Editing Ecology (section)

=== Physical environments ===

==== Water ====
{{Main|Aquatic ecosystem}}
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| quote = Wetland conditions such as shallow water, high plant productivity, and anaerobic substrates provide a suitable environment for important physical, biological, and chemical processes. Because of these processes, wetlands play a vital role in global nutrient and element cycles.
| source = Cronk & Fennessy (2001)<ref name="Cronk01" />{{Rp|29}}
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Diffusion of carbon dioxide and oxygen is approximately 10,000 times slower in water than in air. When soils are flooded, they quickly lose oxygen, becoming [[Hypoxia (environmental)|hypoxic]] (an environment with O<sub>2</sub> concentration below 2&nbsp;mg/liter) and eventually completely [[Anoxic waters|anoxic]] where [[anaerobic bacteria]] thrive among the roots. Water also influences the intensity and [[Electromagnetic spectrum|spectral composition]] of light as it reflects off the water surface and submerged particles.<ref name="Cronk01"/> Aquatic plants exhibit a wide variety of morphological and physiological adaptations that allow them to survive, compete, and diversify in these environments. For example, their roots and stems contain large air spaces ([[aerenchyma]]) that regulate the efficient transportation of gases (for example, CO<sub>2</sub> and O<sub>2</sub>) used in respiration and photosynthesis. 

Salt water plants ([[halophyte]]s) have additional specialized adaptations, such as the development of special organs for shedding salt and [[osmoregulation|osmoregulating]] their internal salt (NaCl) concentrations, to live in [[Estuary|estuarine]], [[brackish]], or [[ocean]]ic environments. Anaerobic soil [[microorganism]]s in aquatic environments use [[nitrate]], [[Manganese|manganese ions]], [[ferric|ferric ions]], [[sulfate]], [[carbon dioxide]], and some [[organic compounds]]; other microorganisms are [[facultative anaerobes]] and use oxygen during respiration when the soil becomes drier. The activity of soil microorganisms and the chemistry of the water reduces the [[Reduction potential|oxidation-reduction]] potentials of the water. Carbon dioxide, for example, is reduced to methane (CH<sub>4</sub>) by methanogenic bacteria.<ref name="Cronk01"/> The physiology of fish is also specially adapted to compensate for environmental salt levels through osmoregulation. Their gills form [[electrochemical gradient]]s that mediate salt excretion in salt water and uptake in fresh water.<ref name="Evans99"/>

==== Gravity ====

The shape and energy of the land are significantly affected by gravitational forces. On a large scale, the distribution of gravitational forces on the earth is uneven and influences the shape and movement of [[tectonic plates]] as well as influencing [[geomorphic]] processes such as [[orogeny]] and [[erosion]]. These forces govern many of the geophysical properties and distributions of ecological biomes across the Earth. 

On the organismal scale, gravitational forces provide directional cues for plant and fungal growth ([[gravitropism]]), orientation cues for animal migrations, and influence the [[biomechanics]] and size of animals.<ref name="Allee49"/> Ecological traits, such as allocation of biomass in trees during growth are subject to mechanical failure as gravitational forces influence the position and structure of branches and leaves.<ref name="Swenson08"/> The [[Circulatory system|cardiovascular systems]] of animals are functionally adapted to overcome the pressure and gravitational forces that change according to the features of organisms (e.g., height, size, shape), their behaviour (e.g., diving, running, flying), and the habitat occupied (e.g., water, hot deserts, cold tundra).<ref name="Garnter10"/>

==== Pressure ====

Climatic and [[osmotic pressure]] places [[physiological]] constraints on organisms, especially those that fly and respire at high altitudes, or dive to deep ocean depths.<ref name="Neri" /> These constraints influence vertical limits of ecosystems in the biosphere, as organisms are physiologically sensitive and adapted to atmospheric and osmotic water pressure differences.<ref name="Allee49"/> For example, oxygen levels decrease with decreasing pressure and are a limiting factor for life at higher altitudes.<ref name="Jacobsen08"/> 

