Trophic structure of macroinvertebrates in tropical pasture streams

Invertebrates were sampled with D nets in three pasture streams. They were identified to genus level and submitted to gut content analysis, except for fluid feeders such as hemipterans, to which diet data was obtained from the literature. Trophic groups were determined based on a similarity analysis using the Bray-Curtis similarity coefficient.

Results

Five trophic groups were defined: fine-detritivores (feed mostly on fine particulate organic matter - FPOM), coarse-detritivores/herbivores (feed mostly on coarse particulate organic matter - CPOM - and plant material), omnivores, specialist-predators (prey upon aquatic insects only), and generalist-predators. Ephemeroptera, Diptera (except Tanypodinae), Coleoptera, and Trichoptera (except Smicridea) were detritivores. The caddis Macronema (Trichoptera) fed exclusively on plant detritus and Tanypodinae and Smicridea were classified as omnivores. The odonate families Calopterygidae and Gomphidae were classified as specialist-predators, while Macrobrachium (Decapoda), Belostoma, and Limnocoris (Hemiptera) were generalist-predators.

Conclusions

The great quantity and frequency of occurrence of FPOM consumed by most taxa highlight the importance of this food resource for macroinvertebrate communities from tropical streams. Furthermore, observed variations on trophic group assignment for some taxa indicate the generalist and opportunistic nature of these aquatic invertebrates. Such findings reinforce the importance of conducting gut content analysis on macroinvertebrates to understand their role in the structure and functioning of tropical streams.

Keywords:
macroinvertebrate diet; detritus; feeding groups; aquatic insects; lotic system

Taxon	N	Food item
Taxon	N	FPOM	CPOM	FUN	AI	NAI	FA	UCA	TG
Chironominae	90	98.7	0	0.2	0	0	0	1,1	F-D
Orthocladiinae	90	98.7	0	0.1	0	0	1.2	0	F-D
Tanypodinae	60	73.2	0	1.2	25.5	0.1	0	0.2	O
Ceratopogonidae	58	99	0	0.6	0	0	0.3	0.1	F-D
Simulium	41	100	0	0	0	0	0	0	F-D
Macronema	13	13.6	86.4	0	0	0	0	0	C-D/H
Smicridea	27	59.2	20.7	4.5	13.3	0.4	1.8	0.1	O
Hetaerina/Mnesarete	41	1	0	0.2	98.8	0	0	0	S-P
Phyllocycla	13	0.4	0	0	99.6	0	0	0	S-P
Progomphus	4	0	0	0	100	0	0	0	S-P
Peruviogomphus	3	0	0	0	100	0	0	0	S-P
Caenis	33	94	0	5.8	0	0	0.2	0	F-D
Traverhyphes	75	93.2	3.2	2.3	0	0	1,1	0.2	F-D
Tricorythodes	45	86.1	7.9	2.2	0	0	3.2	0.6	F-D
Farrodes	52	93.5	1.1	4.7	0	0	0.7	0	F-D
Ulmeritoides	3	93.3	0.3	4.3	0	0	0.4	1.7	F-D
Americabaetis	78	95.2	0.3	4,1	0	0	0.4	0	F-D
Paracloeodes	20	95.3	0.5	2.2	0	0	2	0	F-D
Waltzohyphius	16	98.5	0	1.3	0	0	0.1	0.1	F-D
Apobaetis	13	98.6	0	1.3	0	0	0.1	0	F-D
Heterelmis	35	81.4	12.6	6	0	0	0	0	F-D
Hexacylloepus	19	90.9	1.8	7.3	0	0	0	0	F-D
Microcylloepus	26	93.5	1.1	5.4	0	0	0	0	F-D
Macrelmis	12	94.1	0	5.9	0	0	0	0	F-D
Neoelmis	4	96.2	0	3.8	0	0	0	0	F-D
Macrobrachium	26	10.4	6.5	0.3	79.9	0.3	2.6	0	G-P
Belostoma ^* * The diet of hemipterans could not be determined because they are fluid-feeders. Their trophic group was assigned based on Nieser & Melo (1997).	-	-	-	-	-	-	-	-	G-P
Limnocoris ^* * The diet of hemipterans could not be determined because they are fluid-feeders. Their trophic group was assigned based on Nieser & Melo (1997).	-	-	-	-	-	-	-	-	G-P

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