Heat and biodiversity.

Since the time of Darwin, the latitudinal gradient of increasing species diversity from the poles to the equator has perplexed biologists and shaped ecological and evolutionary theories. A. P. Allen et al. present a model intended to explain this pattern “(Global biodiversity, biochemical kinetics, and the energetic-equivalence rule,” Reports, 30 Aug., p. [1545][1]). Their model is a formalization of the “species-energy hypothesis” and predicts that “biodiversity is positively correlated with productivity because more productive environments contain more individuals and can therefore support more species populations above some minimum size required for persistence” (p. 1547). The model predictions are consistent with patterns of increasing species number with increasing mean air or water temperatures for trees, amphibians, marine gastropods, fish, and fish parasites. In spite of its intuitive appeal, this model suffers from the two fundamental flaws of the species-energy hypothesis. First, “environmental energy” (in this model, mean temperature) does not correspond to the energy actually available to organisms, which is the energy stored in carbon compounds produced by photosynthesis. Although it is true that the tropics tend to be warmer than the temperate zone, higher temperatures do not necessarily result in higher productivity of plants or animals. The most extensive data set on the net primary productivity of plants compiled to date reveals that the mean annual productivity of tropical forests is the same as that of temperate forests ([1][2]). Marine productivity is much higher in the cold high-latitude oceans, where the world's great fisheries are located, than in the warmer tropics ([2][3]). Second, many of Earth's highest diversity areas have low productivity ([3][4]). Examples include the mediterranean climate shrublands of South Africa and Australia, which occur on poor soils with low primary productivity; the diversity of bird species with small range sizes in Africa, which is unrelated to net primary productivity ([4][5]); and the diversity of aquatic and marine phytoplankton, which is higher in unproductive, nutrient-poor environments than in productive environments. All of these patterns directly contradict the predictions of species-energy theory. Thus, it does not seem likely that a temperature-based species-energy model is the explanation for the latitudinal gradient of species diversity. 1. [↵][6]1. H.A. Mooney, 2. J. Roy, 3. B. Saugier 1. W. Cramer 2. et al. , in Terrestrial Global Productivity: Past, Present, and Future, H.A. Mooney, J. Roy, B. Saugier, Eds. (Academic Press, San Diego, CA, 2001), pp. 429-448. 2. [↵][7]1. M. J. Behrenfeld 2. et al. , Science 291, 2594 (2001). [OpenUrl][8][Abstract/FREE Full Text][9] 3. [↵][10]1. M. A. Huston , Biological Diversity: The Coexistence of Species on Changing Landscapes (Cambridge Univ. Press, Cambridge, 1994). 4. [↵][11]1. E. Ravasz, 2. A. L. Somera, 3. D. A. Mongru, 4. Z. N. Oltvai, 5. A.-L. Barabsi , Science 297, 1551 (2002). [OpenUrl][12][Abstract/FREE Full Text][13] # Response {#article-title-2} Huston seems to misinterpret both the substance and the intent of our Report. He suggests that our model is some version of the long-standing species-energy hypothesis and then criticizes it for “suffer[ing] from the two fundamental flaws” of this hypothesis. Huston correctly points out that temperature “does not correspond to the energy actually available to organisms.” Indeed, temperature indexes the average kinetic energy of molecules, not the potential for photons, organic compounds, and other energy and materials to be used by, and fluxed through, organisms and ecosystems. Temperature affects the rate of metabolism, but it is not the fuel for metabolism. Our paper argues that temperature affects biodiversity through its fundamental influence on the rates of biochemical reactions, whole-organism metabolism, and ecological interactions. The traditional species-energy hypothesis attributes species richness in large part to productivity, the rate of flux of biologically usable potential energy. Biodiversity is almost certainly influenced by both kinetics and productivity, but they are not the same thing. Huston is correct that in some cases, high species diversity occurs in cold or low-productivity environments. Temperature and productivity are often, but by no means always, correlated in nature, so it will be a challenge to understand their separate and interacting effects. Although the rate of biological production is powerfully constrained by temperature, it is also affected by other environmental variables—most notably by the supply of water and nutrients. The ability to predict the kinetic effects of temperature from a basic theoretical perspective should aid in understanding the other environmental factors and ecological processes that also affect biodiversity. Contrary to Huston's assertions, we do not claim that “a temperature-based species-energy model is the explanation for the latitudinal gradient of species diversity.” We do claim that the fundamental effect of temperature on rates of biological metabolism and ecological interactions must be an important component of any theory to explain the latitudinal and other major patterns of species diversity. [1]: /lookup/doi/10.1126/science.1072380 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #ref-4 [6]: #xref-ref-1-1 "View reference 1 in text" [7]: #xref-ref-2-1 "View reference 2 in text" [8]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DBehrenfeld%26rft.auinit1%253DM.%2BJ.%26rft.volume%253D291%26rft.issue%253D5513%26rft.spage%253D2594%26rft.epage%253D2597%26rft.atitle%253DBiospheric%2BPrimary%2BProduction%2BDuring%2Ban%2BENSO%2BTransition%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1055071%26rft_id%253Dinfo%253Apmid%252F11283369%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIyOTEvNTUxMy8yNTk0IjtzOjQ6ImF0b20iO3M6MjI6Ii9zY2kvMjk5LzU2MDYvNTEyLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ== [10]: #xref-ref-3-1 "View reference 3 in text" [11]: #xref-ref-4-1 "View reference 4 in text" [12]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DRavasz%26rft.auinit1%253DE.%26rft.volume%253D297%26rft.issue%253D5586%26rft.spage%253D1551%26rft.epage%253D1555%26rft.atitle%253DHierarchical%2BOrganization%2Bof%2BModularity%2Bin%2BMetabolic%2BNetworks%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1073374%26rft_id%253Dinfo%253Apmid%252F12202830%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [13]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIyOTcvNTU4Ni8xNTUxIjtzOjQ6ImF0b20iO3M6MjI6Ii9zY2kvMjk5LzU2MDYvNTEyLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==