By Michael R. Zarfos
Edited by Andrea Rezzonico and Francesco Femia
Human society benefits from environmental and biological predictability. Farmers expect to be able to plant a particular species and variety of crop that will survive and thrive in the soils and under the climate conditions that are typical of their given region.They have systems in place to manage the different pests and diseases that are typical of their environment. Hunters, foresters, and fishers all rely on sustainable stocks of specific species to enable their livelihoods. Similarly, each type of ecosystem exists within an envelope of predictable environmental conditions.
This equilibrium extends beyond the nonliving (abiotic) inputs to the system (e.g., water, heat, and nutrients) to include its living (biotic) components—its native species and pathogens. A newly introduced species may come to dominate the system as its population explodes, leading to local extinctions.Similarly, a native species stimulated by climate change or nutrient pollution can grow out of control, drastically altering the local environment and the services people derive from it. These complex interactions represent a category of potential tipping point, what we term human-driven “biotic eruptions,” which can severely disrupt the world we live in and undermine our security. Policymakers should consider these biotic eruptions in a global security context, and take actions accordingly.
Biotic eruptions—which we define as atypical increases of species’ populations, biomass, or byproducts—are being continually driven by human activity and modifications to the environment. Sometimes the impacts of these eruptions are relatively benign. In other instances, they may threaten our established agricultural, health, or economic systems. In many cases, they undermine our native ecosystems and reduce the biodiversity they contain.
It is useful to bin human-driven biotic eruptions into two categories: 1) eruptions that follow from human alterations of the physical and chemical environment, and 2) those that follow from species introductions or removals.
Eruptions that follow from human alterations to the physical and chemical environment
Climate changeand nutrient additions are two prolific examples of human modifications to the environment that may be contributing to biotic eruptions. For example, warmer temperatures and runoff of nitrogen and phosphorus into water bodies contribute (albeit in nonlinear, complex ways) to algal blooms—rapid increases in the biomass of algae in aquatic systems. These inputs are thought to have contributed to the millions of tons of sargassum (a genus of free-floating seaweed) currently on track to blanket many beaches across the Caribbean and Gulf of Mexico, shutting down tourist economies, emitting toxic hydrogen sulfide emissions, leaching arsenic, and potentially damaging littoral ecosystems.
A sargassum ‘landing event’ along a Florida beach, July 24, 2022. (Matthew Tighe / Adobe)
In terrestrial systems, the impacts of a changing climate and increased nutrient loading (often through atmospheric deposition—an example being acid rain) may be less immediately evident to the public. However, these inputs are altering the species composition of many terrestrial ecosystems. Many species interact (e.g. predator and prey, parasite and host) and compete for resources. A change in temperature, precipitation, or nutrient availability that affects the accessibility of those resources may alter these competitive dynamics and interactions.
These changes in abiotic conditions may also fundamentally alter the habitability of an area for a given species, which could contribute to a shift in its distribution.Thus, these changes to the physical and chemical environment ultimately lead to a change in the composition of the community as some species become more common (erupt) and others are reduced or lost altogether. A dramatic example of this—Arctic greening driven in part by warming—is underway in the far north, where shrubs and other less-hardy plants are gaining biomass within the tundra.
Eruptions that follow from species introductions or removals
While human interventions in the abiotic environment may indirectly lead to biotic eruptions, humans also cause these eruptions directly through the removal or introduction of specific species. Like the dynamics described above, removal of an important species in the environment—sometimes called a keystone species—can have cascading impacts within the ecosystem.For example, where wolves were removed from the environment in North America, herbivores like deer and elk —having been released from this predator constraint on their population size—increased in numbers, putting overwhelming pressure on many plant communities. In the West, this undermined the health of streams and river ecosystems. In the East, it has led to over-browsed forests, contributing to a lack of regenerative potential.
