxonomy of movement, such as commuting, foraging, territorial behavior, stasis, and ranging. Dispersal is usually distinguished from migration because it involves the one-way permanent movement of individuals from their birth population into another population. In metapopulation terminology, migrating individuals are classed as emigrants (when they leave a region) or immigrants (when they enter

2970-461: Is an emergent homeostasis or homeorhesis in the structure of the nest that regulates, maintains and defends the physiology of the entire colony. Termite mounds, for example, maintain a constant internal temperature through the design of air-conditioning chimneys. The structure of the nests themselves is subject to the forces of natural selection. Moreover, a nest can survive over successive generations, so that progeny inherit both genetic material and

3069-404: Is another statistical approach that is often used in conservation research . Metapopulation models simplify the landscape into patches of varying levels of quality, and metapopulations are linked by the migratory behaviours of organisms. Animal migration is set apart from other kinds of movement because it involves the seasonal departure and return of individuals from a habitat. Migration is also

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3168-438: Is greater than respiration) by photosynthesis or chemosynthesis . Heterotrophs are organisms that must feed on others for nourishment and energy (respiration exceeds production). Heterotrophs can be further sub-divided into different functional groups, including primary consumers (strict herbivores), secondary consumers ( carnivorous predators that feed exclusively on herbivores), and tertiary consumers (predators that feed on

3267-480: Is integrated into its desert environment through an often close association with nomadic transhumant livestock farming (very often pastoral and sedentary populations are clearly distinguished). The fertility of the oasis soil is restored by "cyclic organic inputs of animal origin." In summary, an oasis palm grove is a highly anthropized and irrigated area that supports a traditionally intensive and polyculture-based agriculture. Responding to environmental constraints,

3366-590: Is the Park Grass Experiment , which was initiated in 1856. Another example is the Hubbard Brook study , which has been in operation since 1960. Holism remains a critical part of the theoretical foundation in contemporary ecological studies. Holism addresses the biological organization of life that self-organizes into layers of emergent whole systems that function according to non-reducible properties. This means that higher-order patterns of

3465-413: Is the biosphere: the total sum of ecosystems on the planet. Ecological relationships regulate the flux of energy, nutrients, and climate all the way up to the planetary scale. For example, the dynamic history of the planetary atmosphere's CO 2 and O 2 composition has been affected by the biogenic flux of gases coming from respiration and photosynthesis, with levels fluctuating over time in relation to

3564-423: Is the date palm ( Phoenix dactylifera L. ), which forms the upper layer . These palm trees provide shade for smaller understory trees like apricots , dates , figs , olives , and peach trees, which form the middle layer. Market-garden vegetables, some cereals (such as sorghum , barley , millet , and wheat ), and/or mixed animal fodder , are grown in the bottom layer where there is more moisture. The oasis

3663-522: Is the study of the interactions among a collection of species that inhabit the same geographic area. Community ecologists study the determinants of patterns and processes for two or more interacting species. Research in community ecology might measure species diversity in grasslands in relation to soil fertility. It might also include the analysis of predator-prey dynamics, competition among similar plant species, or mutualistic interactions between crabs and corals. These ecosystems, as we may call them, are of

3762-556: Is used for managing wildlife stocks and setting harvest quotas. In cases where basic models are insufficient, ecologists may adopt different kinds of statistical methods, such as the Akaike information criterion , or use models that can become mathematically complex as "several competing hypotheses are simultaneously confronted with the data." The concept of metapopulations was defined in 1969 as "a population of populations which go extinct locally and recolonize". Metapopulation ecology

3861-533: The French in 1852, the Mozabites concluded a convention in 1853 and accepted to pay an annual contribution of 1,800 francs in return for their independence. In November 1882, the M'zab country was definitely annexed to French Algeria . Since the establishment of French control, Beni Isguen has become the depot for the sale of goods from Europe . The Mozabite engineers built a system of irrigation works that made

3960-573: The Western Desert of Egypt ( Kharga , Dakhla , Farafra , Baharyia , and Siwa ) once had "flowing spring and wells" but due to the decline of groundwater heads because of overuse for land reclamation projects those water sources are no more and the oases suffer as a result. Morocco has lost two-thirds of its oasis habitat over the last 100 years due to heat, drought, and water scarcity . The Ferkla Oases in Morocco once drew on water from

