Leaf litter is a major component in the organic matter budgets of streams worldwide. Shredding invertebrates are widely considered to be of central importance for the breakdown of allochthonous organic material in temperate-zone streams. However, various authors report an absence of this group in tropical streams. Various phenomena, including hydraulic disturbance, chemical leaf quality, and biotic control through macroconsumers, may cause variable shredder performance in streams. Our paper discusses the hypothesis that biogeographic distribution and the life-cycle strategies of the shredders are additional factors affecting the contribution of invertebrates to lotic decomposition processes. As a case study, we analyzed the type of organic matter inputs, the community of benthic invertebrate shredders, and the decomposition of temperate zone leaves (alder, Alnusglutinosa) in the Breitenbach (BRB), a temperate stream in Hesse, Germany, and in the Corrego Tenente Amaral (CTA), a neotropical Cerrado ...

https://www.jstor.org/stable/10.1899/0887-3593(2006)25%5B216:DPBISA%5D2.0.CO;2

Detritus processing by invertebrate shredders: a neotropical–temperate comparison

Aquatic insects around the world exhibit similar morphologies and behaviors even though they are in very different taxonomic groups. This is the basis for the functional feeding group (FFG) method that was initially developed in the early 1960s. Taxonomy is applied only to the level of detail that allows assignment to one of the five FFG categories. These are scrapers adapted to feed on periphyton, shredders adapted to feed on riparian derived plant litter, filtering-collectors adapted to remove fine particle detritus from the water column, gathering-collectors adapted to feed on fine particle detritus where it is deposited on surfaces or in crevices, and predators that capture live prey. In this chapter on trophic relationships, we present (1) the general design of this functional classification system; (2) the basic food resources used by stream macroinvertebrates; (3) how to use the FFG approach in the assessment of the ecological condition of freshwater communities; (4) pictorial keys to identify FFGs; and (5) FFG ratios that can be used as surrogates for stream ecosystem attributes.

Trophic Relationships of Macroinvertebrates

Aquatic macroinvertebrates are involved in numerous processes within aquatic ecosystems. They often have important effects on ecosystem processes such as primary production (via grazing), detritus breakdown, and nutrient mineralization and downstream spiraling. The functional feeding groups (FFG) classification was developed as a tool to facilitate the incorporation of macroinvertebrates in studies of aquatic ecosystems. This classification has the advantage of combining morphological characteristics (e.g., mouth part specialization) and behavioral mechanisms (e.g., way of feeding) used by macroinvertebrates when consuming resources. Although recent efforts have greatly advanced our ability to identify aquatic macroinvertebrates, there is limited information on FFG assignment. Furthermore, there has been some variation in the use of the FFG classification, in part due to an emphasis on using gut content analysis to assign FFG, which is more appropriate for assigning trophic guilds. Thus, the main goals of this study are to (1) provide an overview of the value of using the FFG classification, (2) make an initial attempt to summarize available information on FFG for aquatic insects in Latin America, and (3) provide general guidelines on how to assign organisms to their FFGs. FFGs are intended to reflect the potential effects of organisms in their ecosystems and the way they consume resources. Groups include scrapers that consume resources that grow attached to the substrate by removing them with their mouth parts; shredders that cut or chew pieces of living or dead plant material, including all plant parts like leaves and wood; collectors-gatherers that use modified mouth parts to sieve or collect small particles (<1mm) accumulated on the stream bottom; filterers that have special adaptations to remove particles directly from the water column; and predators that consume other organisms using different strategies to capture them. In addition, we provide details on piercers that feed on vascular plants by cutting or piercing the tissue using sharp or chewing mouth parts and consume plant liquids. We also provide a list of families of aquatic insects in Latin America, with an initial assignment to FFGs. We recommended caution when assigning FFGs based on gut contents, as it can provide misleading information. Overall, FFG is a very useful tool to understand the role of aquatic macroinvertebrates in stream ecosystems and comparisons among studies will benefit from consistency in their use. Rev. Biol. Trop. 62 (Suppl. 2): 155-167. Epub 2014 April 01.

/pdf/functional-feeding-groups-of-aquatic-insect-families-in-208zr6whfj.pdf

Functional feeding groups of aquatic insect families in Latin America: a critical analysis and review of existing literature

Summary

1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions.



2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day−1 and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046–0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 μg g−1, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 μg g−1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g−1).



3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves.



4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L−1), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source.

Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shredders

Data on the functional composition of invertebrates in tropical streams are needed to develop models of ecosystem functioning and to assess anthropogenic effects on ecological condition. We collected macroinvertebrates during dry and wet seasons from pools and riffles in 10 open- and 10 closed-canopy Kenyan highland streams. We classified macroinvertebrates into functional feeding groups (FFGs), which we used to assess effects of riparian condition and season on functional organization. We used cluster analysis of gut contents to classify 86 taxa as collectors, predators, scrapers, or shredders. We classified 23 taxa whose guts were empty or had indistinguishable contents based on literature. In total, we identified 43 predators, 26 collectors, 19 scrapers, and 19 shredders. Total abundance was higher in open-canopy agricultural streams, and species richness was higher in closed-canopy forested streams. Predators and shredders dominated richness and biomass, respectively, in the closed-canopy stre...

https://www.jstor.org/stable/10.1086/675681

Macroinvertebrate functional feeding groups in Kenyan highland streams: evidence for a diverse shredder guild

An analysis conducted at nine stream/river sites in the Atlantic Forest region in the State of Parana, Brazil used macroinvertebrate functional feeding group (FFG) assessments to evaluate ecological condition of the sites. The FFG approach categorizes qualitative macroinvertebrate collections according to their morphological-behavioral adaptations for food acquisition (e.g. scrapers that harvest non-filamentous, attached algae from stable surfaces in flowing water). FFG ratios were employed as surrogates for stream/river ecosystem attributes: balance between autotrophy and heterotrophy; linkage between riparian inputs of coarse particulate organic matter and in-stream food webs; relative dominance of fine particulate organic matter in transport (suspended load) compared to that deposited in the sediments; and geomorphic stability of the channel. The analyses indicated that all nine sites were heterotrophic, six of the nine carried expected levels of suspended organic load and showed below expected linkage...

Priscila Cn Andrade

Papers

The use of invertebrate functional groups to characterize ecosystem attributes in selected streams and rivers in south Brazil