PolydomousCrematogaster pilosa(Hymenoptera: Formicidae) Colonies Prefer Highly Connected Habitats in a Tidal Salt Marsh

Abstract

High productivity in salt marshes creates an attractive resource base for terrestrial consumers, but regular tidal inundation creates a harsh environment. numerous terrestrial organisms have adapted to living in salt marshes by timing activity cycles and vertical movements to tidal cycles, while others exhibit physiological adaptations, increasing their tolerance to submersion (Foster 1983; Vaughn & Fisher 1992; petillon et al. 2009). one of the species able to withstand these harsh conditions is the ant Crematogaster pilosa (emery) (Hymenoptera: Formicidae), which has been reported to nest in hollow stems of salt marsh vegetation ranging from Florida to north carolina (davis & gray 1966; mccoy & rey 1987), as well as in trees in mesic forests and within stems of upland plants (teal 1962; Johnson 1988; morgan 2010). little is known about C. pilosa (synonymous with C. clara; Johnson 1988) with the exception of its flexible habitat requirements. the objective of this study was to examine the basic colony attributes and habitat preferences of C. pilosa in a saltmarsh cordgrass [Spartina alterniflora loisel (poales: poaceae)] dominated salt marsh on sapelo island, georgia. connectivity in the S. alterniflora canopy, dead and living stem densities, and maximum stem height were evaluated to examine the influence of habitat structure on ant densities. in october 2011, two marsh transects stretching from the forest edge to the bank of a large tidal creek were demarcated and divided into fourteen 10 × 2 m sections. ant density was sampled in 4 randomly selected 2 m2 quadrats per section by sweep netting for 15 seconds. percent vegetation cover was estimated from photographs taken from ground level and converted to binary sky/ vegetation images using imageJ software. living and dead stem density and tallest stem height were measured in 4 haphazardly placed quadrats (0.25 m2) within a subset of 9 sections. Workers from 15 nests were enumerated, and the presence of eggs or pupae was recorded. to evaluate tidal inundation relative to nest height, 5 fence posts with cups attached at 5 cm intervals covering the lower range of observed nest heights were deployed. Flooded cups were recorded daily for 4 days, which included some of the highest local tides of 2011. the spatial extent and number of colonies examined in this study are small, limiting the potential for generalization to other colonies and habitats. square-root transformed ant densities showed a positive correlation with percent vegetation cover (Fig. 1) when data were averaged over 20 m2 transect sections (r2 = 0.50, p = 0.003). no relationship was found between ant density and living stem density (r2 = 0.21, p = 0.22), dead stem density (r2 = 0.06, p = 0.53), or tallest stem height (r2 = 0.10, p = 0.42). mean nesting stem and entrance heights were 44.6 cm (sd = 14.4) and 35.3 cm (sd = 10.6), respectively. the maximum observed tidal height from substrate was less than 20 cm, and minimum nest entrance height was 21 cm (Fig. 2). nests averaged 242 workers (range: 53-1106, sd = 276), which is conservative because some workers were foraging at the time of collection. eggs and pupae were found in 87% and 46% of the nests, respectively. Workers were observed traveling and carrying eggs among 21 nests within