Dragonfly Study Shows How Ecosystem Changes Affect Biodiversity

April Flowers for redOrbit.com – Your Universe Online

Rice University researchers have found that communities in nature are likely to be a lot more sensitive to change than previously thought.

The study findings, published in Nature Communications, points to a need for scientists concerned with human impact on the biosphere to take a different look at the consequences of altering the dynamics of a population. One example of such alteration would be removing large members of a species through overfishing, according to Rice ecologist Volker Rudolph.

“Natural communities are increasingly altered through human impact, and ecologists have long strived to determine how these changes influence communities,” Rudolf said. Rudolph also noted the disappearance of a species is the most extreme cause of biodiversity loss, but not the only one.

“That’s the last thing that happens after you mess up the entire ecosystem for a long period of time,” he said. By the time a species disappears entirely, changes forced upon the structure of a population — such as the ratio of young to old in a species — have already been felt up and down the food chain.

Species play various roles in the environment, Rudolf suspects, and their effects on the environment change as they progress through their life cycles, to the degree that altering these life “stages” within a species could have a significant impact. To prove this theory, he enlisted the help of Rice graduate student Nick Rasmussen.

The researchers chose dragonflies and water-diving beetles as representative of species that have major impacts on their respective communities — in this case, fishless ponds. The team created dozens of miniature environments to analyze that impact, and then they manipulated the presence of different developmental stages within a predator species in each pond. This helped the researchers determine that such changes did alter the dynamics of complex ecosystems in a measurable way.

“Other than being the largest and most voracious predators in these communities, they’re totally different,” Rudolf said of the apex predators. “We figured if we saw any generalities across these two species, then there’s something to our theory.”

The team found that the structure of the entire community and how the whole ecosystem functioned could be altered by changing which classes of size were present in a population. Rudolf also found it important that changing the structure of populations sometimes had bigger effects on the ecosystem than changing the predator species.

The results, he said, “challenge classical assumptions and studies that say we can make predictions by assuming that all individuals of a species are the same. You don’t expect a toddler to do the same thing as a grownup, and the same is the case for animals.”

The study might also explain the reason why some human activities, such as size-selective harvesting, can alter the structure of entire food webs in some ocean systems. Rudolf said that this happens even when no species had gone extinct and the total biomass of the targeted fish remained the same.

“While these changes would be hard to predict by the classical approach, our results suggests such changes are expected when human activities alter the population structure of keystone species in an ecosystem,” Rudolf said. “Thus, natural ecosystems are likely to be much more fragile then we previously thought.”

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