General Impact
While the Argentine ant (Linepithema humile) is associated with disturbed habitats throughout its introduced range, it can penetrate native habitats that have experienced little human disturbance. Examples include: matorral in Chile, fynbos in South Africa, coastal sage scrub in southern California, riparian woodlands in California, subalpine shrubland in Hawaii, and oak and pine woodland in Portugal (Fuentes 1991, Bond and Slingsby 1984, Suarez Bolger and Case 1998, Ward 1987, Holway 1998, Cole et al. 1992, in Suarez Holway and Case 2001).
L. humile is a dominant ant and an aggressive competitor. It has displaced native ant species in an ecologically sensitive area in Spain (Carpintero et al. 2005) and has been associated with local extinctions of native ants in California (Suarez Bolger and Case 1998). Californian ants that are especially sensitive to displacement are army ants (Neivamyrmex spp.) and harvester ants (genera Messor and Pogonomyrmex), both of which are important ecosystem regulators (Suarez Bolger and Case 1998). Monomorium species, such as M. ergatogyna, may persist because of their chemical defences or their tolerance of higher temperatures (Holway 1999, Adams and Traniello 1981, Andersen et al. 1991, in Holway et al. 2002a). In introduced regions L. humile may be displaced by the red imported fire ant (Solenopis invicta), another invasive ant (Holway et al. 2002a).
Invasive ants have a great potential to alter ecosystem processes, including ant-mediated seed dispersal or plant pollination. In California the removal of seeds produced by the myrmecochorous (ant-dispersed) tree poppy Dendromecon rigida is less in areas inhabited by the Argentine ant (L. humile) than in areas inhabited by the common harvester ant (Pogonomyrmex subnitidus) (Carney et al. 2003). A similar outcome has occured in the South African fynbos, where the displacement of large native ants by L. humile has lead to a reduction in the dispersal of large ant-dispersed seeds and a reduction in the reproduction of those plants (Christian 2001, Holway et al. 2002a).
Native arthropods are greatly threatened by Argentine ants. In South Africa, the Argentine ant can collect up to 42% of available nectar before bees can forage (Buys 1987, in Holway et al. 2002a). In Hawaii the Argentine ant reduces numbers of many native arthropods, including essential pollinators (Cole et al. 1992, in Krushelnycky et al. 2004), the loss of which could threaten insect-pollinated plants such as the endangered “silversword” (Argyroxiphium spp.)
Location Specific Impacts:Easter Is. (Rapa Nui) (Chile) 
Competition: The Argentine ant (Linepithema humile) is numerically dominant over most of the island and may have led to the extinction of several ant species on the island. France
Agricultural: The Argentine ant (Linepithema humile) harms fruiting plants through homopteran tending (Benois 1973).
Competition: The Argentine ant (Linepithema humile) displaces other ants (Benois 1973).
Human nuisance: The Argentine ant (Linepithema humile) is a nuisance for tourism on the Cote d'Azure (Benois 1973). Corsica (France)
Ecosystem change: In Corsica, the Argentine ant (Linepithema humile) appears less effective than Aphaenogaster spinosa, a dominant native ant, at dispersing the seeds of a rare endemic plant, but the consequences for the plant’s population dynamics are unclear (Quilichini and Debussche 2000, Holway et al.. 2002a). Portugal
Competition: Ant species richness and diversity is much lower in woodland invaded by the Argentine ant (Linepithema humile) (Cammell et al.. 1996). South Africa
Agricultural: The Argentine ant (Linepithema humile) may be an agricultural pest, causing population explosions of honeydew-producing Homoptera (Ness and Bronstein 2004). For example, outbreaks of the red scale insect Aonidiella aurantii in South African citrus orchards and outbreaks of the mealybug Planococcus ficus in South African vineyards have both been associated with L. humile (Samways et al.. 1982, Addison and Samways 2000, in Holway et al.. 2002a).