4059-405: The abundance or biomass at each level. When the relative abundance or biomass of each species is sorted into its respective trophic level, they naturally sort into a 'pyramid of numbers'. Species are broadly categorized as autotrophs (or primary producers ), heterotrophs (or consumers ), and Detritivores (or decomposers ). Autotrophs are organisms that produce their own food (production

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4158-436: The logistic equation by Pierre Verhulst : where N(t) is the number of individuals measured as biomass density as a function of time, t , r is the maximum per-capita rate of change commonly known as the intrinsic rate of growth, and α {\displaystyle \alpha } is the crowding coefficient, which represents the reduction in population growth rate per individual added. The formula states that

4257-576: The Berber population adopting Ibadi Islam . After being defeated at Tiaret by the Fatimids in 911, they were banished to Ouargla in the Sahara and founded an independent state in the M'zab in 1012. In 1012, further persecutions made them flee to their present location, where they long remained invulnerable. In the 1500s, they recognized nominal Ottoman authority. After the capture of Laghouat by

4356-551: The Earth and atmospheric conditions within a narrow self-regulating range of tolerance. Population ecology studies the dynamics of species populations and how these populations interact with the wider environment. A population consists of individuals of the same species that live, interact, and migrate through the same niche and habitat. A primary law of population ecology is the Malthusian growth model which states, "a population will grow (or decline) exponentially as long as

4455-484: The Ferkla, Sat and Tangarfa Rivers but they are now dry but for a few days a year. A 1920 USGS publication about watering holes in the deserts of California and Arizona gave this advice for travelers seeking oases: The usual watering places are springs or wells. Springs are frequently clogged with gravel or rubbish or sometimes even with the bodies of dead animals, and it may be necessary to clean them out. For this work

4554-544: The M'zab Jewish population, the French administration incorporated some “culturally Saharan” but ethnically non-indigenous Jews to the north and gave them citizenship under the Crémieux Decree of 1870. That perceived distinction by the French between Berber and non-Berber Jews of the Mzab was not a reflection of “technical precision” but rather “a manufactured form of legal difference”. While the French sought to assimilate

4653-617: The Mozabite Jewish community would remain small, with most Jewish migrants settling in the north. In 1882, when the French military annexed the M'zab, it began an administrative rule that was separate from the northern departments. Unlike their northern Jewish counterparts, many of the Mozabite Berber Jews in Southern Algeria were classified by the French under the “indigenous code”. Given the diversity of

4752-716: The Mozabite Jews from other Algerian Jewish affairs by keeping Mozabite, or “Mosaic” laws for civil matters, and French indigenous laws for public and criminal matters. It was not until 1961, with the French National Assembly Law 61-805, that the Mozabite Jews were granted “common law civil status” and French citizenship. Mozabite people are characterized by a very high level of North African haplogroups E1b1b1b (M81) (86%) and U6 (28%). Oasis In ecology , an oasis ( / oʊ ˈ eɪ s ɪ s / ; pl. : oases / oʊ ˈ eɪ s iː z / )

4851-493: The Northern Jewry as French citizens, they recognised religious rule of the Mozabite Jewish population and kept them separate under indigenous law, which meant severely limiting its political and social power. With anti-Semitism on the rise in the late 1800s, the French colonial powers sought to decrease Jewish commerce in the south and prevent further Jewish collaboration with Muslim communities. They continued to distance

4950-837: The United Nations, "Oases are at the very heart of the overall development of peri-Saharan countries due to their geographical location and the fact they are preferred migration routes in times of famine or insecurity in the region." Oases in Oman , on the Arabian Peninsula near the Persian Gulf , vary somewhat from the Saharan form. While still located in an arid or semi-arid zone with a date palm overstory, these oases are usually located below plateaus and "watered either by springs or by aflaj , tunnel systems dug into

5049-401: The chance of finding them there. Open wells are sometimes contaminated in the same way as springs and need to be cleaned out, particularly in little-frequented places where they are unused for months at a time. Ecology Ecology (from Ancient Greek οἶκος ( oîkos )  'house' and -λογία ( -logía )  'study of') is the natural science of

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5148-435: The city [ medina ] or village [ ksar ] with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system." The location of oases has been of critical importance for trade and transportation routes in desert areas; caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on

