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1.
Darnel ( Lolium temulentum ), a weed of wheat and barley, is either awned or awnless. The role of the darnel awn in dispersal was investigated in relation to human's agricultural practices in cereal cultivation in a Malo village, Gaytsa, south-western Ethiopia. In 24 free-threshing wheat fields and 11 emmer wheat fields, 129 and 88 spikes (one spike per plant), respectively, of darnel were randomly sampled. At the market in Gaytsa, 11 free-threshing wheat grain samples and eight emmer wheat grain samples of 150–200 g were collected. For each grain sample, the number of wheat grains and awned and awnless grains of darnel were recorded. The relative percentage of the awned form in free-threshing wheat fields was 8.53% and that in emmer wheat fields was 70.45%. The relative percentage of awned grains in free-threshing wheat grains from the market collection was 3.55% and that in emmer wheat grain lots was 75.20%. The morphology of awned darnel grains resembles emmer wheat grains and awnless darnel grains resemble free-threshing wheat grains. Thus, grain mimicry controls the close association of the two forms of darnel with the wheat species. The lack of an awn itself functions for darnel grain as a dispersal mechanism in free-threshing wheat cultivation systems compared with other wild grass species. 相似文献
2.
Path analysis of spatial predictors of front-yard landscape in an anthropogenic environment 总被引：4，自引：0，他引：4
Contagious spatial patterns were shown to exist in the landscape of front-yards in street sections of Hochelaga-Maisonneuve, Montréal. Neighbour mimicry was hypothesized as the mechanism behind this pattern (Zmyslony and Gagnon 1998). To assess the role of spatial environmental factors in structuring this pattern, we carried out a path analysis on the front-yard landscape with five spatial factors: relative distance, street side, width, depth and type of front-yard. We removed all non-significant factors from our model with simple Mantel tests and untangled the common spatial component from the relationship between spatial factors and front-yard landscape with partial Mantel tests. We then used path analysis to evaluate the relative importance of all significant spatial factors in structuring front-yard landscape and to determine the r
2 (% of landscape variation explained by spatial factors). Results showed that (1) among all spatial environmental factors, distance (proximity) remained the best predictor of front-yard vegetation – distance alone explained an average of 20% of the landscape variation of a street section, (2) depth, width and type of front-yard also structured the front-yard landscape independently of distance, (3) front-yard landscape expresses greater similarity within the same side of a street section, and (4) in two street sections of Hochelaga-Maisonneuve, spatial factors predicted over 40% of the landscape variation. This suggests (1) that landscape contagion exists also in highly humanized environments and (2) that the mimicry phenomenon was induced not only by proximity, but also by similar environmental conditions in same side street sections and whole street sections. Finally, we suggest that street sections are a very useful and appropriate unit of analysis of urban ecosystems. 相似文献
3.
Jeremy Midgley Huyam Altayeb Patrick Mbosso 《African Journal of Range and Forage Science》2016,33(2):127-129
Pseudo-galls of three East African acacia (Vachellia) species were compared to determine the correlates of gall colour and their potential defensive functions. Although all three species produce white thorns, the pseudo-galls of V. gerrardii and V. drepanolobium are dark coloured. In contrast, pseudo-galls of V. seyal var. fistula are white. Associated with this, they are thin-walled and poorly used by aggressive mutualistic ants. We suggest that this weak functionality is compensated for by the highly visible white colour. This aposematism may also involve mimicry as only the fistula variety of V. seyal has galls and only this variety co-occurs with other Vachellia species that have functional galls. Vachellia seyal seyal does not have pseudo-galls and this variety does not occur with other Vachellia species that have pseudo-galls. 相似文献
4.
Several authors have suggested that edible plants could avoid herbivory by mimicking olfactory cues of toxic plants. However, very few studies have been carried out to test this hypothesis. The aims of the present study were to identify the volatiles of three clover species and to test whether a species lacking chemical defences, such as red clover, could avoid being grazed by rabbits by mimicking the volatiles of the cyanogenic white clover. Two main volatiles were identified in all three clover species, and a further two volatiles were present in white clover only. Rabbits presented with a choice between white clover, red clover and red clover sprayed with white clover extract ate significantly more red clover than white or white-flavoured red clover. The results suggest that the volatiles of toxic plants could be used and exploited as a source of natural, safe and effective repellents to control the impact of pest herbivores on plants. 相似文献
5.
Rose THOROGOOD 《中国鸟类》2013,4(1):39-50
很早人们就已发现一些寄生性繁殖的杜鹃,其外形与Accipiter属的鹰类非常相似。最近的实验表明,大杜鹃(Cuculus canorus)模拟鹰类有助于其接近宿主大苇莺(Acrocephalus scirpaceus)的巢。不过,大苇莺却能够通过公众信息传递来识别大杜鹃的这一计谋。反过来,这也导致了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。通过比较研究,我们发现在寄生性的杜鹃中,模拟鹰类外形(如虹膜黄色,胸腹部具斑纹,脚黄)的杜鹃种类具有明显的外形多态性(29%的种类),远高于不模拟鹰类外形的杜鹃(仅8%的种类具有多态性)。系统发生分析进一步证实了模拟鹰类外形与杜鹃多态性进化之间的相关性。我们认为,杜鹃对鹰类的动态模拟很可能促进了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。 相似文献
6.
7.
