Arthropod Diversity and Conservation in Old-Growth Northwest Forests

Old-growth forests of the Pacific Northwest extend along thecoastal region from southern Alaska to northern California andare composed largely of conifer rather than hardwood tree species.Many of these trees achieve great age (500–1,000 yr).Natural succession that follows forest stand destruction normallytakes over 100 years to reach the young mature forest stage.This succession may continue on into old-growth for centuries.The changing structural complexity of the forest over time,combined with the many different plant species that characterizesuccession, results in an array of arthropod habitats. It isestimated that 6,000 arthropod species may be found in suchforests—over 3,400 different species are known from asingle 6,400 ha site in Oregon. Our knowledge of these speciesis still rudimentary and much additional work is needed throughoutthis vast region. Many of these species play critical rolesin the dynamics of forest ecosystems. They are important innutrient cycling, as herbivores, as natural predators and parasitesof other arthropod species. This faunal diversity reflects thediversity of the environment and the arthropod complex providesa sensitive barometer of the conditions of the forest. Conservationefforts for forest arthropods are limited at present and controlledlargely by land-use policies. For example, an effort is beingmade to include arthropods in conservation efforts for the NorthernSpotted Owl and arthropods will be included in the Forest HealthMonitoring program now underway by the U.S. Forest Service.Evidence from other parts of the world suggest that arthropodsthat depend upon large pieces of dead wood may be particularlythreatened by forest management practices. Much remains to bedone in the conservation of forest arthropods.     

Susceptibilities of different-sized ciliates to direct suppression by small and large cladocerans

• 1 Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris.
• 2 Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris.
• 3 Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml^?1 ranged from 1–30 to 5–24ml ind.^?1 day^?1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.

     

Selective predation by Lestes (Odoiiata, Lestidae) on littoral microcrustacea

• 1 Two experimental approaches were used to examine the predation risk of six littoral cladoceran and ostracod species to two size classes of the damselfly Lestes sp. Behavioural observations were conducted in a 2–1 arena and predation rate experiments in 1–1 jars in the laboratory.
• 2 Behavioural observations revealed that attack and capture efficiencies by Lestes were higher on smaller cladocerans (Polyphemus and Ceriodaphnia) than on other taxa. Small Lestes had little success ingesting the small ostracod Cypridopsis, whereas larger Lestes captured and ate it easily.
• 3 Predation-rate experiments showed that Lestes has a clear preference for smaller cladocerans over both a large cladoceran (Simocephatus) and all three ostracods (Cypricercus, Cyclocypris, and Cypridopsis). Most Lestes were unable to consume the larger Cypricercus.
• 4 Attack rates and predation rates were highly variable among individual predators.
• 5 These data indicate that damselfly larvae are size selective and consume all but very large cladocerans more readily than ostracods.

     

The limnology of Lac ďIfni (High Atlas Mountains, Morocco), an unusually productive mountain lake

• 1 Lac ?Ifni (surface area 30 ha, z_max 60 m, altitude 2300 m) lies in a catchment comprised of Precambrian igneous rocks in the High Atlas Mountains of Morocco. Previously described as a typical ohgotrophic lake, it was also reported to have a warm layer at the base of the hypolimnion which was ascribed to phreatic water supply and drainage.
• 2 Visits to the lake made in May/June and September 1990 showed strong thermal stratification but no hypolimnial warm layer. Drainage from the lake is subterranean, through a natural rubble dam, and the water level dropped by at least 7m through the summer. The flushing rate is about 0.6 year^?1.
• 3 The upper part of the metalimnion and the lower epilimnion were strongly supersaturated with oxygen in June, and there was a pH gradient from 7 to 10.5 between the hypolimnion and the epilimnion. These features were less marked in September when planktonic gross primary productivity was estimated to be about 145mgCm^?2 h^?1. In September the hypolimnion was 38% saturated with oxygen; the areal hypolimnetic oxygen deficit between June and September was 0.073mg O₂ cm^?2 day^?1. Total dissolved phosphate concentrations were 7–14 μgl^?1.
• 4 The open water faunal assemblage consisted of Brachionus calyciflorus and Filinia lotigiseta (Rotifera), Cyclops abyssorum (Copepoda), and stunted Salmo trutta (Pisces). Trout diets were comprised principally of adult copepods and copepodites, which showed diurnal vertical migration, and of algal material apparently scraped from rock surfaces. The dry biomass density of Cyclops was at least 2gm^?2 in June and at least 4.1 gm ^?2 in September.
• 5 Tubifex tubifex (Oligochaeta) dominated the benthos below depths of 40m. Mean dry biomass density was 2.8gm^?2, but ranged from 0.6–8.1 gm^?2 between samples. About 50% of the lake bottom is below 40m depth.
• 6 The persistent oxygen supersaruration of the euphoric zone, the field estimate of primary productivity, the hypolimnetic oxygen deficit, the biomass of zooplankton and the benthic biomass together indicate that Lac ?Ifni is an unusually productive mountain lake. This high level of productivity may be sustained by nutrient addition through contamination by dust originating outside the catchment, aided by efficient nutrient recycling in the euphoric zone.

     

TWO MODELS FOR ESTIMATING THE DISCRIMINABILITY OF FOODS AND BEVERAGES

In order to evaluate the suitability of signal detection theory methods for assessing the discriminability of foods and beverages, the discriminability of two dairy milk products that differed in fat content was measured with two detection-theoretic methods: the single-interval rating method, and the same-different method. The nominal fat contents of the milk products were 0.1 and 1.6%. Measures of discriminability for three observers were derived by fitting receiver operating characteristics (ROCs) based on equal-variance normal models to the ratings of each observer with a procedure that combined jackknifing and maximum-likelihood estimation. The fitted ROCs provided a good fit to the data indicating that the equal-variance models were appropriate for these tasks. The best-fitting estimates of d' obtained for each task were not significantly different, demonstrating that d' is a measure of sensitivity that is largely independent of the task from which it is determined. However, estimates of proportion correct obtained for each task were shown to be significantly different.     

Local genetic structure in red grouse (Lagopus lagopus scoticus): evidence from microsatellite DNA markers

Allelic variation at seven hypervariable tri- and tetranucleotide microsatellite loci was used to determine levels of population differentiation between 14 populations of red grouse ( Lagopus lagopus scoticus ) in northeast Scotland, UK. Despite the potential for long-distance dispersal in grouse, and a semicontinuous habitat, significant population divergence was observed (mean R _ST = 0.153; P < 0.01) and an isolation-by-distance effect detected (Mantel test: P < 0.001). Examination of the spatial trend in principal component scores derived from allele frequencies among populations highlighted a barrier to gene flow that was confounding a simple isolation-by-distance effect. This barrier corresponded to an area of unsuitable habitat for grouse associated with a river system that bisected the study area. Mean genetic relatedness was higher for males than for females in all but one of the study populations, suggesting that the territorial behaviour and natal philopatry displayed by cocks have a manifold effect in generating the observed spatial genetic structure. Lower female relatedness values suggest a higher level of female-mediated gene flow, which is sufficient to prevent the loss of genetic variation from within populations and the onset of inbreeding effects. The potential consequences of local subdivision for red grouse populations are discussed.