Interannual variability and species turnover of crustacean zooplankton in Shield lakes

1999 ◽  
Vol 56 (1) ◽  
pp. 162-172 ◽  
Author(s):  
Shelley E Arnott ◽  
Norman D Yan ◽  
John J Magnuson ◽  
Thomas M Frost
Keyword(s):  
Sampling Error ◽  
Species Turnover ◽  
Crustacean Zooplankton ◽  
Annual Data ◽  
Turnover Rates ◽  
High Turnover ◽  
South Central ◽  
Census Interval ◽  
Shield Lakes

We estimated apparent species turnover rates and richness of the zooplankton annually over a 12-year period in eight lakes in south-central Ontario. Although species richness varied little among years (CV = 13%), apparent species turnover rates averaged 16%/year. This apparent turnover varied among years and was influenced by census interval, the number of censuses, the occurrence of rare species, and lake pH. However, Monte Carlo simulations indicated that turnover attributable to sampling error was high. That is, despite high apparent turnover rates, we cannot be certain whether interannual changes in community composition result from immigration and extinction of species because sampling error could largely account for all apparent turnover. Regardless of the source of apparent turnover (sampling or immigrations and extinctions), high turnover rates imply that zooplankton biodiversity can be underestimated in short-term studies because we detect a different assemblage of species every year. Only one third of the total species pool for each lake was detected every year. Annual data underestimated long-term species pools by 33-50%.

A comparison of pre-industrial and present-day changes in Bosmina and Daphnia size structure from soft-water Ontario lakes

2010 ◽  
Vol 67 (4) ◽  
pp. 754-762 ◽  
Author(s):  
Jennifer B. Korosi ◽  
Andrew M. Paterson ◽  
Anna M. DeSellas ◽  
John P. Smol
Keyword(s):  
Body Size ◽  
Size Structure ◽  
South Central ◽  
Zooplankton Size ◽  
Copepod Predation ◽  
Post Impact ◽  
North Temperate Lakes ◽  
Impact Data ◽  
Shield Lakes

Understanding the long-term controls on cladoceran size structure has important implications for aquatic ecosystems. Although there has been considerable interest in zooplankton size trends for Canadian Shield lakes, data are not available for zooplankton size structure prior to the period of anthropogenic disturbances. Here, we present pre- and post-impact size data for the common pelagic cladocerans Bosmina and Daphnia for 44 well-studied Shield lakes in south-central Ontario (Canada). We show that Daphnia were larger and that the length of Bosmina body appendages (mucrones and antennules) was longer in pre-industrial times than they are today. The reduction in Bosmina appendage length we observed may suggest a reduction in copepod predation pressure since pre-industrial times. Reduced maximum body size in Daphnia is a predicted response to a warming climate in north temperate lakes; however, we suggest that alternate explanations, specifically acidification and subsequent recovery following emission reductions, should also be explored as the primary drivers of Daphnia size changes in this lake set. Overall, our results highlight the importance of pre-impact data for understanding the long-term controls on cladoceran body size from pre-1850 to present.

Long-term declines in phosphorus export from forested catchments in south-central Ontario

2009 ◽  
Vol 66 (10) ◽  
pp. 1682-1692 ◽  
Author(s):  
M. Catherine Eimers ◽  
Shaun A. Watmough ◽  
Andrew M. Paterson ◽  
Peter J. Dillon ◽  
Huaxia Yao
Keyword(s):  
Stream Flow ◽  
Seasonal Patterns ◽  
Forested Catchments ◽  
Annual Average ◽  
Temporal And Spatial Patterns ◽  
South Central ◽  
Hydrologic Event ◽  
Temporal And Spatial ◽  
Shield Lakes

Total phosphorus (TP) levels in many Canadian Shield lakes in central Ontario have declined over recent decades, despite increases in human activity in most watersheds. To investigate the contribution of changes in catchment export to long-term declines in lake TP, we examined temporal and spatial patterns in TP concentrations and export (1980–1981 to 2001–2002) across 11 subcatchments that drain into three lakes in which average ice-free TP levels have declined by approximately 35%. Annual stream export of TP decreased significantly by 30%–89% in eight of the 11 subcatchments, and decreases in export were driven by declines in TP concentration, not changes in stream flow. Annual average TP concentrations varied fivefold among adjacent subcatchments, and temporal patterns in annual average TP concentrations were poorly correlated. Seasonal patterns of TP concentration were most similar among streams in the spring (March–April–May), and TP export in the spring declined significantly in 10 of the 11 subcatchments. Because spring melt is the principal hydrologic event in these seasonally snow-covered basins, decreases in TP export during the spring were primarily responsible for declines observed in annual export. The drivers of changes in TP over time are unclear at this point but are the focus of current research.

Evaluation of the responsiveness of the crustacean zooplankton community size spectrum to environmental change and an exotic invader in a sample of Canadian Shield lakes

2020 ◽  
Author(s):  
Lauren Emily Barth ◽  
Brian J. Shuter ◽  
W. Gary Sprules ◽  
Charles K. Minns ◽  
James A Rusak
Keyword(s):  
Time Series ◽  
Environmental Change ◽  
Canadian Shield ◽  
Ecosystem Change ◽  
Crustacean Zooplankton ◽  
Size Spectrum ◽  
Zooplankton Size ◽  
Shield Lakes ◽  
Change In Mean

We evaluated the crustacean zooplankton size spectrum as an indicator of lake characteristics and ecosystem change. First, we used time-series from seven Canadian Shield lakes to identify the factors associated with among-lake and among-year variability in the spectrum slope (relative abundance of small and large zooplankton) and centered height (total abundance). Second, we used time-series from an invaded and three control lakes to assess change in mean and variability in slope and height due to a Bythotrephes invasion. We found that the slope and the height reflected among-lake predictors related to morphometry. The slope was responsive to long-term declining lake phosphorus levels, whereas the height reflected both increases in dissolved organic carbon and decreases in ice duration. We detected a significant increase (i.e. flattening) in mean slope and substantial (up to 120%) increases in the CV of height after Bythotrephes invaded Harp Lake. Thus, the zooplankton size spectrum was responsive to long-term environmental change and a strong top-down perturbation can be detected through regular and frequent monitoring programs.

Quantitative inferences of past hypolimnetic anoxia in south-central Ontario lakes using fossil midges (Diptera: Chironomidae)

1998 ◽  
Vol 55 (3) ◽  
pp. 587-596 ◽  
Author(s):  
Roberto Quinlan ◽  
John P Smol ◽  
Roland I Hall
Keyword(s):  
Weighted Averaging ◽  
Species Variation ◽  
Calibration Model ◽  
Forward Selection ◽  
Lake Ecosystems ◽  
South Central ◽  
Hypolimnetic Oxygen ◽  
Chironomid Assemblages ◽  
Shield Lakes

The ability to infer long-term changes in hypolimnetic oxygen levels is important for ecological studies of eutrophication and the impacts of climatic change on freshwater lakes. We examined the distributions of fossil midge (Diptera: Chironomidae) assemblages in the surface sediments of 54 south-central Ontario lakes and, using canonical correspondence analysis (CCA), determined if fossil chironomid assemblages could be used to reconstruct levels of hypolimnetic anoxia in thermally stratifying Laurentian Shield lakes. Anoxia was expressed as the anoxic factor (AF), which represents the days per season that a sediment area equal to a lake's surface area is overlain by anoxic water. Forward selection in CCA showed that AF, maximum depth, [SO4], [Na], and watershed area all explained significant portions of species variation. A weighted-averaging regression and calibration model of the chironomid-anoxia relationship was developed which suggests that it is possible to infer AF from fossil chironomid assemblages ( (r2appar ) = 0.70, bootstrapped RMSE = 6.5 days/summer). Quantitative reconstruction of past changes in anoxia using fossil Chironomidae should provide a new and useful tool for paleoecological assessments of lake ecosystems.

