The latitudinal diversity gradient and interspecific competition: no global relationship between lizard dietary niche breadth and species richness

Alison Gainsbury*, Shai Meiri

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Aim: Dietary niche breadth has long been hypothesized to decrease towards lower latitudes as the numbers of competitors increase. Geographical variation in niche breadth is also hypothesized to be linked to high ambient energy levels, water availability, productivity and climate stability – reflecting an increased number of available prey taxa. Range size and body size are also hypothesized to be strongly and positively associated with niche breadth. We sought to determine which of these factors is associated with geographical variation in niche breadth across broad spatial scales and thus potentially drive the latitudinal diversity gradient. Location: Global. Methods: We collated volumetric dietary data for 308 lizard species. For each species, we gathered data on number of sympatric lizard species (a proxy for the number of competitors), annual temperature and precipitation, net primary productivity, seasonality, range size and body size. We examined the relationship between dietary niche breadth and focal parameters using both ordinary and phylogenetic generalized least squares regressions. Results: Niche breadth was positively related to annual precipitation, temperature seasonality and range size, and negatively related to body size. Lizard species richness increased towards lower latitudes. Dietary niche breadth, however, was unrelated to parameters reflecting diversity gradients, such as primary productivity, annual temperature, precipitation seasonality and, crucially, the number of potential competitors. Main conclusions: Contrary to prevailing ecological theory, competition is unrelated to dietary niche breadth. We found no support for interspecific competition driving the latitudinal diversity gradient. Rather, we found variation in niche breadth to be associated with water availability, climate stability, range size and body size. Our study casts doubt on the common assumption that tropical species are specialists, promoting greater alpha diversity, and on the assumption that the number of sympatric species is reflected in the intensity of interspecific competition.

Original languageEnglish
Pages (from-to)563-572
Number of pages10
JournalGlobal Ecology and Biogeography
Issue number5
StatePublished - May 2017


  • Body size
  • climate
  • dietary niche breadth
  • interspecific competition
  • latitudinal diversity gradients
  • lizards
  • species range size
  • species richness


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