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<title>Threshold host density</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Threshold host density</span></span>

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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p><b>Threshold host density (N<sub>T</sub>)</b>, in the context of <a href="Wildlife_disease" title="Wildlife disease">wildlife disease</a> <a href="Ecology" title="Ecology">ecology</a>, refers to the <a href="Population_density" title="Population density">concentration of a population</a> of a particular organism as it relates to disease. Specifically, the threshold host density (N<sub>T</sub>) of a species refers to the minimum concentration of individuals necessary to sustain a given disease within a <a href="Population" title="Population">population</a>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>Threshold host density (N<sub>T</sub>) only applies to density dependent diseases, where there is an "aggregation of risk" to the host in either high host density or low host density patches. When low host density causes an increase in incidence of parasitism or disease, this is known as inverse host density dependence, whereas when incidence of parasitism or disease is elevated in high host density conditions, it is known as direct host density dependence.

</p><p>Host density independent diseases show no correlation between the concentration of a given host population and the incidence of a particular disease. Some examples of host density independent diseases are <a href="Sexually_transmitted_diseases" class="mw-redirect" title="Sexually transmitted diseases">sexually transmitted diseases</a> in both humans and other animals. This is due to the constant incidence of interaction observed in sexually transmitted diseases—even if there are only 20 individuals left of a given population, survival of the species requires sexual contact, and continued spread of the disease.

</p><p>Density dependent diseases are significantly less likely to cause extinction of a population,<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> as the natural course of disease will bring down the density, and thus the propinquity of individuals in the population. In other words, less individuals—as caused by disease—means lower infection rates and a population equilibrium.

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<div class="mw-heading mw-heading2"><h2 id="Host_density-dependent_diseases">Host density-dependent diseases</h2></div>

<ul><li><a href="Brucellosis" title="Brucellosis">Brucellosis</a></li>

<li><a href="Avian_flu" class="mw-redirect" title="Avian flu">Avian flu</a></li>

<li><a href="Echinococcus_multilocularis" title="Echinococcus multilocularis">Echinococcus multilocularis</a></li>

<li><a href="Leptospirosis" title="Leptospirosis">Leptospirosis</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Host_density-independent_diseases">Host density-independent diseases</h2></div>

<ul><li>Chlamydia in koalas</li>

<li><a href="Simian_immunodeficiency_virus" title="Simian immunodeficiency virus">Simian immunodeficiency virus</a> (SIV)</li>

<li><a href="Human_immunodeficiency_virus" class="mw-redirect" title="Human immunodeficiency virus">Human immunodeficiency virus</a> (HIV)<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Contact_between_individuals_within_a_population_as_it_relates_to_density_in_host_density-dependent_disease">Contact between individuals within a population as it relates to density in host density-dependent disease</h2></div>

This graph shows the direct relationship between disease spread through contact and population density. As the population density increases, so do transmission events between individuals.

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<div class="mw-heading mw-heading2"><h2 id="Contact_between_individuals_within_a_population_as_it_relates_to_density_in_sexually_transmitted_infections">Contact between individuals within a population as it relates to density in sexually transmitted infections</h2></div>

</p><p>There is a rapid initial increase in disease transmission as the population increases from zero, and then the plateau of transmission throughout most of the graph. As sexual contact is required in nearly all sexually reproducing species, transmission is not very host density dependent. It is only in cases of near-extinction where sexually transmitted diseases show any dependence on host density. It is for this reason that sexually transmitted diseases are more likely than density dependent diseases to cause extinction.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Contact_between_individuals_within_a_population_as_it_relates_to_density_in_vector-borne_disease">Contact between individuals within a population as it relates to density in vector-borne disease</h2></div>

</p><p>This graph shows the relationship between population density and the transmission of vector-borne disease. Initially, the number of contacts between individuals and vectors increases as population density increases. Eventually, however, the advantage of host density diminishes as the density becomes too great for the vector to maintain its natural ecological relationship with the host, and transmission decreases.

