Alien plant species coexist over time with native ones in Chilean Mediterranean grasslands

Aims Alien species are commonly considered as harmful weeds capa-ble of decreasing native biodiversity and threatening ecosystems.Despite this assumption,little is known about the long-term patterns of the native-alien relationships associated with human disturbed managed landscapes.This study aims to elucidate the commu-nity dynamics associated with a successional gradient in chilean Mediterranean grasslands,considering both native and alien species.Methods Species richness(natives and aliens separately)and life-form(annu-als and perennials)were recorded in four chilean post-agricultural grazed grasslands each covering a broad successional gradient(from 1 to 40 years since crop abandonment).A detrended correspondence analysis(DcA),mixed model effects analyses and cor-relation tests were conducted to assess how this temporal gradient influenced natives and aliens through community dynamics.Important Findings Our results show different life-form patterns between natives and aliens over time.Aliens were mainly represented by annuals(especially ruderals and weeds),which were established at the beginning of succession.Annual aliens also predominated at mid-successional stages,but in old grasslands native species were slightly more representative than alien ones within the community.In the late successional states,positive or no correlations at all between alien and native species richness suggested the absence of competition between both species groups,as a result of differ-ent strategies in occupation of the space.community dynamics over time constitute a net gain in biodiversity,increasing natives and maintaining a general alien pool,allowing the coexistence of both.Biotic interactions including facilitation and/or tolerance processes might be occurring in chilean post-agricultural grasslands,a fact that contradicts the accepted idea of the alien species as contenders.

澳大利亚南部植物群落中的兰花的结实成功率与周围花卉资源无关

为保证生态系统不断补充兰花的种群数量,了解兰花周围的花卉资源如何影响兰花的结实成功率是很有必要的。为此,本论文研究了澳大利亚的两种特有物种Diuris pardina和Glossodia major的结实成功率与其周围花卉资源之间的关系。D.pardina模仿豌豆花,通过视觉欺骗手段吸引Pultenaea共花植物的专化传粉者;G.major展现假花药,吸引泛化传粉者。因为吸引密度更高的本地蜜蜂可以促进兰花传粉,我们假设这两个物种的结实成功率与其周围同种花和异种花的密度呈正相关。我们还假设D.pardina的成功结实与其周围Pultenaea花的丰度呈正相关。我们调查了澳大利亚南部的18个地块,统计了同种花和异种花的物种数、个体数和花朵数,以及成功结实的花朵数。对结实成功率与同种花的密度、周围花资源的多度、丰度和香农指数以及单个物种的花卉丰度进行了Pearson相关分析,发现D.pardina的结实成功率与周围同种花的密度相关,但G.major的结实成功率与周围同种花的密度无关,未发现结实成功率与异种花资源之间存在关联。D.pardina的结实成功率与Pultenaea的丰度无关,而与入侵物种法国薰衣草(Lavandula stoechas)呈正相关。