The man’s place in ecosystems
1 de October 2015
Ecologists have talked and written a lot about how human activities change ecosystems or living conditions, at the local or global scales. We also claim about the need to abolish the persistent gap between human society and Nature in thinking, because humans are a part of Nature. Yet, curiously, we have not much worked in clarifying what is our role or place in ecosystems.
That is, where we stand when we consider the network of material and energy flows of ecosystems. I have criticized in some previous publications the classic depictions of trophic pyramids to explain the energy flows, that give the image of a system “dominated” by a super-predator, such as an eagle, a lion or a whale, ignoring organisms or groups that feed on various trophic levels, as in the case of groups of species of ants, of omnivores or that of our own species (Terradas 2006 Terradas Peñuelas 2012). Sociability and intelligence are closely related to the capability to use many different types of food. And they are also features that help to become dominant in ecosystems: ants (as a group of species) can represent a half of the animal biomass in a rainforest and human species is one that transforms their surroundings and try to organize it according to their needs (indeed, sometimes exceeding some system thresholds of collapse risk). Today, trophic pyramids remain in high school outdated textbooks and we think more in terms of food webs, but we rarely study the trophic networks including man in them. This has much to do with the added complexity that represents quantifying flows into our social organization.
This comment has been motivated by the publication of an article in Science by Darimont et al about the unique behavior of man as a predator. The authors say, explicitly, that “the paradigms of sustainable exploitation focus on the dynamics of populations of prey and yields to humanity, but ignore the behavior of humans as predators”. The essential idea is that, unlike other predators, humans kill adult preys (and healthy preys, I would add) in proportions much higher than any other predator (about 14 times more), and the conclusion is that we are unsustainable super-predators that will alter the ecological and evolutionary processes globally, if managers do not constrain our predator behavior in cultural, economic and institutional aspects. The authors follow a trend that has appeared recently and that seems promising: management should not focus on sustainable yields for humans but on emulating the behavior of other predators. It’s the same idea that we have argued in a recent review (Basnou et al 2015) and that the European Environmental Agency is trying to develop (2015) for certain types of land management. It consists in replacing the ecosystem services (ES) approach (ES is an anthropocentric concept “to explain to economists,” which attempts to quantify the economic “value” of our life support systems) to the concept of management based on ecosystem functions (the concept of green infrastructure can be understood by economists with less risk of become too human-biased than that of ES). This requires a deep understanding of the ecosystem functions and, of course, of the place and behavior that humans have in them.
Basnou C, J Pino, J Terradas. 2015. Ecosystem services provided by green infrastructure in the urban environment. CAB Reviews Perspectives in Agriculture Veterinary Science Nutrition and Natural Resources 10(0004). DOI:10.1079/PAVSNNR201510004
Darimont CT, CH Fox, HM Bryan, TE Reimchen. T 2015. The unique ecology of human predatos. Science 349: 858-860.
EEA, ETC/ULS (2015). Exploring nature-based solutions: The role of green infrastructure in mitigating the impacts of weather- and climate change-related natural hazards. ESA Technical Report 12/2015,Publications Office of the European Union, Luxemburg, 61 pp.
Terradas J. 2006. Biografia del Món. Ed. Columna, Barcelona, 499 pp.
Terradas, J, J Peñuelas. 2012. Misleading ideas about top-down and bottom-up control in communities and the role of omnivores. Polish J. Ecol. 59, 4: 849-850.