Navigation Links
Study challenges long-held assumption about competition in disturbed ecosystems
Date:6/28/2010

Hurricanes, wildfires and influxes of pollutants create disturbances that can put ecological systems under extreme stress. Ecologists had believed that at times like these, competition between species becomes less important as all struggle to survive.

But a new laboratory study of microscopic organisms subjected to varying degrees of acoustic disturbance now challenges that assumption and could lead ecologists to reconsider how organisms compete during challenging times.

"The consistent role of competition at all levels of disturbance found in our study underscores the need for ecologists to examine competitive interactions and their consequences even in highly disturbed habitats," said Lin Jiang, an assistant professor in the Georgia Tech School of Biology.

Sponsored by the National Science Foundation, the research was reported June 28, 2010, in the early online edition of the journal Proceedings of the National Academy of Sciences. The study is believed to be the first to show experimentally that competition could be a factor in regulating ecological communities regardless of the intensity or frequency of disturbance.

Jiang and his team -- Cyrille Violle, formerly a postdoctoral fellow at Georgia Tech currently at the University of Arizona, and Georgia Tech biology graduate student Zhichao Pu -- conducted experiments with freshwater bacterivorous protists in artificial, simplified ecosystems called microcosms.

"A key advantage of this microcosm system is that the rapid reproduction of the microorganisms allowed us to examine multigenerational community dynamics, including competitive exclusion and stable coexistence, in a period of a few weeks," said Jiang.

The researchers assessed the ability of different species of single-celled eukaryotes called protozoa to cope with disturbance in the absence of competition, the competitive ability of species in the absence of disturbance, and the role of competition between species under disturbance. Disturbance was imposed by the application of sound energy to the small ecosystems at 11 different levels, ranging from weak disturbances that had little effect on most species to strong disturbances that caused the direct extinction of most species.

First, the researchers placed all of the protist species in separate microcosms for one month and measured each species' change in population density to assess the ability of each to cope with disturbance. Next, the researchers assessed the competitive ability of species by compelling pairs of species to battle for resources for 10 weeks in the absence of disturbance.

The final set of experiments subjected groups of protist species to both disturbance and competition. The population densities of 11 species -- including three Paramecium species -- in each of 55 microcosms were recorded for five months. The results of the multi-species experiment showed that the number of species decreased with increased disturbance and that most species were no longer present across most levels of disturbance.

"One might think that the observed decline of species diversity with disturbance was because high levels of disturbances directly eliminated most or all species. But this idea was not supported by our first set of experiments, which showed that several species were able to sustain viable populations even at the highest disturbance intensities when they were not with other species," explained Jiang.

Instead, the species extinctions that occurred through different levels of disturbance could be partly attributed to competition between species. And the rate of extinctions attributable to competition was greater at higher levels of disturbance.

The findings contradict the intermediate disturbance hypothesis, which suggests that at high levels of disturbance, the species that survive will be those that are hardy under disturbed conditions. At low disturbance, the hypothesis suggests that the ecosystem will be dominated by species that are good competitors. At some intermediate disturbance level, the good competitors will have an opportunity to gain a foothold without being destroyed by disturbance, but will not be able to out-compete the hardier species or exclude less-fit species.

In this study, the 11 species differed markedly in their competitive ability and in their ability to tolerate disturbance. When considered together, there was a strong tradeoff between the two traits, according to Jiang.

"Each species was most vulnerable to inter-species competition at its upper disturbance limit, which is when its population density was the most severely reduced," noted Jiang.

While this study provided unique experimental evidence that competition can consistently regulate species extinction and community richness over broad disturbance gradients, three characteristics of this experiment may influence the applicability of these results to other systems, according to Jiang.

First, since the protist species in these experiments competed for shared food resources and affected each other by reducing the availability of those resources, these findings may not apply to communities competing in other ways, such as those physically or chemically fighting with each other. Second, there was no outside immigration into the experimental microcosms, unlike natural communities in which other organisms can join the competition.

Finally, given the size of the microcosms, disturbance in the experiments could be considered "global", which contrasts with the more common situation in nature where disturbance is heterogeneous over an area.

In the future, more attention should be focused on examining other mechanisms that may potentially contribute to intermediate disturbance hypothesis patterns, says Jiang.

"Our results challenge conventional thinking and have important implications for understanding relevant ecological issues, such as those related to biodiversity, community assembly and conservation," he added.


'/>"/>

Contact: Abby Vogel Robinson
abby@innovate.gatech.edu
404-385-3364
Georgia Institute of Technology Research News
Source:Eurekalert  

Related biology news :

1. Childhood obesity indicates greater risk of school absenteeism, Penn study reveals
2. A study by the MUHC and McGill University opens a new door to understanding cancer
3. Study begins to reveal clues to the cause and progression of sepsis
4. Clones on task serve greater good, evolutionary study shows
5. New study warns limited carbon market puts 20 percent of tropical forest at risk
6. New study examines how rearing environment can alter navigation
7. Study links cat disease to flame retardants in furniture and to pet food
8. New continent and species discovered in Atlantic study
9. Study shows link between alcohol consumption and hiv disease progression
10. Feeling hot, hot, hot: New study suggests ways to control fever-induced seizures
11. Study finds environmental tests help predict hospital-acquired Legionnaires disease risk
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Study challenges long-held assumption about competition in disturbed ecosystems
(Date:6/22/2016)... -- The American College of Medical Genetics and Genomics was once ... one of the fastest-growing trade shows during the Fastest 50 ... Las Vegas . Winners ... each of the following categories: net square feet of paid ... The 2015 ACMG Annual Meeting was ranked 23 out of ...
(Date:6/20/2016)... DALLAS , June 20, 2016 ... criminal justice technology solutions for public safety, investigation, ... by the prisons involved, it has secured the ... Corrections (DOC) facilities for Managed Access Systems (MAS) ... (4) additional facilities to be installed by October, ...
(Date:6/9/2016)... Paris Police Prefecture ... solution to ensure the safety of people and operations in ... major tournament Teleste, an international technology group specialised ... today that its video security solution will be utilised by ... public safety across the country. The system roll-out is scheduled ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... HOUSTON , June 23, 2016 ... agreement with the Cy-Fair Sports Association to serve ... of the agreement, Houston Methodist Willowbrook will provide ... education and connectivity with association coaches, volunteers, athletes ... partner with the Cy-Fair Sports Association and to ...
(Date:6/23/2016)... 23, 2016   EpiBiome , a precision microbiome ... in debt financing from Silicon Valley Bank (SVB). The ... to advance its drug development efforts, as well as ... "SVB has been an incredible strategic partner to ... traditional bank would provide," said Dr. Aeron Tynes ...
(Date:6/23/2016)... June 23, 2016 Apellis Pharmaceuticals, Inc. ... clinical trials of its complement C3 inhibitor, APL-2. ... multiple ascending dose studies designed to assess the ... subcutaneous injection in healthy adult volunteers. ... as a single dose (ranging from 45 to ...
(Date:6/23/2016)... ... June 23, 2016 , ... ClinCapture, the only free validated ... will showcase its product’s latest features from June 26 to June 30, 2016 ... on Disrupting Clinical Trials in The Cloud during the conference. DIA (Drug ...
Breaking Biology Technology: