J. N. Am. Benthol. Soc. 1990, 9(1):9-16 © 1990 by The North American Benthological Society Empirical evidence for differences among methods for calculating secondary production C. Plante and J. A. Downing Departement de Sciences biologiques, Universite de Montreal, C.P. 6128, Succursale 'A', Montreal, Quebec, Canada H3C 3J7 Abstract. The hypothesis that different secondary production estimation methods yield unbiased and equally precise estimates is tested using published data from 66 benthic invertebrate populations from lentic habitats. Tests are performed by Kruskal-Wallis one-way analysis of the residuals of a published empirical equation accounting for the important covariables biomass, body-mass, and water temperature. While no method was found to be significantly biased, the size-frequency method was less precise than the Allen curve, growth increment summation or instantaneous growth methods, yielding estimates about three times farther from the probable production values than other methods. Imprecision of inferred cohort production interval (CPI) is suggested as one source of error. Key words: secondary production, calculation methods, precision, bias, benthos, cohort produc tion interval. Secondary production measurements are nec pared the removal summation, instantaneous essary for studying the transfer of energy and growth and size-frequency methods and con material in natural ecosystems and managing cluded that all methods yield underestimates if aquatic resources (Downing 1984). Comparing their assumptions are not consistent with the secondary productivity of diverse aquatic eco characteristics of the population. Cushman et systems is useful in forming general theories of al. (1977) suggested that the removal summa aquatic productivity. Such theories will be tract tion method is the most robust and that biases able only if measures of secondary production can be reduced by increasing sampling inten are comparable among ecosystems. Several pro sity. Morin et al. (1987) compared the size-fre cedures based on common concepts of popu quency, the Allen curve, the growth increment lation dynamics are currently used to make such summation, and the instantaneous growth estimates (Benke 1984, Downing 1984). The most methods for populations with different patterns commonly used methods for estimating inver of growth, mortality and recruitment, using dif tebrate population production are Allen curves, ferent degrees of sampling intensity. They dem growth increment summation, instantaneous onstrated that the size-frequency method should growth, and size-frequency. Each technique underestimate population production, makes different simplifying assumptions about cially where hatching is perfectly synchronous. such factors as patterns of growth and mortality All methods were found to underestimate pro espe (Benke 1984, Rigler and Downing 1984). Im- duction if the sampling interval did not cover precisions in these assumptions can be trans intense periods of productivity. In addition, lated into bias in resulting estimates. Morin et al. (1987) showed that sampling errors Side-by-side comparisons of secondary pro can result in both bias and imprecision in pro duction methods suggest that under different duction estimates, especially in the case of the conditions some techniques yield different es size-frequency method. timates. Several authors (e.g.. Waters and Craw ford 1973, Benke 1976, Riklik and Momot 1982, All calculation methods give errors under certain circumstances. Such calculation errors Lauzon and Harper 1986) have found that dif may be insignificant because confidence inter ferent calculation methods yield differences vals around individual production estimates are from 1 to 25% in estimated production. Simu broad (Morin et al. 1987). No study to date has lation studies corroborate this finding and show analyzed production data to see whether dif that different methods