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==Reviews and studies== |
==Reviews and studies== |
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===Overview=== |
===Overview=== |
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A 2014 review noted that "Of all insects with IUCN-documented population trends, 33% are declining ... Globally, a compiled index of all invertebrate population declines over the past 40 years shows an overall 45% decline".<ref name="S14" /><ref name="NYT18" /> |
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The [[Entomologischer Verein Krefeld|Entomological Society Krefeld]] produced a report in 2017 by studying their records of insect collections using [[malaise trap]]s in 63 [[list of nature parks in Germany|nature reserves in Germany]]. They suggested that, in the period 1989 to 2016, there had been a "seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study". The authors wrote that the decline was apparent "regardless of habitat type, while changes in weather, land use, and habitat characteristics" could not explain it.<ref name="PLoS" /><ref name=Main14Feb2019/><ref name="NYT17" /><ref>{{cite news |last1=Carrington |first1=Damian |title=Warning of 'ecological Armageddon' after dramatic plunge in insect numbers |url=https://www.theguardian.com/environment/2017/oct/18/warning-of-ecological-armageddon-after-dramatic-plunge-in-insect-numbers |work=The Guardian |date=18 October 2017}}</ref> |
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A 2018 study of the [[El Yunque National Forest]] in [[Puerto Rico]], by Bradford C. Lister and Andres Garcia and published in the ''[[Proceedings of the National Academy of Sciences]]'', reported a decline in [[arthropod]]s, and in lizards, frogs, and birds ([[insectivore|insect-eating]] species), during the period 1976–2012. The researchers reported "biomass losses between 98% and 78% for ground-foraging and canopy-dwelling arthropods over a 36-year period, with respective annual losses between 2.7% and 2.2%". The decline was attributed to a rise in the average temperature; tropical insect species cannot tolerate a wide range of temperatures.<ref name="PNAS" /><ref name="BC" /><ref name=Main14Feb2019/><ref name="WP" /> |
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In 2019 review,<ref name=BC/><ref name=G/>researchers [[Francisco Sánchez-Bayo]] and Kris A. G. Wyckhuys, noted that most scientific and public attention focuses on the conservation of larger, charismatic vertebrates, while insect biodiversity has been low on the agenda. The study analysed 73 reports and studies and found that, overall, there were "dramatic rates of decline"<ref name=BC/> |
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{{quote|From our compilation of published scientific reports, we estimate the current proportion of insect species in decline (41%) to be twice as high as that of vertebrates, and the pace of local species extinction (10%) eight times higher, confirming previous findings (Dirzo et al., 2014). At present, about a third of all insect species are threatened with extinction in the countries studied (Table 1). Moreover, every year about 1% of all insect species are added to the list, with such biodiversity declines resulting in an annual 2.5% loss of biomass worldwide ...<ref name=BC/> }} |
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===Limitations and criticism of studies=== |
===Limitations and criticism of studies=== |
Revision as of 01:56, 26 March 2019
Several studies have suggested that there appears to be a decline in insect populations in the 21st century. Some of the groups most affected include bees, butterflies, moths, beetles, dragonflies and damselflies. The issue has been described anecdotally as the windshield phenomenon.[2]
Possible causes of the decline have been identified as habitat destruction, agricultural intensification, introduced species and climate change. Not all insect orders are affected in the same way; many groups are the subject of limited research, and comparative figures from earlier decades are often not available.
History
![](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Melanoplus_spretusAnnReportAgExpStaUM1902B.jpg/220px-Melanoplus_spretusAnnReportAgExpStaUM1902B.jpg)
The fossil record concerning insects stretches back for hundreds of millions of years. It suggests there are ongoing background levels of both Speciation (where new species of insects originate) and extinction (where certain species die out). Very occasionally, the record also appears to show mass extinctions of insects. The Permian–Triassic extinction event saw the greatest level of insect extinction, with the Cretaceous–Paleogene being the second highest. Insect diversity has recovered after past mass extinctions, due to periods where new species originate with increased frequency, though the recovery can take millions of years. [3]
The pre-historic extinction events are understood to be caused by natural phenomena such as volcanic activity or meteor impact. Concern over a possibly human caused Holocene extinction has been growing since the late 20th century, though much of the early concern was not focused on insects. While studies finding insect decline have been known for many decades, it was the 2017 re-publication of the German nature reserves study[1] that saw the issue of insect decline receive widespread attention in the media. [4][5]
Causes of decline
Several studies seem to indicate that insect populations are in decline in the late 20th and early 21st centuries. The insects studied have mostly been butterflies and moths, bees, beetles, dragonflies, damselflies and stoneflies. Every species is affected in different ways by changes in the environment, and it cannot be inferred that there is a consistent decrease across different insect groups. When conditions change, some species easily adapt to the change while others struggle to survive.[6]
The most important cause of decline in insect populations is thought to be habitat destruction, itself caused by agricultural intensification, commercial development, recreation and pollution. Other issues include pesticides, introduced species, and climate change.[7][5][8][9][10] The use of increased quantities of insecticides and herbicides on crops have affected not only non-target insect species, but also the plants on which they feed. Climate change and the introduction of exotic species that compete with the indigenous ones put the native species under stress, and as a result they are more likely to succumb to pathogens and parasites.[6] While some species such as flies and cockroaches might increase as a result,[7] the total biomass of insects is estimated to be decreasing by about 2.5% per year.[10]
