Global regressions of ecological population densities on body mass for mammals and for terrestrial animals as a whole show that local population energy-use is approximately independent of adult body mass—over a body mass range spanning more than 11 orders of magnitude. This independence is represented by the slope of the regressions approximating –0.75, the reciprocal of the way that individual metabolic requirements scale with body mass. The pattern still holds for mammalian primary consumers when the data are broken down by geographic area, by broad habitat-type and by individual community. Slopes for mammalian secondary consumers are also not statistically distinguishable from –0.75. For any given body mass temperate herbivores maintain on average population densities of 1.5 to 2.0 times those of tropical ones, though slopes do not differ. Terrestrial animals of all sizes exhibit approximately the same range of population energy-use values. These results agree with those reported for population energy-budgets. It is suggested that rough independence of body mass and the energy-use of local populations is a widespread rule of animal ecology and community structure.

Interspecific allometry of population density in mammals and other animals: the independence of body mass and population energy‐use

Many ecologists and aquaculturists view crayfish as either detritivores or herbivores. The nutritional importance of detritus and plant material, seemingly confirmed by examination of stomach contents is exaggerated. Examination of stomach contents emphasizes indigestible residues, for example, plant fragments and detritus, while neglecting the ingestion of easily digestible soft‐bodied metazoans. The few comparative studies that have measured the assimilation and metabolic use of ingested items reveal animal protein to be the chief substance promoting rapid growth. Crayfish are not indiscriminate omnivores; in fact, they demonstrate a predilection for animal protein. Crayfish rank among the chief carnivores found in lakes and streams. To completely understand their role, crayfish should be viewed from two perspectives: that of an individual attempting to complete its life cycle, and the collective functioning of a population in the ecosystem, which can produce a serious ecological impact. While ...

Redefining the role of crayfish in aquatic ecosystems

We conducted five 4- to 12-wk in situ enclosure–exclosure experiments in four macrophyte assemblages in three northern Wisconsin lakes to test the impact of grazing by the crayfish Orconectes rusti...

Reductions in Submersed Macrophyte Biomass and Species Richness by the Crayfish Orconectes rusticus

Nous avons quantifie les sources d'energie des ecrevisses Orconectes luteus et O. punctimanus dans la riviere Jacks Fork (Missouri) a l'aide d'isotopes stables (δ 13 C et δ 15 N) et de l'analyse du contenu des intestins. Un modele mixte combinant les deux isotopes a fait ressortir que les deux tiers environ de la production des ecrevisses provenaient de sources allochtones de carbone, et que 30-50 % de cette production provenait de la consommation directe de matieres animales. Les jeunes de l'annee et les adultes d'O. luteus etaient plus carnivores que les adultes plus gros d'O. punctimanus. Les contributions des sources d'energie calculees a l'aide du modele combinant les isotopes stables etaient similaires aux resultats de l'analyse du contenu des intestins, apres correction pour l'assimilation differentielle des composantes alimentaires. Les proportions de la production des ecrevisses attribuees a la matiere animale selon ces deux methodes etaient quatre a cinq fois plus elevees que les estimations obtenues sans correction par l'analyse du contenu des intestins. Cette analyse sans correction surestimait le pourcentage de la production provenant de l'absorption directe des detritus. Les calculs des taux de consommation de la nourriture par les ecrevisses a partir de la production indiquaient que ces crustaces etaient les consommateurs dominants des invertebres benthiques, des detritus et des algues, et pourraient avoir une influence importante sur les niveaux trophiques inferieurs, la transformation de la matiere organique et le flux de l'energie dans ce systeme.

