Trophic structure of ground-dwelling insects in the coastal zone of a salt lake in southern Siberia based on the data of isotopic analysis

The trophic structure of a ground-dwelling insect community has been studied in the coastal zone of a salt lake in the southern forest-steppe (Novosibirsk oblast). Five contrasting habitats along a 170-m catena with an altitude drop of 1.8 m were studied. In each habitat, the soil, as well as dominant insect and plant species, were sampled: phytophages, saprophages, and predators. According to a stable-isotope analysis of carbon and nitrogen (δ 13 C and δ 15 N), phytophagous insects (the locust Epachromius pulverilentus and carabid beetle Dicheirotrichus desertus ) are closely connected to their food objects and hardly migrated along the catena. Saprophages (the mole cricket Gryllotalpa unispina and earwig Labidura riparia ) use various food resources; some of them (mole crickets) tend to migrate between the biotopes. Predatory beetles (carabid imagoes) can be separated into three trophic guilds: (1) highly mobile active predators, including the tiger beetles Cephalota chiloleuca and C. elegans ; (2) small generalist predators of Pogonini tribe ( Pogonus cumanus, P. transfuga, Pogonistes rufoaeneus , and Cardiaderus chloroticus ); and (3) relatively large consumers of soil saprophages and aquatic organisms ( Curtonotus propinquus and Cymindis equestris ). The trophic niche overlap of different predators is partially compensated by their confinement to different habitats.