Ant community structure on a small Pacific island: only one native species living with the invaders

Abstract

In most studies about ant communities, species are grouped into competitive hierarchies where top dominants drive the majority of other species away from resources. Nevertheless, in some ecosystems high ground temperatures may disrupt this hierarchical organization. Other changes in community structure are caused by the arrival of invasive ant species, which rapidly disassemble local communities. We studied the effects of competition and temperature on ant community organization on Surprise Island (New Caledonia). Four different habitats were distinguished: a central plain, a sea shore Argusia shrubland, a dense Scaveola shrub, and an arboreal Pisonia strata. Eight ant species were identified from pitfall traps (seven introduced and only one native species, Pheidole oceanica). Ant assemblages in each habitat had a different ecologically dominant species, and a dominant species in one habitat could be non-dominant and less abundant in another. From interactions at baits, we built a competitive hierarchy where the top dominant species was the native Ph. oceanica. Daily foraging activity rhythms of the different species mostly overlapped. The relationship between bait occupation and ground temperature followed a negative linear pattern at all sites and for most species, except for the relatively thermophilous Monomorium floricola. Indices of co-occurrence in pitfall traps indicated that species co-occurred randomly with respect to one another. Conversely, species appeared to be segregated when we examined co-occurrence at baits at the sites where Ph. oceanica was abundant. Oceanic islands are very susceptible to alien species, but on Surprise Island it seems that the sole native species dominates in some habitats when confronted by invasive species.

Competitive dominance in the organisation of Mediterranean ant communities

“…Cerdá et al, 2012). We found random patterns of co-occurrence both in Argentine-ant-invaded sites and in dominant-free sites, but some degree of species segregation in the presence of T. nigerrimum.…”

Alien Insects and Insect Conservation

“…Their impacts have been assessed in many situations, but perhaps nowhere more disturbingly than on the Hawai'ian archipelago, where no native ants occur. Predominance of invasive ants was also evident on Surprise Island, New Caledonia, where seven alien species accompanied a single native species, Pheidole oceanica (Cerda et al 2012 ). The different habitats examined were dominated by different alien species but the overall 'top dominant', assessed from recording interactions at honey/peanut butter baits, was P. oceanica , which recruited large numbers of workers at baits and aggressively excluded other species.…”

“…This Pacifi c native ant is clearly able to resist invasion by some tramp ants, as a form of 'biotic resistance' reported also for several other native ants against invaders. Two life history traits were suggested (Cerda et al 2012 ) to possibly advantage that outcome -the very effi cient mass recruitment system (whereby a mean of 40 workers were attracted to baits in their study) and the occurrence of a soldier caste: P. oceanica was the only species with big-headed workers on the island. Several key Pacifi c region tramp ants, however, were absent from Surprise Island.…”

Alien Species and Insect Conservation

“…They are regarded as amongst the most ecologically harmful of all invasive insects. Two life history traits were suggested (Cerda et al 2012 ) to possibly advantage that outcome -the very effi cient mass recruitment system (whereby a mean of 40 workers were attracted to baits in their study) and the occurrence of a soldier caste: P. oceanica was the only species with big-headed workers on the island. Their impacts have been assessed in many situations, but perhaps nowhere more disturbingly than on the Hawai'ian archipelago, where no native ants occur.…”