5247-744: The context of the environment. It encompasses life processes, interactions, and adaptations ; movement of materials and energy through living communities; successional development of ecosystems; cooperation, competition, and predation within and between species ; and patterns of biodiversity and its effect on ecosystem processes. Ecology has practical applications in conservation biology , wetland management, natural resource management ( agroecology , agriculture , forestry , agroforestry , fisheries , mining , tourism ), urban planning ( urban ecology ), community health , economics , basic and applied science , and human social interaction ( human ecology ). The word ecology ( German : Ökologie )

5346-714: The diversity of life from genes to ecosystems and spans every level of biological organization. The term has several interpretations, and there are many ways to index, measure, characterize, and represent its complex organization. Biodiversity includes species diversity , ecosystem diversity , and genetic diversity and scientists are interested in the way that this diversity affects the complex ecological processes operating at and among these respective levels. Biodiversity plays an important role in ecosystem services which by definition maintain and improve human quality of life. Conservation priorities and management techniques require different approaches and considerations to address

5445-460: The dull bluish or gray green of the feathery crowns of foliage. It is small wonder that a whole folklore of poetic legends and proverbs has grown up around the date palm in the regions where it flourishes. Many historic oases have struggled with drought and inadequate maintenance. According to a United Nations report on the future of oases in the Sahara and Sahel , "Increasingly   ... oases are subject to various pressures, heavily influenced by

5544-530: The dynamic resilience of ecosystems that transition to multiple shifting steady-states directed by random fluctuations of history. Long-term ecological studies provide important track records to better understand the complexity and resilience of ecosystems over longer temporal and broader spatial scales. These studies are managed by the International Long Term Ecological Network (LTER). The longest experiment in existence

5643-456: The ecology and evolution of plants and animals. Ecological theory has also been used to explain self-emergent regulatory phenomena at the planetary scale: for example, the Gaia hypothesis is an example of holism applied in ecological theory. The Gaia hypothesis states that there is an emergent feedback loop generated by the metabolism of living organisms that maintains the core temperature of

5742-510: The effects of climate change , decreasing groundwater levels and a gradual loss of cultural heritage due to a fading historical memory concerning traditional water management techniques. These natural pressures are compounded by demographic pressures and the introduction of modern water pumping techniques that can disrupt traditional resource management schemes, particularly in the North Saharan oases." For example, five historic oases in

5841-434: The energy is transferred through a chain of organisms by consumption. The simplified linear feeding pathways that move from a basal trophic species to a top consumer is called the food chain . Food chains in an ecological community create a complex food web. Food webs are a type of concept map that is used to illustrate and study pathways of energy and material flows. Empirical measurements are generally restricted to

5940-460: The environment experienced by all individuals in the population remains constant." Simplified population models usually starts with four variables: death, birth, immigration , and emigration . An example of an introductory population model describes a closed population, such as on an island, where immigration and emigration does not take place. Hypotheses are evaluated with reference to a null hypothesis which states that random processes create

6039-451: The equilibrium, r / α {\displaystyle r/\alpha } as K , which is known as the "carrying capacity." Population ecology builds upon these introductory models to further understand demographic processes in real study populations. Commonly used types of data include life history , fecundity , and survivorship, and these are analyzed using mathematical techniques such as matrix algebra . The information

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6138-589: The flux of energy and matter through an environment. Ecosystems have biophysical feedback mechanisms that moderate processes acting on living ( biotic ) and abiotic components of the planet. Ecosystems sustain life-supporting functions and provide ecosystem services like biomass production (food, fuel, fiber, and medicine), the regulation of climate , global biogeochemical cycles , water filtration , soil formation , erosion control, flood protection, and many other natural features of scientific, historical, economic, or intrinsic value. The scope of ecology contains

6237-400: The former applies to a community's environment, whereas the latter applies to a species' environment. Definitions of the niche date back to 1917, but G. Evelyn Hutchinson made conceptual advances in 1957 by introducing a widely adopted definition: "the set of biotic and abiotic conditions in which a species is able to persist and maintain stable population sizes." The ecological niche

6336-544: The former relates only to the physical modifications of the habitat whereas the latter also considers the evolutionary implications of physical changes to the environment and the feedback this causes on the process of natural selection. Ecosystem engineers are defined as: "organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials. In so doing they modify, maintain and create habitats." The ecosystem engineering concept has stimulated

