402 The UMAP Journal 22. 4(2001) 2. If a site is determined to be a suitable habitat, will it support a low-or a high-density zebra mussel population? Rather than focusing on developing a complicated model that would predict le exact size of the population, we devised a simple, comprehensive model that answers these questions The inspiration for our model was derived from Ramcharan [1992 Assumptions The density of juveniles collected on the settling plates is proportional to the size of the adult population; this assumption allows us to use the provided data to predict the severity of the zebra mussel infestation. significantly vary with changes in the size of the zebra mussel population The chemical composition and concentrations(such as calcium levels)do no Examining the first data set from Lake A, we find that pH and calcium oncentration are the two most important factors in determining whether zebra mussel population is viable in a given site. This is reasonable, conside that the zebra mussels are very sensitive to ph and they need calcium to br their shells when developing from veligers to juveniles and onto adults We do not include temperature, because although it is important to the ife cycle of the zebra mussel, as long as the temperature is high enough to signal spawning, reproduction will occur. All 10 sites in Lake A had suitable temperatures for spawning We developed a model equation(Model 1)utilizing the values provided for pH and calcium concentration for the 1992 to 1999 period that give a simple measure to predict the viability(v) of a zebra mussel invasion at a particular site. The coefficients of the two variables (ph and [Ca)are used to weight the relative importance of the two factors. The range of values for pH for the ten sites is smaller than the range of values for calcium concentration, thus the coefficients function to equalize the importance of these two factors. The exact values of the coefficients were determined by successively modifying and refining the values until an equation was found that accurately reflected whether the lake site was a suitable habitat or not based on the population data We chose the threshold value of 10. 4 for viability because there appears to be a break there between the sites where zebra mussels survived and the sites where they were absent, and because 10. 4 is close to the value from the equation with 7. 4 for pH and 12 mg/L for calcium concentration. =10pH+0.2la If V >10.4. the site is a suitable habitat for zebra mussel Applying Model 1 to sites 1-10 in Lake A produces Table 1402 The UMAP Journal 22.4 (2001) 2. If a site is determined to be a suitable habitat, will it support a low- or a high-density zebra mussel population? Rather than focusing on developing a complicated model that would predict the exact size of the population, we devised a simple, comprehensive model that answers these questions. The inspiration for our model was derived from Ramcharan [1992]. Assumptions • The density of juveniles collected on the settling plates is proportional to the size of the adult population; this assumption allows us to use the provided data to predict the severity of the zebra mussel infestation. • The chemical composition and concentrations (such as calcium levels) do not significantly vary with changes in the size of the zebra mussel population. Examining the first data set from Lake A, we find that pH and calcium concentration are the two most important factors in determining whether a zebra mussel population is viable in a given site. This is reasonable, considering that the zebra mussels are very sensitive to pH and they need calcium to build their shells when developing from veligers to juveniles and onto adults. We do not include temperature, because although it is important to the life cycle of the zebra mussel, as long as the temperature is high enough to signal spawning, reproduction will occur. All 10 sites in Lake A had suitable temperatures for spawning. We developed a model equation (Model 1) utilizing the values provided for pH and calcium concentration for the 1992 to 1999 period that give a simple measure to predict the viability (V ) of a zebra mussel invasion at a particular site. The coefficients of the two variables (pH and [Ca]) are used to weight the relative importance of the two factors. The range of values for pH for the ten sites is smaller than the range of values for calcium concentration, thus the coefficients function to equalize the importance of these two factors. The exact values of the coefficients were determined by successively modifying and refining the values until an equation was found that accurately reflected whether the lake site was a suitable habitat or not based on the population data. We chose the threshold value of 10.4 for viability because there appears to be a break there between the sites where zebra mussels survived and the sites where they were absent, and because 10.4 is close to the value from the equation with 7.4 for pH and 12 mg/L for calcium concentration. V = 1.0 pH + 0.2 [Ca] If V > 10.4, the site is a suitable habitat for zebra mussels. Applying Model 1 to sites 1–10 in Lake A produces Table 1