The validity of ecogeographical rules is context-dependent: Testing for Bergmann's and Allen's rules by latitude and elevation in a widespread Andean duck

Natalia Gutiérrez-Pinto, Kevin G. McCracken, Luis Alza, Pablo Tubaro, Cecilia Kopuchian, Andrea Astie, Carlos Daniel Cadena

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

Consistent responses by various organisms to common environmental pressures represent strong evidence of natural selection driving geographical variation. According to Bergmann's and Allen's rules, animals from colder habitats are larger and have smaller limbs than those from warmer habitats to minimize heat loss. Although evidence supporting both rules in different organisms exists, most studies have considered only elevational or latitudinal temperature gradients. We tested for the effects of temperature associated with both elevation and latitude on body and appendage size of torrent ducks (Merganetta armata), a widespread species in Andean rivers. We found a negative relationship between body size and temperature across latitude consistent with Bergmann's rule, whereas there was a positive relationship between these variables along replicate elevational gradients at different latitudes. Limb-size variation did not support Allen's rule along latitude, nor along elevation. High-elevation ducks were smaller and had longer wings than those inhabiting lower elevations within a river. We hypothesize that temperature is likely a major selective pressure acting on morphology across latitudes, although hypoxia or air density may be more important along elevational gradients. We conclude that the effect of temperature on morphology, and hence the likelihood of documenting ecogeographical 'rules', depends on the environmental context in which temperature variation is examined.

Original languageEnglish (US)
Pages (from-to)850-862
Number of pages13
JournalBiological Journal of the Linnean Society
Volume111
Issue number4
DOIs
StatePublished - Apr 2014

Keywords

  • Adaptation
  • Andes
  • Biogeography
  • Ecological gradients
  • Merganetta armata
  • Temperature

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

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