Introduction

The purpose of this paper is twofold. The first goal is to review and support the utility of macroinvertebrate Functional Food Group (FFG) analysis as an important tool for evaluating the ecological condition of running water (lotic) ecosystems. The second goal is to describe and discuss how ratios of the relative abundance of FFGs can be used as surrogates for lotic ecosystem attributes if they are measured directly. The basis for this is that Stream and river (lotic) macroinvertebrate communities worldwide can be partitioned into six FFGs defined by their adaptations for acquiring six matching food resource categories. A step by step procedure for FFG analysis is summarized that easily can be performed by individuals with little or no expertise in macroinvertebrate taxonomy.

Suitability of Macroinvertebrates as Monitors of Stream Ecosystem Condition

For over 100 years, benthic macroinvertebrates have been a pillar in the analysis of stream ecosystem conditions [1]. The taxonomic diversity of macroinvertebrate communities in streams has been widely employed to rank the level of degradation of a stream ecosystem relative to a compa rable one of similar geomorphology which is judged to be the most pristine stream available in the same region [2,3]. These comparisons have al ways been hampered by the level of taxonomic resolution used in the evaluations. The methodology referred to as species diversity, has rarely utilized taxonomic identifications at the species level [4]. For example, the Diptera family Chironomidae, often the most abundant taxon in any stream, is given the value of 1 in determining species diversity index, even though the number of species present would likely be 20 or more [5].

Taxonomic resolution issues aside, macroinvertebrates can serve as outstanding monitors of stream ecosystem condition. Their distribution and abundance is word wide, they are large enough to be observed with the unaided eye or a simple 3X hand lens, and they live and grow in streams over the majority of their life cycles of weeks to a year or more [4]. Also, their populations are more abundant and less mobile than stream fishes which simply migrate away from degraded environmental conditions [6].

By contrast, chemical and physical water measurements are severely limited in space and time. Even if recording devices are used, very signi ficant variations in space (lateral and vertical) remain [7]. The lesser mobility and greater population densities of stream macroinvertebrates often provide better monitors of stream contamination than the highly mobile fish populations [7].

Stream Macroinvertebrate Functional Feeding Groups (FFG)

Two insights initiated the development of the Functional Feeding Group (FFG) procedure for analyzing stream macroinvertebrate communities. First in 1964, Bob Pennak, a preeminent North American freshwater invertebrate biologist, maintained that suitable ecological questions using stream macroinvertebrates could only be adequately addressed by species level identifications. This was not possible then, and is largely not possible today. For example, the most recent edition of the Aquatic Insects of North America provides keys to essentially all the North American genera. However, keys to species can be found only in monographs of selected genera [4]. Second, the original iteration of the FFG method resulted from comments made in 1970 by Noel Hynes, arguably the greatest stream ecologist of our time. He observed that whenever he examined a rock in any stream, Europe, North America, Australia, or the tropics, the macroinvertebrates all looked very familiar. But they were all classified as different Taxa. This suggested that there are a limited number of universal general adaptations of stream macroinvertebrates to the stream environment. The result of this realization was the Functional Feeding Group (FFG) concept for evaluation of macroinvertebrate communities in stream ecosystems [8-10]. An example of this phenomenon is seen in the same morphology of the North American mayfly family Heptageniidae and the Brazilian family Leptophlebiidae [11].

The FFG method employs only general levels of taxonomic identification (usually order, family and in some cases genus). The focus is on morphological and behavioral adaptations of the macroinvertebrates to their stream environment that allows acquisition of their required food resources. The FFG method, that was proposed 0ver 40 years ago, is recommended in this article as a tool for stream ecosystem evaluation (Table 1) [8-11].

