Closely related groups can differ dramatically in their diversity, but why this happens is a fundamental question in evolutionary biology, dating back to Darwin's observation that a few hyper-diverse groups dominate the modern biota.
One of the most extreme examples of this observation is found in the comparison of rodents (Rodentia) and rabbits (Lagomorpha). These two mammalian orders are sister groups, but while rodents have diversified to over 2000 living species and an enormous range of body sizes, lagomorphs (rabbits, hares, and pikas) are limited to fewer than 100 relatively small species.
The front row from left shows: Mouse-deer (Field Museum of Natural History specimen no.68770), Andean mountain cavy (FMNH 53654), American pika (FMNH 12590), Alaskan hare (FMNH 9867). Back row shows: capybara (FMNH 79933).
Credit: Photo by S. Tomiya
A new study presented at the Society of Vertebrate Paleontology Annual Meeting shows, surprisingly, that competition with ungulates (hoofed mammals), intensified by climate change, are to blame for the lagomorphs' limited diversity.
Susumu Tomiya of the Field Museum of Natural History and Lauren Miller of the University of California at Berkeley were intrigued by the observation that lagomorphs have spread to all continents except Antarctica and inhabit a variety of environments, but the group contains only about 80 living species of small herbivores, compared to roughly 2,000 species of rodents.
According to Dr. Tomiya, "Mammalian groups that are ubiquitous at the global scale--rodents and bats, for example--tend to be species-rich and show many different ways of living. Lagomorphs are a paradox in this sense." Lagomorphs also show a much more limited range of body size and forms relative to rodents: the average weight of the largest living species (Alaskan hare) is approximately 5 kg (11 lb), whereas the largest living rodent (capybara) is twelve times larger at about 60 kg (133 lb).
Given that the two groups are each other's closest evolutionary relatives, and they have been evolving for roughly the same amount of time (~55 million years, give or take a few million years), the difference in their diversity is striking.
Importantly, fossils from Mediterranean islands show that lagomorphs are capable of becoming much larger than seen today. Nuralagus rex from the Pliocene of Minorca is estimated to have weighed about 12 kg. Ecologists and evolutionary biologists have suggested that such gigantism can take place only in absence of competitors, as is sometimes the case with island faunas.
They reasoned that, if competition were an important factor in determining body size evolution, the conspicuous absence of giant lagomorphs (by today's standards) on continents could be explained by long-standing presence of potential competitors, such as ungulates (e.g., horses, deer, cows, pigs, and their extinct relatives).
Tomiya and Miller tested this hypothesis by examining the rich North American fossil record. They compared the trajectories of maximum lagomorph body size and minimum ungulate body size over the last 30 million years, revealing two phases of body size evolution in lagomorphs. In the late Oligocene, the largest lagomorphs (comparable in body mass to medium-sized hares living today) coexisted with similar-sized and even smaller ungulates (some of which were as small as modern-day cottontails).
This body-size relationship was fundamentally altered following a major climatic transition that prompted opening-up of forests and establishment of grasslands in the early Miocene. For the next 20 million years or so, the maximum lagomorph size shifted in parallel with the minimum ungulate size, suggesting a dynamic body-size boundary between the two groups maintained by competitive interactions.
This study suggests that competitive interactions (and resulting division of resources that minimizes such interactions) may be a key factor determining diversification of mammals over millions of years. From a broader perspective, this study suggests that large-scale shifts in climate and available habitats can leave a long-lasting impact on the subsequent courses of evolution of major mammalian groups by altering their ecological interactions.
As Dr. Tomiya notes, "Much of the discussion about the current biodiversity crisis has revolved around saving species from extinctions. From a paleontological perspective, we believe that it is also important to think about the future of what will turn out to be surviving lineages, that is, how human activities are altering the courses of their evolution through modification of landscapes, seascapes, and atmosphere at the planetary scale. Millions of years from now, our own species may no longer exist, but whatever remains of life on Earth will reflect the decisions we make today about how we live as a species."
Miller, who measured modern lagomorph specimens to estimate body masses of extinct species, adds that natural history collections are crucial in this sense, "This study highlights the creative ways in which museum specimens can be used to provide data over a longer time sequence. Even something as seemingly old-fashioned as rabbit skins with handwritten weight measurements can be utilized with modern techniques to better understand current conditions and future trajectories of biodiversity."
About the Society of Vertebrate Paleontology
Founded in 1940 by thirty-four paleontologists, the Society now has more than 2,300 members representing professionals, students, artists, preparators, and others interested in VP. It is organized exclusively for educational and scientific purposes, with the object of advancing the science of vertebrate paleontology.
Society of Vertebrate Paleontology website: http://www.vertpaleo.org
Journal of Vertebrate Paleontology
The Journal of Vertebrate Paleontology (JVP) is the leading journal of professional vertebrate paleontology and the flagship publication of the Society. It was founded in 1980 by Dr. Jiri Zidek and publishes contributions on all aspects of vertebrate paleontology.
AUTHORS AND AFFILIATIONS:
Integrative Research and Collections Centers
Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, IL 60605-2496
Phone (office): (312) 665 – 7006
University of California, Berkeley
OTHER EXPERTS NOT ASSOCIATED WITH THIS STUDY
BRIAN KRAATZ, PhD
Department of Anatomy
Western University of Health Sciences
Pomona, CA 91766
ALISON BOYER, PhD
Research Assistant Professor
Department of Ecology and Evolutionary Biology
569 Dabney Hall
University of Tennessee
Knoxville, TN 37996
Anthony Friscia | EurekAlert!
GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center
Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy