Are mountain passes higher in the tropics? janzen's hypothesis revisited
2006/01/06 by C. K. Ghalambor, Cameron K. Ghalambor · 854 citations
Environmental Science · #Adaptation (eye) #Altitude (triangle) #Biological dispersal #Biology #Ecology #Ecology and Vegetation Dynamics Studies #Generality #Physiological and biochemical adaptations #Population #Species Distribution and Climate Change #Temperate climate #Tropics
paper · doi:10.1093/icb/icj003
published in Integrative and Comparative Biology 46(1), 5-17 (Oxford University Press)
openalex publication_date 2006/01/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
Abstract
Synopsis In 1967 Daniel Janzen published an influential paper titled "Why Mountain Passes Are Higher in the Tropics." Janzen derived a simple climatic-physiological model predicting that tropical mountain passes would be more effective barriers to organismal dispersal than would temperate-zone passes of equivalent altitude. This prediction derived from a recognition that the annual variation in ambient temperature at any site is relatively low in the tropics. Such low variation within sites not only reduces the seasonal overlap in thermal regimes between low- and high-altitude sites, but should also select for organisms with narrow physiological tolerances to temperature. As a result, Janzen predicted that tropical lowland organisms are more likely to encounter a mountain pass as a physiological barrier to dispersal (hence "higher"), which should in turn favor smaller distributions and an increase in species turnover along altitudinal gradients. This synthetic hypothesis has long been at the center of discussions of latitudinal patterns of physiological adaptation and of species diversity. Here we review some of the key assumptions and predictions of Janzen's hypothesis. We find general support for many assumptions and predictions, but call attention to several issues that somewhat ameliorate the generality of Janzen's classic hypothesis.
Citations
Cited by
- Macrophysiology: A Conceptual Reunification
- The Geography of Metacommunities: Landscape Characteristics Drive Geographic Variation in the Assembly Process through Selecting Species Pool Attributes
- Tropical cities as windows into the ecosystems of our present and future
- Insect overwintering in a changing climate
- Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes
- Climate and ecology predict latitudinal trends in sexual selection inferred from avian mating systems
- The Andes are a driver of physiological diversity in Anolis lizards
- Butterfly and moth habitat specialisation changes along an elevational gradient of tropical forests on Mount Cameroon
- Drivers and mechanisms that contribute to microbial β‐diversity patterns and range sizes in mountains across a climatic variability gradient
- Clear effects of population and sex but not rearing temperature on stress tolerance in a temperate butterfly
- Adaptive Radiation Without Independent Stages of Trait Evolution in a Group of Caribbean Anoles
- The Shape of Water: Physiological Adaptations to Habitat Aridity in the Ornate Tree Lizard (Urosaurus ornatus)
- How robust are signals of local adaptation? Exposure to a common fungal pathogen does not disrupt clinal trends in host thermal tolerance
- Variation in temperature but not diet determines the stability of latitudinal clines in tolerance traits and their plasticity
- Putting the Heat on Tropical Animals
- Going round in cycles but going somewhere: Deciphering cyclical dynamics using Ecological Trajectory Analysis
- Beyond Janzen's Hypothesis: How Amphibians That Climb Tropical Mountains Respond to Climate Variation
- Genomic Evidence for Elevational Segregation and Adaptive Introgression in Prunellidae Radiation
- Global phenology maps reveal the drivers and effects of seasonal asynchrony
- Avian suture zones in Pan Amazonia
- Tectonics, topography, and mammalian diversity
- A Global Meta‐Analysis of Passive Experimental Warming Effects on Plant Traits and Community Properties
- Predicting organismal vulnerability to climate warming: roles of behaviour, physiology and adaptation
- Evolutionary stasis and lability in thermal physiology in a group of tropical lizards
- On the use of elevation, altitude, and height in the ecological and climatological literature
- Critical thermal limits depend on methodological context. [europepmc]
- Climatic zonation drives latitudinal variation in speciation mechanisms. [europepmc]
- Thermal tolerance, acclimatory capacity and vulnerability to global climate change. [europepmc]
- Macrophysiology for a changing world. [europepmc]
- Physiological Diversity in Insects: Ecological and Evolutionary Contexts. [europepmc]
- Why tropical forest lizards are vulnerable to climate warming. [europepmc]
- Phylogeny, niche conservatism and the latitudinal diversity gradient in mammals. [europepmc]
- Projected range contractions of montane biodiversity under global warming. [europepmc]
- Global analysis of thermal tolerance and latitude in ectotherms. [europepmc]
- Latitude, elevational climatic zonation and speciation in New World vertebrates. [europepmc]
- On a collision course: competition and dispersal differences create no-analogue communities and cause extinctions during climate change. [europepmc]
- Predicting organismal vulnerability to climate warming: roles of behaviour, physiology and adaptation. [europepmc]
- Evolutionary stasis and lability in thermal physiology in a group of tropical lizards. [europepmc]
- Global variation in thermal tolerances and vulnerability of endotherms to climate change. [europepmc]
- Spatially varying selection shapes life history clines among populations of Drosophila melanogaster from sub-Saharan Africa. [europepmc]
- Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming. [europepmc]
- Climate change causes upslope shifts and mountaintop extirpations in a tropical bird community. [europepmc]
- Narrow thermal tolerance and low dispersal drive higher speciation in tropical mountains. [europepmc]
- Thermal tolerance patterns across latitude and elevation. [europepmc]
- Integrating within-species variation in thermal physiology into climate change ecology. [europepmc]
- Evolution and plasticity of thermal performance: an analysis of variation in thermal tolerance and fitness in 22 Drosophila species. [europepmc]
- Angiosperm speciation cools down in the tropics. [europepmc]
- Plant adaptation to climate change - Where are we? [europepmc]
- Janzen's Hypothesis Meets the Bogert Effect: Connecting Climate Variation, Thermoregulatory Behavior, and Rates of Physiological Evolution. [europepmc]
- Limited plasticity in thermally tolerant ectotherm populations: evidence for a trade-off. [europepmc]
Related