Abstract
BackgroundThe two sympatric species of Tunisian desert ants, Cataglyphis bicolor and C. mauritanica, do not exhibit any differences in their foraging ecology, e.g. in food preferences and in their spatial and temporal activity patterns. Here we show that instead the two species markedly differ in their life histories.ResultsWe analysed mtDNA of specimens that were collected along a 250-km transect. C. bicolor exhibited a genetically unstructured population (with the genetic and geographic distances among colonies not being correlated). On the contrary the populations of the polygynous C. mauritanica were clearly structured, i.e. exhibited a strong correlation between genetic and geographic distances. This difference is in accordance with large queen dispersal distances due to far-reaching mating flights in C. bicolor and small queen dispersal distances due to colony foundation by budding in C. mauritanica. Furthermore, wherever we found populations of both species to coexist within the same habitat, the habitat was used agriculturally. Mapping nest positions over periods of several years showed that plowing dramatically decreased the nest densities of either species.ConclusionWe conclude that owing to its greater queen dispersal potential C. bicolor might be more successful in quickly re-colonizing disturbed areas, while the slowly dispersing C. mauritanica could later out-compete C. bicolor by adopting its effective nest-budding strategy. According to this scenario the observed sympatry of the two species might be an intermediate stage in which faster colonization by one species and more powerful exploitation of space by the other species have somehow balanced each other out. In conclusion, C. bicolor and C. mauritanica represent an example where environmental disturbances in combination with different life histories might beget sympatry in congeneric species with overlapping niches.
Highlights
The two sympatric species of Tunisian desert ants, Cataglyphis bicolor and C. mauritanica, do not exhibit any differences in their foraging ecology, e.g. in food preferences and in their spatial and temporal activity patterns
Being thermophilic scavengers searching for arthropod corpses, C. bicolor and C. mauritanica rely on the same food sources without any differences either in the type, size, or dry weight of the collected food items
In order to test whether the C. mauritanica population is genetically structured, we sequenced mtDNA of ants that had been collected along a large-scale transect covering a total length of 250 km
Summary
The two sympatric species of Tunisian desert ants, Cataglyphis bicolor and C. mauritanica, do not exhibit any differences in their foraging ecology, e.g. in food preferences and in their spatial and temporal activity patterns. In order to explain the starting point of the study described here, let us briefly conclude the main results of the ecological comparison Both species have sized monomorphic workers (e.g. head width, C. bicolor 1.7 mm, S.D.: 0.4 mm (n = 500), C. mau-. Being thermophilic scavengers searching for arthropod corpses, C. bicolor and C. mauritanica rely on the same food sources without any differences either in the type, size, or dry weight of the collected food items The workers of both species employ the same individual foraging strategies, i.e. depart from the nest for the same distances, do not occupy food territories, and do not avoid the vicinity of conspecific or allospecific Cataglyphis nests. C. bicolor and C. mauritanica inhabit the same microhabitat, as far as physical ground structure and vegetation is concerned, and they exhibit the same daily activity patterns (for a full description of the ecological analyses see [1])
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