{"id":511,"date":"2023-09-25T18:24:14","date_gmt":"2023-09-25T22:24:14","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/?post_type=chapter&p=511"},"modified":"2025-10-30T08:56:25","modified_gmt":"2025-10-30T12:56:25","slug":"other-mortality","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/chapter\/other-mortality\/","title":{"raw":"Ecotrophic efficiency","rendered":"Ecotrophic efficiency"},"content":{"raw":"
Ecotrophic efficiency (EE<\/em>) was defined by Ricker[footnote]Ricker WE. 1969. Food from the Sea. pp 87-108 in: Cloud P (chair) Resources and man, a study and recommendations. Report of the Committee on Resources and Man. US Natl Acad Sci. Freeman, San Francisco, California[\/footnote] as the proportion of a prey's production that is consumed by predators. Polovina used the term for the original Ecopath model of the unexploited French Frigate Shoals.[footnote]Polovina, J.J. 1984. Model of a coral reef ecosystem. Coral Reefs 3, 1\u201311. https:\/\/doi.org\/10.1007\/BF00306135<\/a>[\/footnote]<\/div>\r\n
Subsequently, we have for EwE modified the term to include exports from the system, (which notably are due to fisheries). Based on the second Ecopath Master Equation (See The energy balance of a box<\/a> chapter) we have,<\/div>\r\n
\r\n\r\n[latex]EE_i=\\frac {M2_i \\cdot B_i+C_i+BA_i+E_i}{P_i}\\tag{1}[\/latex]\r\n\r\nso, EE<\/em> can be estimated as the ratio between the summed predation M2<\/em>, catch C<\/em>, biomass accumulation BA<\/em> and net migration E<\/em> relative to the production P<\/em> for any group i.\r\n\r\nIf your model is descriptive (as Polovina's model was), your aim likely is to describe the energy flow in the entire ecosystem. If that's the case, the EE<\/em> indeed is an \"ecotrophic efficiency\" that describes the proportion of the energy produced by a group that it passed on through the trophic web or exported (e.g., through fisheries). So, if EE<\/em> is 0.95 then 95% of the production of the group is passed on to predators or fisheries.\r\n\r\nBut what about predictive (or MICE) models? Such models tend to be focused on the specific policy\/research questions they are built to address, and as such may not give a complete picture of the food web interactions in the given ecosystem. That boils down to there being a considerable amount of unexplained mortality (M1) in the model. In such cases the EE isn't really an \"ecotrophic efficiency\". Hence, the following may be a better way to grasp EE.\r\n
\r\n\r\nEE expresses the proportion of the mortality for which the model describes the fate.\r\n\r\n<\/div>\r\n<\/div>\r\n

Estimating EE<\/h2>\r\n
\r\n\r\nIt is difficult to estimate EE<\/em> independently, and few, if any, direct estimates appear to exist.\u00a0Recognizing this, an EE<\/em> of 0.95, based on Ricker (1968) was used for many groups in Polovina's original model[footnote]Polovina, J.J. (1984) op. cit.<\/em> \u00a0https:\/\/doi.org\/10.1007\/BF00306135<\/a>[\/footnote] and in a number of later models.\r\n

Evaluating EE<\/h2>\r\nIntuitively one would expect EE<\/em> to be very close to 1 for small prey organisms, diseases and starvation probably being, for such groups, much less frequent than predation. For some groups, EE<\/em>, may however, be low.\r\n\r\nIt is often seen that phytoplankton simply die off (as \"snow\") in systems where blooms occur (EE<\/em> of 0.5 or less). Also, kelps and seagrasses are hardly consumed when alive (EE<\/em> of 0.1 or so), and apex predators have very low EE<\/em>s when fishing intensity is low. There are indeed many incidences of tunas or cetaceans simply dying and sinking reported from open oceans, with abyssal organisms (e.g., ratfishes) specialized in feeding on such carcasses.\r\n\r\nIf EE<\/em>s are estimated it is often because of lack of biomasses. It should not be because of lack of P\/B<\/em> or Q\/B<\/em> values \u2013 it is better to guess those than to let them be estimated from the Ecopath mass balance. \u00a0When biomasses are estimated, one needs to carefully examine how realistic those biomasses are. We've seen examples where there were biomasses entered for only unexploited high trophic level groups, and everything else being estimated from guessed EE<\/em>s. So, if you have to used EE<\/em>s as input, check out PreBal[footnote]Link JS. 2010. Adding rigor to ecological network models by evaluating a set of pre-balance diagnostics: A plea for PREBAL, Ecological Modelling, 221(2): 1580-1591, https:\/\/doi.org\/10.1016\/j.ecolmodel.2010.03.012.<\/a>[\/footnote] and compare the estimated biomasses to estimates from similar ecosystems.\r\n\r\n<\/div>","rendered":"
Ecotrophic efficiency (EE<\/em>) was defined by Ricker[1]<\/sup><\/a> as the proportion of a prey’s production that is consumed by predators. Polovina used the term for the original Ecopath model of the unexploited French Frigate Shoals.[2]<\/sup><\/a><\/div>\n
Subsequently, we have for EwE modified the term to include exports from the system, (which notably are due to fisheries). Based on the second Ecopath Master Equation (See The energy balance of a box<\/a> chapter) we have,<\/div>\n
\n

