Root–shoot competition interactions cause diversity loss after fertilization:a field experiment in an alpine meadow on the Tibetan Plateau

Aims A decrease in species diversity after fertilization is a common phenomenon in grasslands;however,the mechanism causing it remains highly controversial.The light competition hypothesis to explain loss of diversity has received much attention.The aim of the present paper was to test this hypothesis.Methods Fertilization was used to control above-and belowground resources simultaneously,while shade was used to control aboveground resource in an alpine meadow on the Tibetan Plateau.Univariate general linear models was used to estimate the effects of fertilization and shade on above-and belowground vegetation characteristics,including photosynthetically active radiation(PAR)in the understory,aboveground biomass,belowground biomass,R:S ratio,species richness and Simpson’s diversity index.Important findings PAR was similar in the understory of shaded and fertilized plots,but only fertilization reduced species richness and diversity,suggesting that light competition alone could not explain diversity loss after fertilization.The root biomass and R:S ratio had a significant increase in shaded plots,but the richness and diversity did not change,suggesting that root competition alone also could not explain diversity loss after fertilization in this community.Our results illustrated that the root–shoot competition interactions,investigated from a functional groups perspective,should be the most reasonable explanation leading to the diversity loss due to fertilization.

Reducing the loss of genetic diversity associated with assisted colonization-like introductions of animals

Translocations, especially assisted colonizations, of animals are increasingly used as a conservation management tool. In many cases, however, limited funding and other logistic challenges limit the number of individuals available for transloeation. In conservation genetics, small populations are predicted to rapidly lose genetic diversity which can deteriorate population survival. Thus, how worried should we be about the loss of genetic diversity when introducing small, isolated populations？ Historical species introductions provide a means to assess these issues. Here we review 13 studies of ＂assisted colonization-like＂ introductions of animals, where only a small known number of founders established an isolated population without secondary contact to the source population. We test which factors could be important in retaining genetic diversity in these cases. In many cases, loss in heterozygosity （-12.1%） was detected, and more seriously the loss in allelic richness （-27.8 %）. Number of founders seemed to have an effect but it also indicated that high population growth rate could help to retain genetic diversity, i.e. future management actions could be effective even with a limited number of founders if population growth would be enhanced. On the contrary, translocated organisms with longer generation times did not seem to retain more genetic diversity. We advocate that, where possible, future studies on translocated animals should report the loss of genetic diversity （both heterozygosity and allelic richness）, which is essential for meta-analyses like this one for deepening our understanding of the genetic consequences of assisted colonization, and justifying management decisions [Current Zoology 61 （5）： 827-834, 2015].