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].