Competition for foraging resources and coexistence of two syntopic species of Messor harvester ants in Mediterranean grassland

Abstract

1. Diet composition of two syntopic species of Messor seed-harvester ants (M. wasmanni Krausse and M. minor André) was evaluated during different periods over the year (May, July, October), by analysing food type (plant parts and species) and food size (weight, length, width). Morphological traits of foragers (head width and femur length) considered important features promoting diet partitioning were measured.2. We used two robust randomisation algorithms (RA2 and RA3), adopted in niche overlap studies, to check for random vs non random utilisation of resources at intraand interspecific level for the different periods.3. Analyses showed high levels of overlap in the diet of the two species and no evidence of interspecific competition during most of the activity season. In particular, there was an aggregated use of resources in summer, whilst niche partitioning and evidence of competition when resources decreased in autumn. Intraspecifically, no evidence of competition was found. 4. Results suggest two different mechanisms for minimising competition: when food resources are abundant (summer), ants collected the same plant species but selected different sizes; when food resource is scarce (autumn), ants foraged on different plants.5. The importance of different factors (morphological, behavioural, ecological) possibly affecting competition and coexistence are discussed.

Seed selection and coexistence in two sympatricMessorharvester ant species (Hymenoptera: Formicidae)

“…For example, larger Messor barbarus and M. capitatus workers are able to collect larger and heavier resources not accessible to smaller M. bouvieri foragers (Arnan et al 2010). Our results partially agree with this finding, with the larger ant species, M. wasmanni (Solida et al 2011a), showing a preference for the heaviest seeds. The foragers of M. minor, on the contrary, preferred to collect larger resources, although the head width of the foragers was significantly smaller than that of M. wasmanni, respectively: 1.45 ± 0.05 vs. 1.80 ± 0.14 mm (Solida et al 2011a).…”

“…minor foragers may also be able to collect seeds of peculiar plant species when their field availability decreases below an optimal level, adopting in this way a sub-optimal foraging strategy (Detrain et al 2000), or may possibly increase in the diet the amount of less-preferred plant parts (Azcárate et al 2005;Solida et al 2011a). Workers of M. wasmanni, conversely, could switch their attention to alternative resources when the environmental abundance of seeds decreased below a particular level (Begon et al 1986;Wilby & Shachak 2000;Pirk et al 2009).…”

“…The ability of sympatric ant species to partition resources on the basis of their availability or size represents an important mechanism promoting coexistence (Davidson 1977;Mehlhop & Scott 1983;Pol et al 2011;Solida et al 2011a). Differences in adopted foraging strategies may be at the base of species coexistence (Hölldobler & Wilson 1990;Arnan et al 2010;Solida et al 2011a).…”

“…Differences in adopted foraging strategies may be at the base of species coexistence (Hölldobler & Wilson 1990;Arnan et al 2010;Solida et al 2011a).…”

“…Diet composition (plant parts and species) and food niche overlap are strictly influenced by season. During summer, when resources are abundant, ants collect the same plant species, whilst in autumn, when the abundance and diversity of resources decrease, niche partitioning is required to permit species coexistence (Solida et al 2011a). Temperature, another important feature influencing foraging strategies, does not have a relevant effect on the foraging behaviour of the two ant species (Solida et al 2014).…”