利用者:Koolah/サンドボックス3
移入種問題
[編集]オオヒキガエルは世界中の多くの地域、特に太平洋地域に、農業害虫駆除の生物農薬として導入された[1]。これらの導入の経緯は一般的に分権化されており、オオヒキガエルは他の移入種よりもよく研究されている生物の一つである[2]。
1840年代前半、オオヒキガエルはフランス領ギアナおよびガイアナからマルティニークおよびバルバドスに導入された[3]。また、ジャマイカへは1844年にネズミの個体数を減らす目的で導入された[4]。このネズミの個体数のコントロールは失敗したにもかかわらず、20世紀初頭にプエルトリコへサトウキビ畑の害虫である甲虫類を駆除する目的で導入された。このプエルトリコの計画は成功し、この甲虫類による経済的な被害をなくすことができ、1930年代には農業害虫を減らす理想的な手法として、科学者により促進された[5]。
結果的に、太平洋岸地域の多くの国でプエルトリコの事例を模倣し、1930年代に導入された[6]。 導入された地域はオーストラリア、フロリダ州[7]、パプアニューギニア[8]、フィリピン[9]、小笠原諸島や琉球諸島[10]、多くのカリブ諸島[6]、フィジー[6]やハワイをはじめとする太平洋の島国である[11][12]。それ以降、オオヒキガエルは多くの国々で害獣となり、土着の生物に重大な影響を与えている[13]。
オーストラリア
[編集]![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Bufo_marinus_australian_range.png/220px-Bufo_marinus_australian_range.png)
オーストラリア北東部沿岸地域を中心に北部準州からニューサウスウェールズ州北部まで分布する。
プエルトリコのサトウキビ・プランテーションやに被害を及ぼしていた甲虫類への対策やハワイやフィリピンの果樹園へのオオヒキガエルの導入の成功に追従する形で、クイーンズランド州のサトウキビ畑に被害を出していた害虫対策として、オオヒキガエルの導入が強く押し進められた[14]。その結果、102匹のオオヒキガエルがハワイで捕獲され、オーストラリアへ持ち込まれた[15]。1935年8月に最初の導入が行われたのち、連邦保健省はオオヒキガエルの生態系への影響が研究されるまで導入を禁止した。1936年に研究は終了し、導入の禁止は解除され、1937年3月に大規模な放獣、つまり62,000匹のオオヒキガエルが野生下へと放たれた[14][15]。オオヒキガエルはクイーンズランド州内に定着し、個体数を増加させつつ、北部準州やニューサウスウェールズ州へと分布域を広げていった[16][15]。近年、オオヒキガエルは西オーストラリア州へと分布を広げ、ブルーム付近の西海岸で発見されている[17]。
一方で、オオヒキガエルによる害虫のコントロールは、サトウキビ畑には捕食者となるオオヒキガエルの日中の隠れ家が不十分であったことなど、いくつかの理由により失敗に終わった[18]。最初の導入以来、オオヒキガエルはオーストラリアの生物多様性へ影響を与え続けている。オオトカゲ科のメルテンスオオトカゲ、ミッチェルオオトカゲ(Varanus mitchelli)、ヒャクメオオトカゲ、陸生ヘビであるPseudechis australisやコモンデスアダー、クロコダイル属のオーストラリアワニなど、土着の捕食者である爬虫類の個体数は減少している一方、ヒャクメオオトカゲの獲物として知られるアガマ科のAmphibolurus gilbertiの個体数が増加している[19]。
カリブ諸島
[編集]オオヒキガエルはカリブ諸島へも、現地農産物への害虫対策として導入された[20]。バルバドス、ジャマイカ、プエルトリコのような諸島などではオオヒキガエルが定着したものの、キューバ(1900年以前や1946年に導入された)、ドミニカ国やグランドケイマンなどにおける導入は失敗に終わった[21]。
初期の記録されている導入はバルバドスやマルティニークへである。バルバドスではサトウキビへ被害を与えている害虫に対する生物農薬として導入されたが[22]、一方でオーストラリアでは大量に増加し、害虫のコントロールは成功しなかった[23]。
マルティニークへは、1944年以前にフランス領ギアナより導入され、定着した。現在ではこれにより蚊やケラの個体数を減少させている[24]。この地域への三回目の導入は、ジャマイカでオオヒキガエルが発見された1884年であり、齧歯類の個体数のコントロールをするためにバルバドスから導入されたとされる。しかしながら、齧歯類へ対する特徴的な影響はなかった一方、オオヒキガエルはよく現地になじみ、定着した[25]。
アンティグア島では、1916年以前に一度導入されたものの、1934年までに大部分が死滅したものと見られ、のちに再導入されたとされている[26]。1879年以前に導入されたモントセラトでは、スーフリエールヒルズ火山が1995年に噴火した際に生き残れるだけの十分な個体数がすでに定着していた[27]。
In 1920, the cane toad was introduced into Puerto Rico to control the populations of white-grub (Phyllophaga spp.), a sugarcane pest.[28] Before this, the pests were manually collected by humans, so the introduction of the toad eliminated labor costs.[28] A second group of toads was imported in 1923, and by 1932 the cane toad was well established.[29] The population of white-grubs dramatically decreased,[28] and this was attributed to the cane toad at the annual meeting of the International Sugar Cane Technologists in Puerto Rico.[13] However, there may have been other factors.[13] The six-year period after 1931—when the cane toad was most prolific, and the white-grub saw dramatic decline—saw the highest ever rainfall for Puerto Rico.[30] Nevertheless, the assumption was that the cane toad controlled the white-grub; this view was reinforced by a Nature article titled "Toads save sugar crop",[13] and this led to large-scale introductions throughout many parts of the Pacific.[31]
More recently, the cane toad has been spotted in Carriacou and Dominica, the latter appearance occurring in spite of the failure of the earlier introductions.[32]
フィジー
[編集]The cane toad was introduced into Fiji to combat insects that infested sugarcane plantations. The introduction of the cane toad to the region was first suggested in 1933, following the successes in Puerto Rico and Hawaii. After considering the possible side effects, the national government of Fiji decided to release the toad in 1953, and 67 specimens were subsequently imported from Hawaii.[33] Once the toads were established, a 1963 study concluded that as the toad's diet included both harmful and beneficial invertebrates, it was considered "economically neutral".[12] Today the cane toad can be found on all major islands in Fiji, although they tend to be smaller than their counterparts in other regions.[34]