6435-518: The full ecological scope of biodiversity. Natural capital that supports populations is critical for maintaining ecosystem services and species migration (e.g., riverine fish runs and avian insect control) has been implicated as one mechanism by which those service losses are experienced. An understanding of biodiversity has practical applications for species and ecosystem-level conservation planners as they make management recommendations to consulting firms, governments, and industry. The habitat of

6534-649: The garden resembles a tropical jungle. Very beautiful are these gardens in the spring, when the apricot and peach trees are in blossom here and there among the palms and the figs and vines are putting forth their leaves. In autumn, when the dates are ripening, the color effects, especially when the tops of the palms are lit up by the last rays of the setting sun, are something that once seen can never be forgotten. The great clusters of fruit, displaying every tint from bright yellow, through orange, vermilion, and maroon, to plum purple and chestnut brown, with their brilliant yellow or rich orange ivory-like stalks, contrast superbly with

6633-613: The ground or carved into the rock to tap underground aquifers." This rainwater harvesting system "never developed a serious salinity problem." In the drylands of southwestern North America, there is a habitat form called Palm Oasis (alternately Palm Series or Oasis Scrub Woodland) that has the native California fan palm as the overstory species. These Palm Oases can be found in California , Arizona , Baja California , and Sonora . People who live in an oasis must manage land and water use carefully. The most important plant in an oasis

6732-408: The herbivore trophic level, food webs are better characterized as a tangled web of omnivores." A keystone species is a species that is connected to a disproportionately large number of other species in the food-web . Keystone species have lower levels of biomass in the trophic pyramid relative to the importance of their role. The many connections that a keystone species holds means that it maintains

6831-406: The human and oceanic microbiomes . To a microbe , the human body is a habitat and a landscape. Microbiomes were discovered largely through advances in molecular genetics , which have revealed a hidden richness of microbial diversity on the planet. The oceanic microbiome plays a significant role in the ecological biogeochemistry of the planet's oceans. The largest scale of ecological organization

6930-404: The interplay among ecological processes that operate and influence patterns at different scales that grade into each other, such as transitional areas or ecotones spanning landscapes. Complexity stems from the interplay among levels of biological organization as energy, and matter is integrated into larger units that superimpose onto the smaller parts. "What were wholes on one level become parts on

7029-412: The interplay of development and environmental expression of traits. Resident species evolve traits that are fitted to the selection pressures of their local environment. This tends to afford them a competitive advantage and discourages similarly adapted species from having an overlapping geographic range. The competitive exclusion principle states that two species cannot coexist indefinitely by living off

7128-402: The latter focuses on materials and energy fluxes. System behaviors must first be arrayed into different levels of the organization. Behaviors corresponding to higher levels occur at slow rates. Conversely, lower organizational levels exhibit rapid rates. For example, individual tree leaves respond rapidly to momentary changes in light intensity, CO 2 concentration, and the like. The growth of

7227-424: The lifespan of a single leaf. Each of those aphids, in turn, supports diverse bacterial communities. The nature of connections in ecological communities cannot be explained by knowing the details of each species in isolation, because the emergent pattern is neither revealed nor predicted until the ecosystem is studied as an integrated whole. Some ecological principles, however, do exhibit collective properties where

7326-432: The lower adjacent level (according to ecological pyramids ) nearer the abiotic source." Links in food webs primarily connect feeding relations or trophism among species. Biodiversity within ecosystems can be organized into trophic pyramids, in which the vertical dimension represents feeding relations that become further removed from the base of the food chain up toward top predators, and the horizontal dimension represents

7425-558: The most various kinds and sizes. They form one category of the multitudinous physical systems of the universe, which range from the universe as a whole down to the atom. Tansley (1935) Ecosystems may be habitats within biomes that form an integrated whole and a dynamically responsive system having both physical and biological complexes. Ecosystem ecology is the science of determining the fluxes of materials (e.g. carbon, phosphorus) between different pools (e.g., tree biomass, soil organic material). Ecosystem ecologists attempt to determine

7524-456: The nature of the unique physical environments that shapes the biodiversity within each. A more recent addition to ecosystem ecology are technoecosystems , which are affected by or primarily the result of human activity. A food web is the archetypal ecological network . Plants capture solar energy and use it to synthesize simple sugars during photosynthesis . As plants grow, they accumulate nutrients and are eaten by grazing herbivores , and