of production calcula ferent production calculation methods actually tion must give rise to differences in estimated give systematically biased or excessively vari production rates. Cushman et al. (1977) com able estimates under actual field conditions. The [Volume 9 C. Plante and J. A. Downing 10 objective of this study was to compare pub Wm from the published production estimates. If lished field production estimates, made with the data collected using all computation meth different methods, to see whether any tech ods are equivalent, analysis of variance should niques yield significantly biased or significant reveal no significant difference among the av ly more variable estimates than others. erage distances between observed production and predictions from Equation 1. Further de tails of such residual analyses, corresponding to the analysis of covariance, are presented by Methods Draper and Smith (1981) and Gujarati (1978). Several factors such as biomass, body-size, rate This study analyzes differences in residuals of growth, voltinism, temperature, and food in published data on benthos production esti availability and quality are known to be im mated using three methods: the size-frequency portant covariables of population production. method (SF), the Allen curve and growth in Direct comparisons of average annual produc crement summation (AC-GS), and the instan tion of populations differing in these charac taneous growth method (IG). Allen curve and teristics would be inappropriate. In this study, growth increment summation were examined therefore, we approached this problem by col together because both are based on the rela lecting published data on the secondary pro tionship between the number of organisms and duction of lentic invertebrate populations from individual body mass in a cohort (Rigler and a diverse array of populations and environ Downing 1984). The data set analyzed consists ments. We then employed these population and of all of the 66 benthic invertebrate production environmental characteristics as covariables in estimates used to compute Equation 1. These an analysis of covariance to test the hypothesis populations come from 22 different ecosystems that different techniques for estimating second (Table 1). They span a range of production from ary production yield equivalent production es 0.03 to 66.40 g dry mass/m2/yr, a range of mean timates for populations of equal biomass and annual biomass from 0.002 to 10 g dry mass/ size, living at similar temperatures. m2, a range of body-size from 0.01 jug to 60 mg Plante and Downing (1989) developed an dry mass, and were found in environments with equation to predict the productivity of lentic, average annual aquatic invertebrate populations based on mul ranging from 4 to 18°C (Table 1). Of these es tiple regression analyses of published second timates, 20 were made with the size-frequency surface water temperatures ary production estimates of 137 populations of technique, 26 were made with the Allen curve benthos and zooplankton from 50 lakes, res or growth increment summation methods, and ervoirs, and ponds. The best regression fit was: 20 were made with the instantaneous growth technique. log10P = 0.05 + 0.79 log10B + 0.05T - 0.16 log10W0 (1) The residuals from Plante and Downing's (1989) regression equation (Equation 1) (ob (R2 = 0.79, n = 138, F = 165, p <k 0.001) where served log P — predicted log P) were calculated P is the annual secondary production (g dry for each of 66 populations and two hypotheses mass/m2/yr), B is the mean annual biomass (g were tested. The hypothesis that all three es dry mass/m2), T is the mean annual surface tem timation procedures yielded equal residuals was perature (°C), and Wm is the maximum individ tested using Kruskal-Wallis one-way analysis ual body mass (mg dry mass/individual). The (Conover 1971). Rejection of the null hypoth equation characterizes covariation of P, 6, T