Invasive Ants

Ants are common in places where people live. Everyone has seen and at least has some casual experience with ants. In many warmer parts of the world ants are much more familiar to local people. They occur in greater abundance and are more often found in homes and other dwellings. Most tropical and subtropical areas also have one or a number of invasive ants, i.e., species of ants that are notable for their ability to become human pests.

For the South Pacific region, PIA Key is focused on invasive and introduced ants of the Pacific islands. It includes a key and excellent information about the species it covers. Many of the non-native ants in this region have also been transported to other parts of the world.

Invasive Ant Species
Invasive ant species are here divided, somewhat arbitrarily, into four sets:
 * Highly Invasive : Species that are essentially or actually world-wide in distribution.
 * Invasive : Species that are very wide spread across multiple regions, but are not world-wide.
 * Limited invasive : Species that occur at a limited number of sites outside their native range and often at low densities or with restricted distributions.
 * Secretly invasive : Species that occur outside their native range but in small numbers at low densities and often in non-disturbed habitats.

Note that these categories form a continuum and precise definitions of each are not possible. They are intended as a general guideline to group similar patterns only and should not be taken too seriously.

Supercoloniality
A combination of life history traits are seemingly playing a part in how a few invasive ants are able to dominate some areas where they are introduced. Supercoloniality is achieved/defined as a species having many nests, many queens, workers that are able to freely move between nests that can be many kilometres from their own, and this occurs across a large area with the ants achieving very high local abundance. Supercoloniality has been observed in numerous ant species that are invasive pests.

Recent Findings
Talaga et al. (2015) - Tank bromeliads, frequently associated with ants, are considered ‘biodiversity amplifiers’ for both aquatic and terrestrial organisms, and thus have a high ecological value. The focal species of this study, Aechmeaaquilega, sheltered the colonies of 12 ant species in a Guianese rural habitat where Odontomachus haematodus, associated with 60% of these plants, was the most frequent. Unexpectedly, the ant species richness was higher in a compared urban habitat with 21 species, but two synanthropic and four invasive ants were noted among them. Consequently, we conducted baiting surveys (on the ground, on trees and on trees bearing A. aquilega) as well as complementary surveys using different sampling modes in urban areas to test if A. aquilega is a surrogate revealing the presence of certain invasive ants. During the bait-ing survey, we recorded four Neotropical and eight introduced invasive ants out of a total of 69 species. Of these 12 invasive species, five were noted by baiting A. aquilega (including two only noted in this way). A bootstrap simulation permitted us to conclude that A. aquilega significantly concentrates certain species of invasive ants. This was confirmed by complementary surveys, where we did not record further species. We conclude that baiting on trees bearing large epiphytes in human-modified, Neotropical areas is a relevant complement to the early detection of invasive ants.

Phillips et al. (2018) - Pest risk analysts frequently ask if the climate of a pest risk analysis area could be suitable for the establishment of an organism of concern. Species distribution models can help to answer this question, but constructing them is technically complex, time consuming, and uninformative for additional non-modelled species. A quicker more broadly applicable approach involves using environmental distance metrics, including climate matching algorithms such as the 'match climates regional' function of CLIMEX (CLIMEX-MCR), to generate indices of climatic similarity between different locations without reference to particular species. Several studies have shown that various environmental distance metrics can provide biologically meaningful results. However, the veracity of the CLIMEX-MCR algorithm remains unevaluated, despite its application in numerous published studies. We used CLIMEX-MCR and high resolution New Zealand climate data to measure climatic similarities between New Zealand and the rest of the world. We then tested the veracity of the climatic match estimates by evaluating if their predictions regarding the suitability of New Zealand's climate for 43 non-native ant species corresponded with empirical observations of those species in New Zealand. Non-native ants that are, or were once, established outdoors in New Zealand had overseas distributions that were climatically well matched with New Zealand. In contrast, species that either are established only indoors in New Zealand, or were observed to temporarily nest outdoors then die in New Zealand, had overseas distributions that were poorly matched. Species that are frequently intercepted at New Zealand's border, but are not established there, generally also had overseas distributions with low climatic similarities to New Zealand. We also measured climatic similarities between New Zealand's 13 national parks and the rest of the world. The overseas distributions of the non-native ants showed poor climatic matches with New Zealand's national parks, which was consistent with the absence of persistent outdoor non-native ant populations in those parks. Our results support the utility of CLIMEX-MCR algorithm for pest risk analysis. A recent paper by Krapf et al. 2018 examined how unicoloniality may be maintained in the ant, Tetramorium alpestre. This species is known to occur in at least one supercolonial population.