Human societies depend on the resources ecosystems provide. Particularly since the last century, human activities have transformed the relationship between nature and society at a global scale. We study this coevolutionary relationship by utilizing a stylized model of private resource use and social learning on an adaptive network. The latter process is based on two social key dynamics beyond economic paradigms: boundedly rational imitation of resource use strategies and homophily in the formation of social network ties. The private and logistically growing resources are harvested with either a sustainable (small) or non-sustainable (large) effort. We show that these social processes can have a profound influence on the environmental state, such as determining whether the private renewable resources collapse from overuse or not. Additionally, we demonstrate that heterogeneously distributed regional resource capacities shift the critical social parameters where this resource extraction system collapses. We make these points to argue that, in more advanced coevolutionary models of the planetary social–ecological system, such socio-cultural phenomena as well as regional resource heterogeneities should receive attention in addition to the processes represented in established Earth system and integrated assessment models.
Whether, when and
how human usage of biophysical resources meets limits that
produce feedbacks onto social functioning has a long history of controversial
discussion
Here, we conceptually explore avenues for a third strand of global modeling,
next to the biophysical and biophysical–economic one, also incorporating
socio-cultural dynamics. Founded on a genuinely social–ecological
perspective, we term these “World–Earth” system models to
emphasize the free coevolution of the social and ecological components
We set out a simple model (see Sect.
As a particular case study for our model we examine the effect of
heterogeneously distributed resources. This is important since in the real-world agents do have access to different amounts of biophysical resources.
Our study examines under which combinations of parameters characterizing a
social learning network process does the model converge to a sustainable regime
for different degrees of resource access heterogeneity. Parameters governing
social learning dynamics are, on the one hand, a homophily parameter
The intention behind our model design is not to closely follow any specific
real-world setting but to explore the coevolution of socio-cultural dynamics with
ecological dynamics. On a conceptual level, human–environment interactions
are happening either in a common-pool or private-pool setting. Common-pool
dilemmas have been studied extensively in the past
Illustration of our stylized social–ecological model. As the
ecological subprocess the agents harvest their private logistically growing
renewable resource with either a sustainable (blue) or non-sustainable (red)
strategy. The social subprocess follows the logics of strategy imitation due
to comparisons of harvest rates and of social network adaptation due to
homophily. The social update times are generated by a Poisson process with
average inter-event time
The social learning
Thus, agent (1) If the degree of agent (2) If (2.1) With rewiring probability (2.2) If (2.1) was not chosen, change the strategy of (3) For the next update, another waiting time is drawn from the exponential
distribution (Eq.
The ecological module of our model consists of private renewable resources
each following a logistic growth function, which is chosen as one of the
simplest and most commonly used models of renewable resource dynamics in a
constrained environment
Heterogeneous access to resources is operationalized by randomly distributing
the resource capacities
Figure
Empirical resource data per country normalized to the respective
average (dots) together with least-squares-fitted lognormal distributions
(lines): biocapacity (
We utilize this distribution to investigate how resource heterogeneity
affects the behavior of the model in comparison to the frequently studied
homogeneous case. We systematically increase parameter
For comparison we also present results for non-heavy-tailed resource
capacities
A model run starts with an initial condition of stocks
First, we study how the fraction of sustainable harvesting nodes at the
steady state
Social interaction timescale–homophily parameter space. Average
fraction of sustainable harvesting agents in the steady state depending on
the social network rewiring probability
Four qualitatively different regimes can be observed: the sustainable regime
in blue, the non-sustainable or collapse regime in red, and the transition
regime in white between these, as well as, for sufficiently large
In turn, for smaller
Our main focus lies on the emergent properties of our model from a complex
system's perspective. Hence, we do not claim that any quantitative choice of
parameters is based on real-world assumptions. Rather, we focus here on
qualitative observations in terms of general parameter regimes which in
correspondence with the arbitrarily chosen ecological timescale cause a
certain differential outcome of the model. However, in order to qualitatively
compare our model with some real-world observations, we first look at the
timescale of social updates
We furthermore observe a linear relationship between critical parameters
In other words, the homophily process in our model is beneficial for reaching
the sustainable regime, where all agents harvest their resource gaining the
maximum sustainable yield. All stochasticity and inherent shocks towards this
sustainable steady state are absorbed and not affecting the final outcome. In
this sense the sustainable regime can be described as resilient. This aligns
with the findings of
Overall, these results demonstrate that immaterial processes distinct from macroeconomic optimization paradigms and residing exclusively in the social sphere, such as homophily and imitation, are capable of determining the eventual state of a material renewable resource. Thereby, these processes are able to govern a coupled social–ecological system such that full sustainability and total collapse are possible outcomes within the investigated social parameter space. Additionally, they show how the interaction of different social processes such as strategy imitation and homophily is able to shape the sustainable regime. This suggests that socio-cultural processes should be considered as a potentially important part of feedback loops also in more elaborate models of the “World–Earth” system.