In the greater than 40 years since the FFG procedure was proposed [8,9], an extensive literature on use of the method has developed. The FFG method has been expanded, modified, and adapted for analyzing wide range of stream ecosystems (e.g. 8,11- 14). In particular, the River Continuum Concept that relates stream drainage geomorphology to predictable biological attributes relied heavily on FFG analysis [7]. Also, the volume edited by Cushing et al. [15] on stream and rivers of the world contains chapters by authors solicited to compare their North American, European, Australian, and tropical streams to the River Continuum Concept, including the FFG component.

The FFGs, their food resource categories, and North American taxonomic examples are summarized in Table 1.

Equipment, Materials and Methods

FFG analysis involves separation of the macroinvertebrates collected in a sample of stream benthos into easily recognized FFG categories. The recommended step by step procedure is summarized in Table 2. The directions are intended for use stream side, in the field, by at least three people. The procedure should be accomplished in the field because separation of the macroinvertebrates into taxonomic and FFGs is measurably easier when live animals are sorted. Before sampling, a data sheet should be prepared with date, time, stream name and description for recording the information obtained.

Semi- quantitative benthic samples are sufficient. A set of 30 second, habitat specific, collections with a Frame 0.5 mm mesh Dip Net [Bioquip™, 4]. Three dip net samples are taken in each major habitat: gravel-cobble riffles, depositional pools and/or back waters, leaf litter accumulations, and rooted vascular plant beds (when present). Each sample should be sorted and tabulated separately. Compositing of sample habitat data can be performed later if desired.

Before heading to the stream bank with a sample in the dip net, pre-treat it. By swishing the net up and down and side to side in the current to remove silt. By hand, remove macroinvertebrates from the surface of cobbles, pebbles, and large pieces of wood, drop them into the net, and discard the substrates back onto the stream.

Analysis of each Dip Net sample begins by emptying the contents of the net into a shallow, white 8 x 10 inch (20.5 x 25.4 cm) plastic or metal tray. Then, the macroinvertebrates are separated into taxa and FFGs as described step by step in Table 2. The picture key in [12] is a very useful aid in following the procedure. The important point in sorting the macroinvertebrates into FFGs is that only a general level of taxonomic resolution necessary to place them in a FFG is required. For example, only insect order is needed to categorize Odonata (dragonflies and damselflies) and Megaloptera (dobsonflies and alderflies) as predators.

A muffin tin with 8 large wells can be used to hold the sorted FFGs. The designation of each FFG can written on the bottom of each well with a white sharpie. That is, SC = Scrapers, DHS = Detrital Shredders, GC = Gathering Collectors, FC = Filtering Collectors, P = Predators, and HSH = Herbivore Shredders. Two wells should be marked for DSH and P because the specimens are larger. Information about the stream reach where the samples are taken should be recorded on the data sheet along with results of the FFG sorting. During sorting, numerical abundance of the macroinvertebrates by taxa and FFG is recorded. Also, an estimate should be made and recorded of the percent stream bottom covered by each habitat type sampled allowing the macroinvertebrate data to be weighted by the percent stream bottom covered by each habitat type in the stream reach. If the numerical data are to be converted to dry biomass, a separate procedure can be found in [16].

The supplies required for sorting the macroinvertebrate samples are long fine point forceps, magnifying glass (3X with a 5X bubble), and a bug scoop™. The bug scoop consists of a 1.5 cm square of plastic screen with a ridge around the edge made with a hot glue gun. A bead of hot glue in the middle of one edge receives a dissecting needle that serves as a handle. This scoop greatly facilitated the capture of rapidly swimming macroinvertebrates such as the usually very abundant mayfly nymphs in the family Baetidae (Table 1).

Step by step directions for field sorting of FFGs are given below in Table 2.

Use of FFG Ratios as Surrogates for Selected Stream Ecosystem Attributes

The relative abundance of a FFG predicts the availability of their required food resources. By extension, this predicts the status of the environmental conditions that produced these food resources. For example, light and nutrient levels regulate the primary production by attached algal food for scrapers and light, nutrients and sediment type limit abundance of vascular plant beds that are the food for herbivore shredders [18].