7623-573: The niche is called the ecotope , which is defined as the full range of environmental and biological variables affecting an entire species. Organisms are subject to environmental pressures, but they also modify their habitats. The regulatory feedback between organisms and their environment can affect conditions from local (e.g., a beaver pond ) to global scales, over time and even after death, such as decaying logs or silica skeleton deposits from marine organisms. The process and concept of ecosystem engineering are related to niche construction , but

7722-531: The number of nitrogen fixers , can lead to disproportionate, perhaps irreversible, changes in the system properties." Biodiversity refers to the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever-changing and adapting. Noss & Carpenter (1994) Biodiversity (an abbreviation of "biological diversity") describes

7821-599: The oases much more fertile than before. Mozabites speak the Mozabite language , a branch of the Zenati group of Berber languages. Many also speak Algerian Arabic as a second language. The Mozabite language is spoken by around 150,000 people. It is not canonically agreed when Jews first came to Southern Algeria, but one theory suggests they were sent there by the Ibadite leadership in the 14th century from Tunisia, as part of

7920-399: The observed data. In these island models, the rate of population change is described by: where N is the total number of individuals in the population, b and d are the per capita rates of birth and death respectively, and r is the per capita rate of population change. Using these modeling techniques, Malthus' population principle of growth was later transformed into a model known as

8019-406: The organization and structure of entire communities. The loss of a keystone species results in a range of dramatic cascading effects (termed trophic cascades ) that alters trophic dynamics, other food web connections, and can cause the extinction of other species. The term keystone species was coined by Robert Paine in 1969 and is a reference to the keystone architectural feature as the removal of

8118-688: The potential evapotranspiration of the areas was reduced by 30 to 50 percent within the oasis." The keystone date palm trees are "a main income source and staple food for local populations in many countries in which they are cultivated, and have played significant roles in the economy, society, and environment of those countries." Challenges for date palm oasis polycultures include "low rainfall, high temperatures, water resources often high in salt content, and high incidence of pests." The oases consist of almost unbroken forests of date palms, divided up into many gardens that are separated by mud walls and intersected by innumerable irrigation and drainage ditches… In

8217-468: The published work of George Perkins Marsh ("Man and Nature"). Within an ecosystem, organisms are linked to the physical and biological components of their environment to which they are adapted. Ecosystems are complex adaptive systems where the interaction of life processes form self-organizing patterns across different scales of time and space. Ecosystems are broadly categorized as terrestrial , freshwater , atmospheric, or marine . Differences stem from

8316-502: The rate of change in population size ( d N ( t ) / d t {\displaystyle \mathrm {d} N(t)/\mathrm {d} t} ) will grow to approach equilibrium, where ( d N ( t ) / d t = 0 {\displaystyle \mathrm {d} N(t)/\mathrm {d} t=0} ), when the rates of increase and crowding are balanced, r / α {\displaystyle r/\alpha } . A common, analogous model fixes

8415-432: The relationships among living organisms and their environment . Ecology considers organisms at the individual, population , community , ecosystem , and biosphere levels. Ecology overlaps with the closely related sciences of biogeography , evolutionary biology , genetics , ethology , and natural history . Ecology is a branch of biology , and is the study of abundance , biomass , and distribution of organisms in

8514-424: The same limiting resource ; one will always out-compete the other. When similarly adapted species overlap geographically, closer inspection reveals subtle ecological differences in their habitat or dietary requirements. Some models and empirical studies, however, suggest that disturbances can stabilize the co-evolution and shared niche occupancy of similar species inhabiting species-rich communities. The habitat plus

8613-399: The shade of the palms are grown many other kinds of fruit trees—oranges, olives, figs, apricots, peaches, pomegranates, and jujubes—interlaced with large grape vines that often hang in festoons from the palm trunks. Beneath the trees are small plots of garden vegetables, barley, and alfalfa. Neither date palms nor other trees are planted with any regularity, and the growth is often so dense that

8712-399: The site will disappear unless rescued by an adjacent source patch or environmental conditions become more favorable. Metapopulation models examine patch dynamics over time to answer potential questions about spatial and demographic ecology. The ecology of metapopulations is a dynamic process of extinction and colonization. Small patches of lower quality (i.e., sinks) are maintained or rescued by

