Nutrient effects on plant diversity loss arise from nutrient identity and decreasing niche dimension
Yang PengJianxia YangEric W. SeabloomAndrew R. LeitchIlia J. LeitchRuzhen WangCunzheng WeiXingguo Han
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Abstract Two hypotheses have been used to explain the loss of plant diversity with nutrient addition. The nutrient identity hypothesis posits that biodiversity loss is due to a specific limiting nutrient, such as nitrogen (N) or phosphorus (P), while the niche dimension hypothesis posits that adding a larger number of limiting nutrients, regardless of their identity, results in biodiversity loss. These two hypotheses have not previously been tested together simultaneously. Here, we conduct that analysis to enable their relative effect sizes to be compared. We manipulated the supply of eight nutrients in the same experimental meadow grassland site to isolate the effects of the identity of added nutrients versus the number of added nutrients on biodiversity loss. We found support for both hypotheses, with the largest negative effects on biodiversity measures being due to N, or N and P treatment, with additional more minor effects of the number of added nutrients. Structural equation models (SEMs) suggested both identity and number of added nutrients had direct negative effects on biodiversity, likely caused by species' innate ability to competitively respond to nutrients, especially in response to disease, herbivory, and stress. SEMs also suggested indirect effects arising from nutrient‐driven increases in aboveground biomass, which resulted in intensified competition for light and the competitive exclusion of short‐statured species. These effects were exacerbated by the nutrients N and P which caused a shift in biomass accumulation from belowground to aboveground. The results highlight that a multi‐nutrient perspective will improve our ability to effectively manage, monitor, and restore ecosystems.Cite
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Understanding interspecific associations in old-growth forests will help to reveal mechanisms of interspecific replacement in the process of forest development and provide a theoretical basis for vegetation restoration and reestablishment. In this study, we analyzed interspecific associations of eleven dominant tree populations of varying development stages in an old-growth oak forest stand in the Qinling Mountains, China. We examined overall interspecific associations (multiple species) and pairwise interspecific associations (two species). Interspecific competition was intense during forest development and was the main factor driving succession. Community structure appears to become more stable over time which supports the harsh-benign hypothesis that interspecific competition is more common in stable sites. Old growth oak (Quercus spp.) forests are distributed widely around the world in part due to oak being a typical K-selected species. K-selected species produce fewer, high-quality offspring with higher survival rates, strong competitive ability, and longevity. The resulting distribution shifted from clumped to random, likely as a result of intense interspecific competition creating ecological niche differentiation.
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This paper analyzed temporal and spatial variation of various vegetation fractions and inner configuration of the grassland in western Songnen Plain where ecological environment was fragile based on the remote sensing data and classification of grassland resource with the support of GIS technology.It educes the quantities and characteristics of transformation among higher-coverage grassland,mid-coverage grassland,and lower-coverage grassland and other land use types from 1989 to 2001.The results indicate that the areas of three kinds of grassland are decreasing during 12 years.The transformation proportions to glebe are 77.78%,70.13% and 36.57% respectively,which illuminate that the main reason for the decrease of grassland is human's durative exploitation of grassland.The transformation proportion from grassland to saline-alkalized land increases with the decrease of grassland's vegetation fraction and is 0%,4.62%,and 32.81% for higher-coverage grassland,mid-coverage grassland and lower-coverage grassland,respectively.It shows that a crucial factor for saline-alkalized grassland is vegetation fraction.From the dynamic changing of grassland's inner configuration,we conclude that degenerative characteristic of grassland is from higher-coverage to mid-coverage and from mid-coverage to lower-coverage;moreover,the evolution is almost non-reversible under the current human activities.The degraded grassland is mostly located at the north of Zhenlai County,the south of Taonan City,the north of Tongyu County and the west of Qian'an County.Analysis of saline-alkalized grassland show that the most important reason causing saline-alkalized grassland is the continuous impact of human activities,and the status of mid-coverage grassland is the key affecting holistic quantity of grassland and the outspread speed of saline-alkalized grassland.Therefore,the only way for socio-economic and ecological environmental sustainable development is to utilize grassland resource soundly and restore the saline-alkalized grassland synthetically.At the end,the authors put forward the measures of ecological environmental restoration and grassland's sustainable development based on rational utilization of existing grassland resource and integrative prevention and rehabilitation of saline-alkalized grassland in research area.
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Response to comment on “Interspecific competition limits bird species’ ranges on tropical mountains”
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Chemical, structural, and morphological defenses are often adjusted to spatial or temporal patterns of attack Herbivory on seaweeds can be intense, with nearly 100% of production being consumed in some habitats (Carpenter 1986).Seaweeds minimize damage from herbivores by any of three strategies (Lubchenco and Gaines 1981).They can escape in space or time so they do not co-occur with important herbivores or are not detected when they do co-occur.They can deter feeding by herbivores that encounter and recognize the plant.And they can minimize the decrease in fitness that results from herbivore attack.Herbivory's profound effects on the organization of seaweed communities has been extensively reviewed (Carpenter 1986, Dayton 1975, Hay 1985, Lewis 1986, Lubchenco and Gaines 1981).In this article, we describe seaweed characteristics that diminish losses to herbivores.Seaweeds are consumed by a diverse assemblage of herbivores that includes fishes, urchins, gastropods, crabs, and numerous smaller herbivores such as amphipods, isopods, and polychaetes (collectively termed mesograzers).In tropical habitats, fish and urchins have the greatest effect on seaweed community struc-
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