Conservationists predict massive extinctions as a result of habitat loss. Habitat loss undoubtedly does drive extinctions, but dealing with an unmet assumption that underlies these predictions yields much lower estimates. See Letter p.368
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Rahbek, C., Colwell, R. Species loss revisited. Nature 473, 288–289 (2011). https://doi.org/10.1038/473288a
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DOI: https://doi.org/10.1038/473288a
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This is a highly unfortunate outcome for conservation science and not because of the great research that He and Hubbell just published. It is unfortunate because their is undue focus and attention on species loss as the core of our problems. Scientists have a responsibility to fix a mistake that has plagued conservationists for too long – our psychological myopia that overemphasizes priority toward unique species units over the common regularity that is inherent in biodiversity. The biodiversity crisis is not just about species, but the loss of ecosystems services via homogenization and ecological transformations stemming from human niche constructing behaviour and the ecologically destructive feedback loops this generates.
It doesn't take a grand calculation or an elegant formula to look at the evidence and conclude that there is a biodiversity crisis going on. An experiment in its most general sense is any measurement. Taking a moment to browse through GoogleEarth you can immediately gather data on the human footprint – you can measure the spatial extent of our land conversion from roads and other pieces of infrastructure that acts as an ecological sealant plus the added impact of forestry clear-cuts and agricultural lands. The species that lived in these spaces may very well remain in adjacent patches – in fact most species outside of the tropics are widely distributed and highly unlikely to go extinct under these circumstances. Still, however, this does not mean that there is no effect on the biodiversity. Biomass is diminished, trophic states are altered, and ecological services are diminished in scale. Perhaps researchers like He and Hubbell are so fixated on the complexity of the species problem that they are missing the obvious point to this biodiversity crisis?
The problem is simple. If you have several billion salamanders of a single species regulating soil and wetland communities that are responsible for the recycling of nutrients through these ecosystems, for example, it matters if you reduce that species down to a few thousand individuals in scattered populations. The species still exists, but the functional regulations are diminished. Trophic cascades can in turn can lead to such things as reduced forestry yields or climate change via the decreased rates of nutrient flow and increased rates of heterotrophic decay releasing CO2 into the atmosphere. What difference does it make if the species still exists or not? It makes a huge difference social-ecologically to have diminished biodiversity in our human constructed environments. School grounds, for example, lack the complexity of nature and are most often stripped down to grass, pavement, and a few metal bars for kids to swing on. How on Earth can these children receive proper mental development without being inundated by the complexity of life? Where will their conservation ethics develop? This process of ecological apartheid separating communities from wild nature takes the wealth and capital of ecology out of the common wealth economy. This problem has very little to do with species extinctions and almost everything to do with population loss, not to mention the mass extinction of migration routes (http://www.plosbiology.org/....
The resilience of the system is what matters and we know that ecosystems have multi-dimensional and dynamic states that can fluctuate in the face of disturbance but shift once criticality has been exceeded. These ecologically resilient 'phase-shifts' tend to homogenize ecosystems, reduce global net or scalar levels of productivity, and diminish future resilience capacity as levels of human disturbance will not let up. I am firmly convinced that the notion of an endangered species as a conservation tool has had a devastating effect on conservation efforts – because it puts way too much emphasis on one piece of the biodiversity puzzle. Peter Kareiva and Michelle Marvier called attention to this in their 2003 article in American Scientist on "Conserving biodiversity coldspots" (http://www.bren.ucsb.edu/ac... and have followed up on the economic prioritization myth surrounding biodiversity hotspots. The mass of research and conservation funds are being directed toward the conservation and preservation of endangered species, which makes no sense in light of prioritizing the ecology of this problem. Ceballos and Ehrlich (2002) touched on this in their article in Science on "Mammal population losses and the extinction crisis", where they stated:
"Most analyses of the current loss of biodiversity emphasize species extinctions (3?5) and patterns of species decline (6?8) and do not convey the true extent of the depletion of humanity's natural capital. To measure that depletion, we need to analyze extinctions of both populations and species."
I would add that we also need to put the extinctions of migration and evolutionary potential into this equation as well. It is time for researchers who report on these issues to de-emphasize the species level connection. He and Hubbell attempt to do this by raising the importance of habitat loss. However, their statements on this seem inadequate because the underlying emphasis is still geared toward species loss. Researchers have a responsibility to properly report on the Anthropocene extinction by including the dynamic and hierarchical fabric of life into their reports. Extinction is more complicated and more rampant than is being reported herein and this is highly unfortunate.