Finally, one of the most visible and dramatic examples of humans causing biotic eruptions is when humans introduce species into regions where they are not native. While thousands of these introductions are inconsequential because the species fails to thrive or simply naturalizes at low densities, there are likely examples in every country of introduced species becoming invasive. These invasions occur when there are insufficient limitations on the species’ growth and reproduction. In those situations, the species often comes to dominate its environment, extirpating many native species in the process.Lates niloticus) which may have contributed to significant losses of native biodiversity in Lake Victoria, water hyacinth (Pontederia crassipes) which clogs waterways and degrades aquatic ecosystems around the world, and fall armyworms which are reducing crop yields across Africa and Asia.Notable examples include the Nile perch (
A deer exclusion plot fenced off by wire in New River Gorge National Park and Preserve, West Virginia. (NPS)
Tipping points, cascades, and feedback loops
The different examples of biotic eruption described above can all lead to tipping points and cascading impacts within socio-ecological systems. Here, “tipping point” is defined as a threshold beyond which change in the system will lead to its transformation into a new stable state. Such change in a system is difficult or impossible to reverse. These state shifts result in significantly altered system function and provision of services to society.Lymantria dispar), or leveling by a hurricane, could lead to a state shift from native forest to a new ecosystem dominated by invasive plants. Where people rely on these forests for subsistence or livelihoods, such a state shift would undermine economic resilience.How dramatic these shifts are, and their consequences for society, will vary between systems. In the example of wolf removal, increases in herbivore density led to reductions in the biomass of vegetation on stream banks. This contributed to bank erosion and loss of beavers, undermining aquatic habitats, and likely reducing the ecosystem services derived by people. In the eastern US, increased deer populations and herbivory of seedlings have helped suppress the reproductive success of trees. This effect, combined with eruptions of several invasive plant species in the ground-layers (understory) of these forests, means that any canopy-removing event such as defoliation by the invasive spongy moth (
A widely observed example of a socio-ecological tipping point following a biotic eruption is the effects of harmful algal blooms (HABs). These blooms do not solely result from human activity, but humans do contribute to and cause HABs. Anthropogenic triggers include nutrient runoff from fertilizer (phosphorus and nitrogen) used in agriculture and on lawns, inputs of untreated sewage, and climate change.Karenia brevis) toxins drift inland on air, causing respiratory symptoms. This and the smell of masses of rotting fish can reduce tourism. Fish kills and toxin accumulation can cause significant economic losses for fisheries. This is only the beginning of the socio-ecological cascade that undermines ecosystem services to society. When the algae die, the mass decomposition of their biomass can contribute to oxygen depletion in the waters beneath the bloom, killing and excluding additional species and completing the ecosystem shift into a new, more-depauperate state. The effects of HABs therefore undermine individual and community health, food, and economic security.Algal blooms are an eruption of one or more species of organism. Some can release toxins that kill fish, mollusks, and potentially swimmers. These toxins can accumulate in aquatic organisms, sickening people or animals that eat them. Red tide’s (
Blooms of the harmful algae Karenia brevis along Flordia’s west coast, October 2022. (Planet Labs / NASA Earth Observatory)
Some dramatic shifts in species composition and number do not manifest as rapid state shifts but may instead take longer to complete. This is the case with the greening Arctic. The slow and complex gains of plant biomass in this region being driven by climate changemay contribute to feedback loops that accelerate and enforce regional and global environmental change. For example, greening may further enforce warming by decreasing the albedo (the reflectance) of the Arctic Circle. Whereas ice and snow reflect sunlight, dark colored vegetation absorbs it. Additionally, increased vegetation traps more snow in the winter, insulating the ground, and possibly speeding the melt of permafrost. That melting contributes greenhouse gasses to the atmosphere. Of course, increased biomass accumulation also means that these plants are drawing down carbon dioxide, but research suggests that the net effect of Arctic greening could be to further warm the region and the planet. If Arctic greening does increase net-global warming, then it is contributing to the decline in global security associated with that warming.
