Ecological pyramid

<h2 id="pyramid-of-energy">Pyramid of Energy</h2>
<p>A <i>pyramid of energy</i> or <i>pyramid of productivity</i> shows the production or turnover (the rate at which energy or mass is transferred from one trophic level to the next) of biomass at each trophic level. Instead of showing a single snapshot in time, <a href="/facts/Primary_production/14RzcF5E">productivity</a> pyramids show the flow of <a href="/facts/Energy/wd8PrQM7">energy</a> through the <a href="/facts/Food_chain/mvDKQTGu">food chain</a>. Typical units are grams per square meter per year or calories per square meter per year. As with the others, this graph shows producers at the bottom and higher trophic levels on top.
</p><p>When an ecosystem is healthy, this graph produces a standard <i>ecological pyramid</i>. This is because, in order for the ecosystem to sustain itself, there must be more energy at lower trophic levels than there is at higher trophic levels. This allows organisms on the lower levels to not only maintain a stable population, but also to transfer energy up the pyramid. The exception to this generalization is when portions of a <a href="/facts/Food_web/YaakLo08">food web</a> are supported by inputs of resources from outside the local <a href="/facts/Biocoenosis/A8YKcnhF">community</a>. In small, forested streams, for example, the volume of higher levels is greater than could be supported by the local <a href="/facts/Primary_production/14RzcF5E">primary production</a>.
</p><p>Energy usually enters ecosystems from the Sun. The primary producers at the base of the pyramid use solar radiation to power <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a> which produces food. However most wavelengths in solar radiation <a href="/facts/Photosynthetic_efficiency/rM0wkUvP">cannot be used for photosynthesis</a>, so they are reflected back into space or absorbed elsewhere and converted to heat. Only 1 to 2 percent of the energy from the sun is absorbed by photosynthetic processes and converted into food.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> When energy is transferred to higher trophic levels, on average only about 10% is used at each level to build biomass, becoming stored energy. The rest goes to metabolic processes such as growth, respiration, and reproduction.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> 
</p><p>Advantages of the <i>pyramid of energy</i> as a representation:
</p>
<ul><li>It takes account of the rate of production over a period of time.</li>
<li>Two species of comparable biomass may have very different <a href="/facts/Life_expectancy/uPc8bWWW">life spans</a>. Thus, a direct comparison of their total biomasses is misleading, but their productivity is directly comparable.</li>
<li>The relative energy chain within an ecosystem can be compared using pyramids of energy; also different <a href="/facts/Ecosystems/kVE8mSmR">ecosystems</a> can be compared.</li>
<li>There are no inverted pyramids.</li>
<li>The input of solar energy can be added.</li></ul>
<p>Disadvantages of the <i>pyramid of energy</i> as a representation:
</p>
<ul><li>The rate of biomass production of an organism is required, which involves measuring growth and reproduction through time.</li>
<li>There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organisms in the food chains there is the problem of assigning the <a href="/facts/Decomposers/QufPBSGu">decomposers</a> and <a href="/facts/Detritivore/nF1yXs9f">detritivores</a> to a particular level.</li></ul>
<h2 id="pyramid-of-biomass">Pyramid of biomass</h2>

<p>A <i>pyramid of biomass</i> shows the relationship between biomass and trophic level by quantifying the biomass present at each trophic level of an ecological community at a particular time. It is a graphical representation of biomass (total amount of living or organic matter in an ecosystem) present in unit area in different trophic levels. Typical units are grams per square meter, or calories per square meter.
The pyramid of biomass may be "inverted". For example, in a pond ecosystem, the <a href="/facts/Standing_crop/ahGskYmL">standing crop</a> of <a href="/facts/Phytoplankton/tK5MUIkA">phytoplankton</a>, the major <a href="/facts/Autotrophs/UDc8bzqD">producers</a>, at any given point will be lower than the mass of the <a href="/facts/Heterotrophs/wtzlgBtz">heterotrophs</a>, such as fish and insects. This is explained as the phytoplankton <a href="/facts/Reproduce/nNu0F5Dy">reproduce</a> very quickly, but have much shorter individual lives.
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<h2 id="pyramid-of-numbers">Pyramid of Numbers</h2>

<p>A <i>pyramid of numbers</i> graphically shows the population, or abundance, in terms of the number of individual organisms involved at each level in a food chain. This shows the number of organisms in each trophic level without considering their individual sizes or biomass. The pyramid is not necessarily upright. For example, it will be inverted if beetles are feeding from the output of forest trees or parasites are feeding on large host animals.
</p>

<h2 id="history">History</h2>
<p>The concept of a pyramid of numbers ("Eltonian pyramid") was developed by <a href="/facts/Charles_Sutherland_Elton/lyyMcJYK">Charles Elton</a> (1927).<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> Later, it would also be expressed in terms of biomass by <a href="/facts/Shimon_Fritz_Bodenheimer/zJBofSkQ">Bodenheimer</a> (1938).<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The idea of the pyramid of productivity or energy relies on the works of <a href="/facts/G._Evelyn_Hutchinson/TgrBPG7c">G. Evelyn Hutchinson</a> and <a href="/facts/Raymond_Lindeman/WaX8pMn0">Raymond Lindeman</a> (1942).<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Trophic_cascade/MNXI4cJJ">Trophic cascade</a></li></ul>

<h2 id="bibliography">Bibliography</h2>
<ul><li>Odum, E.P. 1971.  Fundamentals of Ecology.  Third Edition.  <a href="/facts/W.B._Saunders_Company/Gl7vRga3">W.B. Saunders Company</a>, Philadelphia,</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="https://web.archive.org/web/20120511065617/http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html">Food Chains</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Gates DM, Thompson JN and Thompson MB (2018) Efficiency of solar energy utilization Encyclopædia Britannica. Accessed: 26 December 2019. <a href="https://www.britannica.com/science/biosphere/Efficiency-of-solar-energy-utilization" target="_blank">https://www.britannica.com/science/biosphere/Efficiency-of-solar-energy-utilization</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Pauly, D. and Christensen, V (1995) "Primary production required to sustain global fisheries". Nature 374.6519: 255-257. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Elton, C. 1927. Animal Ecology. New York, Macmillan Co. link. <a href="https://www.biodiversitylibrary.org/bibliography/7435#/summary" target="_blank">https://www.biodiversitylibrary.org/bibliography/7435#/summary</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Bodenheimer, F. S. 1938. Problems of Animal Ecology. Oxford University Press. link. <a href="https://archive.org/details/in.ernet.dli.2015.218303" target="_blank">https://archive.org/details/in.ernet.dli.2015.218303</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Lindeman, R. L. (1942). The trophic-dynamic aspect of ecology. Ecology 23: 399–418. link Archived 2017-03-29 at the Wayback Machine. <a href="http://www.fcnym.unlp.edu.ar/catedras/ecocomunidades/Lindman_1942.pdf" target="_blank">http://www.fcnym.unlp.edu.ar/catedras/ecocomunidades/Lindman_1942.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Trebilco, Rowan; Baum, Julia K.; Salomon, Anne K.; Dulvy, Nicholas K. (2013). "Ecosystem ecology: size-based constraints on the pyramids of life". Trends in Ecology & Evolution. 28 (7): 423–431. doi:10.1016/j.tree.2013.03.008. ISSN 0169-5347. <a href="/wiki/Julia_K._Baum" target="_blank">/wiki/Julia_K._Baum</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Ecological pyramid open-in-new

Ecological pyramid