Mammal diversity influences the carbon cycle through trophic interactions in the Amazon, Sobral 2017
In a mixed forest-savanna landscape of tropical Guyana researchers found that mammal diversity is positively related to carbon concentration in the soil. The authors explain that this is due to increased feeding interaction associated with greater mammal diversity, and specify that animal abundance per se did not increase carbon content in the soil. “The lack of effect of both tree biomass and animal abundance on the response variables highlights the relevance of species richness” [Sobral 2017: 2].
“…mammal and tree richness increase the number of feeding interactions observed. The amount of organic remains (fruit and seed parts, non-fruit plant parts, faeces and animal parts) on the ground is predicted by the number of feeding interactions, and is positively related to carbon concentration in the soil. The organic remains that most affect soil carbon concentration were animal and fruit remains, which were themselves driven by carnivory and frugivory interactions suggesting that both processing of fruits and direct biomass contributions by vertebrates and plants affect soil carbon concentration” [Sobral 2017: 3]
Biodiversity effects in the wild are common and as strong as key drivers of productivity, Duffy 2017
“Biodiversity has a major role in sustaining the productivity of Earth’s ecosystems” [Duffy 2017: 263]. This is the conclusion drawn from an analysis of 133 estimates reported in 67 field studies on the effects of species richness (number of species) on biomass production, isolating biodiversity as a variable from other factors that affect productivity (nutrient availability and climate). The results validate theoretical predictions and corroborate lab experiments showing that greater biodiversity leads to greater ecosystem production, while also refuting prevailing doubts about the significance, after accounting for other factors, of biodiversity’s effect on productivity.
Because of the long history of skepticism that species diversity affects productivity of natural ecosystems, the strength and consistency of results presented here were unanticipated. In every case we found the opposite of long-standing views expressed in the ecological literature. Ecosystems with high species richness commonly had higher biomass and productivity in observational field data from a wide range of taxa and ecosystems, including grassland plants, trees, lake phytoplankton and zooplankton, and marine fishes. Observed positive associations of biodiversity with production in nature were stronger when covariates were accounted for, stronger than biodiversity effects documented in controlled experiments, and comparable to or stronger than associations with climate and nutrient availability, which are arguably two of the strongest abiotic drivers of ecosystem structure and functioning, as well as major global change drivers. Our results also corroborate findings of a recent synthesis of experimental data reporting that biodiversity effects are comparable in magnitude to major drivers of global change, and extend related conclusions based on observational data from forests and dryland plants to a broad range of ecosystems [Duffy 2017: 263].
Integration of this perspective [on the vital role of biodiversity] into global change policy is increasingly urgent as Earth faces widespread and potentially irreversible losses and invasions of species, which are already changing ecosystems [Duffy 2017: 263].
Observed positive associations of biodiversity with production in nature were … comparable to or stronger than associations with climate and nutrient availability, which are arguably two of the strongest abiotic drivers of ecosystem structure and functioning, as well as major global change drivers [Duffy 2017: 263].
Soil biota contributions to soil aggregation, Lehmann 2017
This meta-analysis finds that biodiversity across groups, especially between bacteria and fungi, contributes more to soil aggregation than species from just one group acting alone. For example, fungi specialize in binding macroaggregates, while bacteria can also bind microaggregates, and earthworms can “grind and remould ingested particles into new aggregates” [Lehmann 2017: 1]. There were no such effects from within-group biodiversity, however.
Soil biota potentially contribute to soil aggregation in a number of ways. For example, bacteria can exude biopolymers that act as binding agents for aggregates on the micrometre scale, fungal hyphae can entangle particles to hold them together (on the micrometre to millimetre scale) and geophagous animals, such as earthworms, grind and remould ingested particles into new aggregates and create biopores (on the millimetre to centimetre scale). Due to these various contributions of soil biota to soil aggregation, there is also a clear potential for complementarity among soil aggregation mechanisms, as has been shown in isolated studies [Lehmann 2017: 1].
These findings support the hypothesis that there is functional complementarity contributing to soil aggregation, and the results highlight that this functional complementarity mainly resides at the level of the HTC [Higher Taxonomic Category] . The presence of pronounced organismal interaction effects highlights the opportunity to use soil biota mixtures tailored for enhancing soil aggregation (for example, inoculation for use in restoration). This result also emphasizes the need to manage for overall high levels of soil biodiversity, especially across HTCs, in agroecosystems, which would facilitate the development of such interactions [Lehmann 2017: 4].
