Improved empirical tests of area-heterogeneity tradeoffs

Carnicer J., Brotons L., Herrando S., Sol D. (2013) Improved empirical tests of area-heterogeneity tradeoffs. Proceedings of the National Academy of Sciences of the United States of America. 110: 0-0.
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Doi: 10.1073/pnas.1222681110

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[No abstract available]

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Random sampling, abundance-extinction dynamics and niche-filtering immigration constraints explain the generation of species richness gradients

Carnicer J., Brotons L., Sol D., De Cáceres M. (2008) Random sampling, abundance-extinction dynamics and niche-filtering immigration constraints explain the generation of species richness gradients. Global Ecology and Biogeography. 17: 352-362.
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Doi: 10.1111/j.1466-8238.2007.00380.x

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Aim: The paradigm that species' patterns of distribution, abundance and coexistence are the result of adaptations of the species to their niches has recently been challenged by evidence that similar patterns may be generated by simple random processes. We argue here that a better understanding of macroecological patterns requires an integration of both ecological and neutral stochastic approaches. We demonstrate the utility of such an integrative approach by testing the sampling hypothesis in a species-energy relationship of forest bird species. Location: A Mediterranean biome in Catalonia, Spain. Methods: To test the sampling hypothesis we designed a metacommunity model that reproduces the stochastic sampling from a regional pool to predict local species richness variation. Four conceptually different sampling procedures were evaluated. Results: We showed that stochastic sampling processes predicted a substantial part (over 40%) of the observed variation in species richness, but left considerable variation unexplained. This remaining variation in species richness may be better understood as the result of alternative ecological processes. First, the sampling model explained more variation in species richness when the probability that a species colonises a new locality was assumed to increase with its niche width, suggesting that ecological differences between species matter when it comes to explaining macroecological patterns. Second, extinction risk was significantly lower for species inhabiting high-energy regions, suggesting that abundance-extinction processes play a significant role in shaping species richness patterns. Main conclusions: We conclude that species-energy relationships may not simply be understood as a result of either ecological or random sampling processes, but more likely as a combination of both. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Ltd.

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Community-based processes behind species richness gradients: Contrasting abundance-extinction dynamics and sampling effects in areas of low and high productivity

Carnicer J., Brotons L., Sol D., Jordano P. (2007) Community-based processes behind species richness gradients: Contrasting abundance-extinction dynamics and sampling effects in areas of low and high productivity. Global Ecology and Biogeography. 16: 709-719.
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Doi: 10.1111/j.1466-8238.2007.00324.x

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Aim: To consider the role of local colonization and extinction rates in explaining the generation and maintenance of species richness gradients at the regional scale. Location: A Mediterranean biome (oak forests, deciduous forests, shrublands, pinewoods, firwoods, alpine heathlands, crops) in Catalonia, Spain. Methods: We analysed the relative importance of direct and indirect effects of community size in explaining species richness gradients. Direct sampling effects of community size on species richness are predicted by Hubbell's neutral theory of biodiversity and biogeography. The greater the number of individuals in a locality, the greater the number of species expected by random direct sampling effects. Indirect effects are predicted by the abundance-extinction hypothesis, which states that in more productive sites increased population densities and reduced extinction rates may lead to high species richness. The study system was an altitudinal gradient of forest bird species richness. Results: We found significant support for the existence of both direct and indirect effects of community size in species richness. Thus, both the neutral and the abundance-extinction hypotheses were supported for the altitudinal species richness gradient of forest birds in Catalonia. However, these mechanisms seem to drive variation in species richness only in low-productivity areas; in high-productivity areas, species richness was uncorrelated with community size and productivity measures. Main conclusions: Our results support the existence of a geographical mosaic of community-based processes behind species richness gradients, with contrasting abundance-extinction dynamics and sampling effects in areas of low and high productivity. © 2007 The Authors © 2007 Blackwell Publishing Ltd.

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