8811-524: The study of ecology into a conceptually manageable framework, the biological world is organized into a nested hierarchy , ranging in scale from genes , to cells , to tissues , to organs , to organisms , to species , to populations , to guilds , to communities , to ecosystems , to biomes , and up to the level of the biosphere . This framework forms a panarchy and exhibits non-linear behaviors; this means that "effect and cause are disproportionate, so that small changes to critical variables, such as

8910-432: The sum of the components explain the properties of the whole, such as birth rates of a population being equal to the sum of individual births over a designated time frame. The main subdisciplines of ecology, population (or community ) ecology and ecosystem ecology , exhibit a difference not only in scale but also in two contrasting paradigms in the field. The former focuses on organisms' distribution and abundance, while

9009-593: The surface or underground is necessary and the local or regional management of this essential resource is strategic, but not sufficient to create such areas: continuous human work and know-how (a technical and social culture) are essential to maintain such ecosystems. Some of the possible human contributions to maintaining an oasis include digging and maintaining wells, digging and maintaining canals, and continuously removing opportunistic plants that threaten to gorge themselves on water and fertility needed to maintain human and animal food supplies. Stereotypically, an oasis has

9108-474: The surface. Any incidence of water is then used by migrating birds , which also pass seeds with their droppings which will grow at the water's edge forming an oasis. It can also be used to plant crops. Oases in the Middle East and North Africa cover about 1,000,000 hectares (10,000 km ), however, they support the livelihood of about 10 million inhabitants. The stark ratio of oasis to desert land in

9207-426: The three strata create what is called the " oasis effect ". The three layers and all their interaction points create a variety of combinations of "horizontal wind speed, relative air temperature and relative air humidity." The plantings—through a virtuous cycle of wind reduction, increased shade and evapotranspiration —create a microclimate favorable to crops; "measurements taken in different oases have showed that

9306-670: The tree responds more slowly and integrates these short-term changes. O'Neill et al. (1986) The scale of ecological dynamics can operate like a closed system, such as aphids migrating on a single tree, while at the same time remaining open about broader scale influences, such as atmosphere or climate. Hence, ecologists classify ecosystems hierarchically by analyzing data collected from finer scale units, such as vegetation associations , climate, and soil types , and integrate this information to identify emergent patterns of uniform organization and processes that operate on local to regional, landscape , and chronological scales. To structure

9405-415: The underlying causes of these fluxes. Research in ecosystem ecology might measure primary production (g C/m^2) in a wetland in relation to decomposition and consumption rates (g C/m^2/y). This requires an understanding of the community connections between plants (i.e., primary producers) and the decomposers (e.g., fungi and bacteria). The underlying concept of an ecosystem can be traced back to 1864 in

9504-439: The use of a location by the animal." For example, a habitat might be an aquatic or terrestrial environment that can be further categorized as a montane or alpine ecosystem. Habitat shifts provide important evidence of competition in nature where one population changes relative to the habitats that most other individuals of the species occupy. For example, one population of a species of tropical lizard ( Tropidurus hispidus ) has

9603-648: The water into individual plots, soaking the soil." Oases often have human histories that are measured in millennia. Archeological digs at Ein Gedi in the Dead Sea Valley have found evidence of settlement dating to 6,000 BC. Al-Ahsa on the Arabian Peninsula shows evidence of human residence dating to the Neolithic . Anthropologically , the oasis is "an area of sedentary life, which associates

9702-400: The world means that the oasis ecosystem is "relatively minute, rare and precious." There are 90 “major oases” within the Sahara Desert. Some of their fertility may derive from irrigation systems called foggaras , khettaras , lkhttarts , or a variety of other regional names . In some oases systems, there is "a geometrical system of raised channels that release controlled amounts of

9801-593: Was coined in 1866 by the German scientist Ernst Haeckel . The science of ecology as we know it today began with a group of American botanists in the 1890s. Evolutionary concepts relating to adaptation and natural selection are cornerstones of modern ecological theory . Ecosystems are dynamically interacting systems of organisms, the communities they make up, and the non-living ( abiotic ) components of their environment. Ecosystem processes, such as primary production , nutrient cycling , and niche construction , regulate

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