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Do Invaders Conform to Biogeographic “Rules”? Testing Allen’s, Bergmann’s, and Gloger’s Rules in Monk Parakeets
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  • Flavia Montaño-Centellas,
  • Charles van Rees,
  • Kali Block,
  • Rachel White,
  • Margaret Rubega,
  • Kevin Burgio
Flavia Montaño-Centellas
Louisiana State University
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Charles van Rees
University of Georgia Odum School of Ecology

Corresponding Author:[email protected]

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Kali Block
University of Connecticut
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Rachel White
University of Brighton
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Margaret Rubega
University of Connecticut
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Kevin Burgio
Cary Institute of Ecosystem Studies
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Biogeographic rules illustrate linkages between selective pressures and morphological traits among species that occur along broad environmental (usually latitudinal) gradients. Most research on such rules consists of observational studies, lacking any forms of experimental control. Species invasions, especially those consisting of multiple, independent introductions, present a form of natural experiment by which these rules can be more rigorously assessed. Here, we investigate whether the morphological traits of both native and non-native invasive populations of Monk Parakeet, a widespread invasive parrot distributed in North America, follow Allen’s, Bergmann’s, and Gloger’s rules. Furthermore, we go beyond correlations between latitude and morphological traits, and investigate specific climatic variables pertaining to prevailing precipitation and temperature conditions for their effects on morphology. Analyzing morphological measurements from 148 study skins from North and South America, we found statistical support for latitudinal effects on body mass consistent with predictions from Bergmann’s rule, but no support for Allen’s rule as no effects of latitude on bill length were detected once we corrected it for body size. Our findings show that areas with warmer winters and higher precipitation were associated with smaller specimens with larger wings. We also found areas with higher minimum precipitation were associated with specimens with larger bills relative to body size, a pattern potentially related with feeding resources. We observed no relationship between plumage luminance and latitude or climatic variables, suggesting that monk parakeets do not adhere to Gloger’s rule.