Kenneth W. Cummins

Ecology of Coarse Woody Debris in Temperate Ecosystems

Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.

An Ecosystem Perspective of Riparian ZonesFocus on links between land and water

R iparian zones are the interfaces between terrestrial and aquatic ecosystems. As ecotones, they encompass sharp gradients of environmental factors, ecological processes, and plant communities. Riparian zones are not easily delineated but are comprised of mosaics of landforms, communities, and environments within the larger landscape. We propose a conceptual model of riparian tones that integrates the physical processes that shape valleyfloor landscapes, the succession of terrestrial plant communities on these geomorphic surfaces, the formation of habitat, and the production of nutritional resources for aquatic ecosys-

Structure and Function of Stream Ecosystems

It has been stated often that the selection of appropriate methodological strategies for ecological investigations are highly dependent upon the question being addressed. Unfortunately this awareness has not become fully operational-questions often being formulated only after data collection. Frequently, traditional ecological studies have been taxonomic inventories of biological communities-information of limited use in answering certain functionand process-oriented questions. Such inventories seem an inappropriate fabric from which to weave important ecological generalizations. As long as the species is assumed to be the basic ecological unit, ignoring for the moment problems in defining such units, the perpetually incomplete state of our taxonomic knowledge will constitute a major constraint for the development of ecological theory. This assumption, that species recognition is the fundamental prerequisite for ecological insight, has proven particularly troublesome to the study of flowing water (or lotic) ecological systems. For example, immature stages (nymphs, larvae) of stream insects usually dominate the macroinvertebrate role in energy transformations, but the adults (usually males) constitute the coin of species identification. In addition, diatoms, the dominant lotic algae, present particularly difficult taxonomic problems. However, perhaps only the lack of attention paid the microbial components-bacteria and fungi-of natural communities has allowed the taxonomic focus to endure this long. Discrepancies between morphological, physiological, and genetic species definitions of microorganisms make it apparent how untenable a taxonomic foundation for all ecological questions can be. Thus, there is a need to identify functional groups of organisms, at least partially independent of traditional taxonomic determinations, in order to address important process-oriented ecological questions. It is certainly true that we would not now be in a position to search for other units from which to

Shredders and Riparian Vegetation

Stream invertebrates that feed on leaf litter are intimately tied to the nature and timing of the litter input. These invertebrates are called shredders; they consume streamside, riparian litter that has become trapped in the stream channel. This plant litter accumulates at the leading edge of obstructions in the current and settles out in pools, alcoves, and other depositional zones. Given the extensive literature that has accumulated over the last 20 years, researchers can now develop a general, testable model that relates riparian plant communities to the stream shredders, which depend upon litter derived from those communities.

The Utilization of Leaf Litter by Stream Detritivores

Investigations of large and fine particle feeding detritivores (shredders and collectors) fed on conditioned hickory leaves (Carya glabra) revealed density—dependent intra— and interspecific interactions. Shredder (Tipula and Pycnopsyche) growth rates ranged from 0.47 to 1.53% increase in body wt/day depending upon density, species combinations, and culture temperature. Collector (Stenonema) growth rate ranged from 0.13 to 1.80% body wt/day, being greatest at high densities, particularly in combination with shredders. Food consumption ranged from 15.7 to 33.2% body wt/day for shredders and 4.0 to 23.2% body wt/day for collectors. After non—shredder feeding losses are accounted for, estimated shredder standing crop required to account for processing of report leaf litter inputs compare generally to measured shredder standing crop.

The influence of substrate particle size on the microdistribution of stream macrobenthos

