Testing the directed dispersal hypothesis: are native ant mounds (Formica sp.) favorable microhabitats for an invasive plant?

Abstract

Ant-mediated seed dispersal may be a form of directed dispersal if collected seeds are placed in a favorable microhabitat (e.g., in or near an ant nest) that increases plant establishment, growth, and/or reproduction relative to random locations. We investigated whether the native ant community interacts with invasive leafy spurge (Euphorbia esula) in a manner consistent with predictions of the directed dispersal hypothesis. Resident ants quickly located and dispersed 60% of experimentally offered E. esula seeds. Additionally, 40% of seeds whose final deposition site was observed were either brought inside or placed on top of an ant nest. Seed removal was 100% when seeds were placed experimentally on foraging trails of mound-building Formica obscuripes, although the deposition site of these seeds is unknown. Natural density and above-ground biomass of E. esula were greater on Formica mound edges compared to random locations. However, seedling recruitment and establishment from experimentally planted E. esula seeds was not greater on mound edges than random locations 3 m from the mound. Soil from Formica mound edges was greater in available nitrogen and available phosphorus relative to random soil locations 3 m from the mound. These results suggest Formica ant mounds are favorable microhabitats for E. esula growth following seedling establishment, a likely consequence of nutrient limitation during plant growth. The results also indicate positive species interactions may play an important role in biological invasions.

CO2 efflux from subterranean nests of ant communities in a seasonal tropical forest, Thailand

“…Studies have reported that mound-type nests made from soil and/or litter have nutrient profiles that differ from those of surrounding soil or forest floor (Ohashi et al 2007a; Domisch et al 2008). Moreover, specific fauna and flora are found at ant mounds (Berg-Binder and Suarez 2012; Laakso and Setälä 1997). Similarly, subterranean ant nests can affect water infiltration rates (Lavelle and Spain 2003) and soil erosion (Cerdà and Jurgensen 2008) by decreasing soil bulk density and increasing soil porosity.…”

Native leaf‐tying caterpillars influence host plant use by the invasive Asiatic oak weevil through ecosystem engineering

“…No parasitism of C. castaneus has been observed by us or reported in the literature, although protection against parasitism is often a function of leaf shelters (e.g., LoPresti and Morse 2013). Ants facilitate the abundance of nonnative plant species by providing establishment sites of reduced competition (Farji-Brener et al 2010, Berg-Binder andSuarez 2012), but just the opposite may be the case in our system if multiple species use the same shelters, increasing competition (Sliwinski and Sigmon 2013) or parasitism (Lill et al 2007). …”

“…Understanding these positive effects of ecosystem engineers may help mitigate the spread and resultant impacts of invasive species (Bulleri et al 2008, Pearse andAltermatt 2013). Despite the prevalence of insects, there are only two published studies of native insect species (both ants) influencing the abundance of nonnative species (both nonnative plants) through ecosystem engineering (Farji-Brener et al 2010, Berg-Binder andSuarez 2012).…”

The role of Rhytidoponera metallica (Hymenoptera, Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

“…Several benefits gained by plants have been identified; namely, directed dispersal, distance dispersal, predator avoidance and fire avoidance (Giladi ; Warren & Giladi ), although the relative importance of these benefits varies among ecosystem types (Giladi ; Rico‐Gray & Oliveira ). The directed dispersal of seeds to ant nests can be beneficial when nests are enriched with nutrients (Davidson & Morton ; Beattie & Culver ), resulting in greater plant growth (Culver & Beattie ; Davidson & Morton ; Berg‐Binder & Suarez ) and survival compared with plants derived from undispersed seeds (Davidson & Morton ; Hanzawa et al . ).…”