Biodivers Conserv (2015) 24:705–706 DOI 10.1007/s10531-014-0839-7 LETTER TO THE EDITOR
Biodiversity trends are as bad as expected Anne Teysse`dre • Alexandre Robert
Received: 8 October 2014 / Revised: 20 October 2014 / Accepted: 31 October 2014 / Published online: 8 November 2014 Ó Springer Science+Business Media Dordrecht 2014
In a recent work published in Science, Dornelas et al. (2014) analyzed a large sample of local biodiversity time series, involving more than 35,000 terrestrial and aquatic species from biomes across Earth. Their analysis revealed a systematic change in local community composition and a net biodiversity loss at the global scale. However, the authors were surprised by the absence of negative trend of biodiversity at local scale. We think that Dornelas et al.’s work is very important to the field of biodiversity conservation, not because their last result is contrary to expectations (as stated by the authors), but because their combined results confirm that the scientific community has an accurate understanding of the effects of ongoing anthropogenic pressures on biodiversity processes and patterns. According to the ecological niche theory (Hutchinson 1957; Futuyma and Moreno 1988), massive habitat changes driven by human activities should favor the expansion of (regional and exotic) generalist species, and specialists of Human-altered habitats, while reducing the fitness and range of many species specialized to the ‘‘old’’ disappearing habitats (along with their specific hosts, symbionts and parasites). From the local to the global scale, these two opposed trends should result in a functional and taxonomic homogenization of communities (as defined in Olden et al. 2004). This theoretical expectation was confirmed by tracking temporal changes in average habitat specialization of species at the community level (Clavel et al. 2011). At the local and regional scales, theory and modeling indicate that habitat disturbance (Devictor and Robert 2009), permanent changes of habitats into habitats of lower carrying capacity (Teysse`dre and Robert 2014), and high dispersal rates between biogeographical provinces (Rosenzweig 2001; Teysse`dre and Robert 2014) are expected to increase species richness—until a certain level of habitat modification—as observed in the field (e.g., Sax
Communicated by David Hawksworth. A. Teysse`dre (&) A. Robert Centre d’Ecologie et Sciences de la Conservation (CESCO), Muse´um National d’Histoire Naturelle, Paris, France e-mail:
[email protected]
123
706
Biodivers Conserv (2015) 24:705–706
and Gaines 2003) and confirmed by Dornelas et al. (2014)’s study. Stated shortly, local (a) biodiversity should systematically increase in moderately modified habitats, in which different ecological categories of species (e.g., old habitat specialists, generalists or/and human-altered habitat specialists) have similar fitness and can coexist regionally, depending on dispersal rates. More generally, local biodiversity increases where the colonization by specialists of the new habitats (e.g., nitrogen-rich soils) and by generalist species locally exceeds, in number of species, the loss of old habitat specialists. This local pattern is expected to be frequent in the context of global change since local colonization events rapidly translate into an increase of the species richness measured at that scale, whereas the local or regional extinction of declining species is a long process (e.g., Tilman et al. 1994). At the global scale, these community dynamics lead to a net loss of specialist species, formerly involved in complex ecological webs. A potential risk arising from Dornelas et al.’s assertion that there is surprisingly no systematic loss of local biodiversity is that their results may be interpreted and transmitted (to the general public and decision makers) as an optimistic message about the «resilience of biodiversity», suggesting that the local biodiversity changes currently observed worldwide have no consequences at the global scale (see for instance http://www.scientificamerican.com/podcast/episode/biodiversitysurvives-extinctions-for-now1/), which is obviously wrong and misleading. These changes are associated with numerous ongoing extinction events and rapid genetic and functional losses (e.g., Dirzo et al. 2014, Galetti et al. 2013, Mooney et al. 2009) at the local and global scales, which are not accurately diagnosed by taxonomic-based indicators.
References Clavel J, Julliard R, Devictor V (2011) Worldwide decline of specialist species: toward a global functional homogenization? Front Ecol Environ 9:222–228 Devictor V, Robert A (2009) Measuring community responses to large-scale disturbance in conservation biogeography. Divers Distrib 15:122–130 Dirzo R, Young HS, Galetti M et al (2014) Defaunation in the Anthropocene. Science 345:401–406 Dornelas M, Gotelli NJ, McGill B et al (2014) Assemblage time series reveal biodiversity change but not systematic loss. Science 344:296–299 Futuyma DJ, Moreno J (1988) The evolution of ecological specialization. Ann Rev Ecol Syst 19:207–233 Galetti M, Guevara R, Coˆrtes MC et al (2013) Functional extinction of birds drives rapid evolutionary changes in seed size. Science 340:1086–1090 Hutchinson GE (1957) Concluding remarks. Com Spring Harb Symp Quant Biol 22:415–427 Mooney H, Larigauderie A, Cesario M et al (2009) Biodiversity, climate change and ecosystem services. Curr Opin Environ Sustain 1:46–54 Olden JD, Poff NL, Douglas MR et al (2004) Ecological and evolutionary consequences of biotic homogenization. Trends Ecol Evol 19:18–24 Rosenzweig ML (2001) The four questions: what does the introduction of exotic species do to biodiversity? Ecol Evol Res 3:361–367 Sax DF, Gaines SD (2003) Species diversity: from global decreases to local increases. Trends Ecol Evol 18:561–566 Teysse`dre A, Robert A (2014) Contrasting effects of habitat reduction, conversion and alteration on neutral and non neutral biological communities. Oikos 123:857–865 Tilman D, May R, Lehman C, Nowak M (1994) Habitat destruction and the extinction debt. Nature 371:65–66
123