Facility-Level Factors Associated With CNA Turnover and Retention: Lessons for the Long-Term Services Industry

2020 ◽  
Vol 60 (8) ◽  
pp. 1436-1444 ◽  
Author(s):  
Katherine A Kennedy ◽  
Robert Applebaum ◽  
John R Bowblis
Keyword(s):  
Retention Rate ◽  
Retention Rates ◽  
Nursing Assistant ◽  
Turnover Rates ◽  
High Turnover ◽  
Term Care ◽  
Factors Associated ◽  
The Mean ◽  
Facility Level

Abstract Background and Objectives Certified nursing assistant (CNA) turnover and retention are critical aspects of facilities’ ability to provide cost-effective, high-quality person-centered care. Previous studies and industry practice often treat turnover and retention as similar concepts, assuming that low turnover and high retention are synonymous. The study addressed the question of whether turnover and retention rates differ and if so, what those differences mean for nursing home practice, policy, and research. Research Design and Methods This study examines facility-level factors associated with CNA retention and turnover rates using 2015 data from the Ohio Biennial Survey of Long-Term Care Facilities, Ohio Medicaid Cost Reports, Certification and Survey Provider Enhanced Report, and the Area Health Resource File. Using bivariate tests and regression analysis, we compare rates and the factors associated with retention and turnover. Results The mean facility annual retention rate was 64% and the mean annual turnover rate was 55%. As expected, there was a statistically significant and negative correlation between the rates (r = −0.26). However, some facilities had both high retention and high turnover and some had low rates for both measures. Not all the variables that are associated with turnover are also associated with retention. Discussion and Implications CNA retention is not simply the absence of CNA turnover. Given the differences, nursing homes may need to use strategies and policies designed to target a particular stability measure.

scholarly journals Differential responses of marine communities to natural and anthropogenic changes

2015 ◽  
Vol 282 (1803) ◽  
pp. 20142990 ◽  
Author(s):  
Michał Kowalewski ◽  
Jacalyn M. Wittmer ◽  
Troy A. Dexter ◽  
Alessandro Amorosi ◽  
Daniele Scarponi
Keyword(s):  
Environmental Changes ◽  
Species Turnover ◽  
Homogeneous System ◽  
Turnover Rates ◽  
Time Intervals ◽  
Northern Adriatic ◽  
Marine Communities ◽  
Ecosystem Shift ◽  
Natural Climate

Responses of ecosystems to environmental changes vary greatly across habitats, organisms and observational scales. The Quaternary fossil record of the Po Basin demonstrates that marine communities of the northern Adriatic re-emerged unchanged following the most recent glaciation, which lasted approximately 100 000 years. The Late Pleistocene and Holocene interglacial ecosystems were both dominated by the same species, species turnover rates approximated predictions of resampling models of a homogeneous system, and comparable bathymetric gradients in species composition, sample-level diversity, dominance and specimen abundance were observed in both time intervals. The interglacial Adriatic ecosystems appear to have been impervious to natural climate change either owing to their persistence during those long-term perturbations or their resilient recovery during interglacial phases of climate oscillations. By contrast, present-day communities of the northern Adriatic differ notably from their Holocene counterparts. The recent ecosystem shift stands in contrast to the long-term endurance of interglacial communities in face of climate-driven environmental changes.

Long-term trends in hypolimnetic volumes and dissolved oxygen concentrations in Boreal Shield lakes of south-central Ontario, Canada

2019 ◽  
Vol 76 (12) ◽  
pp. 2315-2325 ◽  
Author(s):  
Clare Nelligan ◽  
Adam Jeziorski ◽  
Kathleen M. Rühland ◽  
Andrew M. Paterson ◽  
John P. Smol
Keyword(s):  
Dissolved Oxygen ◽  
Climatic Factors ◽  
Thermocline Depth ◽  
South Central ◽  
Air Temperatures ◽  
Hypolimnetic Oxygen ◽  
Long Term Trends ◽  
Shield Lakes ◽  
Carbon Concentrations

Temperature–oxygen profiles, collected biweekly to monthly for ∼40 years, were used to calculate end-of-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in six small lakes located in south-central Ontario, Canada. Coherent decreases in thermocline depth and increases in hypolimnetic volume, mean hypolimnetic dissolved oxygen (DO) concentration, and VWHO were observed in five of the six study lakes. All lakes underwent an abrupt increase in VWHO and mean hypolimnetic DO after 2010. In four of the six study lakes, the highest hypolimnetic DO concentrations were observed in years where chlorophyll a concentrations were low, whereas at five of the six study lakes the highest hypolimnetic volumes were observed when dissolved organic carbon concentrations were relatively high. Warmer spring or winter air temperatures were associated with higher hypolimnetic DO concentrations at two sites, and longer ice-free periods were associated with smaller hypolimnetic volumes at two sites. These results suggest that the recent VWHO increases in the studied south-central Ontario lakes may be a function of multiple drivers that include changes in primary production, lake water transparency, and regional climatic factors.

