佛羅里達(dá)大學(xué)（University of Florida）的科學(xué)家們發(fā)現(xiàn),，在動(dòng)物界，一種生物的滅絕可能會(huì)波及其它動(dòng)物,，例如2萬年前多種大型哺乳動(dòng)物的絕滅殃及了一種北美燕八哥,。相關(guān)文章發(fā)表在《古地理學(xué)，古氣候?qū)W,，古生態(tài)學(xué)》（Palaeo-3）雜志上,。
“對陸地生態(tài)系統(tǒng)來說，最大的打擊莫過于失去大型哺乳動(dòng)物,；同樣,，海洋生態(tài)系統(tǒng)若失去鯊魚、金槍魚和其它頂級捕食者,，也會(huì)面臨災(zāi)難,，”研究的承擔(dān)者之一，佛羅里達(dá)自然博物館鳥類部館長D.Steadman說,。“我們發(fā)現(xiàn)非洲部分地區(qū)獅群和象群正在減少,，佛羅里達(dá)的美洲豹種群也漸漸走向衰落，這些現(xiàn)象會(huì)引起一連串不利的多米諾效應(yīng),。”
佛羅里達(dá)自然歷史博物館的鳥類學(xué)家們對墨西哥北部的8種鳴禽類化石進(jìn)行了研究,，其中一種來自Térapa 遺址區(qū)，名叫Pandanaris convexa的燕八哥是當(dāng)?shù)氐某Ｒ姺N,，生活在熱帶環(huán)境,。2萬年前，當(dāng)?shù)氐拇笮筒溉閯?dòng)物遷徙路線呈南北方向,。
燕八哥依靠草原和這些哺乳動(dòng)物為生,，此二者有內(nèi)在聯(lián)系。大型哺乳動(dòng)物來回地踩踏和取食,，使草原不被樹木占據(jù),。而燕八哥不但吃草籽，還捕食哺乳動(dòng)物體表的昆蟲,，這形成了一種互利互惠的種間關(guān)系,。
當(dāng)時(shí)生活在墨西哥北部的遠(yuǎn)古哺乳動(dòng)物有地懶、猛犸,、馬,、貘,、駱駝和野牛。2萬年前它們盡數(shù)滅絕,，食腐動(dòng)物禿鷲,、禿鷹和燕八哥也隨之消失了。集群滅絕可能撼動(dòng)整個(gè)生態(tài)系統(tǒng)的基礎(chǔ),，并從根本上改變物種分布,。所有物種都不能孤立生存，當(dāng)整體中的一小部分遭遇滅絕,，很難推測會(huì)引起怎樣的連鎖反應(yīng),。
科學(xué)家們認(rèn)為，大型哺乳動(dòng)物滅絕所引發(fā)的涓滴效應(yīng)（trickle-down effect）會(huì)影響其它物種,，2萬年前的故事警示我們應(yīng)當(dāng)謹(jǐn)慎地開發(fā)自然資源,。
墨西哥北部的遺址區(qū)曾是一片多沼澤和河流的稀樹草原，生活有多種爬行動(dòng)物,、哺乳動(dòng)物和30多種鳥類,，還不包括鳴禽。雖然鳴禽在鳥類物種中占據(jù)了50%以上,，但化石卻發(fā)現(xiàn)得不多,，特別是中美洲和南美洲。該研究還為墨西哥鳴禽化石記錄作出了貢獻(xiàn),。（生物谷Bioon.com）
生物谷推薦原文出處：
Palaeogeography, Palaeoclimatology, Palaeoecology doi:10.1016/j.palaeo.2010.12.020
Late pleistocene passerine birds from Sonora, Mexico
Jessica A. Oswald, a, and David W. Steadmana
Abstract
Songbirds (Passeriformes) have a very limited fossil record in spite of making up more than one-half of the world's 10,000 living species of birds. From the late Pleistocene fossil site of Térapa in east-central Sonora, Mexico, the identifiable fossils of songbirds consist exclusively of species of Icteridae. The seven extant species (Red-winged Blackbird Agelaius phoeniceus, Yellow-headed Blackbird Xanthocephalus xanthocephalus, Brewer's Blackbird Euphagus cyanocephalus, Great-tailed Grackle Quiscalus mexicanus, Bronzed Cowbird Molothrus aeneus, Brown-headed Cowbird M. ater, and Orchard Oriole Icterus spurius) still occur in Sonora, either as residents or migrants. The eighth fossil icterid from Térapa is an extinct genus and species of cowbird, Pandanaris convexa. The genus Pandanaris was known formerly only from late Pleistocene sites in southern California (P. convexa A. H. Miller) and Florida (P. floridana Brodkorb). We synonymize P. floridana with P. convexa because their supposed differences either cannot be substantiated or can be attributed to sexual dimorphism in size within a single species. Among the few Pleistocene sites from Mexico or the United States with well-studied and substantial assemblages of fossil passerines, Térapa is unique in its dominance of icterids (which may be common elsewhere but not dominant) and in its absence of corvids. Today, tropical “foothills thornscrub” is the vegetation type at Térapa except for riparian forest along the río Moctezuma. The icterid fossils are compatible with previous evidence (from plant, invertebrate, and other vertebrate fossils) that tropical/subtropical marsh, savanna, and riparian forest existed at Térapa during the late Pleistocene. Just as the two extant species of cowbirds associate today with large grazing mammals, the extinct Pandanaris convexa may have foraged in association with Pleistocene mammals whose extinction led to the demise of P. convexa as well.
Keywords: Late Pleistocene bird communities; Icteridae; Pandanaris; Megafaunal extinctions; Historical biogeography; Quaternary vegetation change
