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Keywords:

  • Caste determination;
  • coexistence;
  • competition;
  • foraging;
  • hybrid;
  • Solenopsis;
  • tradeoff
  1. Tradeoffs in functional traits facilitate species coexistence within communities and are important contributors to community assembly. Two aspects of a life-history tradeoff known to structure ant communities include foraging efficiency (i.e. resource discovery and retrieval) and competitive dominance (territoriality and survivorship following competition).
  2. This work examined these aspects in workers of two fire ant species (Solenopsis xyloni and Solenopsis geminata) and their F1 hybrids using laboratory experiments.
  3. Parental foraging strategies were consistent with a tradeoff between discovery efficiency and competitive territorial dominance. Desert-adapted S. xyloni was the most efficient forager but the least effective territory defender; mesic-adapted S. geminata was a less efficient forager, but fared best in competition trials. Hybrid workers were generally intermediate, leading to increased survival by hybrids in competitive encounters with S. geminata compared with the performance of S. xyloni.
  4. These findings suggest that traits associated with foraging and competitive ability in the parental species are subject to environmental filtering; across habitats, species with a similar dominance rank in their respective communities differ in their placement along the discovery–dominance axis.
  5. Interspecific hybridisation may play a role in extending eastern range limits of S. xyloni via shifting colony allocation towards the strategy of its competitor. In the overlap zone, S. xyloni with hybrid workers may be sufficiently competitive to persist with S. geminata, while colonies with S. xyloni workers cannot, providing a substantial selective advantage to hybridisation for S. xyloni queens that may explain the unusual hybridogenetic social structure of this population.