and esis would indicate that one or more of the cal Wm equally well for both benthos and zoo- culation methods yield biased production es plankton (Plante and Downing 1989). It pre timates. Precision of estimation was examined dicts the most probable level of P given the by testing the hypothesis that all three esti population biomass, body-size, and the ambient mation procedures yielded equal absolute val temperature. Because this equation was pro ues of residuals. Rejection of the second null duced from data covering the range of possible hypothesis would indicate that one or more of ecological conditions in lentic habitats (Plante the calculation methods yielded estimates that and Downing 1989), it can be used to remove were significantly farther from the most prob the effect of the important covariates, B, T and able value. 1990] Calculating secondary production Results and Discussion Figure 1 shows that observed production rates 11 significant that some lack of independence poses no practical problem to interpretation. Al though Table 2 shows that the size-frequency rise with predictions with a slope close to 1, method yields no bias if a large number of pro therefore Equation 1 accounts efficiently for the duction estimates are considered, Table 3 shows covariables B, T and Wm for data on benthic that, on average, individual size-frequency pro invertebrate production. Figure 1 also suggests duction estimates were significantly farther from that some methods tend to yield different ob the most probable production value than esti servations from others. For example, estimates mates made with other methods. using the size-frequency method often seem to lie above the others. Figure 2 shows frequency Our results appear to contradict the simula tion studies of Morin et al. (1987). Their work histograms of calculated residuals from Equa suggests that the size-frequency method should tion 1 separated by method. Although Figure 2 yield severe underestimates of secondary pro shows that residuals for the size-frequency duction when cohort synchrony is perfect, and method cluster less tightly around the predict that all production estimation methods should ed values, Table 2 shows that there is no statis yield approximately equal precision for a given tically significant {p > 0.05) tendency for the sampling effort. We found no detectable differ size-frequency method to yield a systematically ence in the bias of various techniques but found positive or negative bias. This analysis suggests that the size-frequency method is the least pre that if a large number of production estimates cise. It is likely that the degree of bias found in is made, none of these techniques will engen cases where cohort synchrony is not perfect (—30 der systematic bias in the average production to +10%) would not be detectable in our anal estimate obtained. yses owing to the errors associated with esti On the other hand, several individual pro duction estimates made with the size-frequency mates of biomass, numbers, and environmental characteristics. The relatively low precision of method seem to fall far from the value expected the size-frequency method in actual field ap on the basis of biomass, body-size and temper plications may be due to factors not examined ature. The median absolute value of the resid by Morin et al. (1987). For example, Benke (1984) uals for the size-frequency method (Fig. 2) is shows that all size-frequency estimates of sec 0.39 compared with medians of 0.14 and 0.06 ondary production must be corrected to annual for the Allen curve-increment summation and production by multiplying the estimate by instantaneous growth techniques, respectively. 