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51.
Lauren M. Hallett Lauren G. Shoemaker Caitlin T. White Katharine N. Suding 《Ecology letters》2019,22(10):1658-1667
Environmental variability can structure species coexistence by enhancing niche partitioning. Modern coexistence theory highlights two fluctuation‐dependent temporal coexistence mechanisms —the storage effect and relative nonlinearity – but empirical tests are rare. Here, we experimentally test if environmental fluctuations enhance coexistence in a California annual grassland. We manipulate rainfall timing and relative densities of the grass Avena barbata and forb Erodium botrys, parameterise a demographic model, and partition coexistence mechanisms. Rainfall variability was integral to grass–forb coexistence. Variability enhanced growth rates of both species, and early‐season drought was essential for Erodium persistence. While theoretical developments have focused on the storage effect, it was not critical for coexistence. In comparison, relative nonlinearity strongly stabilised coexistence, where Erodium experienced disproportionately high growth under early‐season drought due to competitive release from Avena. Our results underscore the importance of environmental variability and suggest that relative nonlinearity is a critical if underappreciated coexistence mechanism. 相似文献
52.
Ferdinand Bohlmann Hubert Suding José Cuatrecasas Robert M. King Harold Robinson 《Phytochemistry》1980,19(2):267-271
The investigation of several species from the newly created subtribe Espeletiinae afforded in addition to known compounds seven new diterpenes and two norditerpenes. The structures were elucidated by intensive 1H-NMR studies. The chemotaxonomic situation is discussed briefly. 相似文献
53.
Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in
N-limited ecosystems. Since the microbial community regulates N-form transformations, plant partitioning of N may be related
to plant–soil feedbacks. We conducted a 15N tracer addition experiment to study the ability of two alpine plant species, Acomastylis rossii and Deschampsia caespitosa, to partition organic and inorganic forms of N. The species are codominant and associated with strong plant–soil feedbacks
that affect N cycling. We manipulated interspecific interactions by removing Acomastylis or Deschampsia from areas where the species were codominant to test if N uptake patterns varied in the presence of the other species. We
found that Deschampsia acquired organic and inorganic N more rapidly than Acomastylis, regardless of neighbor treatment. Plant N uptake—specifically ammonium uptake—increased with plant density and the presence
of an interspecific neighbor. Interestingly, this change in N uptake was not in the expected direction to reduce niche overlap
and instead suggested facilitation of ammonium use. To test if N acquisition patterns were consistent with plant–soil feedbacks,
we also compared microbial rhizosphere extracellular enzyme activity in patches dominated by one or the other species and
in areas where they grew together. The presence of both species was generally associated with increased rhizosphere extracellular
enzyme activity (five of ten enzymes) and a trend towards increased foliar N concentrations. Taken together, these results
suggest that feedbacks through the microbial community, either in response to increased plant density or specific plant neighbors,
could facilitate coexistence. However, coexistence is promoted via enhanced resource uptake rather than reduced niche overlap.
The importance of resource partitioning to reduce the intensity of competitive interactions might vary across systems, particularly
as a function of plant-soil feedbacks. 相似文献
54.
Understanding the factors governing ecological stability in variable environments is a central focus of ecology. Functional diversity can stabilize ecosystem function over time if one group of species compensates for an environmentally driven decline in another. Although intuitively appealing, evidence for this pattern is mixed. We hypothesized that diverse functional responses to rainfall will increase the stability of vegetation cover and biomass across rainfall conditions, but that this effect depends on land-use legacies that maintain functional diversity. We experimentally manipulated grazing in a California grassland to create land-use legacies of low and moderate grazing, across which we implemented rainout shelters and irrigation to create dry and wet conditions over 3 years. We found that the stability of the vegetation cover was greatly elevated and the stability of the biomass was slightly elevated across rainfall conditions in areas with histories of moderate grazing. Initial functional diversity—both in the seed bank and aboveground—was also greater in areas that had been moderately grazed. Rainfall conditions in conjunction with this grazing legacy led to different functional diversity patterns over time. Wet conditions led to rapid declines in functional diversity and a convergence on resource-acquisitive traits. In contrast, consecutively dry conditions maintained but did not increase functional diversity over time. As a result, grazing practices and environmental conditions that decrease functional diversity may be associated with lasting effects on the response of ecosystem functions to drought. Our results demonstrate that theorized relationships between diversity and stability are applicable and important in the context of working grazed landscapes. 相似文献
55.
The investigation of five Espeletiopsis and two Coespeletia species afforded, in addition to numerous known compounds, two new kaurene derivatives 19-acetoxy-ent-kaurene and 17-oxo-ent-kaur- 15-en-19-oic acid, as well as two new tricyclic sesquiterpenes, one being the previously reported oxidation product of copaborneol and the second one the 5-oxo derivative of silphiperfol-6-ene. The structures were elucidated by NMR studies and by chemical transformations. The chemotaxonomic situation is discussed briefly. 相似文献
56.
57.
Elisa Van Cleemput Peter Adler Katharine Nash Suding 《Global Ecology and Biogeography》2023,32(12):2177-2188
Aim
The spectral variability hypothesis (SVH) predicts that spectral diversity, defined as the variability of radiation reflected from vegetation, increases with biodiversity. While confirmation of this hypothesis would pave the path for use of remote sensing to monitor biodiversity, support in herbaceous ecosystems is mixed. Methodological aspects related to scale have been the predominant explanation for the mixed support, yet biological characteristics that vary among herbaceous systems may also affect the strength of the relationship. Therefore, we examined the influence of three biological characteristics on the relationship between spectral and taxonomic diversity: vegetation density, spatial species turnover and invasion by non-native species. We aimed to understand when and why spectral diversity may serve as an indicator of taxonomic diversity and be useful for monitoring.Location
Continental U.S.A.Time Period
Peak greenness in 2017.Major Taxa Studied
Grassland and herbaceous ecosystems.Methods
For nine herbaceous sites in the National Ecological Observatory Network, we calculated taxonomic diversity from field surveys of 20 m × 20 m plots and derived spectral diversity for those same plots from airborne hyperspectral imagery with a spatial resolution of 1 m. The strength of the taxonomic diversity–spectral diversity relationship at each site was subsequently assessed against measurements of vegetation density, spatial species turnover and invasion.Results
We found a significant relationship between taxonomic and spectral diversity at some, but not all, sites. Spectral diversity was more strongly related to taxonomic diversity in sites with high species turnover and low invasion, but vegetation density had no effect on the relationship.Main Conclusions
Using spectral diversity as a proxy for taxonomic diversity in grasslands is possible in some circumstances but should not just be assumed based on the SVH. It is important to understand the biological characteristics of a community prior to considering spectral diversity to monitor taxonomic diversity. 相似文献58.
59.
Ferdinand Bohlmann Jasmin Jakupovic Maniruddin Ahmed Michael Grenz Hubert Suding Harold Robinson Robert M. King 《Phytochemistry》1981,20(1):113-116
The investigation of six Viguiera species afforded in addition to known compounds two new diterpenes, the 9,11-dehydro derivatives of trachylobanic and stachenic acid, two new heliangolides closely related to viguiestenin, and the acetate of falcarinol. The chemotaxonomic situation is discussed briefly. 相似文献