Pathways to Insecurity: a conceptual model
Where biotic eruptions impact socio-ecological systems there is a chance that this will reduce human and societal security, perhaps even contributing to conflict. As with any ecological disruption,the pathway between biotic eruptions and insecurity is likely to be complex (Cf. Figure 1), and at first, subtle. A single eruption on its own may threaten a local population’s health or economic livelihoods such as in the case of a HAB killing fish or swimmers and closing a fishery. These insecurities may cascade (Cf. Figure 1,A), contributing to interpersonal or intergroup contests over resources, and to migration as people seek alternative sources of income or food. Such cascades may ultimately contribute to social instability. Depending on the scale or frequency of the biotic eruption(s), large percentages of a country’s population, or the populations of multiple countries, may be impacted.
Figure 1. Conceptual diagram of the complex cascades, feedbacks, and tipping points that may lead from a biotic eruption to insecurity, system collapse (i.e. regime shifts or state changes), or conflict. Dotted lines and gray bubbles represent the socio-ecological context in which the biotic eruption is occurring, while solid black arrows represent potential cascades and feedbacks.
Where cascades might lead to tipping points, system collapse, or conflict(Cf. Figure 1,B) is likely dependent on the social, political, and ecological context in which they occur (Cf. Figure 1,C). A region with weak political institutions, existing social tension, or an economy dependent on a single industry is probably more vulnerable to disruption. A single biotic eruption will be more consequential in the presence of others and in the context of climate change and more generalized ecological degradation. Cascades may propagate relatively slowly, so that the insecurity that emerges following a biotic eruption may do so long afterward or far away.
The presence of self-enforcing feedback loops(Cf. Figure 1, solid lines) may undermine policymaker ability to intervene and halt the disruption cascade. An example of such a feedback loop might be Arctic greening, where the biotic eruption, by contributing to local warming and permafrost thaw, could make conditions more conducive to additional biomass accumulation. Another example would be if coastal communities, having lost their natural fisheries to HABs, switched to mariculture (fish farmed in the ocean) or coastal aquaculture. Such farms might then cause additional nutrient pollution, making HABs more likely and perhaps even undermining these fish farms.
Lake Victoria: Multiple interacting biotic eruptions in a single international ecosystem
At least three significant biotic eruptions have been disrupting Lake Victoria over the past 50 years. Africa’s largest lake, Victoria is a source of food and livelihoods for about 40 million people.Lake Victoria was once a center of endemism, home to hundreds of species of fish that occurred nowhere else on earth. An estimated 500 of these species substantially declined or were lost in the 1980s. The precise cause is debated, but many accounts agree that some combination of the introduction of the Nile perch (an invasive predator) and eutrophication leading to algal blooms and oxygen depletion in the lake were likely important contributors to this biodiversity loss. The third biotic eruption was of another invasive species—water hyacinth, which at its peak in 1998, covered around 77 square miles of lake surface.
Water hyacinth damages aquatic ecosystems by blocking light to submerged native plants and outcompeting surface organisms for space. So dense are the plant’s mats that fishermen have difficulty navigating them and may avoid them entirely. It clogs infrastructure used to pump water out of the lake, creates breeding habitats for mosquitos, and contributes to aquatic oxygen depletion. Though this invasion has been partially controlled, the species still experiences problematic eruptions.
The algal blooms that have occurred in Lake Victoria may have resulted from a combination of climate change, nutrient runoff, disruption of trophic webs due to loss of native fish species,and land use change (increased urbanization and agriculture at the expense of natural ecosystems).
While many native species were lost in this ecosystem collapse, Nile perch and a few others came to dominate the lake, even enabling increased take from the fishery. Yet the fishery continues to evolve, with some species becoming relatively more abundant and changing average size,suggesting that the system has not stabilized.
Lake Victoria is centered within a region whose countries are particularly vulnerable to climate insecurity. The 2021 US National Intelligence Estimate on climate change identified the three countries abutting Lake Victoria (Uganda, Kenya, and Tanzania) and one in its watershed (Rwanda) as lacking the capacity to adapt to climate change, while being exposed to some of its most extreme effects. Burundi (also in the watershed) and four countries bordering these vulnerable states (The Democratic Republic of the Congo, South Sudan, Ethiopia, and Somalia), were identified as being even more susceptible, and were included in a “arc of vulnerability” where the concentration of states with weak governance and economies may exacerbate the security impacts of climate change regionally.
