An ecosystem is a biological community of interacting organisms and their physical environment. A healthy ecosystem includes multiple species that serve similar functions or roles – for example, more than one species that fertilizes the soil and more than one that controls the population of a certain predator. This redundancy is crucial to supporting the long-term stability of the ecosystem because natural disturbances – such as fires, disease, or changing climate – can sometimes eliminate entire species unable to survive the change. With redundancy in environmental function, if one species dies off, another species that serves a similar role is more likely able to react and thrive after the disturbance. It can then take the place of the previously dominant species, thereby keeping the ecosystem resilient.
For example, consider a situation in which a prairie grassland ecosystem’s main food-producing plant is completely destroyed by a fire. A plant species that was previously less abundant may now be better suited to live in the new soil conditions, and therefore become the new dominant food-producing plant species serving the grassland. As long as the post-fire composition of plant species fills the same functional role as the pre-fire plant community, then the prairie will be able to survive the fire intact.
2a. A high diversity system containing members that serve multiple, overlapping functional roles (shown along the bottom) may not be as productive in the short term, but show long-term stability and productivity. If there is any fluctuation in conditions (represented by the red shape in 2b), the conditions only impact a small portion of the system (2c). As a result, those changes only briefly affect productivity (2d) as the remaining members and replacement members continue to provide all ecosystem functions (2e).
Artist: Emily Harrington. Copyright: All rights reserved. See image in gallery for details.
“In other words, species diversity might support…the stability of ecological services over time. One of the few experiments to investigate this possibility was reported in 1996 by David Tilman of the University of Minnesota, St. Paul. Results of his eleven-year study in the prairie grasslands of the United States Midwest indicate that diversity stabilizes an ecosystem and its processes, but does so at the cost of the individual species that live in these communities.” Author provides a description of the study, ending with, “But when the work of one species is hampered by drought or other conditions, another species in a diverse and multi-talented community is likely to thrive and expand its activities. It is this ability of species to compensate for one another that allows the system as a whole to function steadily over the long term.” (Baskin 1997:24-25)
“More diverse communities have been shown to have higher and more temporally stable ecosystem functioning than less diverse ones, suggesting they should also have a consistently higher level of functioning over time. Diverse communities could maintain consistently high function because the species driving function change over time (functional turnover) or because they are more likely to contain key species with temporally stable functioning. Across 7 y in a large biodiversity experiment, we show that more diverse plant communities had consistently higher productivity, that is, a higher level of functioning over time. We identify the mechanism for this as turnover in the species driving biomass production; this was substantial, and species that were rare in some years became dominant and drove function in other years. Such high turnover allowed functionally more diverse communities to maintain high biomass over time and was associated with higher levels of complementarity effects in these communities. In contrast, turnover in communities composed of functionally similar species did not promote high biomass production over time. Thus, turnover in species promotes consistently high ecosystem function when it sustains functionally complementary interactions between species. Our results strongly reinforce the argument for conservation of high biodiversity.” (Allan et al. 2011:17034)