Aims Darwin’s naturalization hypothesis proposes that successfully established alien species are less closely related to native species due to differences in their ecological niches.Studies have provided support both...Aims Darwin’s naturalization hypothesis proposes that successfully established alien species are less closely related to native species due to differences in their ecological niches.Studies have provided support both for and against this hypothesis.One reason for this is the tendency for phylogenetic clustering between aliens and natives at broad spatial scales with overdispersion at fine scales.However,little is known about how the phylogenetic relatedness of alien species alters the phylogenetic structure of the communities they invade,and at which spatial scales effects may manifest.Here,we examine if invaded understorey plant communities,i.e.containing both native and alien taxa,are phylogenetically clustered or overdispersed,how relatedness changes with spatial scale and how aliens affect phylogenetic patterns in understorey communities.Methods Field surveys were conducted in dry forest understorey communities in south-east Australia at five spatial scales(1,20,500,1500 and 4500 m2).Standardized effect sizes of two metrics were used to quantify phylogenetic relatedness between communities and their alien and native subcommunities,and to examine how phylogenetic patterns change with spatial scale:(i)mean pairwise distance and(ii)mean nearest taxon distance(MNTD).Important Findings Aliens were closely related to each other,and this relatedness tended to increase with scale.Native species and the full community exhibited either no clear pattern of relatedness with increasing spatial scale or were no different from random.At intermediate spatial scales(20-500 m2),the whole community tended towards random whereas the natives were strongly overdispersed and the alien subcommunity strongly clustered.This suggests that invasion by closely related aliens shifts community phylogenetic structure from overdispersed towards random.Aliens and natives were distantly related across spatial scales,supporting Darwin’s naturalization hypothesis,but only when phylogenetic distance was quantified as MNTD.Phylogenetic dissimilarity between aliens and natives increased with spatial scale,counter to expected patterns.Our findings suggest that the strong phylogenetic clustering of aliens is driven by human-mediated introductions involving closely related taxa that can establish and spread successfully.Unexpected scale-dependent patterns of phylogenetic relatedness may result from stochastic processes such as fire and dispersal events and suggest that competition and habitat filtering do not exclusively dominate phylogenetic relationships at fine and coarse spatial scales,respectively.Distinguishing between metrics that focus on different evolutionary depths is important,as different metrics can exhibit different scale-dependent patterns.展开更多
Few studies have to date gone behind the scenes to unveil the hidden metaphor-metonymy structure underpinning the input hypothesis （ Krashen 1981 ） despite overt attention paid to it over the years. In an effort to ...Few studies have to date gone behind the scenes to unveil the hidden metaphor-metonymy structure underpinning the input hypothesis （ Krashen 1981 ） despite overt attention paid to it over the years. In an effort to use a fine-grained metaphor-analysis approach（ e. g. , Lakoffand Johnson 1980, 1999） to revisit the input hypothesis, this study looks into its thrust--the causal effect of comprehensible input upon comprehension--in the hope of charting out its hidden organization. By discovering a theme of CAUSATION pivoted on space-based metaphors and metonyrnies, the present study brings to relief two fallacies committed in the input hypothesis. First, the heavy dependence on the prototypicaUy physical-spatial hierarchy leads to a red-herring fallacy, whose inconsistency defies rather than supports its statement about comprehensible input as the overriding cause. Second, although there is no denying that comprehensible input is a significant source of language gains, to enthrone it as the sole causal variable to the exclusion of all the other important variables, especially the agency of the 1.2 learner who should have been positioned in the spotlight in the first place, is another fallacy of immense magnitude.展开更多
基金supported by the Australian Research Council Discovery Project(DP150103017)and an Australian Government Research Training Program(RTP)Scholarship.
文摘Aims Darwin’s naturalization hypothesis proposes that successfully established alien species are less closely related to native species due to differences in their ecological niches.Studies have provided support both for and against this hypothesis.One reason for this is the tendency for phylogenetic clustering between aliens and natives at broad spatial scales with overdispersion at fine scales.However,little is known about how the phylogenetic relatedness of alien species alters the phylogenetic structure of the communities they invade,and at which spatial scales effects may manifest.Here,we examine if invaded understorey plant communities,i.e.containing both native and alien taxa,are phylogenetically clustered or overdispersed,how relatedness changes with spatial scale and how aliens affect phylogenetic patterns in understorey communities.Methods Field surveys were conducted in dry forest understorey communities in south-east Australia at five spatial scales(1,20,500,1500 and 4500 m2).Standardized effect sizes of two metrics were used to quantify phylogenetic relatedness between communities and their alien and native subcommunities,and to examine how phylogenetic patterns change with spatial scale:(i)mean pairwise distance and(ii)mean nearest taxon distance(MNTD).Important Findings Aliens were closely related to each other,and this relatedness tended to increase with scale.Native species and the full community exhibited either no clear pattern of relatedness with increasing spatial scale or were no different from random.At intermediate spatial scales(20-500 m2),the whole community tended towards random whereas the natives were strongly overdispersed and the alien subcommunity strongly clustered.This suggests that invasion by closely related aliens shifts community phylogenetic structure from overdispersed towards random.Aliens and natives were distantly related across spatial scales,supporting Darwin’s naturalization hypothesis,but only when phylogenetic distance was quantified as MNTD.Phylogenetic dissimilarity between aliens and natives increased with spatial scale,counter to expected patterns.Our findings suggest that the strong phylogenetic clustering of aliens is driven by human-mediated introductions involving closely related taxa that can establish and spread successfully.Unexpected scale-dependent patterns of phylogenetic relatedness may result from stochastic processes such as fire and dispersal events and suggest that competition and habitat filtering do not exclusively dominate phylogenetic relationships at fine and coarse spatial scales,respectively.Distinguishing between metrics that focus on different evolutionary depths is important,as different metrics can exhibit different scale-dependent patterns.
文摘Few studies have to date gone behind the scenes to unveil the hidden metaphor-metonymy structure underpinning the input hypothesis （ Krashen 1981 ） despite overt attention paid to it over the years. In an effort to use a fine-grained metaphor-analysis approach（ e. g. , Lakoffand Johnson 1980, 1999） to revisit the input hypothesis, this study looks into its thrust--the causal effect of comprehensible input upon comprehension--in the hope of charting out its hidden organization. By discovering a theme of CAUSATION pivoted on space-based metaphors and metonyrnies, the present study brings to relief two fallacies committed in the input hypothesis. First, the heavy dependence on the prototypicaUy physical-spatial hierarchy leads to a red-herring fallacy, whose inconsistency defies rather than supports its statement about comprehensible input as the overriding cause. Second, although there is no denying that comprehensible input is a significant source of language gains, to enthrone it as the sole causal variable to the exclusion of all the other important variables, especially the agency of the 1.2 learner who should have been positioned in the spotlight in the first place, is another fallacy of immense magnitude.
