Limiting nutrients for periphyton growth in sub-alpine, forest, agricultural and urban streams

1. Nutrient-diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub-alpine, forested, agricultural and urban catchments in eastern Victoria, Australia. 2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub-alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density. 3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient. 4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream-water nitrogen to phosphorus ratios in many instances.     

Ranking Alaska Moose Nutrition: Signals to Begin Liberal Antlerless Harvests

Abstract: We focused on describing low nutritional status in an increasing moose (Alces alces gigas) population with reduced predation in Game Management Unit (GMU) 20A near Fairbanks, Alaska, USA. A skeptical public disallowed liberal antlerless harvests of this moose population until we provided convincing data on low nutritional status. We ranked nutritional status in 15 Alaska moose populations (in boreal forests and coastal tundra) based on multiyear twinning rates. Data on age-of-first-reproduction and parturition rates provided a ranking consistent with twinning rates in the 6 areas where comparative data were available. Also, short-yearling mass provided a ranking consistent with twinning rates in 5 of the 6 areas where data were available. Data from 5 areas implied an inverse relationship between twinning rate and browse removal rate. Only in GMU 20A did nutritional indices reach low levels where justification for halting population growth was apparent, which supports prior findings that nutrition is a minor factor limiting most Alaska moose populations compared to predation. With predator reductions, the GMU 20A moose population increased from 1976 until liberal antlerless harvests in 2004. During 1997-2005, GMU 20A moose exhibited the lowest nutritional status reported to date for wild, noninsular, North American populations, including 1) delayed reproduction until moose reached 36 months of age and the lowest parturition rate among 36-month-old moose (29%, n = 147); 2) the lowest average multiyear twinning rates from late-May aerial surveys (x = 7%, SE = 0.9%, n = 9 yr, range = 3-10%) and delayed twinning until moose reached 60 months of age; 3) the lowest average mass of female short-yearlings in Alaska (x̄ = 155 ± 1.6 [SE] kg in the Tanana Flats subpopulation, up to 58 kg below average masses found elsewhere); and 4) high removal (42%) of current annual browse biomass compared to 9-26% elsewhere in boreal forests. When average multiyear twinning rates in GMU 20A (sampled during 1960-2005) declined to <10% in the mid- to late 1990s, we began encouraging liberal antlerless harvests, but only conservative annual harvests of 61-76 antlerless moose were achieved during 1996-2001. Using data in the context of our broader ranking system, we convinced skeptical citizen advisory committees to allow liberal antlerless harvests of 600-690 moose in 2004 and 2005, with the objective of halting population growth of the 16,000-17,000 moose; total harvests were 7-8% of total prehunt numbers. The resulting liberal antlerless harvests served to protect the moose population's health and habitat and to fulfill a mandate for elevated yield. Liberal antlerless harvests appear justified to halt population growth when multiyear twinning rates average ≤10% and ≥1 of the following signals substantiate low nutritional status: <50% of 36-month-old moose are parturient, average multiyear short-yearling mass is <175 kg, or >35% of annual browse biomass is removed by moose.     

Woodland Caribou Extirpation and Anthropogenic Landscape Disturbance in Ontario

Abstract: The decline of woodland caribou (Rangifer tarandus caribou) has been attributed to anthropogenic landscape disturbances, but critical distance thresholds and time lags between disturbance and extirpation are unknown. Using a database of caribou presence and extirpation for northern Ontario, Canada, geo-coded to 10 times 10-km cells, we constructed logistic regression models to predict caribou extirpation based on distance to the nearest of each of 9 disturbance types: forest cutovers, fires, roads, utility corridors, mines, pits and quarries, lakes, trails, and rail lines. We used Akaike's Information Criterion to select parsimonious models and Receiver-Operating Characteristic curves to derive optimal thresholds. To deal with the effects of spatial autocorrelation on estimates of model significance, we used subsampling and restricted randomizations. Forest cutovers were the best predictor of caribou occupancy, with a tolerance threshold of 13 km to nearest cutover and a time lag of 2 decades between disturbance by cutting and caribou extirpation. Management of woodland caribou should incorporate buffers around habitat and requires long-term monitoring of range occupancy.     

