Informed conservation decision-making requires meaningful biodiversity assessment, yet performing an inventory of all species present at a site is an impossibility. A small group of species is frequently used as a proxy for "total" biodiversity, and various attributes required by bioindicator groups have been suggested. We synthesized these suggestions as four key criteria: i) tractable taxonomy, ii) easily surveyed, iii) broadly distributed higher taxa but specialized species, and iv) diversity patterns reflected in other groups; and compare three groups-bats, beetles and butterflies-against these criteria to evaluate their potential as bioindicators in Malaysia. DNA barcodes from butterflies, bats and beetles sampled during standardized surveys at Rimba Ilmu Botanic Garden and Ulu Gombak Forest Reserve were sorted into molecular operational taxonomic units (MOTU) and assigned species and family names. Beetle and butterfly sampling required a similar number of person-hours per species, which was an order of magnitude lower than that required for bat sampling. It was easier to generate DNA barcodes for butterflies and bats than for beetles and the number of MOTU assigned a species and/or family name was higher for butterflies and bats (>82%) than for beetles. Most butterfly and bat families were found at both sites but the species of all three groups showed little overlap between sites (<15%). The species richnesses of all three groups were correlated with each other, but only bat and butterfly species richness was strongly correlated and statistically significant. Based on the four criteria, butterflies showed greatest potential as bioindicators.

In large man-made reservoirs such as those resulting from hydroelectric dam construction, bacteria transform the relatively harmless inorganic mercury naturally present in soil and the submerged plant matter into toxic methylmercury. Methylmercury then enters food webs and can accumulate in organisms at higher trophic levels. Bats feeding on insects emerging from aquatic systems can show accumulation of mercury consumed through their insect prey. In this study, we investigated whether the concentration of mercury in the fur of insectivorous bat species was significantly higher than that in the fur of frugivorous bat species, sampled near hydroelectric reservoirs in Peninsular Malaysia. Bats were sampled at Temenggor Lake and Kenyir Lake and fur samples from the most abundant genera of the two feeding guilds-insectivorous (Hipposideros and Rhinolophus) and frugivorous (Cynopterus and Megaerops) were collected for mercury analysis. We found significantly higher concentrations of total mercury in the fur of insectivorous bats. Mercury concentrations also differed significantly between insectivorous bats sampled at the two sites, with bats from Kenyir Lake, the younger reservoir, showing higher mercury concentrations, and between the insectivorous genera, with Hipposideros bats showing higher mercury concentrations. Ten bats (H. cf. larvatus) sampled at Kenyir Lake had mercury concentrations approaching or exceeding 10 mg/kg, which is the threshold at which detrimental effects occur in humans, bats and mice.