Does Argentine ant invasion affect prey availability for foliage-gleaning birds?

Abstract

Food availability during the breeding season plays a critical role in reproductive success of insectivorous birds. Given that the invasive Argentine ant (Linepithema humile) is known to alter arthropod communities, we predicted that its invasion may affect the availability of food resources for coexisting foliage-gleaning birds. With this aim we studied, for 3 years, foliage arthropods occurring on cork oaks (Quercus suber) and tree heaths (Erica arborea) in invaded and non-invaded secondary forests of the northeastern Iberian Peninsula. Our results show that Argentine ants interact with arboreal foliage arthropods in a different manner than the native ants they displace do. The invasive ant impacted the arthropod community by reducing order diversity and ant species richness and by causing extirpation of most native ant species. Arthropod availability for foliage gleaners' nestlings diminished in invaded cork oaks, mainly responding to the abundance and biomass depletion of caterpillars. Results suggest that the reproduction of canopyforaging foliage-gleaning species that mostly rely on caterpillars to feed their young could be compromised by the Argentine ant invasion. Thus, the Argentine ant could be promoting bottom-up effects in the trophic web through its effects on the availability of arthropod preys for insectivorous birds.

Coping with invasive alien species: the Argentine ant and the insectivorous bird assemblage of Mediterranean oak forests

“…In the Mediterranean climate, it is favoured by the proximity of streams and by irrigation, and is confined to these areas in most xeric regions (Holway 1998b;Menke et al 2007;Roura-Pascual et al 2009). By exploiting ground-level and aboveground plant resources, the effect of the Argentine ant on ant communities is huge (Gómez et al 2003) and can be noticeable on beetle abundance (Estany-Tigerström et al 2010;D. Casellas, personal communication).…”

“…and Lasius spp.) coexisting with it at low densities (Estany-Tigerström et al 2010;Gómez et al 2003). Uninvaded areas were those in which only native ant species occurred.…”

“…2) since invaded areas never showed higher values than uninvaded ones. A full explanation of the arthropod sampling and the results obtained are detailed in Estany-Tigerström et al (2010). Strong differences in invasion intensity among invaded sites can be ruled out, since the abundance of the Argentine ant in beating samples (137 out of 240 samples contained the species) did not differ between the four invaded sites (linear mixed-model as explained under 'Data analyses' F 3,236 = 0.569; P = 0.636).…”

“…It also forms nonspecialized associations with honeydew-producing Hemiptera, often in tree foliage. Ant activity especially affects caterpillar availability and Argentine ants could therefore be tough competitors to foliage-gleaning birds (Estany-Tigerström et al 2010).…”

“…Since previous work has shown that this invasive ant may be affecting the prey of insectivorous birds (Estany-Tigerström et al 2010), our aim here is to assess whether the invasion impacts have been extended to higher-order consumers and have measurable effects on the bird community. To this end we compared the species composition and the bird biomass in invaded and uninvaded forest areas.…”