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFBegon,_M.Harper,_J.L.Townsend,_C.R.2009" class="citation book cs1">Begon, M.; Harper, J.L.; Townsend, C.R. (2009). <a rel="nofollow" class="external text" href="https://www.blackwellpublishing.com/Townsend/Glossary/GlossaryH.asp">"Glossary: H"</a>. In Striano, T.; Reid, V. (eds.). <i>Essentials Of Ecology</i> (3rd ed.). Wiley. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1444305340</bdi>.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFHolmes,_E.,_Kareiva,_P.,_Sabo,_J.2004" class="citation journal cs1">Holmes, E., Kareiva, P., Sabo, J. (2004). "Efficacy of Simple Viability Models in Ecological Risk Assessment: Does Density Dependence Matter?". <i>Ecology</i>. <b>85</b> (2): <span class="nowrap">328–</span>341. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2004Ecol...85..328S">2004Ecol...85..328S</a>. <a href="CiteSeerX_(identifier)" class="mw-redirect" title="CiteSeerX (identifier)">CiteSeerX</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.452.245">10.1.1.452.245</a></span>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1890%2F03-0035">10.1890/03-0035</a>. <a href="JSTOR_(identifier)" class="mw-redirect" title="JSTOR (identifier)">JSTOR</a> <a rel="nofollow" class="external text" href="https://www.jstor.org/stable/3450199">3450199</a>.</cite><span class="cs1-maint citation-comment"><code class="cs1-code">{{cite journal}}</code>: CS1 maint: multiple names: authors list (link)</span></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite id="CITEREFWobeser2005" class="citation book cs1">Wobeser, Gary A. (2005). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=JgyS6fxVasYC"><i>Essentials of Disease in Wild Animals</i></a>. Wiley. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-8138-0589-4</bdi>.</cite></span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite id="CITEREFCabaret,_J.Hugonnet,_L.1987" class="citation journal cs1">Cabaret, J.; Hugonnet, L. (1987). <a rel="nofollow" class="external text" href="https://doi.org/10.7589%2F0090-3558-23.1.109">"Infection of roe-deer in France by the lung nematode, <i>Dictyocaulus eckerti</i> Skrjabin, 1931 (Trichostrongyloidea): influence of environmental factors and host density"</a>. <i>J. Wildl. Dis</i>. <b>23</b> (1): <span class="nowrap">109–</span>12. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.7589%2F0090-3558-23.1.109">10.7589/0090-3558-23.1.109</a></span>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/2950246">2950246</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:44765192">44765192</a>.</cite></span>

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<div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2></div>

<ul><li>(scientific journal articles pertaining to host density and disease)</li></ul>

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<ul><li><cite id="CITEREFEbert2005" class="citation book cs1">Ebert, Dieter (2005). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/books/n/daph/ch8/">"Ch. 8: Epidemiology"</a>. <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/books/NBK2036/"><i>Ecology, Epidemiology, and Evolution of Parasitism in </i>Daphnia<i></i></a>. Bethesda MD: National Center for Biotechnology Information (US). <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>1-932811-06-0</bdi>. NBK2036.</cite></li>

<li><cite id="CITEREFJaffe,_B.Phillips,_R.Muldoon,_A.Mangel,_M.1992" class="citation journal cs1">Jaffe, B.; Phillips, R.; Muldoon, A.; Mangel, M. (1992). "Density-Dependent Host-Pathogen Dynamics in Soil Microcosms". <i>Ecology</i>. <b>73</b> (2): <span class="nowrap">495–</span>506. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1992Ecol...73..495J">1992Ecol...73..495J</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.2307%2F1940755">10.2307/1940755</a>. <a href="JSTOR_(identifier)" class="mw-redirect" title="JSTOR (identifier)">JSTOR</a> <a rel="nofollow" class="external text" href="https://www.jstor.org/stable/1940755">1940755</a>.</cite></li>

<li><cite id="CITEREFLentz2007" class="citation thesis cs1">Lentz, Amanda Jean (2007). <a rel="nofollow" class="external text" href="http://hdl.handle.net/10919/28409"><i>The Effect of Aphids in Parasitoid-Caterpillar-Plant Interactions</i></a> (PhD thesis). Blacksburg, VA: University Libraries, Virginia Polytechnic Institute and State University. <a href="Hdl_(identifier)" class="mw-redirect" title="Hdl (identifier)">hdl</a>:<a rel="nofollow" class="external text" href="https://hdl.handle.net/10919%2F28409">10919/28409</a>. etd-07262007-141303.</cite></li></ul>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.wildlifedisease.org/">Wildlife Disease Association, WDA</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-05-23" href="https://en.wikipedia.org/wiki/?title=Threshold_host_density&oldid=1291794560">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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