365/CPI, where CPI is the average cohort pro This difference means that, on average, size- duction interval. This correction was applied in frequency estimates of production are about 3 all studies except the size-frequency estimates times farther (inverse log of the difference be of Tudorancea et al. (1979) where CPI correction tween the median of the methods) from the would have resulted in an even greater depar most probable production value than the other ture from the most probable production value. two classes of methods. Table 3 shows that the Size-frequency estimates are usually made when absolute values of the residuals of estimates complete population life-history data are un made with the size-frequency method are sig available or impossible to collect, e.g., where nificantly (p = 0.0002) greater, on average, than successive cohorts are asynchronous and over the absolute values of the residuals obtained lap considerably. Except in situations where using the other two methods. A Kruskal-Wallis there is no synchrony of reproduction, if enough test shows no significant difference among the population data were collected so that the CPI absolute values of the residuals obtained using and the growth pattern of each cohort could be the Allen curve, increment summation or in known with precision (knowledge of growth stantaneous growth methods (p = 0.17). Al patterns is necessary to find appropriate size though our observations are independent mea classes, Benke 1984), then one would possess surements of production made on autonomous sufficient data to apply cohort methods such as populations, more than one population was in the Allen curve or growth increment summa cluded for several lakes, suggesting some lack tion technique. Thus, such information is rarely of statistical independence. We believe, how well known where the size-frequency method ever, that results shown in Table 3 are so highly is applied. Table 1. Data used to test for empirical differences in bias and precision of secondary production estimates in populations of aquatic insect larvae made using the size-frequency (SF), Allen curve and growth increment summation (AC-GS), and instantaneous growth (IG) methods. Data are listed in decreasing order of absolute values of the residuals from Equation 1. The taxonomic group (Group) is indicated as I for insects, M for molluscs, C for crustaceans, and A for annelids. Resid. is the residual from Equation 1 (log observed — log predicted). Wm is the maximum individual body mass (mg dry mass), B is the annual mean biomass (g dry mass/m2), T is the mean annual water temperature (°C at surface), P is the secondary production (g dry mass/mVyr), and P is the secondary production predicted from Equation 1 (g dry mass/m2/yr). Some temperature data were obtained from other sources (see Plante and Downing 1989). Water-body Taxon Group logWm logB T logP logP Resid. Method Ref, Ceratopogonidae Lake Norman I -1.374 -2.454 18.0 -1.979 -0.829 -1.150 SF 1 Amnicola limosa Lake Manitoba M 2.187 -0.409 13.0 0.896 -0.035 0.931 SF 2 Chironomus sp. Lake Manitoba I 0.784 -1.301 13.0 0.252 -0.518 0.770 SF 2 Pisidium spp. Lake Manitoba M 1.265 -0.721 13.0 0.612 -0.137 0.749 SF 2 Chaoborus punctinatus Lake Norman I -1.337 -1.745 18.0 -0.995 -0.277 -0.718 SF 3 Tanytarsus gracilendicus Myvatn I 0.397 0.578 5.0 1.28 0.605 0.675 AC-GS 4 Tendipes decorus Texas pond I -0.275 -0.971 16.8 0.778 0.105 0.673 SF 5 Procladius sp. Texas pond I -0.102 -1.347 16.8 0.38 -0.218 0.598 SF 5 Valvata tricarinata Lake Manitoba M 2.765 -0.796 13.0 0.139 -0.430 0.569 SF 2 Parartemia zietziana Pink Lake C 0.602 -0.248 16.0 1.053 0.495 0.558 AC-GS 6 Harnischis curtilamellata Lake Manitoba I -1.589 -0.886 13.0 -0.318 0.179 -0.497 SF 2 7 n | SJ Tanytarsus spp. Lake Norman I -2.868 -1.347 18.0 0.684 0.276 0.408 SF Parachironomus mancus Eglwys Nunydd I -0.952 -1.699 12.8 -0.958 -0.571 -0.387 IG 8 Procladius freemani Lake Manitoba I -1.26 -0.569 13.0 0.004 0.377 -0.373 SF 2 ;> Chironomus anthracinus Loch Leven I 0.146 0.815 9.0 1.409 1.039 0.370 AC-GS 9 * Tinodes waemeri Lake Esrom I 0.477 0.244 9.0 0.905 0.538 0.367 AC-GS 10 4 Chironomus islandicus Myvatn I 