Oecologia DOI 10.1007/s00442-014-2973-z
Views and Comments
The importance of developing modeling frameworks to inform conservation decisions: a response to Lonergan Jason Matthiopoulos · Sophie Smout · Marjolaine Caillat · Line Cordes · Beth Mackey · Paul Thompson
Received: 4 April 2014 / Accepted: 12 May 2014 © Springer-Verlag Berlin Heidelberg 2014
In his critique of our recent paper (Matthiopoulos et al. 2014) on the population dynamics of harbor seals, Lonergan (2014a) argues that although our state–space modeling approach represents an interesting academic exercise, it nevertheless risks misleading those attempting to understand and manage observed declines of this species in UK waters. We argue that approaches like ours need not be misleading as long as information is provided on the assumptions and simplifications used. When such information is available, all assumptions (such as the shape and parameters of prior distributions in a Bayesian analysis) can then be subjected to scrutiny [such as that performed by Lonergan (2014a)], inevitably leading to future improvements. Communicated by Helene Marsh. J. Matthiopoulos (*) Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQK, Scotland, UK e-mail: [email protected] S. Smout · M. Caillat Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife KY16 8LB, Scotland, UK L. Cordes Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, CO 80526, USA B. Mackey Royal Haskoning UK Ltd., 10 Bernard Street, Leith, Edinburgh EH6 6PP, Scotland, UK P. Thompson Lighthouse Field Station, Institute of Biological and Environmental Sciences, University of Aberdeen, George Street, Cromarty, Ross‑shire IV11 8YJ, Scotland, UK
Hopefully, this approach represents a process that leads to open and constructive debate, to progress towards a better scientific understanding and to improvements in our ability to manage wildlife. Lonergan has examined our modeling in detail, and his critique raises a series of specific points and also some general questions about how data and expert opinion should be integrated into statistical and modeling frameworks with the aim of advising on conservation methods. We agree with several of Lonergan’s dictums, such as the need for open dialogue between the field biologists collecting data and the modelers subsequently using these data. Indeed, several of his specific points could have been resolved through such dialogue. For example, he queries the lack of data on harbor seal pups after mid-July, but this situation arises because pups cannot be reliably distinguished from juveniles after this time (Thompson and Rothery 1987). Similarly, detailed evaluation of previous studies from the Moray Firth (e.g. Thompson et al. 2007) would also call into question Lonergan’s assertion that shooting is the sole driver of historical declines in this population. Lonergan highlights his concerns about the performance and sensitivity of our model to specific assumptions and priors. These are important questions. We hope that in our publication, prior justification was explicit (pp. 155–158), prior sensitivity methodology was described in detail (Supplement 3) and the implications of our modeling on our predictions were discussed in full (our points 1–5, pp. 158–159; points 1, 2, p 160). Work continues, and our aim is to improve and simplify our modeling—for example, by considering seasonal variation in haulout probability. We are also exploring a question about the mis-match between one datum (2009 population estimate) and model predictions. The sensitivity of our results to these two issues was
13
Oecologia
clearly set out in the discussion of our paper, and continuation of this work, post-publication, has cast no doubt on the estimated trends and relative importance of different demographic rates. Answers to all of the other technical questions raised by Lonergan were also in our original publication, but the following points may be worth reiterating for clarity. The demographic impact of shooting was estimated (not hardwired to a particular value), and the relative shooting effort in different years was based on reported carcass data (our original points 1–5, pp. 157–158). Lonergan challenges the priors for the demographic trends as being too restrictive. However, given the logit transformation used to model demographic rates, these priors are able to generate total collapses in fecundity or survival (i.e. from 1 to 0) over the duration of the survey period (as was hinted on p. 155). Lonergan’s arithmetic on the parameters-to-data ratio is questionable. He ignores that, in addition to aerial counts and total population estimates, the model incorporates a time-series of shooting data and mark–recapture data (used for baseline breeding rates, survival rates and haulout probabilities). In addition, basic biological knowledge (such as the age to maturity) further constrains the behavior of demographic models such as this one. More generally, Lonergan’s critique reflects his preference for describing patterns in data, rather than modeling mechanisms (see also other critiques by Lonergan (2007, 2012a, b, c, 2014b). We agree that there is value in his approach. However, previous analyses demonstrating temporal changes in either abundance (Lonergan et al. 2007; Thompson et al. 2007) or fitness measures (Thompson et al. 1997) in these populations have offered wildlife managers only limited insights into the drivers underlying such changes. Lonergan’s proposed ad-hoc alternatives (Lonergan et al. 2007, 2011) are, by his own description (Lonergan 2014a), limited in their ability to deliver demographic insights and population projections. More worryingly, they lack the support of the technical statistical literature, making them even harder to troubleshoot than state–space models. In our publication, we argue for the use of a combination of tools that can provide both insights and predictive ability. The value of developing modeling frameworks to support conservation and management decisions is widely accepted. Thus, if data really are too sparse, it is now customary to incorporate expert opinion into informative priors (Kuhnert et al. 2010; Runge et al. 2011) rather than avoid using demographic models altogether, as Lonergan proposes. We agree with Lonergan entirely on one very important issue, the drivers affecting different regional harbor seal populations are likely to differ. Therefore, in presenting the results of our model for the Moray Firth––the
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best-documented subpopulation in the UK––we were careful not to exaggerate the generality of our specific results. Nevertheless, despite their regional differences, subpopulations of the same species also have some similarities. Our task now is to identify those in a quantitative and insightful manner, borrowing inferential strength from the similarities and learning from the differences (e.g. contrasts between areas in the strengths of potential ‘drivers’). Contrary to Lonergan’s assertions, nowhere in our paper did we claim that our findings for the Moray Firth necessarily apply elsewhere. We do, however, offer our framework as a general tool, a sensible platform upon which to build. We welcome the use of other approaches where these can help to inform management decisions. However, we argue that modeling frameworks, which explicitly represent the processes underlying population change, are far from ‘uninformative.’ They are essential to our understanding of changes in population, highlighting where further data collection is most valuable and identifying testable hypotheses about potential drivers.
References Kuhnert PM, Martin TG, Griffiths SP (2010) A guide to eliciting and using expert knowledge in Bayesian ecological models. Ecol Lett 13:900–914 Lonergan M (2007) A response to Durban et al. (2005): multisite mark–recapture for cetaceans. Mar Mamm Sci 23:721–729 Lonergan M (2012a) Insufficient data are available to predict the success of protected areas for the vaquita (Phocoena sinus): a critique of Gerrodette and Rojas-Bracho (2011). Mar Mamm Sci 28:785–789 Lonergan M (2012b) The targets of management rules for marine mammal populations require justification: a reply to Cooke et al. (2012). Mar Policy 36:1188–1190 Lonergan M (2012c) Detecting density dependence in recovering seal population is difficult: a response to Svensson et al. (2011). Ambio 41:219–220 Lonergan M (2014a) Modelling beyond data is uninformative––a comment on “state–space modeling reveals proximate causes of harbour seal population declines” by Matthiopoulos et al. (2014). Oecologia. doi:10.1007/s00442-014-2970-2 Lonergan M (2014b) Data availability constrains model complexity, generality, and utility: a response to Evans et al. Trends Ecol Evol 29:301–302 Lonergan M, Duck CD, Thompson D, Mackey BL, Cunningham L, Boyd IL (2007) Using sparse survey data to investigate the declining abundance of British harbour seals. J Zool 271:261–269 Lonergan M, Thompson D, Thomas L, Duck C (2011) An approximate Bayesian method applied to estimating the trajectories of four British grey seal (Halichoerus grypus) populations from pup counts. ICES J Mar Biol 68:2201–2209 Matthiopoulos J, Cordes L, Mackey B, Thompson D, Duck C, Smout S, Caillat M, Thompson P (2014) State–space modelling reveals proximate causes of harbour seal population declines. Oecologia 174:151–162 Runge MC, Converse SJ, Lyons JE (2011) Which uncertainty? Using expert elicitation and expected value of information to design an adaptive program. Biol Conserv 144:1214–1223
Oecologia Thompson PM, Rothery P (1987) Age and sex differences in the timing of moult in the common seal, Phoca vitulina. J Zool 212:597–603 Thompson PM, Tollit DJ, Corpe HM, Reid RJ, Ross HM (1997) Changes in haematological parameters in relation to prey switching in a wild population of harbour seals. Funct Ecol 11:743–750
Thompson PM, Mackey BL, Barton TR, Duck C, Butler JRA (2007) Assessing the potential impact of salmon fisheries management on the conservation status of harbour seals in NE Scotland. Anim Conserv 10:48–56
