在非洲大草原上,一头猎豹和一头狮子因为争夺瞪羚而大打出手;在北美大森林中,一株黑云杉伸展着它的根系与枝叶,只为从松树那里抢夺更多的光线和水源。亲缘关系相近的物种经常会为了获取资源而展开竞争。然而如今研究人员发现了一个不同寻常的例外:一种植物会为了食物与一种动物展开竞争。
据美国《科学》杂志在线新闻报道,科学家所讨论的物种是茅膏菜(Drosera capillaris)和以昆虫为食的狼蛛(Sosippus floridanus)。为了捕捉昆虫,茅膏菜会用黏液形成的小珠覆盖在它们的叶片上,并用消化酶处理掉这些食物;而狼蛛则会织出密集的蛛网。茅膏菜和狼蛛都生活在美国佛罗里达州南部潮湿的沼泽附近,并且都以不同种类的小虫为食,例如苍蝇、蚂蚁、蟋蟀以及跳虫。这种交集不由得让坦帕市南佛罗里达大学的生态学家Jason Rohr寻思——这两个物种是否也会为了资源而战。
Rohr和他的同事在佛罗里达州进行了野外调查,测量并计算了茅膏菜和狼蛛的位置和数量。为了评估这两个物种可用的食物资源,研究人员还在这一地区捕捉了昆虫。他们注意到,一旦周围有茅膏菜,狼蛛便会织出更大的蛛网——这显然是为了捕捉更多的昆虫,反之亦然。Rohr表示:“就蛛网的编织而言,狼蛛似乎对(与茅膏菜的)竞争程度有着敏锐的把握。”
为了搞清来自狼蛛的竞争对茅膏菜产生了怎样的影响,Rohr的研究小组将这场战斗搬回了实验室。研究人员将茅膏菜和狼蛛放置在玻璃容器中,并且将蟋蟀放入其中作为两者的食物。就像预期的那样,在没有狼蛛的玻璃缸内,茅膏菜长出了许多的叶片和芽孢。但是在动植物兼有的容器内,狼蛛会在茅膏菜的叶子捕获到蟋蟀之前便吃掉许多的小虫。这一情况导致茅膏菜只能分得较少的资源,后果是生出更少的叶、结出更少的籽、开出更少的花。研究人员在5月12日的英国《皇家学会学报B卷》网络版上报告了这一研究成果。
尽管人们通常都不会认为植物和动物会限制彼此的食物供给,但Rohr认为,一定还有其他类似的竞争模式等待科学家去发现。他和同事下一步打算研究橡树蟾蜍——一种同样以昆虫为食的生活在沼泽中的小型两栖动物——的存在将对茅膏菜产生怎样的影响。他说:“这种竞争很可能是一种非常普遍的现象,但我们需要证明这一点。”
美国哈佛大学的生态学家Aaron Ellison认为研究人员完成了“一篇非常具有说服力的论文”。他强调,对于那些曾推测过生物界间竞争的科学家而言,这项研究给出了一个非常好的证明。这样一个实例的发现——一种活体能动的蜘蛛与一种仅仅待在原地等待猎物上门的植物之间的竞争,给塔拉哈西市佛罗里达州立大学的生态学家Thomas Miller留下了深刻的印象。他说:“超越了植物与动物的差别,它们完全是两种不同类型的捕猎者,并且它们能够对彼此产生重要影响。”(生物谷Bioon.com)
生物谷推荐原文出处:
Proceedings of the Royal Society B: Biological Sciences
DOI: 10.1098/rspb.2010.0465
Evidence for competition between carnivorous plants and spiders
David E. Jennings1,*, James J. Krupa2, Thomas R. Raffel1 and Jason R. Rohr1
1Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA
2Department of Biology, University of Kentucky, Lexington, KY 40506, USA
Several studies have demonstrated that competition between disparate taxa can be important in determining community structure, yet surprisingly, to our knowledge, no quantitative studies have been conducted on competition between carnivorous plants and animals. To examine potential competition between these taxa, we studied dietary and microhabitat overlap between pink sundews (Drosera capillaris) and wolf spiders (Lycosidae) in the field, and conducted a laboratory experiment examining the effects of wolf spiders on sundew fitness. In the field, we found that sundews and spiders had a high dietary overlap with each other and with the available arthropod prey. Associations between sundews and spiders depended on spatial scale: both sundews and spiders were found more frequently in quadrats with more abundant prey, but within quadrats, spiders constructed larger webs and located them further away from sundews as the total sundew trapping area increased, presumably to reduce competition. Spiders also constructed larger webs when fewer prey were available. In the laboratory, our experiment revealed that spiders can significantly reduce sundew fitness. Our findings suggest that members of the plant and animal kingdoms can and do compete.