1.778 0.671 5.0 0.826 0.462 0.364 AC-GS Chironomus sp. Lake Norman I 0.172 -2.409 18.0 -0.696 -1.035 0.339 SF Tanytarsus barbitarsus Lake Werowrap I -1 0.907 13.2 1.822 L508 0.314 AC-GS Cryptochironomus spp. Lake Norman I -1.929 -2.081 18.0 -0.148 -0.449 0.301 SF Pisidium sp. Lac de Port-Bielh M 0.021 -1.481 4.0 -1.301 -1.009 -0.292 Chironomidae Eglwys Nunydd I 0.212 0.537 12.8 1.296 1.007 0.289 Procladius simplicistilus Loch Leven 0.118 -1.166 9.0 -0.779 -0.516 -0.263 AC-GS 13 AC-GS 14 AC-GA 12 Chironomus anthracinus Lake Esrom ] Zavrelymia melanura Lac de Port-Bielh ] Chironomus plumosus Eglwys Nunydd ] Erpobdella testacea Lake Esrom Psilotanypus ruforittatus Eglwys Nunydd Chironomus anthracinus Lake Memphremagog Tanytarsus inopersus Eglwys Nunydd 0.301 \ ] IG 7 9.5 1.401 1.154 0.247 4.0 -0.769 -0.532 -0.237 0.643 -0.260 12.8 0.545 0.313 0.232 IG 8 1.415 -0.545 9.5 -0,433 -0.204 -0.229 IG 15 -0.473 -0.208 12.8 0.303 0.528 -0.225 IG 8 0.301 0.517 -0.216 AC-GS 0.158 -0.198 IG 8 -0.141 12.8 -0.934 -0.770 12.8 -0.04 16 Asellus obtusus Bob Black Pond C 2.27 -0.796 16.5 0.019 -0.170 0,189 SF 17 Asellus aquaticus Eglwys Nunydd C 1.748 -0.699 12.8 -0.027 -0.205 0,178 IG 8 (■« fr-4 8 0.959 -0.068 I 12 -0.959 -0.4 i AC-GS 7 11 1™! c? Table 1. Taxon Water-body Group log Wm Continued. logP logB logP Resid. 1.079 -0.229 9.5 0.254 0.097 0.157 Method IG Ref. 15 Erpobdella octoculata Lake Esrom Procladius crassinervis Loch Leven [ -0.023 -0.312 9.0 0.024 0.178 -0.154 AC-GS 9 Stempellina spp. Lake Norman I -4.593 -2.721 18.0 -0.686 -0.537 -0.149 SF 7 Psilotanypus rufovittatus Loch Leven [ -0.73 -1.604 9.0 -0.58 -0.728 0.148 AC-GS 9 Brachicerus sp. Texas pond [ -0.236 -0.561 16,8 0.278 0.421 -0.143 SF 5 Cladotanytarsus spp. Lake Norman [ -2.669 -1.959 18,0 -0.103 -0.237 0.134 SF 7 Orconectes virilis Dock Lake C 2.477 0.458 12.8 0.72 0.592 0.128 IG 16 Chironomus ptumosus Federsee [ 1.146 0.931 11.0 0.953 1.078 -0.125 AC-GS 18 Criptocopus ornatus Waldsea [ -0.198 -1.891 10.3 -1.092 -0.970 -0.122 SF 19 Psectrocladius sordidellus Lac de Port-Bielh I -0.4 -0.538 4.0 -0.319 -0.201 -0.118 AC-GS 12 Chironomus comtnutatus Lac de Port-Bielh I 0 -0.569 4.0 -0.402 -0.287 -0.115 AC-GS 20 Limnochironomus pulsus Loch Leven -0.698 -0.836 9.0 -0.23 -0.129 -0.101 AC-GS 9 Procladius choreus Eglwys Nunydd -0.261 -0.284 12.8 0.532 0.435 0.097 IG 8 Stictochirus rosenscholdi Malsj0en -0.198 -0.924 7.0 -0.468 -0.381 -0.087 AC-GS Procladius choreus Loch Leven -0.417 -0.567 9.0 -0.047 0.039 -0.086 AC-GS 13 Sialis lutaria Lac de Port-Bielh 1.176 -0.420 4.0 -0.29 -0.354 0.064 AC-GS 22 0.103 -0.062 0.060 0.847 0.898 -0.051 IG 23 11.5 -0.097 -0.148 0.051 SF 24 -0.495 16.5 0.308 0.355 -0.047 SF 17 2.477 0.972 13.7 1.083 1.043 0.040 IG 23 2.477 0.471 12.8 0.641 0.602 0.039 IG 16 -0.634 -0.620 12.8 0.19 0.229 -0.039 IG 8 Eglwys Nunydd -0.75 -0.495 12.8 0.38 0.345 0.035 IG 8 Penlaneura monilis Loch Leven -0.899 -1.747 9.0 -0.787 -0.815 0.028 AC-GS 9 Procladius barbatus Malsjoen 0,284 -0.646 7.0 -0,259 -0.237 -0.022 AC-GS 21 Orconectes virilis West Lost Lake 2.477 0.970 13.7 1.021 1.042 -0.021 IG 23 Hexagenia limbata Savanne Lake 1.255 -0.638 11.5 -0.168 -0.148 -0.020 AC-GS 24 Hexagenia limbata Savanne Lake 1.255 -0.638 11.5 -0.168 -0.148 -0.020 IG 24 Glyptotendipes paripes Eglwys Nunydd -0.473 -0.284 12.8 0.488 0.468 0.020 IG Clyptotendipes parites Loch Leven 0.556 -0.185 9.0 0.204 0.188 0.016 AC-GS 13 Polypedilum nubeculosum Loch Leven -0.397 -0.845 9.0 -0.193 -0.183 -0.010 AC-GS 9 Microtendipes sp. Eglwys Nunydd -0.107 -0.553 12.8 0.209 0.199 0.010 IG 8 Eglwys Nunydd -0.458 -0.745 12.8 0.041 Parartemia zietziana Lake Cundare c 0.602 -1.019 17.0 0 Orconectes virilis North Twin Lake c 2.477 0.788 13.7 Hexagenia limbata Savanne Lake t 1.255 -0.638 Crangonyx gracilis Bob Black Pond c 0.418 Orconectes virilis South Twin Lake c Orconectes virilis Shallow Lake c Tanytarsus holochlorus Eglwys Nunydd Tanytarsus lugens <c IG AC-GS c 21 -0.060 Limnochironomus pulsus £ c 8 6 8 References:!. Bowen(1983),2. Tudorancea et al. (1979), 3. Eaton (1983), 4. Lindegaard and Jonasson (1979), 5. Benson etal. (1980), 6. Marchant and Williams (1977), 7. Wilda (1983), 8. Potter and Learner (1974), 9. Charles et al. (1974), 10. Dall et al (1984), 11. Walker (1973), 12. Laville (1972), 13. Charles et al. (1976), 14. Jonasson (1975), 15. Dall (1980), 16. Dermott et al. (1977), 17. Martien and Benke (1977), 18. Frank (1982), 19. Swanson and Hammer (1983), 20. Lavilie (1975), 21. Aagaard (1978), 22. Giani and Laville (1973), 23. Momot and Gowing (1977), 24. Riklik and Momot (1982). 2 P *< | [Volume 9 C. Plante and J. A. Downing 9A^D4A»* 0o//OA--1 m U.JQ V A& nn1: I■GAOCD—GSSAF 1 — o (Q-. ZO1Q- ION 14 >o a -2 Ld -2 LOG Fig. 1. "predicted PRODUCTION2 Relationship between observed secondary production of aquatic invertebrates and the produc tion predicted using Equation 1. The solid line indicates a 1:1 relationship. SF indicates that the es timate was made using the size-frequency method, AC-GS indicates the Allen-curve or increment sum mation method and IG indicates the instantaneous growth method. Errors in annual production estimates by the -1.6 size-frequency method will be proportional to -1.2 -0.4 0.0 0.4 0.8 RESIDUALS differences between real and assumed time spent by a cohort to complete its growth. For example, -0.8 Fig. 2. Frequency histogram of the residuals (log some of the large residuals in Table 1 were found observed — log predicted) from Equation 1 grouped for larval chironomid populations in Lake Nor by production estimation technique. Abbreviations man by Wilda (1983). The CPI for these popu are as in Figure 1. lations was inferred from the laboratory-de rived development equation of Mackey (1977). Table 2. Kruskal-Wallis test (Conover 1971) for Table 3. Kruskal-Wallis test (Conover 1971) for differences in precision of various production esti bias in various production estimation methods. The mation methods. The analysis was performed on the analysis was performed on the residuals from Equa absolute value of the residuals of Equation 1 using tion 1 using estimation methods as treatment groups, estimation methods as treatment groups, p is the ap p is the approximate Chi-square probability. proximate Chi-square probability. Num Method ber of Mean cases rank Method Num ber of cases Mean rank Size-frequency 20 37.7 Size-frequency 20 46.9 Allen curve and increment summation 26 32.1 Allen curve and increment summation 26 30.7 Instantaneous growth 20 31.0 Instantaneous growth 20 23.6 Kruskal-Wallis statistic = 1.44 Size-frequency Kruskal-Wallis statistic = 15.6 p = 0.49 20 37.7 Kruskal-Wallis statistic = 1.41 20 46.9 46 27.7 Allen curve, increment summation Allen curve, increment summation and instantaneous growth Size-frequency p = 0.0002 46 31.7 p = 0.24 and instantaneous growth Kruskal-Wallis statistic = 14.1 p = 0.0002 1990] 15 Calculating secondary production Wilda (1983) assumed that these chironomids from the Natural Sciences and Engineering Re were producing the equivalent of 18.5 or 22 search Council of Canada, and a team grant from consecutive cohorts per year, a figure that was the Ministry of Education of the Province of probably too large (T. J. Wilda, Duke Power Quebec (FCAR). We thank the members of the Company, personal communication). If one as Groupe d'Ecologie des Eaux douces, A. Morin, sumes that the cohort P/B is 5 (Waters 1977), A. C. Benke, and two anonymous referees for then Equation 1 can be used to approximate this their comments and criticisms. number of consecutive cohorts produced in one year (Plante and Downing 1989). The actual Literature Cited number of cohorts formed annually probably ranged from about 6 for Chironomus sp. to 36 for Aagaard, K. 1978. The chironomids of Lake Mals- Stempellina spp. if cohorts were consecutive, re j0en. A phenological, diversity, and production sulting in