We next investigate how the transition between sustainable and
non-sustainable steady states depends on the parameter
A more systematic analysis examines the average fraction of sustainable
harvesting nodes at the consensus state
Effects of resource
heterogeneity. Average fraction of sustainable harvesting nodes at the
steady state for several segments of parameter space:
This analysis allows for explicitly showing the effect of resource
heterogeneity on the critical values
At first, the observation that heterogeneity in access to private resources is enlarging the sustainable regime might be contradictory to reasonable assumptions. However, it demonstrates the value of a thorough system's analysis and being critical about one's own perception of what is reasonable. Cautiously comparing this phenomenon with the real world one can interpret the size of the resource capacity as the effective economic power of international macro-agents, such as world regions or nation states. This is justified, since we do not model any other economic processes but resource extraction – for example, trade, innovation and labor. The agents with comparably large economic power that employ a sustainable strategy have greater persuasive power than sustainable agents with smaller economic power. The German energy transition and its perceived impact on other countries regarding the transition towards a sustainable energy supply might be a real-world example where a country that is comparably strong economically also exerts comparably large persuasive power over other countries to move forward towards sustainable energy supply.
Overall, heterogeneity to resource access in our model demonstrates how comparably few sustainable first movers with a large resource capacity are also able to shift the overall system toward a sustainable state at fast social interaction rates.
In this paper, we have studied how social–ecological thresholds between sustainable and non-sustainable resource-use regimes depend on networked social interactions (related to imitation of harvesting strategies and homophily) under conditions of resource heterogeneity. We have employed a stylized model of networked agents harvesting private renewable resources with either a sustainable or non-sustainable strategy. The strategies employed by the agents are updated through a social learning process on an adaptive social network reflecting an interconnected society. Resource heterogeneity is operationalized by lognormally and normally distributed carrying capacities of the resources.
We have shown that the properties of social processes such as strategy formation by bounded rational imitation and homophilic social network adaptation alone can precondition the long-term state of renewable resources with outcomes ranging from environmental collapse to sustainability. This observation is important because it shows that following a purely economic rationale may lead to neglecting decisive processes when modeling coupled social–ecological systems and suggests that more sophisticated models of global coupled human–environment systems need to consider socio-cultural feedbacks as well. Furthermore, we have shown that resource heterogeneities are important model ingredients that must not be neglected, especially when resource distributions possess heavy tails. This is relevant because our findings suggest that accessible biophysical resources may indeed follow heavy-tailed distributions, and therefore the resulting resource heterogeneities may also have significant effects in more sophisticated modeling frameworks.
In the context of the ongoing debate on global change
The code of our model (named
Biocapacity data were downloaded from
The authors declare that they have no conflict of interest.
This work was developed in the context of the COPAN project on Coevolutionary
Pathways in the Earth system at the Potsdam Institute for Climate Impact
Research. Wolfram Barfuss is grateful for intellectual, strategic and financial support
from the Heinrich Böll Foundation. Jonathan F. Donges thanks the Stordalen Foundation (via
the Planetary Boundaries Research Network PB.net), the Earth League's
EarthDoc program and the Leibniz Association (project DOMINOES) for financial
support. Marc Wiedermann has been supported by the German Federal Ministry for Education
and Research via the BMBF Young Investigators Group CoSy-CC