What happens if we lose the elephants and other big beasties?


In contemporary time, thousands of species have gone extinct and tens of thousands of local populations have been extirpated as a consequence of human activities1,2. Although we sometimes possess detailed knowledge about their causes, we know much less about the consequences of these extinctions for ecological systems. Even in cases where extinctions result from the targeting of particular species (e.g., through trophy hunting), the effects of these extinctions can reverberate through food webs, yielding surprising consequences for community structure and ecosystem function. Our lack of understanding likely reflects the fact that the outcomes of species interactions (and thus extinctions) hinge strongly on variable biotic and abiotic factors. This variation occurs both locally within communities, and across more expansive spatiotemporal scales3. For example, when local communities are comprised of functionally redundant4 counterparts, compensation may offset any would-be consequences of extinction within the community5. As another example, regional variation in rainfall may cause changes in species abundances, thereby changing the strengths of species interactions among communities6. Recently, such conditional outcomes of species interactions have been identified as a critical theme at the forefront of ecology7. Understanding this context-dependence is almost certainly key to revealing and predicting the consequences of extinction for ecosystems7.


The long-term goal of our research program is to develop general rules8 for predicting the effects of vertebrate extinction on lower trophic levels, especially plants. Ecology is often conducted at restricted spatiotemporal scales, yet society requires answers to questions across landscapes or even continents. As such, extending our mechanistic understanding from experimental studies to the scales of landscapes is one of the principle challenges of modern ecology. Over the next 5-10 years, we expect our research program to shed light on how species interactions, with an explicit focus on vertebrate extinctions, change emergent patterns across ecological systems.


Specifically, we are studying how communities and ecosystems reorganize following the extinction of native, large mammalian herbivores (> 2kg; hereafter “LMH”) in African savannas. Our previous efforts have addressed the functional equivalence of native and introduced herbivores on the establishment of trees in savanna ecosystems9-11. One of our research foci is to understand how LMH affect demographic rates, abundance, and distribution of the genus Acacia, trees that drive nutrient cycling, fire frequency, and biodiversity within savannas12,13, 14, 15. Research to this end focuses on four processes that occur early in the life cycle of Acacia—pollination, seed production, germination, and seedling recruitment to saplings. These four processes comprise a “black box” in our knowledge of the drivers of savanna structure and function12,13.


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1.   Diamond, JM. 1984. Pgs 824-862 in Quaternary Extinctions, Martin and Klein.

  1. 2.  Ceballos, G and PR Ehrlich. 2002. Science 296:904-907.

  2. 3.  Brown, JH et al. 2001. Science 293:643-650.

  3. 4.  Walker, BH. 1992. Conserv. Biol. 6:18-23.

  4. 5.  Goheen, JR et al. 2005. Ecology 86:567-573.

  5. 6.  Ernest, SKM et al. 1999. Oikos 88:470-482.

  6. 7.  Agwaral, AA et al. 2007. Front. Ecol. Environ. 5:145-152.

  7. 8.  Knapp, AK et al. 2004. Front. Ecol. Environ. 2:483-491.

  8. 9.  Goheen, JR et al. 2004. Ecology 85:1555-1561.

  9. 10.Goheen, JR et al. 2007. J. Ecol. 95:129-138.

  10. 11.Goheen, JR et al. Submitted.

  11. 12.Scholes, RJ and SR Archer. 1997. Ann. Rev. Ecol. Syst. 28:517-544.

  12. 13.Midgley, JJ and WJ Bond. 2001. J. Trop. Ecol. 17:871-886.

  13. 14.Palmer, TM et al. 2008. Science 319:192-195.

  14. 15.Palmer, TM and AK Brody. 2007. Ecology 88:3004-3011

 

megafaunal loss in savannas