errors in annual secondary produc study. Norwegian Journal of Entomology 23:21- tion from +330% to —55%. Other sources of 37. error certainly exist, but our analyses underline Benke, A. C. the difficulty of estimating secondary produc tion without good life-history data, realistic measures of growth rate, or accurate measure ments of larval development time. In conclusion, the biases suggested by sim ulation studies do not appear to be a major prob lem in actual data. Use of the size-frequency method, or characteristics of populations that are studied using the size-frequency method, result in estimates that can be much farther from probable production values than the estimates found using Allen curve, growth increment summation and instantaneous growth tech niques. Much of this imprecision may arise from incorrect CPI correction, but could also stem either from a lack of synchrony in developing cohorts (Morin et al. 1987), the need for cor 1976. Dragonfly production and prey turnover. Ecology 57:915-927. Benke, A. C. 1984. Secondary production of aquatic insects. Pages 289-323 in V. H. Resh and D. M. Rosenberg (editors). Ecology of aquatic insects. Praeger Publishers, New York. Benson, D. J., L. C. Fitzpatrick, and W. D. Pearson. 1980. Production and energy flow in the benthic community of a Texas pond. Hydrobiologia 74: 81-93. Bowen, T. W. 1983. Production of the predaceous midge tribes Sphaeromiini and Palpomyiini (Diptera:Ceratopogonidae) in Lake Norman, North Carolina. Hydrobiologia 99:81-83. Charles, W. N., K. East, and T. D. Murray. 1976. Production of larval Tanypodinae (Insecta:Chironomidae) in the mud at Loch Leven, Kinross, Scotland. Proceedings of the Royal Society of Ed inburgh Sec. B. 75:157-169. Charles, W. N., K. East, D. Brown, M. C. Gray, and rection factors such as Pc/Pa where growth is T. D. Murray. non-linear with time (e.g., Menzie 1980), or the Chironomidae in the mud at Loch Leven, Kin insufficiency of the method's assumptions about several other factors (Hamilton 1969, Rigler and Downing 1984). The size-frequency technique is most accurately applied when sufficient data exist so that proper CPI corrections can be ap plied. If only order-of-magnitude production estimates are required, these can be made using 1974. The production of larval ross, Scotland. Proceedings of the Royal Society of Edinburgh 74:241-258. Conover, W. J. 1971. Practical nonparametric sta tistics. 2nd edition. John Wiley and Sons, New York. Cushman, R. M., H. H. Shugart, S. G. Hildebrand, and J. W. Elwood. 1977. The effect of growth curve and sampling regime on instantaneous- Equation 1 with only measurements of annual growth, removal summation, and Hynes/Ham- mean biomass, body-mass, and temperature. If ilton estimates of aquatic insect production: a more exacting measures are required, we agree computer simulation. Limnology and Oceanog with Morin et al. (1987) that, whenever possi ble, sufficient data should be collected to apply the Allen curve, increment summation or in stantaneous growth methods. raphy 23:184-189. Dall, P. C. 1980. Ecology and production of the leeches Erpobdella octocullata L. and Erpcbdella testacea Sav. in Lake Esrom, Denmark. Archiv fur Hydrobiologia/Supplementband 57:188-220. Dall, P. C, H. Heegaard, and A. F. Fullerton. 1984. Acknowledgements Life history strategies and production of Tinodes waeneri (L.) (Trichoptera) in Lake Ersrom, Den Financial support for this research was pro vided by an operating grant to J. A. Downing mark. Hydrobiologia 112:93-104. Dermott, R. M., J. Kalff, W. C. Leggett, and J. Spence. [Volume 9 C. Plante and J. A. Downing 16 1977. Production of Chironomus, Procladius, and Chaoborus at different levels of phytoplankton biomass in Lake Memphremagog, Quebec-Ver mont. Journal of the Fisheries Research Board of Canada 34:2001-2007. Downing, J. A. Martien, R. F., AND A. C. Benke. 1977. 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