Because the FFG procedure has been used widely used and validated, the intent of this paper is to provide a step by step guide for collecting and using FFG data to evaluate stream ecosystem condition. The guide in Table 2 is suitable for use by people with limited knowledge of stream macroinvertebrates. The case is made that the FFG data collected in the field can be used to calculate ratios of FFG. These ratios can serve as surrogates for direct measures of the condition of a stream from which the samples were taken. The step by step procedure to facilitate this, is provided in Table 2.

Comparing the abundances of FFGs indicates the relative availability of their required food resources. By extension, this predicts the status of the environmental conditions that produce the food resource. For example, light and nutrient levels regulates stream l primary production [19,20].

Because a Limited number of feeding adaptations linked to a limited number of food resource categories, the relative abundance of a FFG indicates the relative availability of the required food resource. By extension, this predicts the status of the environmental conditions that produce the field; for example, light and nutrient levels that regulate primary production; attached algae and rooted vascular plants.

Because the FFG procedure has been used widely and validated, the intent of this paper is to provide a blueprint for collecting and using FFG data to evaluate stream ecosystem condition that can be used by people with limited knowledge of stream macroinvertebrates. The case is made that the FFG data collected in the field can be used to calculate ratios of FFGs to evaluate the condition of a stream from which the samples were taken. A step by step procedure is provided for collecting the FFG data needed (Table 2). The FFG ratios serve as surrogates for directly measured stream ecosystem environmental conditions. The ratios are dimensionless numbers and therefore are relatively independent of sample size. That is, the ratio calculated from collections of one sample are very similar to the ratios calculated by the average of three sample (Cummins, unpublished).

FFG ratios and predicted stream ecosystem conditions are summarized in Table 3.

These ratios and stream ecosystem attributes are based on North American studies. Modified or alternative ratios will undoubtedly be necessary to accommodate streams in other regions [18,20]. However, the general relationships outlined in Table 3 can serve as a general model of how such an analysis works and the evaluations of stream ecosystem conditions can be derived.

Proposed thresholds for the ratios are also given in Table 3 These thresholds are based on studies in Temperate [13,21-23] and tropical [24,25] running water ecosystems. In spite of the limited number of stream ecosystem studies on which the proposed ratios are based, they should serve as general examples for all streams. This implies that if data on the condition of a stream ecosystem are available or can be surmised (e. g. poor vs high water quality), collections for determining the relative abundances of the macroinvertebrate FFGs can be used, or developed to serve as surrogates for a more complete prediction of ecosystem condition of the stream. The development of ratio thresholds should provide a fertile avenue for further investigation. In addition, any published numerical or biomass data on the macroinvertebrates of a given stream can be assigned to FFGs (Table 1 and Table 2) and ratios calculated to predict the condition of the studied stream ecosystem (Table 3). The ultimate reason that such exercises can work is the universal nature of the six FFGs matched to six food resource groups worldwide documented in this article.

FFG analysis and resulting calculation of ratios should facilitate the process of evaluation of stream condition by workers of varying degrees of expertise in invertebrate taxonomy. The usefulness of this approach is based on the unique value of macroinvertebrates as monitors of the stream environment.

Conclusion

The stream macroinvertebrate FFG concept and the procedure for use in the analysis of stream ecosystem environmental condition has been reviewed. The method has worldwide application and can provide rapid analysis of stream condition by people with little or no expertise in stream macroinvertebrate taxonomy. Because stream macroinvertebrates spend the entirety of their growth period in the stream environment, t they are ideal monitors of stream condition. This level of complete monitoring of stream condition by month season or up to 2 years rapidly can provide better integrated data over time and space than most direct measurements of the stream ecosystem parameters. A final goal of this article is to encourage individuals to enlist the participation of their high school or college biology teachers to organize citizen groups to monitor legal streams. The as local stream ecosystem stewards of stream condition they can provide evaluation, monitoring, and restoration of regional streams to local officials.

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