Awards Alexander von Humboldt Medal
The Alexander von Humboldt Medal for Excellence in Vegetation Science is the highest award the IAVS can bestow on a vegetation scientist for an outstanding body of work. The Award was established in 2011 and is awarded at approximately two-year intervals.


 

2019: Pierre Legendre (Canada)Pierre Legendre

Introduction

Abstract:
This paper presents the statistical bases for temporal beta diversity analysis, a method to study the changes in community composition through time from repeated surveys at several sites. Surveys of that type are presently done by ecologists around the world. A Temporal Beta-diversity Index (TBI) is computed for each site, measuring the change in species composition between the first (T1) and second surveys (T2). TBI indices can be decomposed into losses and gains; they can also be tested for significance, allowing one to identify the sites that have changed in composition in exceptional ways. This method will be of value to identify exceptional sites in space-time surveys carried out to study anthropogenic impacts, including climate change.
 
The null hypothesis of the TBI test is that a species assemblage is not exceptionally different between T1 and T2, compared to assemblages that could have been observed at this site at T1 and T2 under H0. Tests of significance of coefficients in a dissimilarity matrix are usually not possible because the values in the matrix are interrelated. Here, however, the dissimilarity between T1 and T2 for a site is computed with different data from the dissimilarities used for the T1–T2 comparison at other sites. It is thus possible to compute a valid test of significance in that case. In addition, the paper shows how TBI dissimilarities can be decomposed into loss and gain components (of species, or abundances-per-species) and how a B-C plot can be produced from these components, which informs users about the processes of biodiversity losses and gains through time found in space-time survey data.
 
An application of the method to the Barro Colorado Forest Dynamics plot (BCI, Panama) will be presented in detail, comparing the 1985 and 2015 surveys. Applications of the method to other ecological communities will be mentioned, including a study of paleo-ecological data. This method is applicable worldwide to all types of communities, marine and terrestrial. R software is available implementing the method.


 

2017: Stuart Chapin III (United States of America)Stuart Chapin

Introduction

Abstract:
My research addresses the effects of changes in climate and wildfire on Alaskan ecology and rural communities. I explore ways that communities and agencies can develop options that increase sustainability of ecosystems and human communities over the long term despite rapid climatic and social changes. Through projections of future climate, ecology, and subsistence resources, my research helps people make more informed choices about options for long-term sustainability. My research in earth stewardship explores ways that society can proactively shape changes toward a more sustainable future through actions that enhance ecosystem resilience and human well-being. I pursue this internationally through the Resilience Alliance, nationally through the Ecological Society of America, and in Alaska through a community partnership that links the sustainability visions of rural indigenous communities with university research expertise to implement those visions.


 

2015: Sandra Lavorel (France)Sandra Lavorel
Introduction

Abstract:
Linking global change impacts on biodiversity to changes in ecosystem functioning, and especially in biogeochemical cycling has stood as a Holy Grail for functional ecology for over two decades. Plant functional trait research was born to address this grand challenge.
 
First, there is now solid evidence that functional properties of vegetation such as community mean leaf nitrogen or fibre content or properties as simple as mean plant height control a series of processes involved in carbon and nitrogen cycling. Therefore, when environmental change modifies plant community composition as a result of plant response traits, these effects flow on to biogeochemical cycling. In 2002, we called this the response-effect framework.
 
Second, recent research has highlighted how plant functional traits impact biogeochemical cycling not only through plant-level processes, but also by driving interactions with other trophic levels including herbivores, soil detritivores and mineralising soil microbial communities. An audacious conceptualisation of these interactions extends the response-effect framework by portraying not only the effects of plant traits on abiotic processes, but also their effects on other biota they interact with. The consideration of not only plant traits, but also of the traits of these other organisms uncovers response – effect linkages across trophic levels. Such novel understanding increases our ability to predict biotic and biogeochemical changes along gradients of environmental change resulting from management, climate change or invasions.
 
Third, these insights provide a powerful means to incorporate our best ecological knowledge for quantifying ecosystem services and their variations in space and time. Trait-based models can hence be developed to map the distribution of provisioning and regulating services across landscapes, and offers great promises for scaling up to larger regions, especially by linking with remote sensing of vegetation spectral properties. Trait-based understanding of ecological tradeoffs and synergies is also powerful to highlight the opportunities and limits for the provision of multiple ecosystem services, and to ground management in sound understanding of ecological constraints.
 


2013: G. David Tilman (United States of America)
Introduction

Abstract:
Numerous lines of evidence support a “Universal Tradeoff Hypothesis,” which posits that the same interspecific tradeoffs that lead to speciation also lead to multi-species coexistence, and cause ecosystem functioning to be strongly dependent on biodiversity. For instance, fossil records for mollusks, mammals, trees, and other taxa show that, with rare exception, ecologically similar species have coexisted for a million years or more after interchange between formerly isolated realms. Because competition theory predicts that multispecies coexistence requires that species have traits that fall on the same interspecific trade-off surface, the observed coexistence after interchange suggests that during their speciation and subsequent evolution, all species have consistently been bound to the same interspecific trade-off surface despite different phylogenetic and geographic origins. Moreover, theories of multi-species competition also predict that higher diversity leads to greater ecosystem productivity and greater stability if the competing species can coexist because of interspecific tradeoffs. 

The Universal Tradeoff Hypothesis thus has the potential to provide a single unifying explanation for the evolutionary origins of biodiversity, for mechanisms of multi-species coexistence, and for ecosystem processes. In so doing, it strengthens the logical basis for the assertion that the loss of biodiversity, whether from species extinctions, community simplification, or loss of genetic variation within populations, can have serious implications for global environmental sustainability.


2011: J. Philip Grime (England)
Introduction

Abstract:
This talk summarizes arguments and evidence that address an old conundrum in plant ecology "How similar must two organisms be to exploit the same environment and how different to coexist?"

 

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