Compilation of biodiversity articles

Biodiversity

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^[7] interactions suggesting that both processing of fruits and direct biomass contributions by vertebrates and plants affect soil carbon concentration” [Sobral 2017: 3]

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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^[8], 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].

Remarkable roles of unremarked creatures

The articles below offer a sampling of the myriad ecosystem roles played by species we may not think much about. For example, fungi, an exemplar ecosystem cooperator, buries carbon in the soil, sources otherwise unavailable nutrients like phosphorus for plant growth, and facilitates bacterial evolution. Great whales transport nutrients through the ocean for other species to consume. Dung beetles reduce methane emissions from manure, while also fertilizing grasses. Termites and ants promote vegetation growth in arid climates by creating tunnels that catch and hold rainwater, and by making nutrients available to plants.

Nutrient acquisition by symbiotic fungi governs Palaeozoic climate transition, Mills 2017

Fossil evidence shows that early land plants hosted fungal symbionts, which are likely to have facilitated phosphorus acquisition by plants and thus increased net primary production, perpetuating the transition to a cooler, oxygen-rich environment suitable for animal life. Mills’ study tests this hypothesis by integrating plant-fungal phosphorus acquisition into a biogeochemical model of the Paleozoic climate transition. The study finds “significant Earth system sensitivity to phosphorus uptake from mycorrhizal fungi” [Mills 2017: 7], and that “efficient phosphorus uptake at superambient CO2 results in enhanced carbon sequestration, which contributes to a reduction in CO2 and drives a rise in O2” [Mills 2017: 6].

Understanding drivers of an historic climate cooling is obviously relevant today given current atmospheric CO2 accumulation. This study points to the importance of plant-fungal symbioses and phosphorus cycling, and thus to the importance of building and protecting soil health to allow such symbioses to flourish.

Mycelia as a focal point for horizontal gene transfer among soil bacteria, Berthold 2016

Fungus is a key component of healthy soil. It is known to “translocate compounds from nutrient-rich to nutrient-poor regions… facilitate the access of bacteria to suitable microhabitats for growth, enable efficient contaminant biodegradation, and increase the functional stability in systems exposed to osmotic stress” [Berthold 2016: 5]. This study shows that, in addition, mycelia facilitate bacterial evolution, thereby bolstering bacterial diversity and adaptability.

Abstract: Horizontal gene transfer (HGT) is a main mechanism of bacterial evolution endowing bacteria with new genetic traits. The transfer of mobile genetic elements such as plasmids (conjugation) requires the close proximity of cells. HGT between genetically distinct bacteria largely depends on cell movement in water films, which are typically discontinuous in natural systems like soil. Using laboratory microcosms, a bacterial reporter system and flow cytometry, we here investigated if and to which degree mycelial networks facilitate contact of and HGT between spatially separated bacteria. Our study shows that the network structures of mycelia promote bacterial HGT by providing continuous liquid films in which bacterial migration and contacts are favoured. This finding was confirmed by individual-based simulations, revealing that the tendency of migrating bacteria to concentrate in the liquid film around hyphae is a key factor for improved HGT along mycelial networks. Given their ubiquity, we propose that hyphae can act as a focal point for HGT and genetic adaptation in soil.

The rhizosphere ­- roots, soil and everything in between, McNear 2013

A variety of intimate, symbiotic relationships exist between the roots of plants and the microorganisms in the soil. For instance, mycorrhizal fungi colonize the surface of plant roots, effectively extending them further through the soil to collect nutrients otherwise out of reach. These mycorrhizal branching structures, known as hyphae, emanating from plant roots also improve soil aggregation and hence improve water infiltration and aeration. In return, Mycorrhiza can demand up to 20-40% of photosynthetically derived carbon from their plant hosts. In the world of rhizospheric bacteria, Rhizobia^[9] are well known for their key role in fixing atmospheric nitrogen for plant uptake. Yet there are, additionally, more than two dozen known genera of rhizobacteria that help plants grow, either directly by releasing growth stimulants (phytohormones) and enhancing mineral uptake, or indirectly by fighting off plant pathogens.

Fungal to bacterial ratios in soils investigated for enhanced C-sequestration, Bailey 2002

Testing paired sites in four ecosystem types, this study finds that higher fungal activity in soil is associated with higher soil carbon content, and that disturbing the soil reduces fungal activity. The paper’s introduction explains why fungi have been found to store more carbon than do bacteria – for example, fungi can store up to 26 times more carbon from leaf litter than bacteria. This is because the chemical composition of fungal biomass is more complex and more resistant to degradation; also, fungi have higher carbon assimilation efficiencies than do bacteria, and thus store more of the carbon they metabolize.