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Views and Comments
The importance of developing modeling frameworks to inform conservation decisions: a response to Lonergan Jason Matthiopoulos · Sophie Smout · Marjolaine Caillat · Line Cordes · Beth Mackey · Paul Thompson
Received: 4 April 2014 / Accepted: 12 May 2014 © Springer-Verlag Berlin Heidelberg 2014
In his critique of our recent paper (Matthiopoulos et al. 2014) on the population dynamics of harbor seals, Lonergan (2014a) argues that although our state–space modeling approach represents an interesting academic exercise, it nevertheless risks misleading those attempting to understand and manage observed declines of this species in UK waters. We argue that approaches like ours need not be misleading as long as information is provided on the assumptions and simplifications used. When such information is available, all assumptions (such as the shape and parameters of prior distributions in a Bayesian analysis) can then be subjected to scrutiny [such as that performed by Lonergan (2014a)], inevitably leading to future improvements. Communicated by Helene Marsh. J. Matthiopoulos (*) Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQK, Scotland, UK e-mail: [email protected] S. Smout · M. Caillat Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife KY16 8LB, Scotland, UK L. Cordes Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, CO 80526, USA B. Mackey Royal Haskoning UK Ltd., 10 Bernard Street, Leith, Edinburgh EH6 6PP, Scotland, UK P. Thompson Lighthouse Field Station, Institute of Biological and Environmental Sciences, University of Aberdeen, George Street, Cromarty, Ross‑shire IV11 8YJ, Scotland, UK
Hopefully, this approach represents a process that leads to open and constructive debate, to progress towards a better scientific understanding and to improvements in our ability to manage wildlife. Lonergan has examined our modeling in detail, and his critique raises a series of specific points and also some general questions about how data and expert opinion should be integrated into statistical and modeling frameworks with the aim of advising on conservation methods. We agree with several of Lonergan’s dictums, such as the need for open dialogue between the field biologists collecting data and the modelers subsequently using these data. Indeed, several of his specific points could have been resolved through such dialogue. For example, he queries the lack of data on harbor seal pups after mid-July, but this situation arises because pups cannot be reliably distinguished from juveniles after this time (Thompson and Rothery 1987). Similarly, detailed evaluation of previous studies from the Moray Firth (e.g. Thompson et al. 2007) would also call into question Lonergan’s assertion that shooting is the sole driver of historical declines in this population. Lonergan highlights his concerns about the performance and sensitivity of our model to specific assumptions and priors. These are important questions. We hope that in our publication, prior justification was explicit (pp. 155–158), prior sensitivity methodology was described in detail (Supplement 3) and the implications of our modeling on our predictions were discussed in full (our points 1–5, pp. 158–159; points 1, 2, p 160). Work continues, and our aim is to improve and simplify our modeling—for example, by considering seasonal variation in haulout probability. We are also exploring a question about the mis-match between one datum (2009 population estimate) and model predictions. The sensitivity of our results to these two issues was
13
Oecologia
clearly set out in the discussion of our paper, and continuation of this work, post-publication, has cast no doubt on the estimated trends and relative importance of different demographic rates. Answers to all of the other technical questions raised by Lonergan were also in our original publication, but the following points may be worth reiterating for clarity. The demographic impact of shooting was estimated (not hardwired to a particular value), and the relative shooting effort in different years was based on reported carcass data (our original points 1–5, pp. 157–158). Lonergan challenges the priors for the demographic trends as being too restrictive. However, given the logit transformation used to model demographic rates, these priors are able to generate total collapses in fecundity or survival (i.e. from 1 to 0) over the duration of the survey period (as was hinted on p. 155). Lonergan’s arithmetic on the parameters-to-data ratio is questionable. He ignores that, in addition to aerial counts and total population estimates, the model incorporates a time-series of shooting data and mark–recapture data (used for baseline breeding rates, survival rates and haulout probabilities). In addition, basic biological knowledge (such as the age to maturity) further constrains the behavior of demographic models such as this one. More generally, Lonergan’s critique reflects his preference for describing patterns in data, rather than modeling