Detrimental effects of two widespread invasive ant species on weight and survival of colonial nesting seabirds in the Hawaiian Islands

Abstract

Invasive ants are a significant conservation concern and can have far-reaching effects in ecosystems they invade. We used the experimental control of ant numbers on two pairs of small (\5 ha) offshore islets dominated by either the big-headed ant, Pheidole megacephala or the tropical fire ant, Solenopsis geminata to investigate the influence of these species on seabird hatching success, fledging success and weight. Limited unpublished observations of both ant species attacking nesting seabirds exist, but the frequency of attacks or how they affect seabird growth and survival are unknown. Islandwide treatments with hydramethylnon resulted in the eradication of P. megacephala and the temporary reduction of S. geminata densities. No difference in hatching success, growth, or fledging success of Wedge-tailed Shearwaters (Puffinus pacificus), a common colonial nesting seabird in the Hawaiian Islands was observed on the pair of islets dominated by P. megacephala. On islets dominated by S. geminata, ant control resulted in a temporary increase in fledging success. Injury frequency increased dramatically on the untreated islet (8.3-100%) while remaining the same on the treated islet (27-38%). Severely injured chicks (i.e., chicks that lost [20% of tissue on their feet) weighed significantly less than uninjured chicks and did not fledge. It is unclear if the chicks were being preyed upon or stung in defense of nearby ant colonies. Radical changes in invasive ant populations have been noted, and booming ant populations could cause short-term, but widespread damage to seabird colonies. The negative effects of invasive ants on seabirds may be difficult to detect, and therefore unknown or underestimated throughout the world where the two groups overlap.

Indirect effects of ant eradication efforts on offshore islets in the Hawaiian Archipelago

“…2). This was confirmed using bait cards which were set out multiple times immediately after application (Plentovich et al 2009), but which tend to be inferior to other passive trapping methods such as pitfall traps since they tend to detect dominant species. Hoffmann and O'Connor (2004) also attempted but failed to eradicate S. geminata from an area of approximately 3 ha using 10?…”

“…This has global significance as hundreds of invasive ant species are undergoing human-mediated range expansions (McGlynn 1999;Holway et al 2002). These invasions can alter the structure and functioning of natural communities (Christian 2001;Holway et al 2002;Hill et al 2003;O'Dowd et al 2003;Krushelnycky and Gillespie 2008) and can be catastrophic to native biota by reducing, extirpating and possibly causing the extinction of arthropod species (Perkins 1913;Risch and Carroll 1982;Cole et al 1992;Gillespie and Reimer 1993;LaPolla et al 2000;Hill et al 2003;O'Dowd et al 2003), directly and indirectly harming vertebrates (Meek 2000;Holway et al 2002;Davis et al 2008;Plentovich et al 2009) and altering plant communities (Bach 1991;Green et al 1997;Christian 2001;Hill et al 2003;O'Dowd et al 2003;Handler et al 2007). Endemic biota, especially those in areas such as the Hawaiian Islands where ants are believed to be absent from the native fauna, seem to experience the most significant losses (Perkins 1913;Zimmerman 1970;Howarth 1985;Cole et al 1992; Gillespie and Reimer 1993;LaPolla et al 2000;Krushelnycky and Gillespie 2010).…”

Ecological restoration following the local eradication of an invasive ant in northern Australia

“…Rehabilitation is important, not only in the sense of ecological integrity, but also to prevent succession of another exotic species into the ecological gap left by the eradicated species (Myers et al 2000). Indeed P. megacephala eradications have resulted in subsequent invasion by S. geminata in both Hawaii and northern Australia (Plentovich et al 2009;Hoffmann unpublished data). While not formally quantified, I did note an increase in the occurrence of the tramp Black crazy ant Paratrechina longicornis through some of the treated area, however, this species is not known to have environmental consequences of concern.…”

“…In 2004, eradications of African big headed ant Pheidole megacephala and Tropical fire ant Solenopsis geminata covering 30 and 3 ha, respectively, within Kakadu National Park, Australia, were declared completed (Hoffmann and O'Connor 2004). Most recently, a 4 ha P. megacephala infestation has been reported eradicated from Mokuauia islet, Hawaii, (Plentovich et al 2009). …”

Effect of an Invasive and Native Ant on a Field Population of the Black Citrus Aphid (Hemiptera: Aphididae)

“…However, invasive species usually have negative, and occasionally devastating, impacts on native ßora and fauna, e.g., Phragmites and other plants (Franklin et al 1999, Gratton andDenno 2005) and zebra mussels (Ludyanskiy and McDonald 1993). Among the most destructive invasive taxa are ants, which are capable of displacing local organisms including arthropods (Holway 1998a), reptiles (Suarez and Case 2002), birds (Plentovich et al 2009), and mammals (Allen et al 2004). Invasive ants, such as the Argentine ant, Linepithema humile (Mayr) (Formicidae: Dolichoderinae), can disrupt entire communities by displacing local ants (e.g., Erickson 1971, Bond and Slingsby 1984, Carpintero et al 2005, in large part because of their aggressive nature and ability to recruit overwhelming numbers of workers (Holway et al 2002a).…”