In 1867, Russian chemist Dmitri Mendeleev was writing a chemistry textbook, but it wasn't going well. At the time, only 56 elements were known to exist, but Mendeleev was having a tough time figuring out how to organize them in a way that would demonstrate their relationships to each other. But then, as legend has it, he had a dream which showed him not only how to organize the known elements by atomic weight and chemical reactivity, but also allowed him to predict other elements that had yet to be discovered.
Mendeleev accomplished in this single night's sleep what scientists from pretty much every discipline would kill for: a straightforward, predictive way to organize and depict complicated information. For ecologists, for instance, this might be a model that could distill the enormous complexity of how an organism functions within the ecological community in which it lives. Holy cow, ecologists would be so pumped if they had that. I mean, after they stopped fighting about it, they'd be ecstatic.
Scientists have been intrigued by the idea since the early 1970s, when Robert MacArthur, an evolutionary ecologist, had the idea of ordering organisms similarly to chemistry’s periodic table, in which elements are organized by the combination of certain chemical properties, the configuration of their electrons and their atomic number (number of protons).
So in 2015, a group of ecologists published a paper in the journal Ecology Letters in order to take a stab at what had long been discussed but had never been attempted: creating a periodic table for ecological niches, similar to the periodic table for elements in chemistry, which would essentially represent the complex roles different species play within a community. This could include how they reproduce, what they do for food and shelter, how they protect themselves, how they interact with their living and nonliving neighbors, and so on.
"Basically, the approach of producing periodic tables of niches is a way to organize species according to sets of functional traits that have known influences for ecological performance," says coauthor Dr. Kirk Winemiller, professor in the Department of Wildlife and Fisheries Sciences at Texas A&M University. "It is an approach that allows us to make an abstract concept approachable for empirical study."
Instead of looking at all the possible demands a species might make on its living situation — acceptable ranges of nutrients like nitrogen and phosphorous, temperature, moisture, soil type (and one species might have hundreds of requirements) — the authors chose just a few essential properties to capture the idea of a niche: diet, habitat, life history, metabolism and defense mechanisms.
The Lizard Model
The research team published a study in November 2017 in The American Naturalist as a way to begin the task of putting this idea to work on ... the world's lizards. They compiled as much data as they could on 134 lizard species, from 24 of the 38 lizard families living on four of Earth's continents today. Then they took their five essential properties of niche, listing between seven and 15 variables for each, and then began crunching the numbers.
Through creating models of their data, they found what they might have expected to find: that lizards are like many other organisms — they evolve to interact with their habitats, forage for food, and observe active and inactive times each day, no matter where they live. For instance, lizards that fill a certain niche in South America have similar traits to lizards that fill similar niches in Australia, Africa or America, even though they're not very closely related, evolutionarily speaking.
Because we can see similarities between lizards that occupy similar niches in completely different places, summarizing and simplifying the idea of niche in this way might eventually help researchers to predict how different ecosystems will evolve as a result of climate change.
Simplifying the Structure
The researchers have used this lizard study to confirm that it may just be possible to simplify the idea of niche from hundreds of dimensions to just five. So, while we don't have an ecological periodic table just yet, perhaps it's not too far off.
"One of the greatest ecologists of all time, the late Robert H. MacArthur, expressed the periodic table of niches as a germ of an idea over half a century ago," says lead author Dr. Eric Pianka, professor of Integrative Biology in the College of Natural Sciences at the University of Texas at Austin. "It has taken the expertise of five of us to finish this analysis — it's been a lifetime goal."