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What is Normal Variation? Setting Baselines for Amphibian Monitoring in the Credit River Watershed Kirk Bowers Introduction • Baselines…. – Monitoring results must have an ecological context – How do we know if an indicator is changing? – What are the reference conditions? • Thresholds…. – What amount of change in indicator values is acceptable? – After what amount of change should flags be raised? • Widely used thresholds and established baseline data sets are not always available Amphibian Monitoring at CVC • 26 Monitoring Sites • Marsh monitoring protocols • Auditory system based on call level • 7 years of data (20032009) • Includes frogs and toads (no salamanders) • 10 species recorded CVC Monitoring Thresholds • 3 Standard Deviations - Critical Threshold – Values exceeding this threshold are associated with significant increasing or decreasing trends and should always be investigated thoroughly • 2 Standard Deviations – Warning Threshold – Implemented for the early detection of changing trends or significant decline in a parameter; recognize problems before they become irreversible • A time series with values falling within the 2 SD warning limits (in the “Green Zone”) is exhibiting natural variability and is considered to be stable and not of concern based on variance alone Statistical Process Control • Uses ecological time series to identify baselines and develop monitoring thresholds • Identifies instances when a time series exhibits nonrandom behaviour • Series exhibiting natural variability around a reference point (e.g. mean) is considered to be “In-Control” • Series demonstrating non-random behaviour is considered to be out of control • Only a time series that is “In-Control” can be used as a monitoring baseline Statistical Process Control • Control charts divided into 6 zones based on mean and standard deviation of time series • Parameter values on x-axis and time on y-axis Statistical Process Control • Distribution of data points is arranged around the time series mean (green line) Statistical Process Control • Upper and lower critical limits, defined by +/- 3 SD, encompass the “in-control” range of the series (red lines) Statistical Process Control • Upper and lower warning limits are defined by +/- 2 standard deviations Example 1: Mean species per site Question: Can data collected from 2003 to 2009 be used as a baseline for future monitoring of per-site species richness? 4 Mean species per site 3.5 3 2.5 2 1.5 1 0.5 0 2003 2004 2005 2006 Year 2007 2008 2009 Example 1: Mean species per site Example 1: Mean species per site • Data In Control? - YES • Can Data be used as a Monitoring Baseline – YES • Can Data be used to set Monitoring Thresholds? - YES Example 1: Mean species per site Upper Critical Threshold = 3.45 species per site Lower Critical Threshold = 1.87 species per site Example 1: Mean species per site Upper Warning Threshold = 3.19 species per site Lower Warning Threshold = 2.14 species per site Example 2: Green Frog Site Occupancy* Question: Can data collected from 2003 to 2009 be used as a baseline for future monitoring of Green Frog site occupancy?* * Not actual monitoring data Example 2: Green Frog Site Occupancy* Example 2: Green Frog Site Occupancy* Example 2: Green Frog Site Occupancy* • Data In Control? - NO • Can Data be used as a Monitoring Baseline – NO • Can Data be used to set Monitoring Thresholds? – NO • Non-random pattern in data could be... – An isolated anomaly (data will subsequently return to “in-control” status) or – A sign of significant change in the Green Frog population • This monitoring indicator must be tracked closely Baseline Length Question: How many sequential monitoring years should compose a baseline? • Answer may be dependant on the needs of the particular monitoring program and the indicator being considered • Generally, need a minimum of 5 sequential years of “InControl” data • “In-Control” sequence should be as current as possible Baseline Length Question: How many sequential monitoring years should compose a baseline? Seven sequential years of data Baseline Length Question: How many sequential monitoring years should compose a baseline? Seven-year sequence is not “In-Control” But... Baseline Length Question: How many sequential monitoring years should compose a baseline? ...Last 5 years of data are “In-Control” Baselines and Monitoring Design Question: How can the identified baseline be applied to monitoring design? • Properties of the baseline data set (mean, standard error) can be used in power analysis • Power analysis can help answer such questions as: – Does the program have sufficient statistical power to detect threshold changes in the given indicator? – How many sampling points (sites, visits, etc.) are required to detect threshold changes in the given indicator at a desired level of statistical power? Review • Baselines are a key component of monitoring because… – They describe reference conditions – They represent randomly variable data against which future trends can be compared – They allow for the development of monitoring thresholds – They aid in program design and assessment • We would like to extend special thanks to… – Rob Milne and Lorne Bennet – Paul Zorn – Private and Municipal land owners Any Questions?