[[Xylem|Water transportation]] by plants is another important [[ecophysiology|ecophysiological]] process affected by osmotic pressure gradients.<ref name="Strook08"/><ref name="Pockman95"/><ref name="Zimmermann02"/> [[Fluid pressure|Water pressure]] in the depths of oceans requires that organisms adapt to these conditions. For example, diving animals such as [[whale]]s, [[dolphin]]s, and [[seal (animal)|seals]] are specially adapted to deal with changes in sound due to water pressure differences.<ref name="Kastak98"/> Differences between [[hagfish]] species provide another example of adaptation to deep-sea pressure through specialized protein adaptations.<ref name="Nishiguchi10"/>

==== Wind and turbulence ====

[[File:Grassflowers.jpg|thumb|The architecture of the [[inflorescence]] in grasses is subject to the physical pressures of wind and shaped by the forces of natural selection facilitating wind-pollination ([[anemophily]]).<ref name="Friedman04"/><ref name="Harder09"/>]]

[[Turbulent forces]] in air and water affect the environment and ecosystem distribution, form, and dynamics. On a planetary scale, ecosystems are affected by circulation patterns in the global [[trade winds]]. Wind power and the turbulent forces it creates can influence heat, nutrient, and biochemical profiles of ecosystems.<ref name="Allee49"/> For example, wind running over the surface of a lake creates turbulence, mixing the [[water column]] and influencing the environmental profile to create [[thermally layered zones]], affecting how fish, algae, and other parts of the [[aquatic ecosystem]] are structured.<ref name="Shimeta95"/><ref name="Etemad01"/> 

Wind speed and turbulence also influence [[evapotranspiration rates]] and energy budgets in plants and animals.<ref name="Cronk01" /><ref name="Wolf96"/> Wind speed, temperature and moisture content can vary as winds travel across different land features and elevations. For example, the [[westerlies]] come into contact with the [[coastal]] and interior mountains of western North America to produce a [[rain shadow]] on the leeward side of the mountain. The air expands and moisture condenses as the winds increase in elevation; this is called [[orographic lift]] and can cause precipitation. This environmental process produces spatial divisions in biodiversity, as species adapted to wetter conditions are range-restricted to the coastal mountain valleys and unable to migrate across the [[xeric]] ecosystems (e.g., of the [[Columbia River Drainage Basin|Columbia Basin]] in western North America) to intermix with sister lineages that are segregated to the interior mountain systems.<ref name="Daubenmire75"/><ref name="Steele05"/>

==== Fire ====
{{Main|Fire ecology}}

{{multiple image
| footer = Forest fires modify the land by leaving behind an environmental mosaic that diversifies the landscape into different [[seral community|seral]] stages and habitats of varied quality (left). Some species are adapted to forest fires, such as pine trees that open their cones only after fire exposure (right).
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| image1 = Mosaic fire burn.jpg
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| image2 = Lodgepole pine cone after fire.jpg
| width2 = {{#expr: (100 * 1999 / 1355) round 0}}
}}

Plants convert carbon dioxide into biomass and emit oxygen into the atmosphere. By approximately 350 million years ago (the end of the [[Devonian period]]), photosynthesis had brought the concentration of atmospheric oxygen above 17%, which allowed combustion to occur.<ref name="Lenton00"/> Fire releases CO<sub>2</sub> and converts fuel into ash and tar. Fire is a significant ecological parameter that raises many issues pertaining to its control and suppression.<ref name="Lobert93"/> While the issue of fire in relation to ecology and plants has been recognized for a long time,<ref name="Garren43"/> [[Charles F. Cooper (ecologist)|Charles Cooper]] brought attention to the issue of forest fires in relation to the ecology of forest fire suppression and management in the 1960s.<ref name="Cooper60"/><ref name="Cooper61"/>

