BDG Paper Blitz: March 3, 2011
Differential effects of functional traits on aboveground biomass in semi-natural grasslands
Schumacher, J. & Roscher, C. 2009. Oikos 118: 1659-1668
Abstract: Despite increasing evidence on the importance of species functional characteristics for
ecosystem processes, two major hypotheses suggest different mechanisms: the ‘mass ratio
hypothesis’ assumes that functional traits of the dominant species determine ecosystem
processes, while the ‘complementarity hypothesis’ predicts that resource niches may be used
more completely when a community is functionally more diverse. Here, we present a method
which uses two different groups of biotic predictor variables being (1) abundance-weighted
mean (aggregated) trait values and (2) functional trait diversity based on Rao’s quadratic
diversity (FDQ) to test the competing hypotheses on biodiversity_ecosystem functioning
relationships after accounting for co-varying abiotic factors. We applied this method to data
recorded on biodiversity_biomass relationships and environmental variables in 35 semi-natural
temperate grasslands and used a literature-based matrix of fourteen plant functional traits to
assess the explanatory power of models including different sets of predictor variables.
Aboveground community biomass did not correlate with species richness. Abiotic factors, in
particular soil nitrogen concentration, explained about 50% of variability in aboveground
biomass. The best model incorporating functional trait diversity explained only about 30%, while
the best model based on aggregated trait values explained about 54% of variability in
aboveground biomass. The inclusion of all predictor variable groups in a combined model
increased the predictive power to about 75%. This model comprised soil nitrogen concentration
as abiotic factor, aggregated traits being indicative for species competitive dominance (rooting
depth, leaf distribution, specific leaf area, perennial life cycle) and functional trait diversity in
vegetative plant height, leaf area and life cycle. Our study strongly suggests that abiotic factors,
trait values of the dominant species and functional trait diversity in combination may best
explain differences in aboveground community biomass in natural ecosystems and that their
isolated consideration may be misleading.
Soil fungal pathogens and the relationship between plant diversity and productivity.
Maron, J.L., Marler, M., Kilronomos, J.N., Cleveland, C.C. 2011. Ecology Letters 14: 36-41
Abstract: One robust result from many small-scale experiments has been that plant community
productivity often increases with increasing plant diversity. Most frequently, resource-based or
competitive interactions are thought to drive this positive diversity–productivity relationship.
Here, we ask whether suppression of plant productivity by soil fungal pathogens might also
drive a positive diversity–productivity relationship. We created plant assemblages that varied in
diversity and crossed this with a ± soil fungicide treatment. In control (nonfungicide treated)
assemblages there was a strong positive relationship between plant diversity and above-ground
plant biomass. However, in fungicide-treated assemblages this relationship disappeared. This
occurred because fungicide increased plant production by an average of 141% at the lower
ends of diversity but boosted production by an average of only 33% at the higher ends of
diversity, essentially flattening the diversity–productivity curve. These results suggest that soil
pathogens might be a heretofore unappreciated driver of diversity–productivity relationships.
Competitive exclusion along climate gradients: energy efficiency influences the distribution of
two salmonid fishes
Finstad et al. 2011. Global Change Biology 17: 1703-1711
Abstract: We tested the importance of thermal adaptations and energy efficiency in relation to
the geographical distribution of two competing freshwater salmonid fish species. Presenceabsence data for Arctic char and brown trout were obtained from 1502 Norwegian lakes
embracing both temperature and productivity gradients. The distributions were contrasted with
laboratory-derived temperature scaling models for food consumption, growth and energy
efficiency. Thermal performances of the two species were almost identical. However, Arctic char
exhibited double the growth efficiency (per unit of food) and appear to have out-competed
brown trout fromcold, low-productivity lakes, perhaps by scramble competition. Brown trout, for
which previous reports have shown to be aggressive and dominant, have likely excluded the
more energy-efficient Arctic char from relatively warm, productive lakes, perhaps by contest
competition. Competitive interaction changing in outcome with lake productivity, rather than
thermal performance, is likely a major determinant of the range distribution of the two species.
Our study highlights the need for more focus on choice of relevant ecophysiological traits in
ecological climate impact studies and species distribution modelling.
Dark diversity: shedding light on absent species
Meelis Partel, Robert Szava-Kovats and Martin Zobel. 2011. TREE 26: 124-128.
Abstract: Ecological theory and nature conservation have traditionally relied solely on observed
local diversity. In this review, we recommend including those species that are absent from an
ecosystem but which belong to its species pool; that is, all species in the region that can
potentially inhabit those particular ecological conditions. We call the set of absent species ‘dark
diversity’. Relating local and dark diversities enables biodiversity comparisons between regions,
ecosystems and taxonomic groups, and the evaluation of the roles of local and regional
processes in ecological communities. Dark diversity can also be used to counteract biodiversity
loss and to estimate the restoration potential of ecosystems. We illustrate the dark diversity
concept by globally mapping plant dark diversity and the local:dark diversity ratio.
