When I first started teaching at Lincoln University in New Zealand, one of my colleague, Jon Sullivan, had a lecture entitled “Where the wild things are”. Jon had a talent to find attractive names for his lectures and I was always worried that I could never come up with such exciting titles and that students would probably desert my lectures as a result.
This particular lecture was an introduction to biodiversity, with some island biogeography concepts and natural history of recently discovered and very weird life forms like photosynthetic salamanders or infrared chlorophyll. It was aimed at second year students, to capture their interest, show them that there were exciting animals and plants being discovered everyday and convince them to stick to ecology courses (rather than tourism or landscape architecture).
But the title itself “where the wild things are” was also a great example of an ecological question that has withstand the curiosity of scientists and remains in part unresolved. First there is a huge number of species that we have not discovered yet and which may be lurking around in the Amazonian forest, on the ocean floor, or underground in your backyard. The latter was certainly true in New Zealand. But there are also lots of species that we know are there, but for which we may only have a limited idea of their exact distribution. Yes, we know that pandas live in China and bold eagles can be found throughout most of North America. But within their distribution range, where exactly are most plants and animals found?
This question has important implications for the conservation of endangered species. Because if resources are limited, as they usually are, you may want to focus conservation efforts in the most densely populated area. One somewhat intuitive hypothesis is that organisms are more abundant in the centre of their geographic range or climatic niche. Of course this idea does not always hold true. For king penguins the centre of their range would be located near the South pole, few thousand kilometres away from the sea, where these birds feed. But for most species, finding more organisms in the centre of their range or niche seems legitimate.
Dallas et al. (2018) used census datasets for 1,400 species of birds, mammals and trees, to test this hypothesis. They could not detect significant correlations between population density and distance to the centre of species’ distributions. Thus, they concluded that species are not most abundant in the centre of their geographic range or climatic niche. In a response paper published in Rethinking Ecology, Soberón et al. (2018) exposed four methodological issues that may have impacted the results of Dallas et al. Namely, Soberón et al. point to incomplete and potentially inaccurate census data, difference in resolution between the geographical coordinates of species data and those of climate data and a method for calculating the centre of species’ distributions which was not optimal.
So what does it all mean? Well, probably that we are still not sure where most of the wild things are and that Jon can keep the title of his lecture as a great example of a long lasting question yet to be answered and exciting discoveries yet to be made by future ecologists.
Dallas T, Decker RR, Hastings A (2017) Species are not most abundant in the centre of their geographic range or climatic niche. Ecology Letters 20: 1526–1533. https://doi.org/10.1111/ele.12860
Soberón J, Peterson TA, Osorio-Olvera L (2018) A comment on “Species are not most abundant in the centre of their geographic range or climatic niche”. Rethinking Ecology 3: 13-18. https://doi.org/10.3897/rethinkingecology.3.24827
