Editing Parasitism (section)

=== Rationale for conservation ===

{{further|Conservation biology of parasites}}

{{external media |width = 210px |float = right |headerimage= |video1 = [https://knowablemagazine.org/article/living-world/2018/why-you-should-care-about-parasites "Why you should care about parasites"], 14 December 2018, ''[[Knowable Magazine]]'' }}

Although parasites are widely considered to be harmful, the eradication of all parasites would not be beneficial. Parasites account for at least half of life's diversity; they perform important ecological roles; and without parasites, organisms might tend to asexual reproduction, diminishing the diversity of traits brought about by sexual reproduction.<ref name="Holt2010">{{cite journal |last=Holt |first=R. D. |url=https://people.clas.ufl.edu/rdholt/files/247c.pdf |archive-url=https://web.archive.org/web/20150908060622/http://people.clas.ufl.edu/rdholt/files/247c.pdf |archive-date=8 September 2015 |url-status=live |title=IJEE Soapbox: World free of parasites and vectors: Would it be heaven, or would it be hell? |journal=Israel Journal of Ecology and Evolution |volume=56 |issue=3 |pages=239–250 |year=2010 |doi=10.1560/IJEE.56.3-4.239 }}</ref> Parasites provide an opportunity for the transfer of genetic material between species, facilitating evolutionary change.<ref name="Combes">{{cite book |last=Combes |first=Claude |title=The Art of being a Parasite |publisher=University of Chicago Press |year=2005 |isbn=978-0-226-11438-5}}</ref> Many parasites require multiple hosts of different species to complete their life cycles and rely on predator-prey or other stable ecological interactions to get from one host to another. The presence of parasites thus indicates that an ecosystem is healthy.<ref name="HudsonDobson2006">{{cite journal |last1=Hudson |first1=Peter J. |last2=Dobson |first2=Andrew P. |last3=Lafferty |first3=Kevin D. |url=http://www.personal.psu.edu/users/p/j/pjh18/downloads/184_Hudson_2006_Healthy_ecosystem_is_infected_TREE.pdf |title=Is a healthy ecosystem one that is rich in parasites? |journal=Trends in Ecology & Evolution |volume=21 |issue=7 |year=2006 |pages=381–385 |doi=10.1016/j.tree.2006.04.007|pmid=16713014 |archive-url=https://web.archive.org/web/20170810105426/http://www.personal.psu.edu/users/p/j/pjh18/downloads/184_Hudson_2006_Healthy_ecosystem_is_infected_TREE.pdf |archive-date=10 August 2017 }}</ref>

An ectoparasite, the California condor louse, ''[[Colpocephalum californici]]'', became a well-known conservation issue. A large and costly captive breeding program was run in the United States to rescue the [[California condor]]. It was host to a louse, which lived only on it. Any lice found were "deliberately killed" during the program, to keep the condors in the best possible health. The result was that one species, the condor, was saved and returned to the wild, while another species, the parasite, became extinct.<ref name="Stringer2014">{{cite journal |last1=Stringer |first1=Andrew Paul |last2=Linklater |first2=Wayne |title=Everything in Moderation: Principles of Parasite Control for Wildlife Conservation |journal=BioScience |date=2014 |volume=64 |issue=10 |pages=932–937 |doi=10.1093/biosci/biu135 |doi-access=free }}</ref>

Although parasites are often omitted in depictions of [[food web]]s, they usually occupy the top position. Parasites can function like [[keystone species]], reducing the dominance of superior competitors and allowing [[competition (biology)|competing species]] to co-exist.<ref name="Sukhdeo2012"/><ref name="LaffertyAllesina2008">{{cite journal |last1=Lafferty |first1=Kevin D. |last2=Allesina |first2=Stefano |last3=Arim |first3=Matias |last4=Briggs |first4=Cherie J. |display-authors=etal |title=Parasites in food webs: the ultimate missing links |journal=Ecology Letters |volume=11 |issue=6|year=2008 |pages=533–546 |doi=10.1111/j.1461-0248.2008.01174.x|pmid=18462196 |pmc=2408649 |bibcode=2008EcolL..11..533L }}</ref><ref name="Chase2013">{{cite journal |last1=Chase |first1=Jonathan |title=Parasites in Food Webs: Untangling the Entangled Bank |journal=PLOS Biology |volume=11 |issue=6 |year=2013 |pages=e1001580 |doi=10.1371/journal.pbio.1001580|pmid=23776405 |pmc=3678997 |doi-access=free }}</ref>

[[File:Aggregated distribution of parasites on hosts.svg|thumb|upright=1.35|Parasites are [[Aggregated distribution|distributed unevenly]] among their hosts, most hosts having no parasites, and a few hosts harbouring most of the parasite population. This distribution makes sampling difficult and requires careful use of statistics.]]