ニューギニア
[編集]The cane toad was successfully introduced into New Guinea to control hawk moth larvae that were eating sweet potato crops.[8] The first release occurred in 1937 using toads imported from Hawaii, with a second release the same year using specimens from the Australian mainland. Evidence suggests there was a third release in 1938, consisting of toads that were being used for human pregnancy tests—many species of toad were found to be effective for this task, and were employed for approximately 20 years after the discovery was announced in 1948.[35][36] Initial reports argued that the toads were effective in reducing the incidence of cutworm and it was suggested that sweet potato yields were improving.[37] As a result, these first releases were followed by further distributions across much of the region,[37] although their effectiveness on other crops, such as cabbages, has been questioned—when the toads were released at Wau, the cabbages provided insufficient shelter and the toads rapidly left the immediate area for the superior shelter offered by the forest.[38] A similar situation had previously arisen in the Australian cane fields, but this experience was either unknown or ignored in New Guinea.[38] The cane toad has since become abundant in rural and urban areas.[39]
アメリカ合衆国
[編集]The cane toad naturally exists in southern Texas, but attempts (both deliberate and accidental) have been made to introduce the species to other parts of the country. These include introductions to the mainland state of Florida and to the islands of Hawaii, as well as largely unsuccessful introductions to Louisiana.[40]
Initial releases into Florida failed. Attempted introductions before 1936 and 1944, made with the objective of controlling sugarcane pests, were unsuccessful as the toads failed to proliferate. Later attempts failed in the same way.[41][42] However, the toad gained a foothold in the state after an accidental release by an importer at Miami International Airport in 1957, and deliberate releases by animal dealers in 1963 and 1964 established the toad in other parts of Florida.[42][43] Today, the cane toad is well established in the state, from the Florida Keysto north of Tampa, and they are gradually extending further northward.[44] In Florida, the toad is a regarded as a threat to both native species [45] and to pets,[46] so much so that the Florida Fish and Wildlife Conservation Commission recommends that residents euthanize them.[47]
![A selection of cane toad merchandise, including key rings made from their legs, a coin purse made from the head, front limbs and body of a toad, and a stuffed cane toad.](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3c/Cane_Toad_Products.jpg/220px-Cane_Toad_Products.jpg)
Around 150 cane toads were introduced to Oahu in Hawaii in 1932, and the population swelled to 105,517 after 17 months.[6] The toads were sent to the other islands, and more than 100,000 toads were distributed by July 1934;[48] eventually over 600,000 were transported.[49]
脚注
[編集]- ^ Tyler 1989, p. 111
- ^ Easteal 1981, p. 94
- ^ Easteal 1981, p. 96
- ^ Lannoo 2005, p. 417
- ^ Tyler 1989, pp. 112–113
- ^ a b c d Tyler 1989, pp. 113–114
- ^ Smith 2005, pp. 433–441
- ^ a b Zug, Lindgrem & Pippet 1975, pp. 31–50
- ^ Alcala 1957, pp. 90–96
- ^ Kidera et al. 2008, pp. 423–440
- ^ Oliver & Shaw 1953, pp. 65–95
- ^ a b Hinckley 1963, pp. 253–259
- ^ a b c d Tyler 1989, p. 113
- ^ a b Tyler 1976, p. 77 引用エラー: 無効な
<ref>
タグ; name "Tyler1976p77"が異なる内容で複数回定義されています - ^ a b c Easteal 1981, p. 104
- ^ Cameron(2009)
- ^ Cane toads found on WA coast, Australian Geographic, July 21, 2010
- ^ Tyler 1976, p. 83
- ^ Doody et al. 2009, pp. 46–53. On snake populations seeShine 2009, p. 20.
