Why Mountain Passes Are Higher in the Tropics. Janzen, D. H. 101(919):233–249.
Why Mountain Passes Are Higher in the Tropics [link]Paper  doi  abstract   bibtex   
This paper is designed to draw attention to the relation between tropical climatic uniformity at a given site and the effectiveness of topographic barriers adjacent to the site in preventing movements of plants and animals. This is not an attempt to explain tropical species diversity (see Pianka, 1966, for a review of this subject), but rather to discuss a factor that should be considered in any discussion of the relation between topographic and climatic diversity, and population isolation. Simpson (1964) states that "Small population ranges and numerous barriers against the spread and sympatry of related populations would therefore tend to increase density of species in a region as a whole. It will be suggested below that this is a factor in the increase of species densities in regions of high topographic relief. I do not, however, know of any evidence that it is more general or more effective in the tropics." I believe that the climatic regimes discussed below, and the reactions of organisms to them, indicate that topographic barriers may be more effective in the tropics. Mountain barriers and their temperature gradients in Central America, as contrasted to those in North America, are used as examples; but it is believed that the central idea equally applies to other tropical areas, types of barriers, and physical parameters. There are three thoughts central to the argument to be developed: (1) in respect to temperature, it is the temperature gradient across a mountain range which determines its effectiveness as a barrier, rather than the absolute height; (2) in Central America, terrestrial temperature regimes are generally more uniform than North American ones, and differ in their patterns of overlap across geographic barriers; and (3) it can be assumed that animals and plants are evolutionarily adapted to, and/or have the ability to acclimate to, the temperatures normally encountered in their temporal and geographic habitat (or microhabitat).
@article{janzenWhyMountainPasses1967,
  title = {Why Mountain Passes Are Higher in the Tropics},
  author = {Janzen, Daniel H.},
  date = {1967-05},
  journaltitle = {The American Naturalist},
  volume = {101},
  pages = {233--249},
  issn = {1537-5323},
  doi = {10.1086/282487},
  url = {http://mfkp.org/INRMM/article/14496917},
  abstract = {This paper is designed to draw attention to the relation between tropical climatic uniformity at a given site and the effectiveness of topographic barriers adjacent to the site in preventing movements of plants and animals. This is not an attempt to explain tropical species diversity (see Pianka, 1966, for a review of this subject), but rather to discuss a factor that should be considered in any discussion of the relation between topographic and climatic diversity, and population isolation. Simpson (1964) states that "Small population ranges and numerous barriers against the spread and sympatry of related populations would therefore tend to increase density of species in a region as a whole. It will be suggested below that this is a factor in the increase of species densities in regions of high topographic relief. I do not, however, know of any evidence that it is more general or more effective in the tropics." I believe that the climatic regimes discussed below, and the reactions of organisms to them, indicate that topographic barriers may be more effective in the tropics. Mountain barriers and their temperature gradients in Central America, as contrasted to those in North America, are used as examples; but it is believed that the central idea equally applies to other tropical areas, types of barriers, and physical parameters. There are three thoughts central to the argument to be developed: (1) in respect to temperature, it is the temperature gradient across a mountain range which determines its effectiveness as a barrier, rather than the absolute height; (2) in Central America, terrestrial temperature regimes are generally more uniform than North American ones, and differ in their patterns of overlap across geographic barriers; and (3) it can be assumed that animals and plants are evolutionarily adapted to, and/or have the ability to acclimate to, the temperatures normally encountered in their temporal and geographic habitat (or microhabitat).},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14496917,~to-add-doi-URL,100-ecology-articles,climate,diversity,fragmentation,habitat-suitability,mountainous-areas,temperature},
  number = {919}
}
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