Impact of above- and below-ground invertebrates on temporal and spatial stability of grassland
of different diversity
Eisenhauer, N., Milcu, A., Allan, E., Nitschke, N., Scherber, C., Temperton, V., Weigelt, A.,
Weisser, W. W. and Scheu, S. 2011. Journal of Ecology, 99: 572–582
Summary
Recent theoretical studies suggest that the stability of ecosystem processes is not
governed by diversity /per se/, but by multitrophic interactions in complex communities.
However, experimental evidence supporting this assumption is scarce.
We investigated the impact of plant diversity and the presence of above- and belowground invertebrates on the stability of plant community productivity in space and time, as well
as the interrelationship between both stability measures in experimental grassland communities.
We sampled above-ground plant biomass on subplots with manipulated above- and
below-ground invertebrate densities of a grassland biodiversity experiment (Jena Experiment) 1,
4 and 6 years after the establishment of the treatments to investigate temporal stability.
Moreover, we harvested spatial replicates at the last sampling date to explore spatial stability.
The coefficient of variation of spatial and temporal replicates served as a proxy for
ecosystem stability. Both spatial and temporal stability increased to a similar extent with plant
diversity. Moreover, there was a positive correlation between spatial and temporal stability, and
elevated plant density might be a crucial factor governing the stability of diverse plant
communities.
Above-ground insects generally increased temporal stability, whereas impacts of both
earthworms and above-ground insects depended on plant species richness and the presence of
grasses. These results suggest that inconsistent results of previous studies on the diversity–
stability relationship have in part been due to neglecting higher trophic-level interactions
governing ecosystem stability.
Changes in plant species diversity in one trophic level are thus unlikely to mirror
changes in multitrophic interrelationships. Our results suggest that both above- and belowground invertebrates decouple the relationship between spatial and temporal stability of plant
community productivity by differently affecting the homogenizing mechanisms of plants in
diverse plant communities.
Species extinctions and accompanying changes in multitrophic interactions are likely to
result not only in alterations in the magnitude of ecosystem functions but also in its variability
complicating the assessment and prediction of consequences of current biodiversity loss.
Disentangling the role of environmental and human pressures on biological invasions across
Europe.
Pysek, P. et al. 2010. PNAS 107:12157-12162
Abstract: The accelerating rates of international trade, travel, and transport in the latter half of
the twentieth century have led to the progressive mixing of biota from across the world and the
number of species introduced to new regions continues to increase. The importance of
biogeographic, climatic, economic, and demographic factors as drivers of this trend is
increasingly being realized but as yet there is no consensus regarding their relative importance.
Whereas little may be done to mitigate the effects of geography and climate on invasions, a
wider range of options may exist to moderate the impacts of economic and demographic
drivers. Here we use the most recent data available from Europe to partition between
macroecological, economic, and demographic variables the variation in alien species richness
of bryophytes, fungi, vascular plants, terrestrial insects, aquatic invertebrates, fish, amphibians,
reptiles, birds, and mammals. Only national wealth and human population density were
statistically significant predictors in the majority of models when analyzed jointly with climate,
geography, and land cover. The economic and demographic variables reflect the intensity of
human activities and integrate the effect of factors that directly determine the outcome of
invasion such as propagule pressure, pathways of introduction, eutrophication, and the intensity
of anthropogenic disturbance. The strong influence of economic and demographic variables on
the levels of invasion by alien species demonstrates that future solutions to the problem of
biological invasions at a national scale lie in mitigating the negative environmental
consequences of human activities that generate wealth and by promoting more sustainable
population growth.
Mutualisms in a changing world: an evolutionary perspective
Kiers et al. 2010. Ecology Letters 13: 1459-1474
There is growing concern that rapid environmental degradation threatens mutualistic
interactions. Because mutualisms can bind species to a common fate, mutualism breakdown
has the potential to expand and accelerate effects of global change on biodiversity loss and
ecosystem disruption. The current focus on the ecological dynamics of mutualism under global
change has skirted fundamental evolutionary issues. Here, we develop an evolutionary
perspective on mutualism breakdown to complement the ecological perspective, by focusing on
three processes: (1) shifts from mutualism to antagonism, (2) switches to novel partners and (3)
mutualism abandonment. We then identify the evolutionary factors that may make particular
classes of mutualisms especially susceptible or resistant to breakdown and discuss how
communities harbouring mutualisms may be affected by these evolutionary responses. We
propose a template for evolutionary research on mutualism resilience and identify conservation
approaches that may help conserve targeted mutualisms in the face of environmental change.