Natural communities

5 de November 2015

When I studied the subject of ecology at the University of Barcelona, about the years 1964-65 (fifty years ago!), Margalef was our teacher. Even though he was still not a university professor but the director of the Fisheries Research Institute of the CSIC (now Institute of Marine Sciences) where he concentrated his research. The ecology classes were at the building of the University Square, the practices at the Institute. There was by then only a book on ecology, by G.L. Clarke, with a Spanish translation but scarce connections with the ecology topics that Margalef explained. I do not know how but we acquired a cyclostyled book, gray soft-bounded, written by Margalef himself for a course at the University of Puerto Rico (1962). It was entitled Comunidades naturales.

Aiguamoll. Foto: J.P.Roja (CC BY-NC 2.0)

Wetland. Photo: J.P.Roja (CC BY-NC 2.0)

The concept of community was familiar to us because it was also the starting point for the geobotanical school of Josias Braun-Blanquet, followed by Oriol Bolòs and Josep Vigo, our teachers of Botany. Community was for us the basic unit for the study of ecology. We soon discovered that this was not so obvious to everyone. Discussions on this concept were old; they had been very active during the first three decades of the twentieth century.

While Frederick Clements had seen the community as something entailing a high level of organization, almost organic, Henry Gleason said that the links between species in a community were very weak and their coexistence, except for special cases of symbiosis, was mostly due to similar environmental requirements. Many years later, paleoecological studies on how communities were disaggregated and reorganized as a result of recent climatic glacial fluctuations supported the individualistic Gleason’s thesis. During the 1980’s, many ecologists adopted a reductionist view focused on populations rather than on communities, while the study of these last did not disappear from the field.

This year, the Ramon Margalef international prize of Ecology has been awarded to the American ecologist and ornithologist Robert Ricklefs. He is author of two ecology textbooks (Ecology 1973 and The economy of nature 1983) that were very used in Spanish universities for a number of years, in a period between the Margalef’s Ecología (1974)– an extraordinary book but too much difficult for a one year course- and the Ecología: individuos, poblaciones, comunidades by Begon et al (1986).

Ricklefs has been not awarded for his well-known textbooks but especially for his contributions to the study of the community. In his lecture of October 28th at the Faculty of Biology of the University of Barcelona, he questioned what is normally considered as a central point in community ecology: that competition has a key role in the communities’ organization.

Foto: A. Maseda (CC BY-NC-SA 2.0)

Foto: A. Maseda (CC BY-NC-SA 2.0)

The traditional view of a community composed of niches, each of which is occupied by that species which competitively excludes its rivals, does not convince Ricklefs (Margalef also believed that the concept of niche had been overcome, and modern ecology admits that there are no pre-existing niches, while each species builds its own niche).

Ricklefs thinks that competition plays a little role and that local communities need to be understood bearing in mind the regional scale, moving the focus from local ecology to biogeography.

Populations undergo, he says, expansions and regressions in their distribution areas over time, linked to small changes that include complex interactions, mostly with pathogens. These expansion-regression cycles can last many centuries or millennia and lead to potential fragmentation and isolation of small groups of individuals, thus promoting species evolution. Ricklefs claims, rightly, that we have to consider complex large-scale processes beyond the community.

However, his “gleasonian” appeal to disintegrate the local community in a number of overlapping distributions (in practice to abandon the study of species diversity and composition at the thin scales) was made in 2008 in an American Naturalist paper, is not mainstreaming between ecologists and it was replicated by Brooker and others (one of them Francisco Pugnaire) in the same journal the following year. These authors defended the need to study the local communities and to search the integration across different spatial scales. In fact, Ricklef’s position seems to many ecologists an excessively radical one, but it is stimulating thinking.

It is impossible to review here more than a century of disputes over the community concept, but the prize to Ricklefs can be an opportunity to recall that the debate on the community is alive because new views are still possible and this are good news.

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Jaume Terradas
Emeritus Professor of Ecology at the UAB. CREAF researcher on issues of vegetation ecology. He has also worked in environmental education. Member of the Institute of Catalan Studies.
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