Energy sources and ecological role of crayfishes in an Ozark stream: insights from stable isotopes and gut analysis

By comparing distributions of functional group production among different habitats in an Appalachian mountain stream, the influence of site-specific geomorphology upon the overall functional group composition of the animal community was demonstrated. By replicated monthly sampling, substrate particle size distributions, current velocity, standing crops of benthic organic matter, and production of macrofauna were measured in each of three principal habitats: bedrock-outcrop, riffle, and pool. Samples were taken at randomly assigned locations and the relative number of samples taken from each habitat was assumed to be proportional to the area of the habitat within the stream. These proportions were used to weight production measured in each habitat and the resulting values were summed to obtain production per unit area of average stream bed. The bedrock-outcrop habitat was characterized by high material entertainment and export as indicated by significantly higher current velocities and lower standing crops of detritus compared to the riffle and pool habitats. Pools were sites of low entertainment and high retention of organic matter as demonstrated by significantly lower current velocities and higher accumulations of detritus than other habitats. The riffle habitat was intermediate to the bedrock-outcrop and pool habitats in all parameters measured. Annual production of collector-filterers was highest in the bedrock-outcrop (ash-free dry mass 1920 mg/m2 ), followed by riffle (278 mg/m2 ) and pool (32 mg/m2 ). Although constituting only 19% of the stream area, the bedrock-outcrop habitat contributed 68% of the habitat-weighted collector-filterer production. Annual production of shredders was highest in pools (2616 mg/m2 ), followed by riffles (1657 mg/m2 ) and bedrock-outcrop (579 mg/m2 ). The pool habitat, constituting 23% of stream area, contributed 36% of shredder production. Annual production of scrapers was highest in the riffle habitat (905 mg/m2 ), followed by bedrock-outcrop (517-mg/m2 ) and pool (238 mg/m2 ). Riffles constituted 58% of total stream area and were the source of 77% of the habitat-weighted scraper production. Annual production of engulfing predators was greatest in the pool habitat (2313 mg/m2 ), followed by riffles (1765 mg/m2 ) and bedrock-outcrop (687 mg/m2 ). The relatively lower production of engulfing predators in the bedrock-outcrop habitat reflects a functional shift in mode of resource acquisition by predators, with predaceous collector-filterers (Arcto-psychinae: Trichoptera) predominating in the bedrock-outcrop. Collector-gatherer production was more evenly distributed, with the bedrock-outcrop, riffle, and pool habitats each contributing 14, 54, and 33% to the habitat-weighted production, respectively. Unlike all other functional groups, this distribution was not significantly different from the distribution of stream area among habitats and reflected lack of dependence on specific physical attributes of the local environment for access to food by members of this functional group. Local geomorphology determined the diversity and spatial distribution of bedrock-outcrops, riffles, and pools in the study stream. In turn, the functional structure of the macrofauna, when viewed holistically, was the result of the integration of the relative contributions of each habitat type of total stream area. Total habitat-weighted annual production in the study stream was estimated at 5093 and 1921 mg/m2 for primary and secondary consumers, respectively. The distribution of habitat-weighted production among functional groups was: collector-gatherers (39%), followed by shredders (225), engulfing predators (22%), scrapers (13%), and collector-filterers (8%). This functional structure agrees favorably with current conceptual models of head water streams draining forested catchments.

Local Geomorphology as a Determinant of Macrofaunal Production in a Mountain Stream.

