A version of this post has also been published as an online comment in PLoS Biology
In his recent meta-analysis, “Climate-Related Local Extinctions Are Already Widespread among Plant and Animal Species“, Wiens looked at changes in species ranges and local extinctions driven by climate change.
Wiens claims to have broad taxonomic and geographic coverage of studies. Unfortunately, this is not the case. In fact, from the true tropics (i.e., excluding studies from the Santa Catalina Mountains of Arizona, USA, the Appalachian Mountains of north Georgia, USA, and the high eastern Himalayas that Wiens categorizes as “tropical” for the purposes of his analyses), only 5 studies representing a total of just 341 species (35% of species, 18% of studies) are included. All but one of these tropical studies (of 55 Andean bird species) are from oceanic islands (Borneo [insects], New Guinea [birds], Madagascar [amphibians], and Hawaii [plants]). All tropical plants are represented by just 4 grasses in Hawaii.
The lack of data from the tropics is not Wiens’ fault but rather reflects a true underlying disparity in the state of knowledge about different systems of the world. Simply put, we know much more about the effects of climate change in North America and Europe than we do the effects of climate change in the tropics. That said, Wiens needs to be more forthright in acknowledging this disparity. Furthermore, given this extreme lack of data, it is clearly premature to conclude that “there were significant effects of climatic region overall, with extinction more common in tropical regions” and that “this pattern of more frequent tropical extinction arose from a much lower frequency of extinctions for temperate plants”. Four grasses from Hawaii tell us next to nothing about how the thousands of tropical plants are responding to climate change. Or even if we lump the tropics and subtropics together as does Wiens, 4 grasses from Hawaii, 27 mountain desert plants from Arizona and 124 high-elevation Himalayan plant species (all with ranges restricted to elevations >3500 m asl) provide little information about how the thousands of other tropical and subtropical plants are responding to climate change. The tropical data void is real and it is troublesome (Feeley et al. 2016a,b). But before we can begin to address this lack of data it needs to be acknowledged and recognized for the problem that it is.
Wiens JJ. 2016. Climate-Related Local Extinctions Are Already Widespread among Plant and Animal Species. PLOS Biology 14(12): e2001104. doi: 10.1371/journal.pbio.2001104
Feeley KJ, Stroud JT, and Perez TM. 2016. Most “global” reviews of species’ responses to climate change aren’t truly global. Diversity and Distributions. In Press.
Feeley KJ, Silman M, and Duque A. 2016. Where are the tropical plants? A call for better inclusion of tropical plants in studies investigating and predicting the impacts of climate change. Frontiers of Biogeography. 7(4). fb_27602.