Bait visitation by Formica lemani (Hymenoptera: Fomicidae) indicates shortage of carbohydrates in alpine grasslands

Abstract

Insights can be gained by analysing the feeding decisions of animals in terms of nutrient demands at a species or community level. Using carbohydrate and protein food baits, resource use and food preferences of Formica (Serviformica) lemani were determined at nine locations situated at different altitudes (1875 to 2400 m a.s.l.) in the alpine grassland belt above the tree line in Austria and northern Italy. F. lemani is the most common species of ant in this habitat. Sucrose baits placed around ant colonies were visited by signifi cantly (3.9 times) more workers than protein baits. This indicates that sources of sugar (carbohydrate) are in short supply in the alpine zone, whereas availability of prey items appears to be less constraining. Overall, we recorded a decrease in the incidence of visits to baits from low (31.9% baits attracting ants at least once) to high altitudes (16.7%). Foraging ants never visited 51.5% of the baits exposed for periods of 75 min. This indicates that with increasing altitude competition for food among ant colonies becomes less intense in alpine grassland ant communities.

Consistent shift in nutritional ecology of ants reveals trophic flexibility across alpine tree‐line ecotones

“…In the present study, however, lipids were clearly avoided by all ant species occurring around the alpine tree line and were even visited less frequently than pure water. This rejection of lipids by ants in the European Alps was also observed by Spotti et al (2015) (using virgin olive oil) and Guariento et al (2018a) (using peanut butter) and therefore seems to be a consistent characteristic of alpine ants. The rejection of lipid baits might depend on the resource offered (olive oil, i.e.…”

“…The strong demand of alpine ants for carbohydrates has earlier been found by Spotti et al (2015) (along a montane to subalpine gradient) and by Guariento et al (2018a) in alpine grassland. This sugar demand appears to be a consistent characteristic of ant communities of alpine habitats.…”

“…Therefore, from information on bait visitation, it is possible to infer which nutrients are most limiting for a given ant species or community (Kaspari & Yanoviak, 2001) or how limitations might change over environmental gradients (Stadler & Dixon, 2008;Lasmar et al, 2021). The scarcity of trophobiotic partners at high elevations (Stadler et al, 2003) is concordant with a more intense usage of carbohydrates by ants observed in the alpine vegetation zone (Spotti et al, 2015;Guariento et al, 2018a). In contrast, the visitation of carbohydrate baits exposed in forest is expected to be lower, mainly because of the natural abundance of trophobiotic Cinara Curtis, 1835 aphids on conifers, which offer a consistent and reliable supply of carbohydrates for ants (Domisch et al, 2016).…”

“…Some studies on resource use of ants along elevational gradients have been conducted in the tropics (Peters et al, 2014;Orivel et al, 2018) and few also on temperate-zone mountains (Fowler et al, 2014;Spotti et al, 2015;Guariento et al, 2018a). Even if all ant species in the alpine zone essentially forage on the same resources, differences in their responses to various baits can be expected.…”

Nectar robbing rather than pollinator availability constrains reproduction of a bee‐flowered plant at high elevations

“…However, even though our data cast doubt on the pollinator‐filtering hypothesis in the way it was proposed (Pellissier et al, 2010), biotic interactions with flower visitors might still play a role in determining the elevational range limitations of plants with bilateral flowers. Insects foraging at colder temperatures have higher energetic needs (Heinrich & Raven, 1972) so that they will try to increase their sugar intake rate (Guariento et al, 2018). It is therefore likely that an elevational increase in the rates of nectar robbing and theft, as we reported it here, is a general phenomenon on temperate mountains (see Utelli & Roy, 2001, who found higher frequencies of nectar robbing in Aconitum lycoctonum at two high‐elevation populations compared with two low‐elevation populations in Switzerland).…”