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Tropical bird species have less variable body sizes.

Quentin D Read1,2, Benjamin Baiser3, John M Grady2,4

  • 1Ecology, Evolutionary Biology, and Behavior Program, Michigan State University, East Lansing, MI, USA qdr@msu.edu.

Biology Letters
|January 26, 2018
PubMed
Summary

Tropical birds exhibit less intraspecific body size variation compared to their non-tropical relatives. This finding suggests a potential link between stable environments and reduced body size diversity in equatorial species.

Keywords:
birdsbody sizemacroecologyniche

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Area of Science:

  • Ecology
  • Zoology
  • Evolutionary Biology

Background:

  • Ecologists predict declining species' niche breadths towards the Equator, attributed to climatic constraints or resource specialization.
  • While thermal niches show this pattern, other niche dimensions, like body size, are less explored.
  • Body size in vertebrates influences diet, competition, and environmental tolerance, making it a key niche dimension.

Purpose of the Study:

  • To investigate whether tropical bird species have lower intraspecific body-size variation than their non-tropical sister species.
  • To explore the relationship between geographic location (tropical vs. non-tropical) and body size variability in birds.

Main Methods:

  • Identified 68 pairs of tropical and non-tropical sister bird species using a comprehensive phylogeny.
  • Utilized the VertNet specimen database to quantify intraspecific body mass variation for each species.

Main Results:

  • Tropical bird species demonstrated significantly less intraspecific variability in body mass compared to non-tropical sister species (p = 0.009).
  • The drivers explaining the variation in body-size variability were poorly elucidated by both abiotic and biotic factors.

Conclusions:

  • The reduced body size variation in tropical birds may be an evolutionary response to more stable climatic and resource conditions.
  • Further research is needed to fully understand the mechanisms underlying this observed pattern in body size diversity.