[[Indigenous peoples of the Americas|Native North Americans]] were among the first to influence fire regimes by controlling their spread near their homes or by lighting fires to stimulate the production of herbaceous foods and basketry materials.<ref name="Wagtendonk07"/> Fire creates a heterogeneous ecosystem age and canopy structure, and the altered soil nutrient supply and cleared canopy structure opens new ecological niches for seedling establishment.<ref name="Boerner82"/><ref name="Goubitz03"/> Most ecosystems are adapted to natural fire cycles. Plants, for example, are equipped with a variety of adaptations to deal with forest fires. Some species (e.g., ''[[Pinus halepensis]]'') cannot [[germination|germinate]] until after their seeds have lived through a fire or been exposed to certain compounds from smoke. Environmentally triggered germination of seeds is called [[serotiny]].<ref name="Neeman04"/><ref name="Flematti04"/> Fire plays a major role in the persistence and [[Resilience (ecology)|resilience]] of ecosystems.<ref name="Holling73"/>

==== Soils ====
{{main|Soil ecology}}

Soil is the living top layer of mineral and organic dirt that covers the surface of the planet. It is the chief organizing centre of most ecosystem functions, and it is of critical importance in agricultural science and ecology. The [[decomposition]] of dead organic matter (for example, leaves on the forest floor), results in soils containing [[minerals]] and nutrients that feed into plant production. The whole of the planet's soil ecosystems is called the [[pedosphere]] where a large biomass of the Earth's biodiversity organizes into trophic levels. Invertebrates that feed and shred larger leaves, for example, create smaller bits for smaller organisms in the feeding chain. Collectively, these organisms are the [[detritivore]]s that regulate soil formation.<ref name="Coleman04"/><ref name="Wilkinson09"/> Tree roots, fungi, bacteria, worms, ants, beetles, centipedes, spiders, mammals, birds, reptiles, amphibians, and other less familiar creatures all work to create the trophic web of life in soil ecosystems. 

Soils form composite phenotypes where inorganic matter is enveloped into the physiology of a whole community. As organisms feed and migrate through soils they physically displace materials, an ecological process called [[bioturbation]]. This aerates soils and stimulates heterotrophic growth and production. Soil [[microorganisms]] are influenced by and are fed back into the trophic dynamics of the ecosystem. No single axis of causality can be discerned to segregate the biological from geomorphological systems in soils.<ref name="Phillips09">{{cite journal| last1=Phillips| first1=J. D.| year=2009| title=Soils as extended composite phenotypes| volume=149| issue=1–2| pages=143–151| journal=Geoderma| doi=10.1016/j.geoderma.2008.11.028| bibcode=2009Geode.149..143P}}</ref><ref name="Reinhard10">{{cite journal| last1=Reinhardt| first1=L.| last2=Jerolmack| first2=D.| last3=Cardinale| first3=B. J.| last4=Vanacker| first4=V.| last5=Wright| first5=J.| title=Dynamic interactions of life and its landscape: Feedbacks at the interface of geomorphology and ecology| journal=Earth Surface Processes and Landforms| volume=35| issue=1| pages=78–101| doi=10.1002/esp.1912| url=http://snre.umich.edu/cardinale/wp-content/uploads/2012/04/reinhardt_earthsur_2010.pdf| bibcode=2010ESPL...35...78R| archive-url=https://web.archive.org/web/20150317140954/http://snre.umich.edu/cardinale/wp-content/uploads/2012/04/reinhardt_earthsur_2010.pdf| archive-date=17 March 2015| year=2010| s2cid=14924423| access-date=2 January 2015}}</ref> [[Paleoecology|Paleoecological]] studies of soils places the origin for bioturbation to a time before the Cambrian period. Other events, such as the [[Tree#Evolutionary history|evolution of trees]] and the [[colonization of land]] in the Devonian period played a significant role in the early development of ecological trophism in soils.<ref name="Wilkinson09"/><ref name="Davic04"/><ref name="Hasiotis03"/>

==== Biogeochemistry and climate ====
{{Main|Biogeochemistry}}
{{See also|Nutrient cycle|Climate}}

