Revealing the “Invisible Hand” of Ecosystem Long-Distance Interactions

“Long-distance interaction” is a basic feature and law that exists in complex systems. Whether it is the well-known “Wei Wei to save Zhao”, or the traditional Chinese medicine that emphasizes not to “cure the head with a headache and heal the foot with a sore foot”, the long-distance interaction between the seemingly distant and far-flung system elements will lead to rapid changes in the hierarchy of complex systems, which is the so-called “pulling a hair and moving the whole body”. Although the basic characteristics of this complex system have long been known to humans, no mathematical model has yet abstracted long-distance interactions into general laws.


Salt marsh wetland in Yancheng district of eastern China Courtesy of respondents

On June 27, scientists from East China Normal University, Nanjing University, Fudan University, the Royal Netherlands Institute of Oceanography, Brown University and other institutions collaborated to publish a paper in the Proceedings of the American Academy of Sciences based on the typical coastal wetland landscape of the Yellow Sea in China, taking the specific form of long-distance interaction in the coastal wetland ecosystem, constructing a theoretical model of partial differential equations of the law, and answering the core ecological question of “what determines the distribution pattern of species” based on the general law.

For a long time, the mainstream view was that the distribution of species at macro scales depended mainly on environmental conditions. Biological interactions usually occur between biological individuals who are close to each other.

“In recent years, more and more studies have found that there may also be significant interactions between different ecosystems that are tens or even hundreds of meters apart (usually mediated by the long-distance migration of animals and the long-distance transmission of non-living materials). Liu Quanxing, one of the corresponding authors of the paper and a professor at East China Normal University, told China Science News, “This ‘long-distance interaction’ is becoming a new direction for ecological research, but its role in shaping the structure of ecosystems has yet to be studied.” ”


Schematic diagram of the long-distance interaction mechanism Courtesy of the interviewee

By analyzing the multi-source data of remote sensing, biochemistry and dynamic landforms in Jiangsu Yancheng Wetland Rare Birds National Nature Reserve for 40 years, the interdisciplinary research team established a comprehensive ecological geomorphological model coupled with biological population-dynamic sedimentary system, studied the change law of the spatial distribution of reeds and alkali pons of local species during the colonization and expansion of alien species, and revealed that long-distance interaction is the “invisible hand” driving the evolution of the spatial hierarchy of the system.

Through remote sensing image interpretation, the researchers found that after 5 years of colonization and occupation of the low-tide area, the alkali community area in the middle tide position showed a rapid shrinking trend. Interestingly, the habitat of alkaline pon is not invaded by the invasive species erythrophyllum, but by reeds in the high tide position. The research team further decoupled the relationship between vegetation distribution and other biogeographic factors, incorporated long-distance interactions into the classical “reaction-diffusion” through data-driven modeling methods, and constructed a new “reaction-scatter-convection-long-distance interaction” partial differential equation model.

“The model describes the basic ecological geomorphological processes such as systematic population growth, spatial diffusion, interspecific competition and bio-geomorphological feedback, revealing that salt-mediated ‘long-distance interactions’ are the ‘killers’ that have led to the rapid shrinkage of alkaline red beaches in recent years.” Wang Bo, co-first author of the paper and a doctoral candidate at Nanjing University, explains, “Erythroxylum has a well-developed rhizome system that can promote low-tide sedimentation by capturing sediments and lead to local uplift of the surface, thereby having a damping effect on tidal water, reducing the flooding time and salt input of the ecosystem.” The long-term accumulation of this action leads to the decline of the salt content of the proto-alkali phong habitat to a critical threshold suitable for the growth of reeds, thus breaking the original ecological balance between reeds and alkali pon, and ultimately leading to the loss of the alkali phong beach. ”

The study found that the spatial scale of this action can reach 10 kilometers, which is one of the longest distances reported so far. What’s more, the study proposes a mathematical way to describe long-distance interactions, opening the way for studying long-range interactions in other complex systems. (Source: China Science Daily, Zhang Shuanghu, Huang Xin)

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