Use of stable isotopes to assess the intraspecific foraging niche of males and female colour morphs of the damselfly Enallagma hageni

Abstract

For the first time, diet and isotopic niche overlap among males and two female‐specific colour morphs of a damselfly were quantified to test whether sexual conflict could cause intra‐sexual diet variation. Relative to the green female morph, blue females, similar in coloration to the blue males, may be more likely overlooked by mate‐searching males. If so, blue females should be more likely to forage unmolested at lake shores, where the density of males and prey is high. The blue morph's isotopic niche space should therefore differ from that of green females and be more similar to that of males. Stable isotope analyses of two Michigan populations failed to support these predictions. Despite population differences in δ13C and diet, within sites isotopic niches overlapped among males and females, with little difference between the two female colour morphs. Males exhibited the broadest isotopic niche area, which increased across years, whereas that of blue females became more restricted, possibly due to greater sexual harassment in forest feeding sites. There was an unexpectedly high shift in δ13C from prey to predator. Future work is merited to determine whether such trophic shifts are characteristic of Odonata, a group of important aquatic and terrestrial predators.