SummarySubstrate microhabitat preferences of ten species of benthic macroinvertebrates were investigated in a laboratory flowing water system and compared with preliminary field data. Eight particle size categories of both silted and non-silted substrates were tested in the laboratory.The correspondence between field and laboratory data indicated primary microhabitat selection on the basis of substrate particle size by the stonefly Perlesta placida, the riffle beetle Stenelmis crenata and the caddisflies Pycnopsyche guttifer and P. lepida. Broad substrate responses in the laboratory and lack of correspondence with field data indicated a secondary importance of substrate particle size in microhabitat selection by the pulmonate snail Helisoma anceps, the caddisfly Helicopsyche borealis, the cranefly Tipula caloptera, the alderfly Sialis vagans and the mayflies Caenis latipennis and Ephemera simulans.Silting had minor effects on substrate selection patterns in all species tested except Caenis latipennis and Perlesta placida in which it enhanced selection for the intersticies of coarse sediments.ZusammenfassungDie Vorliebe für Substratarten mit Rücksicht auf die Substratpartikelgrösse von zehn Arten im Benthos lebender Wirbelloser wurde in einer Labor-Fliesswasseranlage untersucht und mit vorläufigen Feldergebnissen verglichen. Acht Anordnungen von Substratpartikelgrössen, sowohl verschlammt als auch nicht verschlammt, wurden im Labor untersucht.Die Entsprechung zwischen Feld- und Laborergebnissen zeigte dass die Wahl des Lebensraumes in erster Linie durch die Substratpartikelgrösse bestimmt wurde für die Steinfliege Perlesta placida, den Hakenkäfer Stenelmis crenata und die Köcherfliegen Pycnopsyche gutiffer und P. lepida. Die breite Streuwirkung des Substrates im Labor und der Mangel an Übereinstimmung mit den Feldergebnissen zeigte, dass die Substratpartikelgrösse in der Wahl des Lebensraumes eine untergeordnete Rolle spielte bei der Lungenschnecke Helisoma anceps, der Köcherfliege Helicopsyche borealis, der Schnake Tipula caloptera, der Schlammfliege Sialis vagans und den Eintagsfliegen Caenis latipennis and Ephemera s simulans.Die Verschlammung hatte geringen Effekt auf die Auswahl des Substratesbei allen untersuchten Arten mit Ausnahme von Caenis latipennis und Perlesta placida. In diesen Fällen verstärkte sich die Besiedlung wegen der Zwischenräume in dem groben Sediment.

Effects of food quality on growth of a stream detritivore, Paratendipes albimanus (MEIGEN) (Diptera : Chironomidae)

Laboratory-determined larval growth rates of the detritivore (collector-gatherer) Par- atendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources. Substrates with higher microbial activities and biomasses produced greater growth rates in the order: pignut hickory (Carya glabra) leaves > white oak (Quercus alba) > insect feces > natural stream detritus. Laboratory growth rates of P. albimanus were linearly related to quantitative esti- mates of food quality based on substrate adenosine triphosphate (ATP) and respiration rates but were not statistically related to total N or C. Although P. albimanus is univoltine in Augusta Creek, Michigan, an experimental laboratory population of first-instar larvae completed a 2nd generation during the summer when fed detritus generated from hickory leaves. A second experimental popu- lation failed to develop past the first instar when fed natural detritus. The natural growth pattern of P. albimanus involves the interaction of temperature and food quality.

Organic Matter Budgets for Stream Ecosystems: Problems in their Evaluation

Since the pioneering work at Hubbard Brook (Fisher and Likens, 1972, 1973; Bormann et al., 1969, 1974; Bormann and Likens, 1979), there has been ever increasing interest in watershed budgets, both for total organic matter, usually expressed as carbon (Wetzel et al., 1972), and various ions (Fisher and Likens, 1973; Johnson and Swank, 1973; Swank and Douglass, 1975; Fisher, 1977; Webster and Patten, 1979; Fahey, 1979; Mulholland and Kuenzler, 1979; Gurtz et al., 1980; Mulholand, 1981). The primary interest in stream dynamics within a budget context has been in the rate of loss of organic matter from the land as well as storage and biological conversion of organic matter in the stream. Impetus for most studies has come from the realization that energetics of small streams (generally orders 1 to 3 [Strahler, 1957]) are heavily dependent on organic nutritional resources of terrestrial origin (Ross, 1963; Hynes, 1963; Cummins, 1974; Hynes, 1975). New insights into the structure and function of running water ecosystems and terrestrial-aquatic linkages (Waring, 1980) are based on the changing terrestrial dependence with increasing channel size (Cummins, 1975, 1977; Vannote et al., 1980; Minshall et al., 1983), varying stream-side vegetation (Minshall, 1978), and the dynamics of input, storage or processing, and output of organic matter (Vannote et al., 1980; Minshall et al., 1983; Elwood et al., 1982; Newbold et al., 1982 a, b).

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

An analysis conducted at nine stream/river sites in the Atlantic Forest region in the State of Paraná, 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 with riparian inputs, and in only two were stable substrates limiting. The implications of the findings and recommendations for further analysis and modifications of the protocol are discussed.

Microbial and animal processing of detritus in a woodland stream

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