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2008 Harvard Forest REU Student Symposium Abstracts

Charlotte Chang - Pomona College

Soil salinity in a temperate forest ecosystem impacts ant foraging behavior


Although sodium is one of the 25 essential elements for life, it is rarely found in nature. Compared to other bionutrients, sodium loss via excretion is more pronounced because animals typically lack sodium reserves. We tested two hypotheses regarding sodium limitation in ants: 1) ants are more sodium-limited farther from an anthropogenic supply of sodium, namely, road-salting, and 2) higher temperatures elevate rates of activity and excretion, precipitating an increase in sodium intake. We studied eight sites distanced 1, 10, 100, and 1000m from Massachusetts Rt. 32. We collected ants foraging in vials containing one of the following solutions: distilled water, aqueous sodium chloride (0.1, 0.5, or 1.0% w/w), and aqueous sucrose (1.0, 5.0, or 10.0% w/w). As the distance from Rt. 32 increased, ants foraged for more sodium and exhibited greater preference for higher concentrations of sodium (p<0.05). In contrast, ants uniformly selected for higher concentrations of sucrose at all sites. Additionally, the species Tapinoma sessile significantly increased its usage of sodium relative to sucrose at sites farther from Rt. 32 (p<0.05), indicating that sodium facilitates sucrose metabolism. Community composition did not obviously shift toward species with higher sodium affinity along the sodium gradient, suggesting that ants selectively forage for sodium, and are thus sodium-limited. There was insufficient evidence to examine if warmer temperatures augment sodium use. Therefore, comparisons between regions with different mean temperatures may yield clearer patterns on the impact of temperature on sodium foraging.

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