Towards a Comparative Framework of Demographic Resilience
Authors: Pol Capdevila, Iain Stott, Maria Beger, Roberto Salguero-Gómez
Journal: Trends in Ecology & Evolution (2020)

The global biodiversity crisis demands a broad understanding of the ability of species to respond to external disturbances caused by global change.A common framework to quantify, compare, contrast, and predict the resilience of species to global change is urgently needed.Resilience includes the resistance of populations to change after disturbance and their recovery from it.Measurements of short-term population growth following disturbances, and any of its longer-term consequences, allow quantification of demographic resilience.Quantifying demographic resilience with common semantic and numeric definitions enables comparisons of resilience across species, enabling us to predict their responses to disturbances. In the current global biodiversity crisis, the development of tools to define, quantify, compare, and predict resilience is essential for understanding the responses of species to global change. However, disparate interpretations of resilience have hampered the development of a common currency to quantify and compare resilience across natural systems. Most resilience frameworks focus on upper levels of biological organization, especially ecosystems or communities, which complicates measurements of resilience using empirical data. Surprisingly, there is no quantifiable definition of resilience at the demographic level. We introduce a framework of demographic resilience that draws on existing concepts from community and population ecology, as well as an accompanying set of metrics that are comparable across species. In the current global biodiversity crisis, the development of tools to define, quantify, compare, and predict resilience is essential for understanding the responses of species to global change. However, disparate interpretations of resilience have hampered the development of a common currency to quantify and compare resilience across natural systems. Most resilience frameworks focus on upper levels of biological organization, especially ecosystems or communities, which complicates measurements of resilience using empirical data. Surprisingly, there is no quantifiable definition of resilience at the demographic level. We introduce a framework of demographic resilience that draws on existing concepts from community and population ecology, as well as an accompanying set of metrics that are comparable across species. Contemporary global change is increasingly eroding natural resources [1.Pecl G.T. et al.Biodiversity redistribution under climate change: Impacts on ecosystems and human well-being.Science. 2017; 355eaai9214Crossref PubMed Scopus (999) Google Scholar, 2.Scheffers B.R. et al.The broad footprint of climate change from genes to biomes to people.Science. 2016; 354aaf7671Crossref PubMed Scopus (445) Google Scholar, 3.Vitousek P.M. et al.Human domination of Earth's ecosystems.Science. 1997; 277: 494-499Crossref Scopus (6221) Google Scholar]. Thus, understanding how ecological systems withstand environmental disturbances (see Glossary) is a major challenge [4.Hughes T.P. et al.New paradigms for supporting the resilience of marine ecosystems.Trends Ecol. Evol. 2005; 20: 380-386Abstract Full Text Full Text PDF PubMed Scopus (678) Google Scholar, 5.Parmesan C. et al.Overstretching attribution.Nat. Clim. Chang. 2011; 1: 2-4Crossref Scopus (105) Google Scholar, 6.Parmesan C. Ecological and evolutionary responses to recent climate change.Annu. Rev. Ecol. Evol. Syst. 2006; 37: 637-669Crossref Scopus (5337) Google Scholar]. 'Resilience' is a key concept that describes the ability of natural systems to handle disturbances [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar]. Indeed, international environmental policy objectives, including the UN Sustainable Development Goals [8.United Nations Transforming Our World: The 2030 Agenda for Sustainable Development (A/RES/70/1). UN, 2015Google Scholar] and Aichi Targets [9.Convention on Biological Diversity Decision X/2, The Strategic Plan for Biodiversity 2011–2020 and the Aichi Biodiversity Targets, Secretariat of the Convention on Biological Diversity.2010Google Scholar], specifically include preserving resilience as a key objective. Resilience describes the ability of a system to resist and recover from a disturbance [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar]. However, translating resilience into quantifiable metrics is challenging due to the complexities of ecological systems [11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar], and has generated multiple debates over the past decades regarding its definition, meaning, and application [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,12.Allen C.R. et al.Resilience reconciled.Nat. Sustain. 2019; 2: 898-900Crossref Scopus (18) Google Scholar,13.Pimm S.L. et al.Measuring resilience is essential to understand it.Nat. Sustain. 2019; 2: 895-897Crossref PubMed Scopus (27) Google Scholar] (Box 1). Discrepancies between approaches mean that both theoretical and empirical works lack parity between the primary components of resilience studied, rendering comparisons challenging if not impossible. These limitations ultimately prevent ecologists from applying resilience-based solutions to real-world problems (e.g., [14.Donohue I. et al.Navigating the complexity of ecological stability.Ecol. Lett. 2016; 19: 1172-1185Crossref PubMed Scopus (206) Google Scholar]). Developing a unifying framework with comparable definitions and quantifications across different ecological systems is therefore an urgent task [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,16.Pimm S.L. The complexity and stability of ecosystems.Nature. 1984; 307: 321Crossref Scopus (1595) Google Scholar].Box 1Defining ResilienceSince its first appearance in the ecological literature in the late 1970s, the study of resilience has attracted significant attention (Figure I). However, the rate at which resilience research has increased matches the diversity of definitions and interpretations of resilience. The term resilience was first introduced into ecology by Holling [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar], who defined it as 'a measure of the persistence of systems and their ability to absorb change and disturbance and still maintain the same relationships between populations or state variables'. Holling's definition was interpreted in different ways across subdisciplines [60.Quinlan A.E. et al.Measuring and assessing resilience: broadening understanding through multiple disciplinary perspectives.J. Appl. Ecol. 2016; 53: 677-687Crossref Scopus (202) Google Scholar]. For example, some have considered resilience to be the speed of recovery of a natural system, quantified as the time required to return to equilibrium [16.Pimm S.L. The complexity and stability of ecosystems.Nature. 