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On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions

We use a simulation model to examine four of the most common hypotheses for the latitudinal richness gradient and identify patterns that might be diagnostic of those four hypotheses. The hypotheses examined include (1) tropical niche conservatism, or the idea that the tropics are more diverse becaus...

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Autores principales: Hurlbert, Allen H., Stegen, James C.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4251432/
https://www.ncbi.nlm.nih.gov/pubmed/25520738
http://dx.doi.org/10.3389/fgene.2014.00420
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author Hurlbert, Allen H.
Stegen, James C.
author_facet Hurlbert, Allen H.
Stegen, James C.
author_sort Hurlbert, Allen H.
collection PubMed
description We use a simulation model to examine four of the most common hypotheses for the latitudinal richness gradient and identify patterns that might be diagnostic of those four hypotheses. The hypotheses examined include (1) tropical niche conservatism, or the idea that the tropics are more diverse because a tropical clade origin has allowed more time for diversification in the tropics and has resulted in few species adapted to extra-tropical climates. (2) The ecological limits hypothesis suggests that species richness is limited by the amount of biologically available energy in a region. (3) The speciation rates hypothesis suggests that the latitudinal gradient arises from a gradient in speciation rates. (4) Finally, the tropical stability hypothesis argues that climatic fluctuations and glacial cycles in extratropical regions have led to greater extinction rates and less opportunity for specialization relative to the tropics. We found that tropical niche conservatism can be distinguished from the other three scenarios by phylogenies which are more balanced than expected, no relationship between mean root distance (MRD) and richness across regions, and a homogeneous rate of speciation across clades and through time. The energy gradient, speciation gradient, and disturbance gradient scenarios all produced phylogenies which were more imbalanced than expected, showed a negative relationship between MRD and richness, and diversity-dependence of speciation rate estimates through time. We found that the relationship between speciation rates and latitude could distinguish among these three scenarios, with no relation expected under the ecological limits hypothesis, a negative relationship expected under the speciation rates hypothesis, and a positive relationship expected under the tropical stability hypothesis. We emphasize the importance of considering multiple hypotheses and focusing on diagnostic predictions instead of predictions that are consistent with multiple hypotheses.
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spelling pubmed-42514322014-12-17 On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions Hurlbert, Allen H. Stegen, James C. Front Genet Genetics We use a simulation model to examine four of the most common hypotheses for the latitudinal richness gradient and identify patterns that might be diagnostic of those four hypotheses. The hypotheses examined include (1) tropical niche conservatism, or the idea that the tropics are more diverse because a tropical clade origin has allowed more time for diversification in the tropics and has resulted in few species adapted to extra-tropical climates. (2) The ecological limits hypothesis suggests that species richness is limited by the amount of biologically available energy in a region. (3) The speciation rates hypothesis suggests that the latitudinal gradient arises from a gradient in speciation rates. (4) Finally, the tropical stability hypothesis argues that climatic fluctuations and glacial cycles in extratropical regions have led to greater extinction rates and less opportunity for specialization relative to the tropics. We found that tropical niche conservatism can be distinguished from the other three scenarios by phylogenies which are more balanced than expected, no relationship between mean root distance (MRD) and richness across regions, and a homogeneous rate of speciation across clades and through time. The energy gradient, speciation gradient, and disturbance gradient scenarios all produced phylogenies which were more imbalanced than expected, showed a negative relationship between MRD and richness, and diversity-dependence of speciation rate estimates through time. We found that the relationship between speciation rates and latitude could distinguish among these three scenarios, with no relation expected under the ecological limits hypothesis, a negative relationship expected under the speciation rates hypothesis, and a positive relationship expected under the tropical stability hypothesis. We emphasize the importance of considering multiple hypotheses and focusing on diagnostic predictions instead of predictions that are consistent with multiple hypotheses. Frontiers Media S.A. 2014-12-02 /pmc/articles/PMC4251432/ /pubmed/25520738 http://dx.doi.org/10.3389/fgene.2014.00420 Text en Copyright © 2014 Hurlbert and Stegen. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
spellingShingle Genetics
Hurlbert, Allen H.
Stegen, James C.
On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title_full On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title_fullStr On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title_full_unstemmed On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title_short On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
title_sort on the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions
topic Genetics
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4251432/
https://www.ncbi.nlm.nih.gov/pubmed/25520738
http://dx.doi.org/10.3389/fgene.2014.00420
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