Of these countries, all but Tanzania is ranked in the top 50 of the (most) Fragile States Index. All three of Lake Victoria’s abutting nations experienced declining food security between 2015 and 2020, with the percentage of the population experiencing severe food insecurity rising from between 15 and 20% to between 23 and 26%.Of these three, Uganda is the most impacted by organized violence. It is subject to armed contests between the government, rebels, militias, gangs, and ethnic groups. Some of these conflicts cross national borders. There is evidence that internal displacements from Uganda’s civil war in the late 1990’s to early 2000’s contributed to increased fishing pressure in the lake.
Evidence suggests that biodiversity likely increases the resilience of ecosystems and their services to external perturbationslike climate change and nutrient pollution. Past ecosystem collapse and simplification (loss of native species diversity and substantial replacement by Nile perch) following biotic eruptions, has likely left Lake Victoria more vulnerable to a loss of its major fisheries in the future. These biotic eruptions and the loss of biodiversity have altered the socio-ecological context of the region (Cf. Figure 1), likely reducing the resilience of the lake’s food and economic systems (its fishery). A collapse in these systems could arguably impact around 40 million people locally. Such a dislocation from historic sources of food and income could lead to political instability in and between the vulnerable states around the lake. Indeed, between 2007 and 2010 increased pressure on the lake’s fishery may have contributed to a dispute over fishing grounds around Migingo Island between Uganda and Kenya which resulted in harassment and violence against fishers, troop deployments, arrests, and diplomatic overtures.
China: Biotic eruptions and global security
China and its ruling Chinese Communist Party (CCP) are also vulnerable to biotic eruptions in the context of a challenging domestic and international environment. These challenges include poor environmental quality, growing domestic debt, a reconcentration of power in the President, increased suppression of civil society, declining economic growth, a demographic bubble, encirclement by the US and its partners, sanctions, trade disputes,inequality, and climate change.
Food security has long been a top priority of the CCP. In pre-industrial China, famines were often associated with regime change and in recent years food insecurity tied to pollutant contamination and COVID lockdowns have contributed to public dissatisfaction with the CCP.Though famine today is unlikely, the CCP continues to strive for food self-sufficiency as a national security priority and source of legitimacy. China is a top producer of many agricultural products. Yet, with only around 10% of the world’s arable land to feed about 20% of the world’s population, China is still not self-sufficient. In fact, its ratio of imported to domestically produced agricultural products continues to increase. The CCP has taken steps to boost yields, conserve farmland, clean up contaminated soils and water, subsidize farmers, and diversify import sources. Still, China’s consumers increasingly demand a more varied and high-quality international diet. Past and continued desertification, water and soil pollution, and climate change and ozone pollution all undermine agricultural productivity. Overfishing and HABs in coastal waters have diminished fisheries. Swine and bird flu threaten meat production. International crises like the war in Ukraine, climate change, and pandemics all threaten food imports.
Since China needs to import food and agricultural products to meet its demand, the country is vulnerable to global supply shocks. The CCP has taken several controversial steps to try and ensure China’s food security. First, in recent years, the government has stockpiled unprecedented amounts of food, contributing to global price rises.China also continues to purchase agricultural land abroad. Finally, its fishing fleets are often implicated in illegal, unreported, and unregulated fishing in international waters and those of other states. All three of these practices are considered provocative by the countries impacted. China is competing for food in global markets, global commons, and across sovereign borders. Since acute domestic and global shortages of food would lead to food security winners and losers, such shortages could also raise international tensions with China.
Biotic eruptions remain an unpredictable threat to food security globally and in China. Since China relies on food imports, and given its tremendous consumption, eruptions beyond its borders should be considered alongside those within. In many parts of the world, the pests and diseases that lower crop yields are invasive and are becoming more common.In China, crop pest and disease incidence quadrupled between 1970 and 2016 with a 5th of that trend linked to climate change. Climate change alone may increase the overall incidence of crop pests and diseases in China by around one to six-fold by the end of the century.
