Impact of human activity on ecosystems


There are many systems organized into networks: a set of interconnected nodes. This is how the metro network, the Internet or the ecosystems work. In these networks there are strongly interconnected nodes (Google or Wikipedia in the case of the Internet and key species like trees in the case of ecosystems) and others that have fewer connections between them, although they are connected to the most relevant nodes.

The study, led by researcher at the National Museum of Natural Sciences (MNCN-CSIC) Miguel Bastos Araújo, which has just been published in the journal Ecology Lettersempirically corroborates the theory which ensures that the type of disturbances undergone by these networks influences their architecture.

“The networks in which complex systems are organized have a repeating architecture. The regularity of patterns in this conception, as well as its exceptions, is a subject of great interest because if we understand how complex systems such as ecosystems self-organize, we will be better placed to anticipate the impact of human activities. on their structure and functioning”contextualizes Araujo.

In this work, they analyzed 351 terrestrial and aquatic food webs, distributed around the world and exposed to varying degrees of anthropogenic disturbance. For the first time, the team empirically verified the theory defended in 2020 by Albert et al. in a scientific article published in Nature which demonstrated, with simulated networks, that the architecture of networks determines their resilience to external attacks.

“Albert’s work is very inspiring. If the type of network architecture really offers different resilience depending on the type of attack to which they are exposed, we can deduce that, in nature, we will find networks with different architectures depending on the attacks they are regularly confronted with. exposed. exposed “Araujo clarifies.

Networks for ecosystems

There are two common types of organization of these networks. On the one hand, there are those based on architectures that obey the law of force or power, in which a few key species of the ecosystem, such as trees or large mammals, are closely linked to the majority beings in the ecosystem, while the rest of the species that live there are poorly connected to each other. The other form of organization follows a so-called random architecture, a network in which the majority of nodes have an intermediate number of connections and a minority are very or poorly connected.

Thus, networks that follow the power law, with few highly connected nodes and many poorly connected nodes, are better able to withstand random disturbances, while networks with a more random structure have greater tolerance if the attacks or disturbances they receive are directed at specific nodes. with greater connectivity. In this case, the researchers analyzed the food webs of ecosystems in which the nodes are the species and the links between nodes are represented by the food relationship between the different living beings.

human impact

“We predict that ecosystems that experience greater human pressure are associated with disturbances or attacks directed at specific nodes, for example, larger, longer-lived or more specialized species, while those that experience less human pressure are exposed to normal disturbances in ecosystem dynamics, which are more fortuitous. Thus, when the human presence is less, the networks organized according to the law of power predominate and when the human impact is greater, the most common networks are those which are organized at random.Araujo clarifies.

“Continuing the analysis of the structuring of ecosystems and their networks provides us with a basis that allows us to understand and predict the consequences of human pressure on ecosystems and therefore to take measures to reduce its impact on living beings. At the same time, the accumulation of evidence on the universality of network behavior allows us to deepen our understanding of the dynamics of complex systems, both with ecological networks and in other contexts where the study of networks is relevant.Araujo concludes.

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