Ecologists study and measure nutrient budgets to understand how these materials are regulated, flow, and [[recycling (ecological)|recycled]] through the environment.<ref name="Allee49"/><ref name="Ricklefs96"/><ref name="Kormondy95"/> This research has led to an understanding that there is global feedback between ecosystems and the physical parameters of this planet, including minerals, soil, pH, ions, water, and atmospheric gases. Six major elements ([[hydrogen]], [[carbon]], [[nitrogen]], [[oxygen]], [[sulfur]], and [[phosphorus]]; H, C, N, O, S, and P) form the constitution of all biological macromolecules and feed into the Earth's geochemical processes. From the smallest scale of biology, the combined effect of billions upon billions of ecological processes amplify and ultimately regulate the [[biogeochemical cycle]]s of the Earth. Understanding the relations and cycles mediated between these elements and their ecological pathways has significant bearing toward understanding global biogeochemistry.<ref name="Falkowoski08"/>

The ecology of global carbon budgets gives one example of the linkage between biodiversity and biogeochemistry. It is estimated that the Earth's oceans hold 40,000 gigatonnes (Gt) of carbon, that vegetation and soil hold 2,070 Gt, and that fossil fuel emissions are 6.3 Gt carbon per year.<ref name="Grace04"/> There have been major restructurings in these global carbon budgets during the Earth's history, regulated to a large extent by the ecology of the land. For example, through the early-mid Eocene volcanic [[outgassing]], the oxidation of methane stored in wetlands, and seafloor gases increased atmospheric CO<sub>2</sub> (carbon dioxide) concentrations to levels as high as 3500&nbsp;[[Parts per million|ppm]].<ref name="Pearson00"/>

In the [[Oligocene]], from twenty-five to thirty-two million years ago, there was another significant restructuring of the global [[carbon cycle]] as grasses evolved a new mechanism of photosynthesis, [[C4 carbon fixation|C<sub>4</sub> photosynthesis]], and expanded their ranges. This new pathway evolved in response to the drop in atmospheric CO<sub>2</sub> concentrations below 550 ppm.<ref name="Pagani05"/> The relative abundance and distribution of biodiversity alters the dynamics between organisms and their environment such that ecosystems can be both cause and effect in relation to climate change. 

Human-driven modifications to the planet's ecosystems (e.g., disturbance, [[biodiversity loss]], agriculture) contributes to rising atmospheric greenhouse gas levels. Transformation of the global carbon cycle in the next century is projected to raise planetary temperatures, lead to more extreme fluctuations in weather, alter species distributions, and increase extinction rates. The effect of global warming is already being registered in melting glaciers, melting mountain ice caps, and rising sea levels. Consequently, species distributions are changing along waterfronts and in continental areas where migration patterns and breeding grounds are tracking the prevailing shifts in climate. 

Large sections of [[permafrost]] are also melting to create a new mosaic of flooded areas having increased rates of soil decomposition activity that raises methane (CH<sub>4</sub>) emissions. There is concern over increases in atmospheric methane in the context of the global carbon cycle, because methane is a [[greenhouse gas]] that is 23 times more effective at absorbing long-wave radiation than CO<sub>2</sub> on a 100-year time scale.<ref name="Zhuan07"/> Hence, there is a relationship between global warming, decomposition and respiration in soils and wetlands producing significant climate feedbacks and globally altered biogeochemical cycles.<ref name="Liu09"/><ref name="Cox00"/><ref name="Erwin09">{{cite journal| last1=Erwin| first1=D. H.| year=2009 | title=Climate as a driver of evolutionary change| journal=Current Biology| volume=19|issue=14| pages=R575–R583| doi=10.1016/j.cub.2009.05.047| pmid=19640496| s2cid=6913670| doi-access=free| bibcode=2009CBio...19.R575E}}</ref><ref name="Bamber12">{{cite journal|last1=Bamber|first1=J.|year=2012|title=Shrinking glaciers under scrutiny|journal=Nature|volume=482|pages=482–483|url=ftp://cola.gmu.edu/pub/klinger/CLIM690/onjacobetal12.pdf|doi=10.1038/nature10948|bibcode=2012Natur.482..482B|issue=7386|pmid=22318516|s2cid=7311971|access-date=12 June 2017}}</ref><ref name="Heiman08"/><ref name="Davidson06"/>