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Original Article

Morphological characteristics of ant assemblages (Hymenoptera: Formicidae) differ among contrasting biomes

Schofield, S.F., Bishop, T.R. & Parr, C.L.

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Abstract: The environment is thought to strongly shape the ecology and evolution of species. Similar environments may cause species to look the same or converge upon particular traits. Dissimilar environments can cause species to look different or to diverge in their traits. These ideas have been explored at the single species level or within restricted geographic areas for ants. We ask whether the signature of environmental filtering can be detected within ant faunas at the biogeographic scale. We quantify differences in the morphological traits of ant faunas between two contrasting biomes: a rainforest in Costa Rica and a desert in Iran. Lists of species from each habitat type were compiled, and measurements of ten functional traits were taken from scaled images. Body size, relative femur length, and tibia length were significantly smaller in Costa Rica suggesting species in more complex environments are smaller in response to environmental complexity. Relative eye width was also smaller in Costa Rica, and individuals were lighter in colour. Eye size and body pigmentation showed differences which may be a result of altered foraging patterns or protection against UV-B irradiance. The Costa Rican fauna also had a much wider trait space (higher functional richness), and Iranian species occupied a narrow range in terms of mandible and leg size suggesting species invest less in foraging specialism in unproductive environments. Significant differences in morphological traits and their degree of overlap can therefore be observed in ant faunas occupying contrasting biomes. We suggest that this is due to the environment influencing the trait composition of these faunas at biogeographic scales.