Whales as marine ecosystem engineers, Roman 2014

Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. With high metabolic demands and large populations, whales probably had a strong influence on marine ecosystems before the advent of industrial whaling: as consumers of fish and invertebrates; as prey to other large-bodied predators; as reservoirs and vertical and horizontal vectors for nutrients; and as detrital sources of energy and habitat in the deep sea. The decline in great whale numbers, estimated to be at least 66% and perhaps as high as 90%, has likely altered the structure and function of the oceans, but recovery is possible and in many cases is already underway. Future changes in the structure and function of the world’s oceans can be expected with the restoration of great whale populations.

The role of dung beetles in reducing greenhouse gas emissions from cattle farming, Slade 2015

“Dung beetles (Scarabaeidae: Scarabaeinae, Aphodiinae, Geotrupidae) are some of the most important invertebrate contributors to dung decomposition in both temperate and tropical agricultural grasslands. As such, they may help mitigate GHG [Greenhouse Gas] emissions and aid carbon sequestration through removing dung deposited on the pastures, increasing grass growth and fertilization” [Slade 2015: 1]. This Finland study analyzed the percent of GHGs removed by dung beetles at three levels: dung pat, pasture, and dairy/beef production life-cycle, finding reduced GHG emissions of 7%, 12%, and 0.05 to 0.13%, respectively. Dung beetles reduce methane emissions by aerating the dung pats, thereby preventing methane-producing anaerobic decomposition of the dung.

The reason dung beetles have a minimal effect in the full life-cycle analysis for Finland cattle is that the animals spend only a short portion of the year grazing in pasture, and thus emissions from dung on pasture is “dwarfed in comparison to other emissions of milk and meat production, such as methane emissions from enteric fermentation, nitrous oxide emissions from soils, and carbon dioxide emissions from energy use” [Slade 2015: 5]. However, “in regions where outdoor livestock grazing is more commonly used, the emissions from manure left on pasture will have a larger contribution to total agricultural emissions, with estimated fractions ranging from 11% in Asia up to 35% in Africa. Such patterns are combined with likely differences in dung beetle efficiency: In tropical regions, dung beetles can remove the majority of a fresh dung pat within the first few days after deposition – whereas in temperate conditions, a substantial fraction will remain throughout the grazing season” [Slade 2015: 5].

The authors recommend further research in tropical regions, predicting: “that effects at all levels from dung pats through pastures to the whole lifecycle of milk or beef production may be strongly accentuated at low latitudes” [Slade 2015: 5].

Termite mounds can increase the robustness of dryland ecosystems to climatic change, Bonachela 2015

Termites are particularly important in savannas of Africa, Australasia, and South America, and their nest structures (“mounds”) shape many environmental properties; analogous structures built by ants and burrowing mammals are similarly influential worldwide. Mound soils differ from surrounding “matrix” soils in physical and chemical composition, which enhances vegetation growth, creating “islands of fertility.” Moreover, mounds are frequently spatially over-dispersed owing to competition among neighboring colonies, which creates spotted vegetation patterns [Bonachela 2015: 652].

This study seeks to characterize landscape patterns created by termites in order to distinguish between that and other causes of spotted vegetation patterns that have been assumed to indicate imminent ecological collapse. “Rather, mound-field landscapes are more robust to aridity, suggesting that termites may help stabilize ecosystems under global change” [Bonachela 2015: 651].

Ants and termites increase crop yield in a dry climate, Evans 2011

Testing the effects of ants and termites on crop yield in an arid part of Australia, this study showed “that ants and termites increase wheat yield by 36% from increased soil water infiltration due to their tunnels and improved soil nitrogen” [Evans 2011: 1]. The authors conclude: “Our results suggest that ants and termites have similar functional roles to earthworms, and that they may provide valuable ecosystem services in dryland agriculture, which may become increasingly important for agricultural sustainability in arid climates” [Evans 2011: 1].

Ants and termites have similar functional roles to earthworms, and . . . they may provide valuable ecosystem services in dryland agriculture, which may become increasingly important for agricultural sustainability in arid climates [Evans 2011: 1].