Abstract
The classification of functional feeding groups of aquatic insects is often misleading in tropical/subtropical streams because their feeding habits are assumed to be the same as their temperate counterparts according to the mouthpart structure and foraging behavior. This study aimed to examine the diets and preferences of mayfly grazers (Baetis spp. and Rhithrogena ampla) in a subtropical mountain stream in the dry and wet seasons. In the stream, epilithic algal communities on insect-excluded bricks (as a grazer-excluded control) were dominated by small adnate diatoms, most likely due to the high current velocity. Both grazers preferred understory and small adnate diatoms, Achnanthes spp. and Achnanthidium pyrenaicum, in both seasons. However, the stalked diatoms Gomphonema spp. were preferred only by Baetis, but not by Rhithrogena, in the dry season when the current velocity became relatively slower. The results of pairwise tests further showed that the algal compositions on the insect-excluded bricks coincided with the diets of both grazers in the wet season but were distinct from those on the bricks in the dry season. Seasonal variations in the algal compositions of the diets of Rhithrogena and on the insect-excluded bricks were apparent, but not in the diets of Baetis. The algal physiognomy was most likely attributed to the impact of the high current velocity in the stream. Our results suggest that the diet preference by mayfly grazers in the stream is potentially influenced by algal availability.
Highlights
The classification of functional feeding groups of aquatic insects is often misleading in tropical/ subtropical streams because their feeding habits are assumed to be the same as their temperate counterparts according to the mouthpart structure and foraging behavior
Our objectives are (1) to identify algal compositions in the gut contents of two dominant mayfly grazers in this subtropical mountain stream, (2) to determine whether there is a seasonal variation in the diet of these grazers, and (3) to assess the degree of food selectivity by these grazers by comparing the algal composition of their gut contents with the algal composition of bricks in the stream where grazing by aquatic insects was excluded
We discovered that the preference of diatom species by Baetis and Rhithrogena was different; stalked diatoms Gomphonema spp. were preferred by Baetis, but not by Rhithrogena, in the dry season
Summary
The classification of functional feeding groups of aquatic insects is often misleading in tropical/ subtropical streams because their feeding habits are assumed to be the same as their temperate counterparts according to the mouthpart structure and foraging behavior. Algal biomass can be effectively reduced by herbivores in a neotropical stream (Barbee 2005), research on the functional feeding mode of grazers in tropical and subtropical streams is still limited. Can they limit algal biomass, but they can alter the physiognomy and community structure of algae, exerting strong indirect effects within food webs and on nutrient cycling (Holomuzki et al 2010). The mouthpart structure and foraging behavior of aquatic insects vary among different taxa They most likely select food on the basis of algal size or growth form (Tall et al 2006)
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