Is there such a thing as too much good habitat?


It may seem obvious that for an endangered species, more habitat is better.

But scientists who study giant pandas in the mountain bamboo forests of central China say a close examination of the animals’ genetic profiles suggests this is not always the case.

The findings have implications for how conservation scientists think about what goals to set for habitat protection or restoration to be effective, says Thomas Connor, ecologist and postdoctoral student at the University of California, Berkeley, who led the research.

“I think the results suggest that we should probably move away from that kind of maximalist view of either trying to totally reduce habitat fragmentation or trying to absolutely restore wilderness or habitat to 100. percent, “said Connor, who conducted the research while earning a doctorate from Michigan State University (MSU).

The destruction of habitat by humans is often blamed for decline and extinction of cash in the middle of the sixth great extinction event in Earth history. But there is disagreement among scientists over the details of how changing habitat conditions influence the health of a species.

Generally, the more animals of a species mix and avoid being cut off from potential mates, the greater the genetic diversity within a population and the lower the risk of inbreeding. But does pristine habitat best promote gene flow? And is there a threshold at which habitat loss begins to take its toll?

Pandas offer a potential test case to answer these questions. The charismatic black and white bears are picky about their habitat, living only in the bamboo forests of central China. There, hunting and deforestation have reduced populations to around 2,000 animals. Although their numbers are on the rise, they are still considered “vulnerable” due to their relatively low numbers, the fragmentation of their habitat and the threat climate change poses to bamboo forests, according to the Union. International for Nature Conservation.

Thus, a team of scientists under the supervision of Jianguo “Jack” Liu of MSU, a sustainability scientist decorated, investigated how gene flow was influenced by variations in habitat conditions in the 2,000 square kilometer Wolong Nature Reserve in China.

To do this, the teams spent two years scouring the forest for fresh panda droppings. By studying the DNA in the feces, scientists identified 142 individual pandas, traced their parentage, and looked for signs of inbreeding. The researchers then superimposed this genetic map on a detailed computer model of habitat conditions in the reserve. Statistical analysis explored how the amount of panda habitat and different landscape features – rugged cliffs, roads, farmland, villages, and other interruptions in the forest – correlated with how DNA varied from bear to bear. the other.

Surprisingly, the results showed that the greatest genetic diversity did not occur where the bamboo forest was fully intact and continuous. On the contrary, gene flow among bears appeared to peak in places where about 80% of an area was prime habitat for bears, according to the results. published on September 20 in the review Conservation biology.

The results do not answer why this is happening. But Connor suspects bears in an uninterrupted habitat might have such comfortable lives that there is little incentive to roam. Those stay-at-home bears would be less likely to seek out other habitats and meet mates along the way. “They don’t really have to (move) until there’s a certain level of not being able to support these people here,” says Connor. “This kind of forced dispersal is what drove the gene flow.”

The researchers note that the right habitat for growing populations can also force animals to search for new homes. It is not clear whether pandas densities were too low to trigger this behavior at peak habitat levels.

Connor warns that the habitat conditions that maximize gene flow will not be the same for different species, or even for other populations of pandas. But he believes the results could mean that a variety of species – not just pandas – can thrive even with damaged habitat. That, says Connor, could be a good thing. “I really hope this will be some kind of a message of hope,” says Connor. “Environmental groups that do restoration are not going to completely write off areas that seem impractical to revert to pristine conditions.”

Connor, Et. Al. “Complex effects of habitat quantity and fragmentation on functional connectivity and inbreeding in a population of giant pandas. ” Conservation biology. September 20, 2021.

Photo courtesy of Jindong Zhang, Michigan State University


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