Fred W. Rabe

The Effect of Macrophyte Removal on the Distribution of Selected invertebrates in a Littoral Environment

ABSTRACT Submergent vegetation was removed from four locations in a shallow wetland lake containing a dense concentration of aquatic macrophytes. The distributions of selected species of zooplankton and macroinvertebrates were compared over a two month period between the vegetated sites and locations in which vegetation was removed. Chydorus, Al onella, Graptoleboris and Scapholebrus showed a preference for vegetated stations. Daphnia schodleri was collected mostly in the open water. Three macro invertebrate predators, Enallagma boreale, Notonecta unifasciata, and Hesperocorixa leavigata showed a significant attraction to submergent plants over sites where vegetation had been removed as was also the case with Hyallela azteca and Callibaetis. Chaoborus an open water predator did not occur in significant numbers at vegetated stations but was most commonly observed in the deep water stations over the shallow sites. It is thought that predation of D. schodleri by E. boreale is an important mechanism in reduci...

A methodology for the selection of aquatic natural areas

Abstract A methodology is presented for selection of aquatic natural areas based on numerical ranking of sites. Non-weighted points are assigned to 24 physical and biological characteristics of the aquatic and terrestrial components of a proposed natural area. Cumulative score reflects both natural diversity and occurrence of unusual species or conditions. A systematic selection procedure is described which can be utilised by land managers or natural area organisations to arrive at and support objective decisions involving natural area selection.

Effect of Drought on the Western Painted Turtle, Chrysemys picta belli, in a Small Wetland Ecosystem

Abstract Middle Findley Lake, a small watershed located on the Turnbull Wildlife Refuge in Washington, dried up late in the summers of 1987 and 1988. Water remained in the lake in 1989. Population size of the western painted turtle (Chrysemys picta belli) decreased by approximately 70 percent following two years drought, with indications that both mortality and emigration contributed to this reduction. Growth of individual turtles was markedly suppressed during the second drought year when compared to the first year of recovery, but not to the point that the average sizes of cohorts were affected.

Brook troot populations in Colorado beaver ponds

SummaryA habitat inventory and evaluation of the brook trout populations from 57 beaver ponds in Colorado permitted comparisons of stunted and non-stunted populations of fish and the environmental conditions under which the populations occurred. High standing crops of small fish were usually present in ponds with favorable spawning areas. Seep ponds with few gravel or sandy areas did not favor spawning. As a result, a smaller number of larger fish were recovered. Four-to five-inch stunted trout reached maturity at the end of their second growing season while non-stunted trout matured at the end of their third and fourth growing seasons at lengths of seven to eight inches.

Stream types in Idaho: An approach to classification of streams in natural areas

Abstract Five types among small streams are described: ephemeral streams, spring streams, and three types among permanent streams. Key features used to designate stream type are order, gradient, pattern of flow, and substrate which are readily identifiable, nonvariable characteristics. Type designation is supported on an ecological basis by analysis of extensive collections of aquatic plants and invertebrates.

A limnological comparison of two small Idaho reservoirs

SummarySome limnological aspects of two small, widely fluctuating reservoirs were studied for one year. A well defined thermocline did not form in either reservoir. Annual heat budgets were about 15,000 cal/cm2 for both waters. Dissolved oxygen concentrations were low on the bottom during the summer months. Both reservoirs were alkaline with the pH ranging from 7.5 to 8.9.The mean primary production summer rates of nannoplankton were 9.9 mg C/m3/hr for Crowthers Reservoir and 6.7 mg C/m3/hr for Deep Creek Reservoir. Standing crop of zooplankton was highest in Deep Creek Reservoir. Biomass of detrital heterotrophs was highest in Crowthers.ResumenAlgunos aspectos limnológicos de dos reservorios pequeños con extensa fluctuación se estudiaron por un año. Termocline (thermocline)bien definido no se formó en uno u otro reservorio. Las acumulaciones anuales de calor fueron más o menos 15,000 cal/cm2 (calorías por centímetros cuadrados) por ambas aguas. La concentración de oxígeno disuelto fué bajo en el fondo durante los meses del verano. Ambos reservorios fueron alcalinos con el pH fluctuando desde 7.5 hasta 8.9.Les clasificaciones del pequeño plankton (nannoplankton) durante la producción en el verano fueron 9.9 mg (miligramos) C/m3/hr (carbóno por metro cúbico por hora) para el Reservorio Crowthers y 6.7 mg C/m3/hr para el Reservorio Deep Creek. La cosecha fija de zooplancton fué más fuerte en el Reservorior Deep Creek. La biomasa de heterótrofo detríticos fué más fuerte en Crowthers.

The Influence of Damselfly Naiads, Phytoplankton, and Selected Physicochemical Factors on the Population Growth of Daphnia schødleri

ABSTRACT The effect of selected biotic and abiotic factors on the population growth rate of Daphnia schodleri was studied over a five month period in a wetland ecosystem. Among the factors studied, only the density of damselfly naiads with head capsule width greater than 2.0 mm was significantly correlated with D. schodleris population growth rate. The presence of small and medium damselfly naiads did not affect the D. schodleri population growth rate. No significant correlations with growth rate were observed for high and low quality phytoplankton, water temperature, dissolved oxygen, pH, turbidity, or photoperiod.

The Effect of an Artificial Substrate on Damselfly Predation

Two laboratory experiments were conducted to determine what effect access to the water column might have on the predation of Daphnia schodleri by damselflies. In both trails, the presence of a perching substrate significantly increased predation by increasing the predator-prey encounter rate. Larger damselflies were observed to have higher predation rates than smaller size forms.