Among the hundreds of non-native species that are present in China,Spodoptera frugiperda) is a recent entrant of particular concern. Arriving in 2019, this native of the Americas undermined crop yields on at least 90,000 hectares of land in its first year and 1.07 MM hectares in 2020. Fall armyworms are generalists, impacting many of the important crops grown in China and around the world. While their reductions to yields remain uncertain due to limited high quality data, they are considered a global food security threat.the fall armyworm (
There are many other examples of biotic eruptions that have and will continue to undermine food security in China and abroad. Many of China’s keystone species have also experienced significant declines or are endangered.Ambrosia artemisiifolia) or are likely to (e.g. boll weevil, Anthonomus grandis) eventually impact Chinese ecosystems and agriculture.Annual coastal HABs in China can exceed 200,000 square kilometers with combined annual direct economic losses estimated up to $100 MM (though this is likely a considerable underestimate, particularly if one were to estimate the value of lost ecosystem services). Many other invasive species do (e.g. common ragweed,
Spodoptera frugiperda and its damage to a corn leaf. (Egor Eremenko / Adobe)
Human-induced biotic eruptions have complex impacts on natural and managed ecosystems which increasingly undermine human, community, and global security. However, there are many ways for policymakers to help prevent, combat, and adapt to biotic eruptions. Below are five recommendations.
Restore keystone species
Restoring keystone or foundational species to their native ranges may be an efficient method for regaining balance in ecosystems where biotic eruptions followed a species’ extirpation. A successful example of this kind of intervention is the reintroduction of wolves to Yellowstone National Park in the United States.
Reduce nutrient pollution
Establish laws and incentives and fund agencies and programs that reduce air and water pollution—particularly by nitrogen and phosphorus. The Clean Airand Clean Water Acts and Environmental Protection Agency are relevant examples from the US, though the latter two in particular require additional support to fully achieve their aims.
Fund scientific research
The causes and effects of biotic eruptions are complex and more knowledge will help policymakers address them efficiently and effectively. For example, HABs do not respond linearly to warming and nutrient inputs and the species involved vary.While research supports some broad conclusions about Arctic greening, much more field research is needed to interpret what satellite data implies about ecosystem change and greenhouse gas fluxes.
Support foresight, defense, monitoring, and management of non-native species
Where a species might be or become invasive, regulators should embrace the precautionary principleand require strong evidence that it will not become a problem before permitting live trade. Incidental introductions, for example in shipping crates or pallets, can be reduced by funding inspectors at ports of entry (e.g. Animal and Plant Health Inspection Service of the US Department of Agriculture). Where invasive species are already a problem, funding should be available to monitor their populations and impacts, support management programs, and develop efficient countermeasures such as biological controls. Countries should collaborate on developing such controls and on identifying species that, if translocated, could erupt in the future.
Invest in diversified economies and food systems
Nonprofits and governments assisting communities with economic development should support diverse food systems and economies. Such diversity should increase societal resilience when a biotic eruption overwhelms ecosystems.
Human-driven biotic eruptions (atypical increases in the population, biomass, or byproducts of organisms) continue to occur around the world. These eruptions upset the balance of socio-ecological systems, undermining biodiversity and ecosystem services, and consequently food systems and livelihoods. Aggregated across time and space, these tipping points have the potential to undermine regional and even global security. Policymakers can reverse, prevent, and combat biotic eruptions by restoring keystone species, reducing nutrient pollution, funding scientific research, and supporting agencies that monitor and combat invasive species. They can also make society more resilient to the eruptions that go unchecked by supporting diversified economies and food systems.
About the Author
Dr. Michael R. Zarfos is an Ecological Security Research Fellow in the Center for Climate and Security at the Council on Strategic Risks. He maintains a postdoctoral affiliation with the Dovciak Lab at the State University of New York College of Environmental Science and Forestry (SUNY ESF).
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