mechanisms (see also other critiques by Lonergan (2007, 2012a, b, c, 2014b). We agree that there is value in his approach. However, previous analyses demonstrating temporal changes in either abundance (Lonergan et al. 2007; Thompson et al. 2007) or fitness measures (Thompson et al. 1997) in these populations have offered wildlife managers only limited insights into the drivers underlying such changes. Lonergan’s proposed ad-hoc alternatives (Lonergan et al. 2007, 2011) are, by his own description (Lonergan 2014a), limited in their ability to deliver demographic insights and population projections. More worryingly, they lack the support of the technical statistical literature, making them even harder to troubleshoot than state–space models. In our publication, we argue for the use of a combination of tools that can provide both insights and predictive ability. The value of developing modeling frameworks to support conservation and management decisions is widely accepted. Thus, if data really are too sparse, it is now customary to incorporate expert opinion into informative priors (Kuhnert et al. 2010; Runge et al. 2011) rather than avoid using demographic models altogether, as Lonergan proposes. We agree with Lonergan entirely on one very important issue, the drivers affecting different regional harbor seal populations are likely to differ. Therefore, in presenting the results of our model for the Moray Firth––the
13
best-documented subpopulation in the UK––we were careful not to exaggerate the generality of our specific results. Nevertheless, despite their regional differences, subpopulations of the same species also have some similarities. Our task now is to identify those in a quantitative and insightful manner, borrowing inferential strength from the similarities and learning from the differences (e.g. contrasts between areas in the strengths of potential ‘drivers’). Contrary to Lonergan’s assertions, nowhere in our paper did we claim that our findings for the Moray Firth necessarily apply elsewhere. We do, however, offer our framework as a general tool, a sensible platform upon which to build. We welcome the use of other approaches where these can help to inform management decisions. However, we argue that modeling frameworks, which explicitly represent the processes underlying population change, are far from ‘uninformative.’ They are essential to our understanding of changes in population, highlighting where further data collection is most valuable and identifying testable hypotheses about potential drivers.
References Kuhnert PM, Martin TG, Griffiths SP (2010) A guide to eliciting and using expert knowledge in Bayesian ecological models. Ecol Lett 13:900–914 Lonergan M (2007) A response to Durban et al. (2005): multisite mark–recapture for cetaceans. Mar Mamm Sci 23:721–729 Lonergan M (2012a) Insufficient data are available to predict the success of protected areas for the vaquita (Phocoena sinus): a critique of Gerrodette and Rojas-Bracho (2011). Mar Mamm Sci 28:785–789 Lonergan M (2012b) The targets of management rules for marine mammal populations require justification: a reply to Cooke et al. (2012). Mar Policy 36:1188–1190 Lonergan M (2012c) Detecting density dependence in recovering seal population is difficult: a response to Svensson et al. (2011). Ambio 41:219–220 Lonergan M (2014a) Modelling beyond data is uninformative––a comment on “state–space modeling reveals proximate causes of harbour seal population declines” by Matthiopoulos et al. (2014). Oecologia. doi:10.1007/s00442-014-2970-2 Lonergan M (2014b) Data availability constrains model complexity, generality, and utility: a response to Evans et al. Trends Ecol Evol 29:301–302 Lonergan M, Duck CD, Thompson D, Mackey BL, Cunningham L, Boyd IL (2007) Using sparse survey data to investigate the declining abundance of British harbour seals. J Zool 271:261–269 Lonergan M, Thompson D, Thomas L, Duck C (2011) An approximate Bayesian method applied to estimating the trajectories of four British grey seal (Halichoerus grypus) populations from pup counts. ICES J Mar Biol 68:2201–2209 Matthiopoulos J, Cordes L, Mackey B, Thompson D, Duck C, Smout S, Caillat M, Thompson P (2014) State–space modelling reveals proximate causes of harbour seal population declines. Oecologia 174:151–162 Runge MC, Converse SJ, Lyons JE (2011) Which uncertainty? Using expert elicitation and expected value of information to design an adaptive program. Biol Conserv 144:1214–1223
Oecologia Thompson PM, Rothery P (1987) Age and sex differences in the timing of moult in the common seal, Phoca vitulina. J Zool 212:597–603 Thompson PM, Tollit DJ, Corpe HM, Reid RJ, Ross HM (1997) Changes in haematological parameters in relation to prey switching in a wild population of harbour seals. Funct Ecol 11:743–750
Thompson PM, Mackey BL, Barton TR, Duck C, Butler JRA (2007) Assessing the potential impact of salmon fisheries management on the conservation status of harbour seals in NE Scotland. Anim Conserv 10:48–56
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