“Elephants can’t cross oceans.”
The focus of the paper is determining if dispersal limitations constrain the range limits of a species rather than the abiotic and biotic conditions of an area. This allows for a better understanding of the drivers of species distributions and traits that limit the range expansion. Transplant experiments and Ecological Niche models are used to examine if the range limits are also the niche limits of a species. If both of these approaches are appropriately designed, they should give very similar results to if the range limits are the same as the niche limits. It is expected that both the studies and models would have a decline in fitness and suitability measures across the range limits (Featured Image). However, if the species range is dispersal limited, there is no change in these two measures across the limits. In the study, the authors surveyed the results of transplant studies of 40 species and built the ENM for each species (using MaxEnt). To compare the results of each and determine if there is a decline in fitness and suitability across range limits, they generated linear mixed-effects models (independently).
For most species, a decline in fitness and suitability from sites inside the range to outside the range. However, overall there is a decline in both measures from sites inside to outside the limit. The authors highlight that these results support that the range limits of a species is also often the niche limit. Further, the dispersal of a species does not the range limit. Also, the authors point out that better designs of transplant experiments and ENM along with the combination of the two methods would lead to a better understanding if the range limit of a species is also the niche limit of the species.
The authors close by pointing out that outside influences (such as human interactions and dispersal limits) may cause the range limit to a subset of the niche limit.
Lee-Yaw, J. A., Kharouba, H. M., Bontrager, M., Mahony, C., Csergő, A. M., Noreen, A. M. E., Li, Q., Schuster, R. & Angert, A. L. 2016 A synthesis of transplant experiments and ecological niche models suggests that range limits are often niche limits. Ecol. Lett. (doi:10.1111/ele.12604)