Reviews and studies
Overview
A 2014 review noted that "Of all insects with IUCN-documented population trends, 33% are declining ... Globally, a compiled index of all invertebrate population declines over the past 40 years shows an overall 45% decline".[11][12]
In 2019 review,[5][8]researchers Francisco Sánchez-Bayo and Kris A. G. Wyckhuys, noted that most scientific and public attention focuses on the conservation of larger, charismatic vertebrates, while insect biodiversity has been low on the agenda. The study analysed 73 reports and studies and found that, overall, there were "dramatic rates of decline"[5]
Limitations and criticism of studies
![](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/SympetrumInfuscatum.jpg/220px-SympetrumInfuscatum.jpg)
In their 2019 systemic review, Sánchez-Bayo & Wyckhuys noted that few studies had been done on such insect groups as Diptera, Orthoptera and Hemiptera. Data from the past from which to calculate trends was largely unavailable, and what did exist mostly related to Western Europe and North America, with the tropics and southern hemisphere (which are the major habitats of a large amount of insects) under-represented.[13][5] The insect studies that had been undertaken were largely concentrated on the more popular insect groups: butterflies and moths, bees, dragonflies and beetles.[5]
A reason that studies are limited is that the science of studying insects – entomology – is itself in decline.[14] Similarly in decline is the profession of taxonomy, necessary to record the diversity of species.[13] General biology courses in college give less attention to insects and the number of biologists specialising in entomology is reducing as other specialities such as genetics expand.[4][15][16] Also, these studies tend to be done by collecting the insects and killing them in traps which is an ethical problem for conservationists.[17][18]
A March 2019 statement by the Entomological Society of America said there is not yet sufficient data to predict an imminent mass extinction of insects and that some of the extrapolated predictions might "have been extended well past the limits of the data or have been otherwise over-hyped". They did though agree that the studies were "very concerning".[19]
Entomology professor Simon Leather suggested that reports of an "Ecological Armageddon" may be exaggerated and advocated for more funding to allow better collection of long term data on the decline.[20] The methodology of the Sánchez-Bayo & Wyckhuys study has been questioned; the search string used to sift through the scientific literature was "(insect* + decline* + survey)". This meant that the authors identified studies finding insect declines, but mostly ignored those that found increases in insect populations or stability.[21] Several entomologists agree that the data on insect declines are too piecemeal and unrepresentative of the general population to support some of the hyperbolic extrapolations.[13]
Conservation measures
Citing a 2010 warning from Lord May, the authors of the 2019 worldwide review suggest decisive action is needed "to avert a catastrophic collapse of nature's ecosystems." [5]
Following the 2016 report of the Entomologischer Verein Krefeld and other studies, the German environment ministry – the BMU – started its Action Program for Insect Protection (Aktionsprogramm Insektenschutz).[22] This initially contained nine goals:[23]
- "Promote insect habitats and structural diversity in the agricultural landscape"
- "Restore and connect habitats for insects in other landscape areas"
- "Strengthen protected areas as habitats for insects"
- "Reduce the use of pesticides"
- "Reduce inputs of nutrients and pollutants in soil and water"
- "Reduce light pollution"
- "Deepening research - multiplying knowledge - closing gaps"
- "Improve funding - create incentives"
- "Promote the commitment of society"
In a 2019 paper, scientists Olivier Dangles and Jérôme Casas suggested previous attempts to arrest the repeatedly reported "massive insect decline" have been largely ineffective. They argue that the best approach may be for the global policy making community to transition from the current "insects as providers of ecosystem-services" view to one that see "insect as solutions for SDGs". They list 100 studies and other references showing how insects can assist with meeting the Sustainable Development Goals [24]
Citizen science contributes to the monitoring of insect populations. People have noticed a decline in the number of insects splattered on car windshields when they drive across their country – the windshield phenomenon. In 2004, the Royal Society for the Protection of Birds (RSPB) organised a Big Bug Count, issuing "splatometers" to about 40,000 volunteers so that they could count the number of insects colliding with their number plate. They found an average of one insect per 5 miles (8 km) which was less than expected.[25]
The Entomological Society of America advise that measures regular people can take include maintaining plant diversity in their gardens, and leaving "natural habitat, like leaf litter and dead wood." [19]
Phone apps such as iNaturalist can be used to photograph and identify specimens and these are being used in programs such as the City Nature Challenge. Activities and projects may focus upon a particular type of insect such as National Moth Week and monarch butterfly conservation in California.[26]
See also
- Biodiversity decline
- Colony collapse disorder
- Decline in amphibian populations
- Holocene extinction
- Pollinator decline
References
- ^ a b Hallmann, CA; Sorg, M; Jongejans, E; Siepel, H; Hofland, N; Schwan, H (18 October 2017), "More than 75 percent decline over 27 years in total flying insect biomass in protected areas", PLoS ONE, 12 (10): e0185809, doi:10.1371/journal.pone.0185809, PMID 29045418
{{citation}}
: CS1 maint: unflagged free DOI (link) - ^ McCarthy, Michael (21 October 2017). "A giant insect ecosystem is collapsing due to humans. It's a catastrophe". The Guardian.
