Resource partitioning among Odonata (Insecta: Anisoptera and Zygoptera) larvae in a Hong Kong forest stream

Larvae of four odonate species were common in Tai Po Kau Forest Stream, Hong Kong: Euphaea decorata (Zygoptera: Euphaeidae), Zygonyx iris (Anisoptera: Libellulidae), Heliogomphus scorpio and Onychogomphus sinicus (Anisoptera: Gomphidae). All co‐occurred within a single riffle reach and had similar life cycles. Consequently, available dimensions for niche partitioning were likely to have been microhabitat and diet. Across–stream gradients in population density, and the results of multivariate regression analyses of abundance against microhabitat parameters, were similar for all species except Z. iris. This species avoided microsites near the stream banks, and had no significant best–fit regression model predicting abundance. Nevertheless, microhabitat overlaps among all four species were high (Oxy > 0–81). The scale of this investigation (sampling units = 1000 cm2) may have obscured partitioning of space within microsites, because burrowing O. sinicus were unlikely to have occupied the same sediment patches as epibenthic H. scorpio or Z. iris. Dietary overlaps between Z. iris and the other species were low. Heliogomphus scorpio and O. sinicus had the most similar diets of any species–pair, but among these two species intraspecific overlaps between large and small individuals were generally less than interspecific comparisons between equivalent–sized larvae. Ontogenetic dietary shifts and asynchronous larval development in both of these gomphids may have contributed to intraspecific partitioning of food. Euphaea decorata had the broadest niche axes along food and microhabitat dimensions, whereas Z. iris was relatively specialized. Heliogomphus scorpio and O. sinicus made similar use of resources. In the absence of evidence that resources were limiting or depletable, competition could not be invoked as an explanation for niche partitioning. Instead, determination of morphology by phylogeny, and resultant influences on microhabitat selection and foraging behaviour, probably determined patterns of resource use resulting in closely related species showing the greatest niche overlap.