- ^ Lever 2001, p. 67
- ^ Lever 2001, pp. 73–74
- ^ Lever 2001, p. 71
- ^ Kennedy, Anthony quoted in Lever 2001, p. 72
- ^ Lever 2001, p. 81
- ^ Lever 2001, pp. 78–79
- ^ Easteal 1981, p. 98
- ^ Lever 2001, pp. 81–82
- ^ a b c Tyler 1989, p. 112
- ^ Van Volkenberg 1935, pp. 278–279. "After a completely successful method of killing white grubs by chemical means was found, the only opportunities for its use in Puerto Rico have been limited to small areas in pineapple plantations at elevations where the toad is even yet not present in sufficient abundance."
- ^ Freeland 1985, pp. 211–215
- ^ Tyler 1989, pp. 113–115
- ^ Lever 2001, pp. 72–73
- ^ Lever 2001, pp. 128–129
- ^ Lever 2001, pp. 130–131
- ^ Easteal 1981, p. 103
- ^ Tyler, Wassersug & Smith 2007, pp. 6–7
- ^ a b Lever 2001, p. 118
- ^ a b Tyler 1976, pp. 83–84
- ^ Lever 2001, p. 119
- ^ Easteal 1981, pp. 100–102
- ^ Lever 2001, p. 57
- ^ a b Easteal 1981, p. 100
- ^ Lever 2001, p. 58
- ^ Lever 2001, p. 59
- ^ “Bufo Marinus @ Florida Wildlife Extension at UF/IFAS”. Wec.ufl.edu. 2010年4月26日閲覧。
- ^ “Poisonous Bufo May Have Toad Hold On Temple Terrace”. .tbo.com (2007年11月2日). 2010年4月26日閲覧。
- ^ “WEC 11/UW046: Marine Toads (Bufo marinus)”. Edis.ifas.ufl.edu. 2010年4月26日閲覧。
- ^ Lever 2001, p. 64
- ^ Easteal 1981, p. 101
参考文献
[編集]- Alcala, A. C. (1957). "Philippine notes on the ecology of the giant marine toad". Silliman Journal 4 (2).
- Cameron, Elizabeth (June 10, 2009). "Cane Toad". Wildlife of Sydney. Australian Museum. Retrieved June 18, 2009.
- Doody, J. S.; Green, B.; Rhind, D.; Castellano, C. M.; Sims, R.; Robinson, T. (2009). "Population-level declines in Australian predators caused by an invasive species". Animal Conservation 12 (1).
- Easteal, Simon (1981). "The history of introductions of Bufo marinus (Amphibia : Anura); a natural experiment in evolution". Biological Journal of the Linnean Society (16).
- Hinckley, A. D. (1963). "Diet of the giant toad, Budo marinus (L.) in Fiji". Herpetologica 18 (4).
- Kidera, N.; Tandavanitj, N.; Oh, D.; Nakanishi, N.; Satoh, A.; Denda, T.; Izawa, M.; Ota, H. (2008). "Dietary habits of the introduced cane toad Bufo marinus (Amphibia : Bufonidae) on Ishigakijima, southern Ryukyus, Japan". Pacific Science 62 (3).
- Lannoo, Michael J. (2005). Amphibian Declines: The Conservation Status of United States Species. University of California Press. ISBN 0-520-23592-4.
- Lever, Christopher (2001). The Cane Toad. The history and ecology of a successful colonist. Westbury Publishing. ISBN 1-84103-006-6.
- Oliver, J. A.; Shaw, C. E. (1953). "The amphibians and reptiles of the Hawaiian Islands". Zoologica (New York) 38 (5).
- Smith, K. G. (2005). "Effects of nonindigenous tadpoles on native tadpoles in Florida: evidence of competition". Biological Conservation 123 (4).
- Tyler, Michael J. (1976). Frogs. William Collins (Australia). ISBN 0-002-11442-9.
- Tyler, Michael J. (1989). Australian Frogs. Penguin Books. ISBN 0-670-90123-7.
- Zug, G. R.; Lindgrem, E.; Pippet, J. R. (1975). "Distribution and ecology of marine toad, Bufo marinus, in Papua New Guinea". Pacific Science 29 (1).