These Brazilian primates are critically endangered, but in the past 30 years a population on a private reserve has grown from just 60 individuals to some 300, now comprising almost a third of the total remaining animals.
As the population grows, though, it is offering researchers a glimpse into a new phase of recovery as it begins to face the limitations of its habitat. A recent analysis of the factors contributing to this population's tremendous growth reveals surprising trends that raise new questions about conservation, recovery and what constitutes a healthy population.
University of Wisconsin–Madison anthropologist Karen Strier has led observational field studies of this muriqui population for 30 years, meticulously charting demographics and life history of hundreds of individual monkeys. An analysis, published Sept. 17 in the journal PLOS ONE with UW–Madison mathematical ecologist Anthony Ives, provides the most comprehensive, quantitative look to date at long-term demographic trends and the role of individual features such as fertility, mortality, and sex ratios.
The researchers used statistical models designed to handle multiple levels of data so they could construct a comprehensive view of the population while still accounting for variation among individual animals. The approach allowed them to identify specific demographic trends and their effects on the overall population size.
"By separating out these components we were able to see the patterns in the data," Strier says, many of which were unexpected. For example, the analyses revealed increases in both fertility and mortality – a surprising combination, especially in a population that is still growing. In addition, they documented a remarkable and unexplained shift in infant birth sex ratios from about one-third male to two-thirds male in just 28 years.
"It is an analysis that leads to more questions than answers," Ives says. A birth rate that continues to grow as the population expands flies in the face of most ecological thinking, he says, since demand for resources by larger populations usually reduces fertility. But without the observed fertility increases, the muriqui population would likely have plateaued around 200 individuals; instead, it has reached 300 and is still growing.
Strier believes the trends may be driven by behavioral changes. Though muriquis are typically arboreal animals, her field team has observed increased use of the ground – first for drinking and eating, then gradually for traveling, playing, and even mating. These data are still qualitative, but she suspects this behavioral innovation could help explain the rises in both fertility and mortality. The ground expands the monkeys' pool of available habitat and food resources but exposes them to additional dangers as well.
"On the ground, there are risks. We suspect there may be more pathogenic risks, and we know there are more predators," she says. Supporting a connection, mortality increased primarily in prime-aged males, who spend more time on the ground than females. "I've always thought it was increasing population size that was driving this increasing use of the ground, but never thought about what the potential consequences of the use of the ground might be for the population's rate of growth," she adds.
The apparent interactions between demography and behavior emphasize the need for ongoing population monitoring, Strier says. Her long-term study, in collaboration with Brazilian colleagues including biologist Sergio Mendes of the Universidade Federal do Espirito Santo, is showing that assumptions about population dynamics based on past observations may not hold true in the future.
Ives views the results as a cautionary tale for other threatened and endangered species, the vast majority of which are not monitored anywhere near as closely as Strier's muriquis.
"From the conservation standpoint I think a main message is, don't presume that the demographics will respond in a 'normal' way," he says. "Even if an area is protected you need to have a close gauge on what's going on. Protecting an area is not necessarily protecting a species."
Strier agrees that the analysis raises important questions about environmental carrying capacity – basically, how large of a population a habitat can support. "How long will it be able to grow, and if it does continue to grow, is it in danger of crashing?" she asks.
These are critical questions when considering management decisions, she adds, especially given that her study population represents a third of the entire muriqui species. On paper, population growth alone can look like success, but their demographic analysis reveals early indications of stress even as the population continues to expand.
At the same time, Strier says, their studies suggest a solution. "We know exactly what we need to do to alleviate it – expand the area, and there is area to expand the forest into. In a world with so many unsolvable problems, this seems like a solvable one."
Jill Sakai, (608) 262-9772, email@example.com
Note: Images to accompany this story are available at http://www.news.wisc.edu/newsphotos/strier-monkeys.html
Contact: Karen Strier, (608) 262-0302, firstname.lastname@example.org; Anthony Ives, (608) 262-1519, email@example.com
Karen Strier | EurekAlert!
Preservation of floodplains is flood protection
27.09.2017 | Technische Universität München
Conservationists are sounding the alarm: parrots much more threatened than assumed
15.09.2017 | Justus-Liebig-Universität Gießen
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
19.10.2017 | Materials Sciences
19.10.2017 | Materials Sciences
19.10.2017 | Physics and Astronomy