- ^ Labandeira, Conrad (1 January 2005), "The fossil record of insect extinction: new approaches and future directions", American Entomologist, 51: 14–29, doi:10.1093/ae/51.1.14
- ^ a b Leather, Simon (January 2007), "British Entomology in terminal decline?", Antenna, 31 (4): 192
- ^ a b c d e f g Sánchez-Bayo, Francisco; Wyckhuys, Kris A.G. (31 January 2019), "Worldwide decline of the entomofauna: A review of its drivers", Biological Conservation, 232: 8–27, doi:10.1016/j.biocon.2019.01.020
- ^ a b Reckhaus, Hans-Dietrich (2017). Why Every Fly Counts: A Documentation about the Value and Endangerment of Insects. Springer International Publishing. pp. 1–5. ISBN 978-3-319-58765-3.
- ^ a b McGrath, Matt (11 February 2019), Global insect decline may see 'plague of pests', BBC
- ^ a b Carrington, Damian (10 February 2019). "Plummeting insect numbers 'threaten collapse of nature'". The Observer.
- ^ Vogel, Gretchen (10 May 2017), "Where have all the insects gone?", Science
- ^ a b Main, Douglas (14 February 2019). "Why insect populations are plummeting—and why it matters". National Geographic. Archived from the original on 15 February 2019.
{{cite news}}
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ignored (|url-status=
suggested) (help) - ^ Dirzo, Rodolfo; Young, Hillary; Galetti, Mauro; Ceballos, Gerardo; Isaac, Nick; Collen, Ben (25 July 2014), "Defaunation in the Anthropocene" (PDF), Science, 345 (6195): 401–406, doi:10.1126/science.1251817, PMID 25061202
- ^ Jarvis, Brooke (27 November 2018), "The Insect Apocalypse Is Here", The New York Times
- ^ a b c Yong, Ed (2019-02-19). "Is the Insect Apocalypse Really Upon Us?". The Atlantic. Retrieved 2019-03-16.
- ^ Alexandra Sifferlin (14 February 2018), "Fewer Scientists Are Studying Insects. Here's Why That's So Dangerous", TIME
- ^ Gangwani, Kiran; Landin, Jennifer (12 December 2018), "The Decline of Insect Representation in Biology Textbooks Over Time", American Entomologist, 64 (4): 252–257, doi:10.1093/ae/tmy064
- ^ Blakemore, Erin (12 December 2018), "Insects are disappearing from science textbooks—and that should bug you", Popular Science
- ^ Hart, Adam, "Inside the killing jar", The Biologist, 65 (2): 26–29
- ^ Fischer, Bob; Larson, Brendan (25 February 2019), "Collecting insects to conserve them: a call for ethical caution", Insect Conservation and Diversity, doi:10.1111/icad.12344
- ^ a b Global Insect Biodiversity:Frequently Asked Questions (PDF), Entomological Society of America, March 2019
- ^ Leather, Simon (20 December 2017), ""Ecological Armageddon" – more evidence for the drastic decline in insect numbers", Annals of Applied Biology, 172: 1–3, doi:10.1111/aab.12410
- ^ Saunders, Manu (16 February 2019). "Insectageddon is a great story. But what are the facts?". Retrieved 16 March 2019.
- ^ Bélanger, J.; Pilling, D., eds. (2019), The State of the World's Biodiversity for Food and Agriculture (PDF), Rome: FAO Commission on Genetic Resources for Food and Agriculture, p. 133
- ^ Action program insect protection (in German), Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit, 10 October 2018
- ^ Dangles, Olivier; Casas, Jérôme (February 2019), "Ecosystem services provided by insects for achieving sustainable development goals", Ecosystem Services: Science, Policy and Practice, 35: 109–115, doi:10.1016/j.ecoser.2018.12.002
- ^ Kirby, Alex (1 September 2004), Scarce insects duck UK splat test, BBC
- ^ Katherine Roth (15 January 2019), Apps let everyone help track health of insect populations, Associated Press
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