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 d
|Contact: Abby Vogel Robinson|
Georgia Institute of Technology Research News