Anthropogenic environmental changes affect ecosystem stability via biodiversity, Hautier 2015
This study illustrates the importance of biodiversity for maintaining ecosystem stability. It tests the hypothesis that “other drivers of global environmental change may have biodiversity-mediated effects on ecosystem functioning – that changes in biodiversity resulting from anthropogenic drivers may be an intermediate cause of subsequent changes in ecosystem functioning” [Hautier 2015: 337]. Researchers found that “changes in plant diversity in response to anthropogenic drivers, including N, CO2, fire, herbivory, and water, were positively associated with changes in temporal stability of productivity,” and that “this positive association was independent of the nature of the driver” [Hautier 2015: 338]. In other words, the experimental interventions (N, CO2, fire, etc.) affected biodiversity, which in turn affected ecosystem stability; the interventions didn’t affect ecosystem stability directly, but only through changes in biodiversity as an intermediary.
For example, whether a 30% change in plant diversity … resulted from elevated N, CO2, or water or from herbivore exclusion, fire suppression, or direct manipulation of plant diversity, stability tended to decrease in parallel by 8%… This conclusion is supported by analyses showing that there was no remaining effect of anthropogenic drivers on changes in stability after biodiversity-mediated effects were taken into account [Hautier 2016: 338].
Biodiversity for multifunctional grasslands: equal productivity in high-diversity low-input and low-diversity high-input systems, Weigelt 2009
This English grasslands study, comparing alternative strategies for increasing productivity, showed that “increasing plant species richness levels were more effective than the imposed levels of increasing management intensity” [Weigelt 2009: 1701]. The management intensification strategy included synthetic fertilization and mowing, while the biodiversity strategy increased species richness from 1 to 16 species. The authors conclude that:
For permanent grasslands, which cover one third of the utilised agricultural area in Europe (Smit et al., 2008), highly diverse communities composed of complementary species and N2-ﬁxing legumes could provide an excellent agro-economic and ecological option for sustainable and highly productive grassland use [Weigelt 2009: 1704].
Low-cost agricultural waste accelerates tropical forest regeneration, Treuer 2017
This study illustrates how ecosystem restoration enhances biodiversity and productivity. A one-time application in 1998 of 1,000 truckloads of agricultural waste (orange peels) to 3 ha of degraded pasture accelerated tropical forest regeneration in this Costa Rica study. The treatment led to a tripling in species richness (24 tree species from 20 families, compared to 8 tree species from 7 families in the control plot), and 176% increase in aboveground biomass after 16 years, and without any human input after the original orange waste treatment of that site. The thick layer of orange peels suppressed existing non-native pasture grasses and added macro- and micronutrients to the soil, ultimately allowing for the natural (unmanaged) repopulating of the treated area from adjacent forest seedstock.
Our results provide nuance and detail to what was overwhelmingly obvious during informal surveys in 1999 and 2003: depositing orange waste on this degraded and abandoned pastureland greatly accelerated the return of tropical forest, as measured by lasting increases in soil nutrient availability, tree biomass, tree species richness, and canopy closure. The clear implication is that deposition of agricultural waste could serve as a tool for effective, low-cost tropical forest restoration, with a particularly important potential role at low-fertility sites [Treuer 2017: 6].
A one-time application in 1998 of 1,000 truckloads of agricultural waste (orange peels) to 3 ha of degraded pasture accelerated tropical forest regeneration in this Costa Rica study. The treatment led to a tripling in species richness (24 tree species from 20 families, compared to 8 tree species from 7 families in the control plot), and 176% increase in aboveground biomass after 16 years [Treuer 2017].
Duffy, J. Emmett, et al, 2017, Biodiversity effects in the wild are common and as strong as key drivers of productivity, Nature 549, http://www.nature.com/nature/journal/v549/n7671/full/nature23886.html
Hautier, Yann, et al, 2015, Anthropogenic environmental changes affect ecosystem stability via biodiversity, Science 348: 6232, sciencemag.org, http://science.sciencemag.org/content/348/6232/336.
Lehmann, Annika, Weishuang Zheng & Matthias C. Rillig, 2017, Soil biota contributions to soil aggregation, Nature Ecology and Evolution, https://www.nature.com/articles/s41559-017-0344-y.
Sobral, Mar, et al, 2017, Mammal diversity influences the carbon cycle through trophic interactions in the Amazon, Nature Ecology and Evolution, https://www.nature.com/articles/s41559-017-0334-0.
Treuer, Timothy, et al, 2017, Low-cost agricultural waste accelerates tropical forest regeneration, Restoration Ecology, http://onlinelibrary.wiley.com/doi/10.1111/rec.12565/full
Weigelt, A., et al, 2009, Biodiversity for multifunctional grasslands: equal productivity in high-diversity low-input and low-diversity high-input systems, Biogeosciences 6:1695–1706, www.biogeosciences.net/6/1695/2009.
 “Frugivory” is consumption of fruits.
 Herbivory is the consumption of plants.