Ants and moths: Analysis of biodiversity and abundance in revegetated pastoral land

Insect bioindicators have been used the world over, but they have seldom been used to evaluate revegetation efforts on previously pastoral land. The present study aimed to evaluate the health and biodiversity of a 3-year-old revegetated plot of previously pastoral land in Australia by comparing it to a mature forest, using ants and flying insects as bioindicators. Using ant baits and a nocturnal light trap, the study was conducted at these two sites over the course of two days and nights. Three genera of ants were found in the mature forest, and one (Ochetellus) was found in the revegetated forest, but in much greater abundance than in the mature forest. Ochetellus also exhibited superior recruitment over the other ants. Greater abundance but lower diversity was also seen in the flying insect results, with 32 morphospecies across 6 orders present in the mature forest, compared to 18 morphospecies in the revegetated forest. These results were interpreted considering physical and biological differences between the sites, the limitations of light traps, and ants’ and flying insects’ applicability as bioindicators. T relationship between modern agriculture and native vegetation is often exploitative and disruptive to the natural processes at work, but humans occasionally seek to restore previously disturbed habitats to their original state. In doing so, biological indicators, or bioindicators, are useful for informing environmental managers or rehabilitators about the success of restoration efforts. While an abundance of literature exists on bioindicator work with rehabilitated mine sites and sand dune systems, relatively little work has focused on previously pastoral or agricultural rehabilitation efforts, especially relating to rainforests (Majer, 1983; Majer & Nichols, 1998; Campbell, 1998; Nakamura, Proctor, & Catterall, 2003). In seeking to assess the health of a revegetated plot of previously agricultural land, the present study used ants and nocturnal flying insects as bioindicators. A good bioindicator species should be highly correlated with the diversity of other organisms in an environment, have a specific habitat niche, exhibit sensitivity to disruption of the habitat, and be easy to collect and identify (Angelstam, 1998; Armbrecht & Ulloa-chaco, 2003). Fortunately, ants (family Formicidae) and moths (order Lepidoptera) both fulfill this role well. In fact, in a review of different bioindicator species, ants and Lepidoptera came out on top as the most useful and suitable bioindicators for forests (Armbrecht & Ulloa-chaco, 2003). Lepidoptera diversity is especially wellcorrelated with overall habitat quality and ants specifically are highly correlated with the abundance, richness, and composition of the flora and other invertebrates with which they share a biological system (Uehara-Prado & Freitas, 2009; Majer, 1985). In short, with a comprehensive knowledge of the ants or moths in a system, one also has a good understanding of the diversity of the other organisms and the overall health of an ecosystem. Furthermore, beyond serving as an indicator of other ecosystem processes, ants (and other invertebrates) are themselves essential for ecosystem health, providing services such as soil aeration and drainage, litter decomposition, nutrient cycling, pollination, and (a task especially characteristic of ants) seed distribution (Majer, 1985). Accordingly, the overall diversity of insect orders seen in an ecosystem is obviously a direct indicator of ecosystem diversity. It should be noted, however, that most of the background on using ants and flying insects as bioindicators in Australia has focused on mine site rehabilitation, and their applicability to reforested farmland has a limited literature, to which the present study might contribute (Nakamura, Proctor, & Catterall, 2003). From an abundance of previous literature comes a few of the important background characteristics of the three genera of ants represented in the present study: Pheidole, Iridomyrmex, and Ochetellus. For one, Pheidole is not an abundant species in habitats annually disturbed by fire, but Iridomyrmex is, leading to the prediction that Pheidole would not be present in the revegetated site (which was “disturbed” and planted only three years ago) while the Iridomyrmex might be (Andersen, 1991). Pheidole is also reported to be a highly competitive genus with colonies operating with great efficiency, so one might expect its numbers to be higher than those of other ants when both are found in the same area (Anderson, 2000). For Ochetellus, a slight discrepancy exists in the literature. Some have found Ochetellus, an opportunist, to be characteristic of disturbed sites: a ruderal specialist (it is one of the first species to colonize newly disturbed sites) (Andersen, 1997; King, Andersen, & Cutter, 1998). Others have found Ochetellus to be abundant in mature forests and unimportant in interacting with other ant fauna. The present study aims to shed some light on that discrepancy in the literature (Majer & Nichols, 1998). Working on a revegetated forest site and a mature forest site, the present study aimed to investigate the biodiversity of the revegetated forest by using ants and flying insects as bioindicators of overall biodiversity and health of the forest systems. Is three years a long enough time for a revegetated site to demonstrate the biodiversity typical of a mature forest stand? We predicted that it would not be. More specifically, our hypotheses were 1: that the mature rainforest would yield higher species richness (more species of ants represented in the baits and more species of flying insects represented in the traps) than the revegetated forest would; 2: that the mature rainforest would yield higher abundance in insects (higher overall numbers summed across the different species) than the revegetated forest; and 3: that the revegetated forest would have ant genera represented that are purportedly characteristic of disturbed sites such as Ochetellus or the infamous invasive African Big-Headed ant, Pheidole megencephala.