Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan; Institute of Decision Science for a Sustainable Society, Kyushu University, Fukuoka, Japan.
Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo, Japan.
J Theor Biol. 2020 Jun 21;495:110247. doi: 10.1016/j.jtbi.2020.110247. Epub 2020 Mar 14.
The evolution of group cooperation is still an evolutionary puzzle and has been studied from the perspective of not only evolutionary ecology but also social sciences. Some socio-ecological problems are caused by collapse of group cooperation. By applying theoretical studies about the evolution of cooperation, we can elucidate what causes the problems and find solutions. One of the appropriate examples is maintaining rice paddy field landscapes, which are a grand spectacle in Asia, and some are UNESCO world heritage sites. These magnificent landscapes and the associated biodiversity are at risk of abandonment for social and financial reasons. Rice paddy fields can be preserved not only by regular cultivation, which requires farmers to invest effort in cultivation, but also by the maintenance of common facilities such as irrigation canals. To investigate how this landscape might be preserved, we developed an agent-based model in which each farmer makes two types of efforts: an effort for land cultivation and an effort for collective action such as common facility maintenance. Additionally, we consider the side effects of rice production such as field deterioration from abandonment and water use competition. These factors determine the utility of each player who imitates the level of efforts necessary to invest in land cultivation and common facility maintenance of one with higher utility. This decision-making of each player can be described by the evolutionary game theory. We find that maintenance effort promotes cultivation effort, but not vice versa, even though we usually consider that each farmer's cultivation effort makes rice field landscape sustainable. We also find that if players and their near neighbors are responsible for maintaining their common facilities together, they continue to maintain them and cultivate, but if all players are responsible for maintaining all facilities in the whole farmland, players are likely to quit facility maintenance and stop cultivation. Competition for water use among all players, however, promotes cultivation more than competition among neighbors only. Therefore, rice paddy field landscapes can be sustainable if neighbors, but not the whole players, are responsible for maintaining their common facilities and cooperate together, and if the water usage of all players, but not neighbors, influences the productivity of each rice field.
群体合作的演化仍然是一个进化谜题，不仅从进化生态学的角度，而且从社会科学的角度进行了研究。一些社会生态问题是由于群体合作的崩溃而引起的。通过应用关于合作演化的理论研究，我们可以阐明导致这些问题的原因并找到解决方案。一个合适的例子是维护稻田景观，这是亚洲的一大奇观，其中一些还是联合国教科文组织的世界遗产。这些壮丽的景观和相关的生物多样性由于社会和经济原因而面临废弃的风险。稻田不仅可以通过常规的耕种来保护，这需要农民投入精力进行耕种，还可以通过维护灌溉渠等公共设施来保护。为了研究如何保护这种景观，我们开发了一个基于主体的模型，其中每个农民都要做出两种努力：土地耕种的努力和集体行动（如公共设施维护）的努力。此外，我们还考虑了稻田废弃导致的田地退化和用水竞争等负面影响。这些因素决定了每个参与者的效用，他们会模仿那些投资于土地耕种和公共设施维护的参与者的努力水平。每个参与者的这种决策可以通过进化博弈论来描述。我们发现，维护努力会促进耕种努力，但反之则不然，尽管我们通常认为每个农民的耕种努力使稻田景观得以可持续发展。我们还发现，如果玩家及其近邻共同负责维护他们的公共设施，他们就会继续维护和耕种；但是，如果所有玩家都负责维护整个农田的所有设施，那么玩家可能会放弃设施维护并停止耕种。然而，与仅仅是邻居之间的竞争相比，所有玩家之间的用水竞争会促进更多的耕种。因此，如果只是邻居而不是所有玩家负责维护他们的公共设施并共同合作，并且如果所有玩家的用水量而不是邻居的用水量影响每个稻田的生产力，那么稻田景观就可以是可持续的。
