|This phylogenetic tree of life was created by David Hillis, Derreck Zwickil and Robin Gutell. It depicts the evolutionary relationships of about 3,000 species throughout the Tree of Life. Less than 1 percent of all the known species. Download the pdf from the Hillis Lab.|
It has been established that the current rate of species extinction has far outpaced those rates we see in the fossil record. By "far outpaced," we're talking about a sixth mass extinction within 240 years (that's the projection as of now at least). There have been hundreds of experiments that have tackled this question of biodiversity and ecosystem processes, particularly in plant systems. Take a big statistical spoon and mix all the experiments together and you find that the loss of plant biodiversity affects biomass production and decomposition. Experiments to manipulate biodiversity in controlled environments have actually found that biodiversity can act as an independent variable that directly controls such ecosystem functions as nutrient cycling and biomass production. Studies have shown that greater biodiversity also increases these effects over time, likely by either a saturating response curve (large increases in ecosystem functioning as species are added to communities, leveling off after a while, with any additional species only increasing ecosystem functioning by small amounts) or a linear response curve (think: straight[er] line). These temporal aspects of diversity-productivity relationships are still somewhat obscure, particularly the mechanisms of these changes over time. Now add global climate change. It is uncertain the sizes these effects will be and how the direct effects of other types of environmental change (like atmospheric composition, nutrient pollution, etc.) will affect ecosystem functioning.
So far the month of May has yielded some big, interesting papers on the impacts of biodiversity loss. A paper by Peter Reich et al. in Science takes a look at the time component of biodiversity loss and how it affects the growth curves I mentioned above. In this paper, the authors present data from two long-running (≥13 years) grassland biodiversity experiments at the National Science Foundation's (NSF) Cedar Creek Long-Term Ecological Research (LTER) site in Minnesota, USA: the “Cedar Creek Biodiversity Experiment” (BioDIV), planted in 1994–1995, and the “Biodiversity, CO2, and N Experiment” (BioCON), planted in 1997. At these sites a number of plots are planted with different numbers of species of plants including various C3 and C4 plants and nitrogen (N)-fixing and non-fixing dicotyledonous herbs. The authors looked at the effects of diversity on biomass productivity and found that productivity (aboveground and belowground) increased and became less saturating over time; the diversity-productivity relationship became more linear and less strongly decelerating over time. Their evidence suggests that this may be due to the accumulating effects of complementary resource acquisitions and use and such ecosystem feedback effects as soil N cycling. Basically, the plants are complementing each other, increasing the functional diversity of the system. The greater the diversity of plants the more natural components (carbon, water, etc.) of the system can be capitalized on over time, a result that short-term experiments may underestimate.
|The Cedar Creek LTER site (Credit: David Tilman, UMN)|
|Figure from Cardinale (2012)|
I hope I've made my point that biodiversity = good, extinction = bad, and climate change = worse. I also hope I (and these authors) made the case that the loss of biodiversity isn't just a consequence but rather a major driver in key processes that affect our planet. Think about it.
You can read more in the articles:
Reich, P., Tilman, D., Isbell, F., Mueller, K., Hobbie, S., Flynn, D., & Eisenhauer, N. (2012). Impacts of Biodiversity Loss Escalate Through Time as Redundancy Fades Science, 336 (6081), 589-592 DOI: 10.1126/science.1217909
Cardinale, B. (2012). Impacts of Biodiversity Loss Science, 336 (6081), 552-553 DOI: 10.1126/science.1222102
Hooper, D., Adair, E., Cardinale, B., Byrnes, J., Hungate, B., Matulich, K., Gonzalez, A., Duffy, J., Gamfeldt, L., & O’Connor, M. (2012). A global synthesis reveals biodiversity loss as a major driver of ecosystem change Nature DOI: 10.1038/nature11118
Cardinale, B. (2011). Biodiversity improves water quality through niche partitioning Nature, 472 (7341), 86-89 DOI: 10.1038/nature09904
And here are some additional write-ups:
NSF story "Ecosystem Effects of Biodiversity Loss Rival Climate Change and Pollution"
NSF story "Plant Diversity Is Key to Maintaining Productive Vegetation" also at Science Daily
And some related websites you may want to visit:
Cedar Creak LTER site