Extinctions Drive Ongoing 'Ecological Retreat' By Surviving Species
May 26, 2012

Extinctions Drive Ongoing ‘Ecological Retreat’ By Surviving Species

Brett Smith for Redorbit.com

A new study on the extinctions of species suggests that the disappearance of one species does not necessarily allow remaining competitor species to thrive by filling in the vacuum.

University of Cincinnati researchers studying lemur extinctions over the past 2,000 years, found that changes in inter-species dynamics via extinction can force that remaining species to go into a so-called “ecological retreat” that may not be suited to the extant animal´s evolution.

The study, published in the online edition of the Proceedings of the Royal Society B, said radiocarbon and isotope analysis from fossils of extinct lemur species showed the type of habitat in which the primates lived, what they ate, when they became extinct and whether other still-extant species vacated their environmental habitats.

The UC research team, led by Brooke Crowley, was able to show that prior to extensive human interruption, lemurs inhabited the woody savannah and spiny thicket found in southwestern Madagascar. Today, the island nation´s lemurs exist primarily in protected areas of thick forest.

“The reasons behind the increased reliance on densely forested habitats are uncertain, but it´s likely that low hunting and logging pressures in forest reserves are contributing factors,” said Crowley, assistant professor of anthropology and geology at the university.

Interestingly, after the larger-sized lemurs that once inhabited those regions went extinct, their smaller counterparts could not fill the empty niches that were left behind. Instead, contemporary lemur species have shown increasing reliance on habitats with dense forest cover.

“It´s been assumed that lemurs were in the forests because that´s where the resources that best suited them were,” Crowley said.

“Our fossil analysis shows that lemur species once preferred a much wider, more distinctive habitat range, which may mean that modern lemurs prefer the densely forested areas simply because these areas offer greater protection. The forest is more of a refuge.”

Crowley noted that while forested areas have had some human disturbance, the unprotected open areas where lemur species once flourished have seen even greater disturbances. In addition to the usual encroachments of civilization, the Madagascar countryside has likely seen the effects of political and military instability with the country on the brink of civil war many times during the past decade.

The UC team´s findings could explain why some other researchers previously reported finding inconsistencies between the extant lemur species´ anatomy and their observed behavior in the dense forest environments. These mismatches could be indications that today´s lemurs are in retreat and at greater risk because they are not living in their preferred habitats.

“In other words,” explained Crowley, “We now have long-term historical data, a broadened historical perspective indicating that what lemurs are doing today — preferring densely forested areas — is not representative of their ecological niche over past millennia. That´s an indication that we need to rethink our assumptions on their current habitat choices and on our own conservation efforts. And this form of historically informed research can also be applied to other locales and animals to benefit threatened species.”

Crowley laid the groundwork for this study with her previous research involving radioactive isotope techniques and applications in the course of primate study. Her findings were published last year in the International Journal of Primatology.