Editing Periodical cicadas (section)

==Predator satiation survival strategy==
{{Further|Antipredator adaptation}}

The nymphs emerge in very large numbers at nearly the same time, sometimes more than 1.5 million individuals per [[acre]] (>370/m<sup>2</sup>).<ref>{{Cite journal |last1=Dybas |first1=H. S. |last2=Davis |first2=D. D. |year=1962 |title=A populations census of seventeen-year periodical cicadas (''Homoptera: Cicadidae: Magicicada'') |journal=[[Ecology (journal)|Ecology]] |volume=43 |issue=3 |pages=432–444|doi=10.2307/1933372 |jstor=1933372|bibcode=1962Ecol...43..432D }}</ref> Their mass emergence is, among other things, a survival trait called [[predator satiation]]. The details of this strategy are simple: for the first week after emergence the periodical cicadas are easy prey for [[reptile]]s, [[bird]]s, [[squirrel]]s, [[cat]]s, [[dog]]s and other small and large [[mammal]]s.<ref name="Williams"/><ref>{{Cite journal |last1=Williams |first1=K. S. |last2=Smith |first2=K. G. |last3=Stephen |first3=F. M. |year=1993 |title=Emergence of 13-year periodical cicadas (''Cicadidae, Magicicada''): phenology, mortality, and predator satiation |journal=Ecology |volume=74 |issue=4 |pages=1143–1152|doi=10.2307/1940484 |jstor=1940484|bibcode=1993Ecol...74.1143W }}</ref> In their present range the periodical cicadas have no effective predators, and all other animals feeding on them after emergence quickly become irrelevant with respect to their impact on total cicada populations.

Early entomologists maintained that the cicadas' overall survival mechanism was simply to overwhelm predators by their sheer numbers, ensuring the survival of most of the individuals. Later, the fact that the developmental periods were each a [[prime numbers|prime number]] of years (13 and 17) was hypothesized to be a predator avoidance strategy, one adopted to eliminate the possibility of potential predators receiving periodic population boosts by synchronizing their own generations to [[divisor]]s of the cicada emergence period.

On this prime number hypothesis, a predator with a three-year reproductive cycle, which happened to coincide with a brood emergence in a given year, will have gone through either four cycles plus one year (12''&nbsp;''+''&nbsp;''1) or five cycles plus two years (15''&nbsp;''+''&nbsp;''2) by the next time that brood emerges. In this way prime-numbered broods exhibit a strategy to ensure that they nearly always emerge when some portion of the predators they will confront are sexually immature and therefore incapable of taking maximum advantage of the momentarily limitless food supply.<ref>{{Cite journal |last1=Goles |first1=E. |last2=Schulz |first2=O. |last3=Markus |first3=M. |year=2001 |title=Prime number selection of cycles in a predator-prey model |journal=Complexity |volume=6 |issue=4 |pages=33–38 |doi=10.1002/cplx.1040|bibcode=2001Cmplx...6d..33G }}</ref>

Another viewpoint turns this hypothesis back onto the cicada broods themselves. It posits that the prime-numbered developmental times represent an adaptation to prevent hybridization ''between'' broods. It is hypothesized that this unusual method of sequestering different populations in time arose when conditions were extremely harsh. Under those conditions the mutation producing extremely long development times became so valuable that cicadas which possessed it found it beneficial to protect themselves from mating with cicadas that lacked the long-development trait.

In this way, the long-developing cicadas retained a trait allowing them to survive the period of heavy selection pressure (i.e., harsh conditions) brought on by isolated and lowered populations during the period immediately following the retreat of glaciers (in the case of periodical cicadas, the North American [[Interglacial|Pleistocene glacial stadia]]). When seen in this light, their mass emergence and the predator satiation strategy that follows from this serves only to maintain the much ''longer-term'' survival strategy of protecting their long-development trait from hybridizations that might dilute it.<ref name="Cox, R. T., and C. E. Carlton 1988 183–193">{{cite journal |author1=Cox, R. T. |author2=C. E. Carlton |s2cid=4213280 |name-list-style=amp |year=1988 |title=Paleoclimatic influences in the evolution of periodical cicadas (Homoptera: Cicadidae: ''Magicicada'' spp.) |journal=[[American Midland Naturalist]] |volume=120 |issue=1 |pages=183–193 |jstor=2425898 |doi=10.2307/2425898}}</ref>

This hybridization hypothesis was subsequently supported through a series of mathematical models and remains the most widely-accepted explanation for the unusually lengthy and mathematically sophisticated survival strategy of these insects.<ref>{{cite journal |last1=Tanaka |first1=Y |first2=J. |last2=Yoshimura |author3-link=Chris Simon (biologist) |first3=C. |last3=Simon |first4=J. |last4=Cooley|first5=K. |last5=Tainaka |year=2009 |title=Allee effect in the selection for prime-numbered cycles in periodical cicadas |journal=[[Proceedings of the National Academy of Sciences]] |volume=106 |issue=22 |pages=8975–8979 |bibcode=2009PNAS..106.8975T |pmid=19451640 |doi=10.1073/pnas.0900215106 |pmc=2690011 |doi-access=free }}</ref> The length of the cycle was hypothesized to be controlled by a single gene locus, with the 13-year cycle dominant to the 17-year one,<ref name="Cox, R. T., and C. E. Carlton 1991 63–74">{{cite journal |author1=Cox, R. T. |author2=C. E. Carlton |name-list-style=amp |year=1991 |title=Evidence of genetic dominance of the 13-year life cycle in periodical cicadas (Homoptera: Cicadidae: ''Magicicada'' spp.) |journal=[[American Midland Naturalist]] |volume=125 |issue=1 |pages=63–74 |jstor=2426370 |doi=10.2307/2426370}}</ref> but this interpretation remains controversial and unsubstantiated at the level of [[DNA]].

===Impact on other populations===
Cycles in cicada populations are significant enough to affect other animal and plant populations. For example, tree growth has been observed to decline the year before the emergence of a brood because of the increased feeding on roots by the growing nymphs.<ref name="Yang" /> [[Mole (animal)|Moles]], which feed on nymphs, have been observed to do well during the year before an emergence, but suffer population declines the following year because of the reduced food source.<ref>{{Cite web |url=http://news.nationalgeographic.com/news/2007/05/070530-cicadas-food.html |title=National Geographic: Cicada Outbreaks Linked to Other Animals' Booms, Busts. |access-date=23 June 2009 |archive-url=https://web.archive.org/web/20080722221700/http://news.nationalgeographic.com/news/2007/05/070530-cicadas-food.html |archive-date=22 July 2008 |url-status=dead }}</ref> [[Wild turkey]] populations respond favorably to increased nutrition in their food supply from gorging on cicada adults on the ground at the end of their life cycles. Uneaten carcasses of periodical cicadas decompose on the ground, providing a resource pulse of nutrients to the forest community.<ref name="Yang">{{cite journal |doi=10.1126/science.1103114 |pmid=15567865 |bibcode=2004Sci...306.1565Y |title=Periodical Cicadas as Resource Pulses in North American Forests |journal=Science |volume=306 |issue=5701 |pages=1565–1567 |last1=Yang |first1=Louie H. |s2cid=27088981 |year=2004 }}</ref>

Cicada broods may also have a negative impact. [[Eastern gray squirrel]] populations have been negatively affected, because the egg-laying activity of female cicadas damaged upcoming [[mast (botany)|mast]] crops.{{Citation needed|date=June 2011}}