An understanding of the population dynamics of crayfish and their trophic position is critical to understanding energy transformation in lakes. In many lakes crayfish dominate the annual production of the benthic biomass, at times reaching mean biomass values of 1000 1400 kg/ha and numerical densities of 15/m2. Density determines the rate of growth of various populations and determines reproductive capacity, age at maturity and life span. For Orconectes virilis, within the lakes we studied, population stability was mostly due to the short lag between a change in population density and an adjustment in fecundity. As a result, these populations appear to be self-regulated through density-dependent control of brood stock size. In Orconectes virilis, annual production was a function of mean annual biomass. Examination of available data on the ratio between other species showed them to fall within the same range as O. virilis. It seems that the evolutionary strategy governing crayfish biomass replacement and energy turnover has remained essentially unchanged. As regards their role in the community, crayfish do not fit the trophic level concept. Attempts to quantify their food habits show them to be polytrophic and a key energy transformer between various trophic links through utilization of all the trophic levels in lakes. Because of the multiple trophic roles of the crayfish, a comparison with the bioenergetics of various freshwater crust?cea is difficult. Crayfish may be most important in lakes with low phytoplankton production. In such lakes detritus and benthic algae, both of which are ingested by the crayfish, are important sources of overall energy flow. Since crayfish also function as major predators on the benthos, they most likely contribute to the stability of lake communities by interacting with a whole subweb of species ranging from large benthic invertebrates and submerged higher aquatics to the periphytic microcommunity. Hence, crayfish act as an important mechanism contributing to the regulation of most production processes and most specifically to the regulation of benthic production available to fish. In low nutrient lakes, because of their biomass dominance and functional role, crayfish greatly surpass the usual role assigned to them from their occurrence in fish diets. Manipulation of the benthic food chain would seem to be the most appropriate strategy to increase the fish production of such lakes. However, a greater appreciation of the complexity of the trophic organization of such food webs is necessary before such modifications can be attempted. 1 A contribution under Dingell-Johnson Project F-30-R, Michigan. 2 Present address: Department of Biology, Lakehead University, Thunder Bay, Ontario, Canada.

The dynamics of crayfish and their role in ecosystems.

Fluctuations in mortality rather than in growth rates produced most of the year-to-year differences in biomass accumulation of three different populations of the crayfish Orconectes virilis. Yearly...

Production and Population Dynamics of the Crayfish Orconectes virilis in Three Michigan Lakes

Populations of the crayfish Orconectes virilis were exploited using the Paulik–Bayliff modification of the Ricker model in two small lakes. After harvesting with traps at maximum sustained yield (MSY) for 3 yr, fishing effort was increased fourfold in one lake, West Lost, for two successive seasons, while in North Twin Lake it was not changed. In West Lost yields were stable during MSY; yields increased with overexploitation, but growth and recruitment declined. Distortions occurred in the age composition of the catch. In North Twin this pattern was repeated except that in 1975 the catch dropped drastically even though fishing effort had not been increased. Because of declining recruitment, North Twin was actually overfished by about 20% in 1974 and greatly overfished in 1975. Decreased recruitment in both lakes can be attributed to two factors: (1) a decreased survival of hatchlings in both lakes due to a decline in nursery habitat; as a consequence the stock-recruitment relationship was altered; and (2)...

Results of an Experimental Fishery on the Crayfish Orconectes virilis

In an earlier study during 1962 and 1963, movement of female Orconectes virilis from shallow to deeper water in summer was noted in West Lost Lake, Otsego County, Michigan. The present additional observations on O. virilis, during three summers and in three lakes, confirm this migration. Evidence from other areas suggest that this movement is a general phenomenon of the species throughout most of its range. Migration of females appears to be associated essentially with muturation of the gonads. See full-text article at JSTOR

https://www.jstor.org/stable/info/1934236

Differential Seasonal Migration of the Crayfish, Orconectes Virilis (Hagen) in Marl Lakes

A mathematical model of trout-stream fisheries was developed that can be used to evaluate a variety of fishing regulations. Density-dependent mortality was found in the first 2 years of life for each of the two brook trout (Salvelinus fontinalis) and three brown trout (Salmo trutta) populations studied in Michigan. Regression equations were used to describe the density-dependent relationships for modeling purposes. Equations were developed that used mortality, growth, and length-frequency information to calculate the number of fish in a population, number caught and harvested, number caught and released, number of deaths due to hooking mortality, number of natural deaths, and number recruited for any time period and age-group. Also, addition of a length-weight regression allowed equations to be developed for calculating yield in weight harvested, yield in weight caught and released, and gross biomass production for any time period and age-group. Effects of imposing different types of length limit...

Howard Gowing

Papers

The dynamics of crayfish and their role in ecosystems.

Production and Population Dynamics of the Crayfish Orconectes virilis in Three Michigan Lakes

Results of an Experimental Fishery on the Crayfish Orconectes virilis

Differential Seasonal Migration of the Crayfish, Orconectes Virilis (Hagen) in Marl Lakes

Mathematical Description of Trout‐Stream Fisheries