Spatial dynamics of ecological public goods

Abstract

The production, consumption, and exploitation of common resources ranging from extracellular products in microorganisms to global issues of climate change refer to public goods interactions. Individuals can cooperate and sustain common resources at some cost or defect and exploit the resources without contributing. This generates a conflict of interest, which characterizes social dilemmas: Individual selection favors defectors, but for the community, it is best if everybody cooperates. Traditional models of public goods do not take into account that benefits of the common resource enable cooperators to maintain higher population densities. This leads to a natural feedback between population dynamics and interaction group sizes as captured by ''ecological public goods.'' Here, we show that the spatial evolutionary dynamics of ecological public goods in ''selection-diffusion'' systems promotes cooperation based on different types of pattern formation processes. In spatial settings, individuals can migrate (diffuse) to populate new territories. Slow diffusion of cooperators fosters aggregation in highly productive patches (activation), whereas fast diffusion enables defectors to readily locate and exploit these patches (inhibition). These antagonistic forces promote coexistence of cooperators and defectors in static or dynamic patterns, including spatial chaos of ever-changing configurations. The local environment of cooperators and defectors is shaped by the production or consumption of common resources. Hence, diffusioninduced self-organization into spatial patterns not only enhances cooperation but also provides simple mechanisms for the spontaneous generation of habitat diversity, which denotes a crucial determinant of the viability of ecological systems.cooperation ͉ evolutionary game theory ͉ pattern formation ͉ population dynamics S pontaneous and complex pattern formation represents a common principle in physical, chemical, and biological systems ranging from hydrodynamical phenomena such as the ripples in the sand, to interacting chemical fronts (1), and the coloration of plants and animals such as the spots of the jaguar (2, 3), or vegetation patterns in arid ecosystems (4). Mathematical models of pattern formation use either cellular automata (5) or differential equations (6). Here, we show that similar types of patterns emerge in evolutionary settings of social dilemmas (7,8). Social dilemmas are characterized by a conflict of interest between individuals and the group. Such conflicts arise in humans (9) and microorganisms alike (10-12). In antibiotic resistance, for example, bacteria secrete an enzyme that prevents cell wall degradation (11,13,14). Synthesizing the enzyme is costly to the bacterium, and releasing the enzyme creates a public good by protecting not only the bacterium itself but also the surrounding bacteria. Thus, enzyme production represents an act of cooperation that is prone to exploitation by mutant strains, which synthesize fewer or no enzymes. Such situations are captured by public...

Cell–cell contacts confine public goods diffusion inside Pseudomonas aeruginosa clonal microcolonies

“…In liquid conditions, mutants that do not produce siderophores have, in fact, been shown to outcompete WT strains (5)(6)(7)(8). However, the limited spatial dispersal of public goods can challenge this picture and has been proposed as a general mechanism for explaining the maintenance of cooperation (8)(9)(10)(11)(12). When dispersal is limited, public good molecules tend to stay in the vicinity of the producing subpopulations, allowing them to benefit preferentially from their own production, and thus to balance the advantage of opportunistic nonproducing strains.…”

Conditional strategies and the evolution of cooperation in spatial public goods games

“…Inspired by the seminal paper introducing games on grids [18], evolutionary games on graphs and complex networks [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] have proven instrumental in raising the awareness of the fact that relaxing the simplification of well-mixed interactions may lead to qualitatively different results that are due to pattern formation and intricate organization of the competing strategies, which reveals itself in most unexpected ways. Specifically for the spatial public goods game [38,39], it has recently been shown that inhomogeneous player activities [40], appropriate partner selection [41,42], diversity [43][44][45], the critical mass [46], heterogeneous wealth distributions [47], the introduction of punishment [48,49] and reward [50], as well as both the joker [51] and the Matthew effect [52], can all substantially promote the evolution of public cooperation.…”

Cooperators trade off ecological resilience and evolutionary stability in public goods games

“…As discussed by Hauert et al [10][11][12], small population densities favour cooperators. This is because the benefit that a single cooperator gets from its own investment is spread over fewer individuals, and thus may exceed its cost.…”

“…To investigate potential coupling between ecological resilience and stability to freeloader invasion, we studied the behaviour of the Ecological Public Goods Game (EPGG) [10][11][12].…”

“…Historically, cooperation has mostly been studied as an evolutionary problem. A vast body of work in the field of evolutionary game theory has been devoted to understanding the conditions that lead to the emergence of cooperation and its stability to invasion by freeloaders, most of which involve some form of self-assortment of cooperators [2][3][4][5][6][7][8][9][10][11][12].…”