Competition: Honeybees (Apis mellifera) in West Cape experience competitive pressure from the Argentine ant (Linepithema humile), which collects 42% of nectar before bees forage (Buys 1987, in Holway et al.. 2002a). Southern South Africa (South Africa)
Competition: The Argentine ant (Linepithema humile) excludes native ant species in fynbos habitat, leading to reduced seed dispersal of native plants (Bond and Slingsby 1984; Christian 2001). Also, L. humile reduces diversity and abundance of arthropods on protea plants (Visser et al.. 1996). Donana National Park (Spain)
Competition: Aggressiveness tests have shown that the Argentine ant (Linepithema humile)displays a higher level of aggressive behaviour, including attacking behaviour, than does any other native ant species found in the Doñana National Park.
Reduction in native biodiversity: A survey by Carpintero and colleagues (2005) found that out of 182 cork trees (Quercus suber) in the park, 115 were occupied by Argentine ants. The second most common species was the native ant Camponotus scutelaris which occupied 40 trees. It is known that between 1992 and 2000 Argentine ants displaced native ant species from at least 23 trees. While C. scutelaris tolerates the presence of C. truncatus and C. lateralis (submissive native ants that form small colonies) it cannot survive with Argentine ants, which occupy trees on their own. Argentine ants are able to displace all native ant species in the Doñana National Park, causing a decrease in ant biodiversity. Haleakala National Park (United States (USA))
Ecosystem change: The Argentine ant (Linepithema humile) has displaced endemic beetles, which are natural keystone invertebrate predators in the park (Cole et al.. 1992, in Earlham College 2002).
Reduction in native biodiversity: Hawaiian arthropods evolved in the absence of ants and are highly vulnerable to the pressures imposed by ant predation and competition (Perkins 1913, Gillespie and Reimer 1993 1994, in Krushelnycky et al.. 2004). Because of this the Argentine ant (Linepithema humile) is considered to be the single greatest threat to the survival of a number of unique arthropod species endemic to the upper Haleakala volcano (Haleakala National Park, Hawaii). Endemic arthropods are affected by Argentine ants by competitive pressures (e.g. spiders and acrabid beetles) and/or by predation by the ant (collembolans, lepidoptera larvae, bee larvae and flies) (Cole et al.. 1992, in Holway et al.. 2002a). Studies have found eight orders of arthropods to be reduced or absent in areas invaded by L. humile in Hawaii (Cole et al.. 1992, in Holway et al.. 2002a). These include essential arthropod pollinators (Cole et al.. 1992, in Krushelnycky et al.. 2004), and (Krushelnycky et al.. 2004).
Threat to endangered species: As the Argentine ant (Linepithema humile) reduces the numbers of native insect species, including pollinators, consequent indirect effects may be felt on native plants dependant on such pollinators. For example, there are at least two endangered plant species on upper Haleakala National Park that are dependent on native pollinators for seed set, including the “silversword” (Argyroxiphium spp.) (HEAR 2005). California (United States (USA))
Agricultural: Pests such as mealybugs and aphids may increase in number due to the activities of Argentine ants (Linepithema humile), threatening the cultivation of certain crops. Infestations of the mealybug Pseudococcus adonidum have been positively correlated with the Argentine ant in California (Phillips et al.. 1987, in Holway et al.. 2002a). L. humile has also been observed to remove parasitised individuals of the walnut aphid (Chromaphis juglandicola), improving the health of the aphid population by reducing the spread of these parasites (Frazer and Van den Bosch 1973, in Holway et al.. 2002a).
Competition: The Argentine ant (Linepithema humile) has displaced most native ants in areas of California where it has become established (Ward 1987, Suarez et al.. 1998, Erickson 1971, Human and Gordon 1996, Holway 1998 in Tsutsui et al.. 2000). The Argentine ant is classified as a “dominant Dolichoderine” as it is highly active, abundant and behaviourally dominant to most other ant species (including those classified as “subordinate Camponotini”) (McGlynn 1999). According to this schema they are expected to have a typically large impact on native ant communities (McGlynn 1999).