Survival of Wood Duck Ducklings and Broods in Mississippi and Alabama

ABSTRACT Although North American wood ducks (Aix sponsa) are well-studied throughout their range, researchers know little about demographic and environmental factors influencing survival of ducklings and broods, which is necessary information for population management. We studied radiomarked female and duckling wood ducks that used nest boxes and palustrine wetlands at Noxubee National Wildlife Refuge (NNWR) in Mississippi, USA, in 1996–1999, and riverine wetlands of the Tennessee-Tombigbee Rivers and Waterway (TTRW) system in Alabama in 1998–1999. We estimated survival of ducklings and broods and evaluated potentially important predictors of duckling survival, including age and body mass of brood-rearing females, hatch date of ducklings, duckling mass, brood size at nest departure, inter-day travel distance by ducklings, site and habitat use, and daily minimum air temperature and precipitation. At NNWR, survival of 300 radiomarked ducklings ranged from 0.15 (95% CI = 0.04-0.27) to 0.24 (95% CI = 0.13-0.38) and was 0.21 (95% CI = 0.15-0.28) for 1996–1999. Our overall estimate of brood survival was 0.64 (n = 91; 95% CI = 0.54-0.73). At TTRW, survival of 129 radiomarked ducklings was 0.29 in 1998 (95% CI = 0.20-0.41) and 1999 (95% CI = 0.13-0.45) and was 0.29 (95% CI = 0.20-0.40) for 1998–1999. Our overall estimate of brood survival was 0.71 (n = 38; 95% CI = 0.56-0.85). At NNWR, models that included all predictor variables best explained variation in duckling survival. Akaike weight (w_i) for the best model was 0.81, suggesting it was superior to other models (<0.01 < w_i < 0.18). We detected 4 competing models for duckling survival at TTRW. Inter-day distance traveled by ducklings was important as this variable appeared in all 4 models; duckling survival was positively related to this variable. Patterns of habitat-related survival were similar at both study areas. Ducklings in broods that used scrub-shrub habitats disjunct from wetlands containing aggregations of nest boxes had greater survival probabilities than birds remaining in wetlands with such nest structures. Managers may increase local wood duck recruitment by promoting availability of suitable brood habitats (e.g., scrub-shrub wetlands) without aggregations of nest boxes that may attract predators and by dispersing nest boxes amid or adjacent to these habitats. We did not determine an optimal density of nest boxes relative to local or regional population goals, which remains important research and conservation needs.     

Coordinated approaches to quantify long‐term ecosystem dynamics in response to global change

Many serious ecosystem consequences of climate change will take decades or even centuries to emerge. Long‐term ecological responses to global change are strongly regulated by slow processes, such as changes in species composition, carbon dynamics in soil and by long‐lived plants, and accumulation of nutrient capitals. Understanding and predicting these processes require experiments on decadal time scales. But decadal experiments by themselves may not be adequate because many of the slow processes have characteristic time scales much longer than experiments can be maintained. This article promotes a coordinated approach that combines long‐term, large‐scale global change experiments with process studies and modeling. Long‐term global change manipulative experiments, especially in high‐priority ecosystems such as tropical forests and high‐latitude regions, are essential to maximize information gain concerning future states of the earth system. The long‐term experiments should be conducted in tandem with complementary process studies, such as those using model ecosystems, species replacements, laboratory incubations, isotope tracers, and greenhouse facilities. Models are essential to assimilate data from long‐term experiments and process studies together with information from long‐term observations, surveys, and space‐for‐time studies along environmental and biological gradients. Future research programs with coordinated long‐term experiments, process studies, and modeling have the potential to be the most effective strategy to gain the best information on long‐term ecosystem dynamics in response to global change.     

The ontogeny and homology of the Weberian apparatus in the zebrafish Danio rerio (Ostariophysi: Cypriniformes)

The ontogeny of the Weberian apparatus was examined in the zebrafish, Danio rerio , using both cleared and stained specimens and histology. Over 300 individuals from four independent zebrafish lineages, ranging in size from 3 to 28 mm TL, were examined for this study. Results provide a basic understanding of the development of the Weberian apparatus in the wild-type zebrafish. Our results, in conjunction with those already published, point to substantial variation in the development of the Weberian apparatus among otophysans and new interpretations of the homology of certain ossicles (e.g. tripus and claustrum). Hypotheses of homology among various Weberian ossicles are considered and represent an important step in understanding the evolution of sound transmission in ostariophysan fishes.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 241–254.