A. R. Main 《Agroforestry Systems》1999,45(1-3):23-41
This paper addresses the question of how much biodiversity is enough in the context of the concept of agriculture as a mimic
of nature. Following an historical review of the likely origins of ecosystems I show that the currently accepted components
of biodiversity, viz. genetic, species and ecosystem, and their functional expression, are relevant to agriculture. Examples
of adequate biodiversity are given and it is concluded that what constitutes enough biodiversity in an agricultural system
is dependent upon the goal in question and will be different depending on whether the aim is, for example, to increase yield
stability or deal with salinity, ground water levels, soil erosion, leaching of nutrients or weed control. The point is made
that ecosystems and their composition are contingent in nature so the history of events, their frequency and intensity all
need to be considered when interpreting the natural biodiversity present and thus determining what is enough in particular
circumstances.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Naomi E.LANGMORE 《中国鸟类》2013,4(1):86-92
长期以来,人们一直对寄生性繁殖的杜鹃所采用的种种计谋惊叹不已。本文对澳大利亚的寄生杜鹃如何增加寄生巢的可获得性、如何寻找和接近巢以及如何让宿主接受它们的寄生卵与雏鸟进行了综述。这些杜鹃所采用的对策,有一些是世界上其他杜鹃种类也采用的,但有一些对策,如产隐蔽的卵和模拟的雏鸟,却似乎仅见于澳大利亚的杜鹃。泛性寄生的杜鹃因为要应对较多种类的宿主,难度自然远大于专一性寄生的杜鹃种类,这同时也解释了为什么不同种类的杜鹃进化出不同的寄生策略,以避免不同宿主的识别。 相似文献
9.
Robert W. Pemberton 《Biological conservation》2008,141(7):1758-1764
Cyrtopodium punctatum is a rare epiphytic orchid in southern Florida, made rare by historical over-collection. We examined the potential pollination of this orchid by the recently naturalized orchid bee (Euglossa viridissima), recorded as a pollinator of the orchid in tropical America, and found that this orchid bee is not a pollinator of the plant. We sought to learn what is responsible for relatively heavy fruit set in a Fairchild Tropical Botanic Garden population of C. punctatum, and determined that the native oil-collecting bee, Centris errans, is the most important pollinator. C. punctatum flowers at Fairchild have 18 times the fruit set of flowers in Everglades National Park. The difference is probably due to the many species and individuals of oil-reward plants in the Malpighiaceae in the garden, compared to one uncommon native species in the park. Female C. errans visit these oil-reward flowers to obtain edible oils to provision their brood. Cyrtopodium flowers appear to mimic the oil-reward flowers of the Malpighiaceae to attract Centris bee pollinators, much as many Oncidium orchids do in tropical America. We recommend that Brysonima lucida, a rare native malpighiaceous shrub, and C. punctatum be planted together in Everglades National Park and other natural areas to attempt to increase C. errans pollination, to restore and enhance the long-term survival of the orchid. Planting model malpighiaceous plants to enhance Centris bee pollination may be a useful restoration tactic for other rare orchid mimics in the American tropics, including Atlantic Forest in Brazil. 相似文献
10.
Yuji Yamasue 《Weed Biology and Management》2001,1(1):28-36
Echinochloa oryzicola Vasing. (= Echinochloa phyllopogon Stapf ex Kessenko) is an obligate weed with an elaborated survival strategy in the flooded rice of Japan. In this review various adaptive characters of the weed, which comprise the survival strategy, are discussed through the life cycle. The weed is distributed only in flooded rice. Seeds (spikelets) buried in the soil exhibit annual cycles between dormant and non‐dormant state, and non‐dormant seeds recurrently appear in spring when rice growers start to prepare seedling beds and fields for rice transplanting. The non‐dormant seeds have unique characters metabolically adapted to submerged conditions to germinate and grow by the anaerobic respiration through alcohol fermentation. The weed has seemingly perfect mimicry of the rice plants throughout its development from seedling to heading, by which the weed escapes from manual weeding. In a rice paddy, the weed starts heading coincidentally with the rice plants at the period when the growers are reluctant to walk in the rice paddy to weed. Irrespective of plant height of the rice cultivar, the weed develops a few upper leaves above the rice canopy during the heading period of rice. This phenotypic plasticity of E. oryzicola in plant height is one of the characters conferring its competitive aggressiveness in flooded rice. When weeding is begun again after heading, the dormant weed seeds escape weeding by shattering and join the soil seedbank. The dormant seeds express the gene of an enzyme catalyzing ATP synthesis through the mitochondrial oxidative phosphorylation more abundantly, and have larger oxygen absorption and enzyme activity of the aerobic respiration than the non‐dormant seeds, suggesting that the dormant seeds maintain viability by the conventional aerobic respiration in the paddy soil drained from rice harvesting in fall to the next early spring. The various adaptive characters comprising the survival strategy of E. oryzicola in flooded rice consist of those inherited from the wild progenitor and those selected by the crop cultivation pressure. It is suggested that both the mimicry of the weed and the heading coincident with the rice plants have been acquired by the large selection pressure of frequent weeding, which has been done over the past hundred years. However, today, the manual weeding is substituted with herbicides, which cannot detect the mimicry and heading photoperiodic sensitivity. As a result, the dominant species of Echinochloa weeds in flooded rice is changing from E. oryzicola to Echinochloa crus‐galli var. crus‐galli that has neither mimicry nor photoperiodic sensitivity synchronizing to that of rice, but is more competitive against rice. 相似文献