[latex]EE_i=\\frac {M2_i \\cdot B_i+C_i+BA_i+E_i}{P_i}\\tag{1}[\/latex]<\/p>\n

so, EE<\/em> can be estimated as the ratio between the summed predation M2<\/em>, catch C<\/em>, biomass accumulation BA<\/em> and net migration E<\/em> relative to the production P<\/em> for any group i.<\/p>\n

If your model is descriptive (as Polovina’s model was), your aim likely is to describe the energy flow in the entire ecosystem. If that’s the case, the EE<\/em> indeed is an “ecotrophic efficiency” that describes the proportion of the energy produced by a group that it passed on through the trophic web or exported (e.g., through fisheries). So, if EE<\/em> is 0.95 then 95% of the production of the group is passed on to predators or fisheries.<\/p>\n

But what about predictive (or MICE) models? Such models tend to be focused on the specific policy\/research questions they are built to address, and as such may not give a complete picture of the food web interactions in the given ecosystem. That boils down to there being a considerable amount of unexplained mortality (M1) in the model. In such cases the EE isn’t really an “ecotrophic efficiency”. Hence, the following may be a better way to grasp EE.<\/p>\n

\n

EE expresses the proportion of the mortality for which the model describes the fate.<\/p>\n<\/div>\n<\/div>\n

Estimating EE<\/h2>\n
\n

It is difficult to estimate EE<\/em> independently, and few, if any, direct estimates appear to exist.\u00a0Recognizing this, an EE<\/em> of 0.95, based on Ricker (1968) was used for many groups in Polovina’s original model[3]<\/sup><\/a> and in a number of later models.<\/p>\n

Evaluating EE<\/h2>\n

Intuitively one would expect EE<\/em> to be very close to 1 for small prey organisms, diseases and starvation probably being, for such groups, much less frequent than predation. For some groups, EE<\/em>, may however, be low.<\/p>\n

It is often seen that phytoplankton simply die off (as “snow”) in systems where blooms occur (EE<\/em> of 0.5 or less). Also, kelps and seagrasses are hardly consumed when alive (EE<\/em> of 0.1 or so), and apex predators have very low EE<\/em>s when fishing intensity is low. There are indeed many incidences of tunas or cetaceans simply dying and sinking reported from open oceans, with abyssal organisms (e.g., ratfishes) specialized in feeding on such carcasses.<\/p>\n

If EE<\/em>s are estimated it is often because of lack of biomasses. It should not be because of lack of P\/B<\/em> or Q\/B<\/em> values \u2013 it is better to guess those than to let them be estimated from the Ecopath mass balance. \u00a0When biomasses are estimated, one needs to carefully examine how realistic those biomasses are. We’ve seen examples where there were biomasses entered for only unexploited high trophic level groups, and everything else being estimated from guessed EE<\/em>s. So, if you have to used EE<\/em>s as input, check out PreBal[4]<\/sup><\/a> and compare the estimated biomasses to estimates from similar ecosystems.<\/p>\n<\/div>\n

  1. Ricker WE. 1969. Food from the Sea. pp 87-108 in: Cloud P (chair) Resources and man, a study and recommendations. Report of the Committee on Resources and Man. US Natl Acad Sci. Freeman, San Francisco, California ↵<\/a><\/li>
  2. Polovina, J.J. 1984. Model of a coral reef ecosystem. Coral Reefs 3, 1\u201311. https:\/\/doi.org\/10.1007\/BF00306135<\/a> ↵<\/a><\/li>
  3. Polovina, J.J. (1984) op. cit.<\/em> \u00a0https:\/\/doi.org\/10.1007\/BF00306135<\/a> ↵<\/a><\/li>
  4. Link JS. 2010. Adding rigor to ecological network models by evaluating a set of pre-balance diagnostics: A plea for PREBAL, Ecological Modelling, 221(2): 1580-1591, https:\/\/doi.org\/10.1016\/j.ecolmodel.2010.03.012.<\/a> ↵<\/a><\/li><\/ol><\/div>","protected":false},"author":1909,"menu_order":5,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-511","chapter","type-chapter","status-publish","hentry"],"part":404,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapters\/511","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/wp\/v2\/users\/1909"}],"version-history":[{"count":18,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapters\/511\/revisions"}],"predecessor-version":[{"id":3354,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapters\/511\/revisions\/3354"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/parts\/404"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapters\/511\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/wp\/v2\/media?parent=511"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/pressbooks\/v2\/chapter-type?post=511"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/wp\/v2\/contributor?post=511"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/ewemodel\/wp-json\/wp\/v2\/license?post=511"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}