By a giant log beside the Connell plot. Image credit: Janet Gagul
Ecologists are pious nerds, and from time to time we embark on pilgrimages to visit sites of ecological significance. This post is on one such site.
The year 1978 marked a significant advance in ecological science. It was the year that saw the publication of what is perhaps one of the most cited papers in theoretical ecology, written by Joseph Connell and titled “Diversity in tropical rain forests and coral reefs”.
In this paper, Joseph Connell expounded on the “intermediate disturbance hypothesis”. He proposed that within ecosystems such as rainforests and coral reefs, species diversity is highest at an intermediate level of disturbance. This idea, published in the journal Science nearly 40 years ago, has been tested and retested, refined and debated to this day. The paper has been cited close to 8000 times – more than the total number of citations that most academics get throughout their entire careers.
In an even earlier work in 1971, Connell proposed a mechanism for the maintenance of co-existence and diversity in rainforests (known now as the Janzen-Connell hypothesis), stating that specialist predators, pests, and pathogens keep key plant species rare enough to reduce their competitive ability enough so as to make space available for many other species.
All great theories need good experimental evidence. Although Connell’s work is often cited , the source of his evidence is seldom mentioned. One of Connell’s study site was actually a patch of tropical rainforest, not in the Amazon, not in Asia, but in the Tableland mountains near Cairns, Australia.
In his work, Connell used seedling abundance and mortality data from a 1.7 hectare rainforest monitoring plot from Davies Creek, which he had been working on with Australian ecologists John Geoffrey Tracey and Leonard James Webb since 1963.
With a nerdy desire akin to historians wanting to sleuth a site of historical significance, a group of friends and I embarked on a pilgrimage to visit our ecological “mecca” – what we had affectionately but unimaginatively come to call the Connell plot.
It became very apparent to me very quickly how the fame of an idea can quickly overshadow the importance of it’s components. We drove along a dirt road through savanna for 45 minutes until the road ended at what seem to be a cul de sac in a rainforest. The road used to continue past the cul de sac and would have brought us closer to the plot, but of which calves were the only way to access now. It took another 45 minutes by foot (or would have been if we didn’t stop frequently to enthuse about plants and fungi) along what is now a walking track before we finally got to the plot – which we conclude by tell-tale trees with paint marks, and tags on seedlings.
Sitting at the foot of a giant in the Connell plot. This tree is a large Karrabina biagiana (Cunoniaceae), an endemic species of Far North Queensland
As a biologist working in the Australian tropics, and having been involved setting up forest plots, I can appreciate and celebrate how great theories could have been built in part on the study of a local patch of forest. Like true nerds, my friends and I mused on trees and their seedlings. We identified a shrub, a fallen fruit here and there. We sat beneath a behemoth of a buttress, and posed for a group photo.
We set off with the intention to “sit at the feet of giants”. But beyond any academic inspiration we might have hoped to obtain from the Connell plot, our journey, rather than our destination, was the highlight of our pilgrimage.
Along the way, we met the true muses – the trees, the fungi, and the various uncredited individual characters who collectively form the inspiration for any ecological theory.
Orania palm – the silent sentinel to the Connell plot.
As we approached the “mecca” of our pilgrimage, we came before the Orania palm (Oraniopsis appendiculata), a palm representing a single genus and single species, found only in tropical Queensland, stood by our entrance to the plot – like a sentinel by a doorway to mystical realms. By a little creek we had to cross to get to the plot, we espied the delicate white blossoms of Bailey’s Cyrtandra (Cyrtandra baileyi) – a relative of the commonly cultivated African violet. Did the solemn charisma of Oraniopsis and the fragile beauty of Cyrtandra play some role in genesis of the intermediate disturbance hypothesis? I’d love to think it did.
Connell, J. H. (1971). On the role of natural enemies in preventing competitive exclusion in some marine animals and in rain forest trees. Dynamics of populations, 298, 312.
Connell, J. H. (1978). Diversity in tropical rain forests and coral reefs. Science, 199(4335), 1302-1310.