Posted on 7 February 2018
Scientists have long debated why some regions of the Earth, such as the tropics, have more species than other regions. Now an international team has, for the first time, tested all of the major hypotheses simultaneously and come up with an answer—time. In other words, groups of organisms that have occupied areas longer have more species because they have had more time to produce them. This conclusion goes against the prevailing thought in the fields of ecology and evolution that ecological factors—such as the interactions of species and their environment—primarily determine the diversity and distribution of species around the globe.
“Previous studies usually focus on one or two explanations” said Julie Marin, Research Assistant Professor at Temple University’s Center for Biodiversity and lead author of the work just published online in the Royal Society journal Proceedings B. “We found that the simplest explanation—time—was the winner when we evaluated the relative contribution of all of the previous suggested explanations, using data from 27,000 species of terrestrial vertebrates such as mammals, birds, reptiles, and amphibians.”
Although time is a simple concept, it is difficult information to obtain because the vast majority of species have no fossil record. Instead, these researchers used ‘timetrees,’ which are evolutionary trees scaled to geologic time, built from DNA sequence data. “Timetrees are accelerating research in many areas including this one,” said Blair Hedges, Carnell Professor and Director of the Center for Biodiversity at Temple University. “With these important data we could directly test the time hypothesis against the others.”
The researchers used statistical tests called ‘structural equation models’ to evaluate all of the different explanations at the same time. In the past, authors have suggested that speciation speeds up and slows down depending on ecological factors, leading to geographic differences in the number of species. Other authors have invoked dispersal, the movement of species from one region to another, as influencing species diversity. However, neither speciation rate nor dispersal were found to be as important as time in determining species diversity.
“Although time was the most important driver in explaining patterns of species diversity in terrestrial vertebrates, speciation rate and the indirect effects of ecological and environmental factors also were contributing factors,” said Marin.
The team included other researchers from Temple University (Matthew R. Helmus, Jocelyn E. Behm), and from the International Union for Conservation of Nature (Thomas M. Brooks), NatureServe (Giovanni Rapacciuolo, Bruce Young), Auburn University (Gabriel Costa), University of Wisconsin (Volker C. Radeloff), and Swiss Federal Institute for Forest, Snow, and Landscape (Catherine H. Graham).
Posted on 27 July 2017
Professor Hedges was invited to Oxford’s Bodleian Library in May to study the biology of a 900-year old book in pristine condition, along with other scientists and scholars. Some results were reported at the meeting and a news article on the event appeared in Science, with a video and podcast.
Posted on 22 October 2016
New images of destruction from Hurricane Matthew in southwest Haiti taken by the Haiti National Trust team.
On Monday (17 October) they flew over southwest Haiti to survey hurricane damage to the communities surrounding Grand Bois National Park, and took these images showing flooding still affecting communities in the region, with fallen trees and others stripped of leaves. The eye of the hurricane passed through this region where we work. Photos taken along the road near Port Salut also show the impact of the storm, with overturned cars and destroyed houses. Clearly many people in this area were affected and are without housing.
We can help rebuild permanent housing for members of the Grand Bois community who were displaced by the hurricane, with help from your donations.