At my age, I feel there are three research areas that represent unfinished business. By presenting these, I hope those involved in active research will consider the issues.
Number 1: Stream Macroinvertebrate Functional Feeding Groups (FFG)
The macroinvertebrate Functional Feeding Group (FFG) procedure for evaluating stream ecosystem condition has been used widely since its inception in the 70s [1-3]. The FFG has been modified (e. g. ) and Validated (e. g. [5-8]).
The issue of obligate vs facultative FFGs requires direct validation. It is well established that a limited number of macroinvertebrate adaptations for acquiring food can be matched to a corresponding limited number of food resource categories (Table 1). The fitness of obligate FFGs resides with their maximum efficiency in converting ingested food to growth, directly measured as Relative Growth Rate (RGR). For example, the obligate scraper Heptageniidae mayfly nymphs are adapted to remove attached non-filamentous algae from hard substrates like cobbles in riffles. When they are held in laboratory streams, on fungal conditioned riparian leaf litter or Fine Particulate Organic Matter (FPOM) as their only food available, they scrape the surface of the leaves or ingest FPOM and survive. However, they lose weight and never emerge into normal sized adults (Cummins and Petersen unpublished). By contrast, facultative FFGs feed on more than one food resource, but at a lower RGR. Fitness is served because by survive and mature on changing or patchily distributed food resources. FFG Gathering collectors are all facultative FFGs and the usual food resource is the ubiquitous FPOM (Table 1). Consequently, gathering collectors, and the predators they support, usually dominate the macroinvertebrate fauna in impacted streams . In “Aquatic Insects of North America” , ecological tables assign essentially all North American genera to a functional group. For those designated as facultative, the first listed of the alternatives are the most widely reported condition in the literature. This facultative designation is almost always based on gut analyses and not RGR.