Species Turnover Rates on Islands: Dependence on Census Interval

Science ◽  
1977 ◽  
Vol 197 (4300) ◽  
pp. 266-270 ◽  
Author(s):  
J. M. DIAMOND ◽  
R. M. MAY
Keyword(s):  
Species Turnover ◽  
Turnover Rates ◽  
Census Interval

Detection of Metal Toxicity Using Natural Phytoplankton as Test Organisms in the Great Lakes

1993 ◽  
Vol 28 (1) ◽  
pp. 155-176
Author(s):  
Mohiddin Munawari ◽  
Milos Legner
Keyword(s):  
Great Lakes ◽  
Metal Toxicity ◽  
Structural Changes ◽  
System Response ◽  
Turnover Rates ◽  
High Turnover ◽  
Spectra Analysis ◽  
Test Organisms ◽  
Future Potential ◽  
Natural Phytoplankton

Abstract This paper presents an overview of techniques utilizing natural phytoplankton for the detection of metal-Induced stress in the Great Lakes. Both field and laboratory procedures are designed to evaluate either structural changes or functional response of test organisms. This up-to-date compendium provides a choice of techniques, which permits a holistic assessment of the stress caused by toxic metals. Recently introduced techniques, such as normalized size spectra analysis, flow cytometry, and the evaluation of a continuous-flow system response to metal toxicity, are discussed in more detail to explore their future potential. Owing to their key position in the food web, high turnover rates, abundance, and sensitivity to environmental perturbation, phytoplankton serve as reliable early warning indicators of ecosystem deterioration and its restoration.

scholarly journals Quantitative analysis of the CD8 + T–cell response to readily eliminated and persistent viruses

2000 ◽  
Vol 355 (1400) ◽  
pp. 1093-1101 ◽  
Author(s):  
P. C. Doherty ◽  
J. M. Riberdy ◽  
G. T. Belz
Keyword(s):  
T Cells ◽  
T Cell ◽  
Influenza A ◽  
Flow Cytometric Analysis ◽  
T Cell Response ◽  
Basic Question ◽  
Cell Mediated Immunity ◽  
Specific Response ◽  
Turnover Rates

The recent development of techniques for the direct staining of peptide–specific CD8 + T cells has revolutionized the analysis of cell–mediated immunity (CMI) in virus infections. This approach has been used to quantify the acute and long–term consequences of infecting laboratory mice with the readily eliminated influenza A viruses (fluA) and a persistent γherpesvirus (γHV). It is now, for the first time, possible to work with real numbers in the analysis of CD8 + T CMI, and to define various characteristics of the responding lymphocytes both by direct flow cytometric analysis and by sorting for further in vitro manipulation. Relatively little has yet been done from the latter aspect, though we are rapidly accumulating a mass of numerical data. The acute, antigen–driven phases of the fluA and γHV–specific response look rather similar, but CD8 + T–cell numbers are maintained in the long term at a higher ‘set point’ in the persistent infection. Similarly, these ‘memory’ T cells continue to divide at a much greater rate in the γHV–infected mice. New insights have also been generated on the nature of the recall response following secondary challenge in both experimental systems, and the extent of protection conferred by large numbers of virus–specific CD8 + T cells has been determined. However, there are still many parameters that have received little attention, partly because they are difficult to measure. These include the rate of antigen–specific CD8 + T–cell loss, the extent of the lymphocyte ‘diaspora’ to other tissues, and the diversity of functional characteristics, turnover rates, clonal life spans and recirculation profiles. The basic question for immunologists remains how we reconcile the extraordinary plasticity of the immune system with the mechanisms that maintain a stable milieu interieur. This new capacity to quantify CD8 + T–cell responses in readily manipulated mouse models has obvious potential for illuminating homeostatic control, particularly if the experimental approaches to the problem are designed in the context of appropriate predictive models.

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