The data produced from a survey of 40 fragments of scrub habitat in California (Suarez Bolger and Case 1998) indicates that local extinctions of native ant species occur in habitat fragments in coastal southern California. The relative vulnerability of native ants to habitat fragmentation and the presence of Argentine ants was found to vary. The most sensitive species include army ants (Neivamyrmex spp.) and harvester ants (genera Messor and Pogonomyrmex) both of which are important to ecosystem-level processes (Suarez Bolger and Case 1998). L. humile excludes native and introduced ants (Suarez et al.. 1998), reducing the food resource base for coastal horned lizards, possibly causing lower lizard abundances in Argentine ant invaded areas (Suarez et al.. 2000).
Ecosystem change: The Argentine ant (Linepithema humile) may have indirect affects on seedling recruitment of myremecochorous plants in San Diego County (California). A study was conducted to measure the rates of removal seeds of the myrmecochorous tree poppy Dendromecon rigida from ant-accessible seed stations in various coastal sites in the region. The study found that significantly less seeds were collected in areas dominated by the Argentine ant (L. humile) than were collected in areas inhabited by the common harvester ant (Pogonomyrmex subnitidus). The latter is a native ant disperser that is sensitive to displacement by L. humile (Carney et al.. 2003).
In behavioural trials, L. humile was seldom able to carry whole seeds and, if it could, was only able to carry them a few centimetres. The displacement of native harvester ants by L. humile appears to decrease the dispersal of Dendromecon rigida seeds and may be increasing loss of seeds due to predation (Carney et al.. 2003).
Interaction with other invasive species: A survey of 40 fragments of scrub habitat in California showed invasive ants to be more abundant near developed edges and in areas dominated by exotic species (Suarez Bolger and Case 1998).
Predation: On Coronado Island, the Argentine ant (Linepithema humile) attacks and kills the endangered California least tern chicks (see Sterna antillarum browni) The status of this species in 1999 was 'stable'. (Hooper 1995).
Reduction in native biodiversity: In California many arthropods have been found to be reduced or absent in areas invaded by the Argentine ant (Linepithema humile), including: collembola, flies, spiders and beetles (Human and Gordon 1997, Bolger et al.. 2000, in Holway et al.. 2002a). Nest failure of the California gnatcatcher, Polioptila melanura, has been linked with the presence of L. humile. A negative relationship between numbers of gray shrew (Notiosorex crawfordi) captures and the abundance of L. humile has been detected (Sockman 1997, Laakkonen et al.. 2001, in Holway et al.. 2002a).
Horned lizards (Phyrynosoma spp.) are particularly vulnerable to the effects of an Argentine ant invasion as their range is declining and they have a specialist diet consisting of native ant species (Pianka and Parker 1975, in Suarez Richmond and Case 2000). In areas invaded by the Argentine ant most native ants have been displaced and coastal horned lizards (P. coronatum), which usually feed on harvester ants such as Pogonomyrmex and Messor, are forced to incorporate non-ant arthropods and smaller ants into their diet (Suarez Richmond and Case 2000) as the lizards do not feed on the Argentine ants (Suarez Richmond and Case 2000). The displacement of coastal horned lizards by L. humile may be inferred from the lack of range overlap between the species (Fisher et al.. 2002, in Holway et al.. 2002a). Hawaii (United States (USA))
Competition: The Argentine ant (Linepithema humile) competes with native arthropods for limited food resources and nesting/shelter sites. Native arthropod abundances, including larvae of important pollinators, are consequently reduced (Cole et al.. 1992).
Predation: The Argentine ant (Linepithema humile) actively predates upon a number of native arthropod taxa, notably soft-bodied and flightless forms (Cole et al.. 1992; Krushelnycky pers. obs.). Also has been seen attacking eggs of the Hawaiian goose, or Nene (F. Duvall pers. comm.). Southeast US (United States (USA))
Competition: The Argentine ant (Linepithema humile) excludes native and introduced ants (Wilson 1951).
Human nuisance: The Argentine ant (Linepithema humile) enters homes, often in large numbers.
|
