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

• Published in: Global ecology and biogeography Vol. 17; no. 3; pp. 352 - 362
• Main Authors: Carnicer, Jofre, Brotons, Lluís, Sol, Daniel, de Cáceres, Miquel
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.05.2008; Blackwell Publishing Ltd; Blackwell Publishing; Blackwell
• Subjects: Animal and plant ecology; Animal ecology; Animal, plant and microbial ecology; Aves; Biological and medical sciences; Birds; Ecological genetics; Ecological modeling; Ecological niches; ecosystems; Extinct species; extinction; forests; Fundamental and applied biological sciences. Psychology; General aspects; interspecific variation; Mediterranean biome; migratory behavior; Modeling; neutral theory; niche width; niche-filtering; niches; population density; population dynamics; Population ecology; prediction; risk; sampling; Spain; Species; species diversity; Species extinction; species richness; stochastic processes; Synecology; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; wild birds; Europe; Spain; Spain, Catalonia; Random sampling; Neutral theory; Extinction; sampling; Biogeography; niche width; Birds; Ecology; Spain; Vertebrata; niche-filtering; Biome; Mediterranean biome; Dynamics; Ecological niche; Immigration; Aves; Width; Species richness; Ecological abundance
• ISSN: 1466-822X; 1466-8238; 1466-822X
• DOI: 10.1111/j.1466-8238.2007.00380.x

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. A Mediterranean biome in Catalonia, Spain. 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. 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. 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.