Assessing the effects of sodium on fire ant foraging in the field and colony growth in the laboratory

Abstract

Sodium is an essential dietary element and preferential foraging for high concentrations of sodium by inland herbivorous and omnivorous ants suggests it may be limiting. If so, increased sodium availability through altered deposition and anthropogenic sources may lead to increased colony and population growth and cascading ecological impacts. For red imported fire ants, Solenopsis invicta Buren, the present study tests: (i) whether colonies from coastal and inland sites differ in their responses to NaCl baits; and (ii) whether supplemental NaCl increases growth of fire ant colonies in the laboratory. Fire ants in inland sites with low sodium deposition responded roughly an order of magnitude more strongly to high concentrations of NaCl baits than did fire ants in coastal sites with high sodium deposition. Laboratory colonies of fire ants, however, showed no signs of sodium limitation or benefits of increased sodium. The link between behavioural responses to baits in the field and effects on colony growth deserves further investigation to assess the ecological impacts of altered sodium availability.

Crazy ants craving calcium: macronutrients and micronutrients can limit and stress an invaded grassland brown food web

“…1A). Plant concentrations of K far exceed the requirements of consumers (Mickelson and Christian 1991) and Na has shown signs of stress or toxicity for other ants at coastal sites (Kaspari et al 2008, Resasco et al 2014). Na and K stress may be due to increased metabolic demands for excretion of these elements in maintaining Na and K homeostasis (e.g., Na‐K pump; Kaspari 2020).…”

“…For example, Na and Ca are scarce in hemipteran honeydew and make up less than 10% and 5% of honeydew cation content, respectively, whereas K is abundant and makes up about 50–80% of honeydew cation content (Shaaban et al 2020). Na can limit the activity and abundance of native ants (Kaspari et al 2020) and populations of S. invicta (Resasco et al 2014) in Na‐poor ecosystems, but the potential for invasive ants to be limited by Ca has seldom been tested.…”

Towards a geography of omnivory: Omnivores increase carnivory when sodium is limiting

“…Ants are easily manipulated in laboratory studies, and consistently implicated as indicators of Na‐limitation, N‐limitation and productivity (Davidson, ; Kaspari et al., ; Kaspari, Yanoviak, et al., ). Moreover, the trophic behaviour of ant populations varies across communities (Resasco, Porter, Sanders, & Levey, ; Wilder et al., ).…”

Limitação por sódio em assembléias de formigas no cerrado

“…Isso sugere que o sódio apesar de ser um nutriente limitante, pode ser tóxico quando utilizado em doses elevadas. Já para a formiga Solenopsis invicta, uma espécie predadora de solo, diferentes níveis de sódio na dieta não resultaram em diferenças significativas no crescimento das colônias (Resasco et al 2013).…”

“…É importante ressaltar que o recrutamento das formigas para iscas de sal é direcionado pelo Na + e não pelo Cl - (Kaspari et al 2009). Como visto, o sódio é um nutriente essencial para os organismos, e os estudos com formigas parecem dar apoio à ideia de que os organismos preferem nutrientes que estão escassos localmente (Kaspari et al 2008, 2010, O'Donnell et al 2010, Hernandez et al 2012, Resasco et al 2013. O cerrado na região oeste de Minas Gerais e sul de Goiás está localizado a cerca de 600-750 km de distância do litoral.…”