1984; 307: 321Crossref Scopus (1595) Google Scholar]. By contrast, others have measured resilience as the probability of the system to remain in a stable state [61.Mumby P.J. et al.Thresholds and the resilience of Caribbean coral reefs.Nature. 2007; 450: 98Crossref PubMed Scopus (573) Google Scholar]. Consequently, Holling later [62.Holling C.S. Engineering resilience versus ecological resilience.Eng. Ecol. Constraints. 1996; 31: 32Google Scholar] distinguished two types of resilience: engineering and ecological resilience. He defined engineering resilience as 'resistance to disturbance and speed of return to the equilibrium' following a shock. Ecological resilience was described as the 'magnitude of a disturbance that can be absorbed before the system changes its structure' [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar,62.Holling C.S. Engineering resilience versus ecological resilience.Eng. Ecol. Constraints. 1996; 31: 32Google Scholar].To frame demographic resilience, we draw on ideas and terminology from community/ecosystem resilience and stability [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar]. We define resilience following Hodgson et al. [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar] as 'the capacity of system to persist and maintain its state and functions in the face of exogenous disturbance'. Similar to the ecological stability literature, several authors consider resilience to be a function of resistance and recovery [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,63.Oliver T.H. et al.Biodiversity and resilience of ecosystem functions.Trends Ecol. Evol. 2015; 30: 673-684Abstract Full Text Full Text PDF PubMed Scopus (508) Google Scholar, 64.Darling E.S. Côté I.M. Seeking resilience in marine ecosystems.Science. 2018; 359: 986-987Crossref PubMed Scopus (38) Google Scholar, 65.Willis K.J. et al.What makes a terrestrial ecosystem resilient?.Science. 2018; 359: 988-989Crossref PubMed Scopus (40) Google Scholar]. Such bivariate frameworks incorporate resistance, representing the magnitude of change of the state variable, and recovery, a component of its recovery trajectory (recovery magnitude or rate) after the disturbance ends. Populations have stable demographic structures representing 'states' from which the population are displaced and then return to after disturbance. Such characteristics align demographic resilience to the general bivariate resilience [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,63.Oliver T.H. et al.Biodiversity and resilience of ecosystem functions.Trends Ecol. Evol. 2015; 30: 673-684Abstract Full Text Full Text PDF PubMed Scopus (508) Google Scholar, 64.Darling E.S. Côté I.M. Seeking resilience in marine ecosystems.Science. 2018; 359: 986-987Crossref PubMed Scopus (38) Google Scholar, 65.Willis K.J. et al.What makes a terrestrial ecosystem resilient?.Science. 2018; 359: 988-989Crossref PubMed Scopus (40) Google Scholar] and ecological stability [11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar,16.Pimm S.L. The complexity and stability of ecosystems.Nature. 1984; 307: 321Crossref Scopus (1595) Google Scholar,22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar] frameworks, which both have an engineering resilience perspective. Since its first appearance in the ecological literature in the late 1970s, the study of resilience has attracted significant attention (Figure I). However, the rate at which resilience research has increased matches the diversity of definitions and interpretations of resilience. The term resilience was first introduced into ecology by Holling [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar], who defined it as 'a measure of the persistence of systems and their ability to absorb change and disturbance and still maintain the same relationships between populations or state variables'. Holling's definition was interpreted in different ways across subdisciplines [60.Quinlan A.E. et al.Measuring and assessing resilience: broadening understanding through multiple disciplinary perspectives.J. Appl. Ecol. 2016; 53: 677-687Crossref Scopus (202) Google Scholar]. For example, some have considered resilience to be the speed of recovery of a natural system, quantified as the time required to return to equilibrium [16.Pimm S.L. The complexity and stability of ecosystems.Nature. 1984; 307: 321Crossref Scopus (1595) Google Scholar]. By contrast, others have measured resilience as the probability of the system to remain in a stable state [61.Mumby P.J. et al.Thresholds and the resilience of Caribbean coral reefs.Nature. 2007; 450: 98Crossref PubMed Scopus (573) Google Scholar]. Consequently, Holling later [62.Holling C.S. Engineering resilience versus ecological resilience.Eng. Ecol. Constraints. 1996; 31: 32Google Scholar] distinguished two types of resilience: engineering and ecological resilience. He defined engineering resilience as 'resistance to disturbance and speed of return to the equilibrium' following a shock. Ecological resilience was described as the 'magnitude of a disturbance that can be absorbed before the system changes its structure' [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar,62.Holling C.S. Engineering resilience versus ecological resilience.Eng. Ecol. Constraints. 1996; 31: 32Google Scholar]. To frame demographic resilience, we draw on ideas and terminology from community/ecosystem resilience and stability [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar]. We define resilience following Hodgson et al. [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar] as 'the capacity of system to persist and maintain its state and functions in the face of exogenous disturbance'. Similar to the ecological stability literature, several authors consider resilience to be a function of resistance and recovery [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,63.Oliver T.H. et al.Biodiversity and resilience of ecosystem functions.Trends Ecol. Evol. 2015; 30: 673-684Abstract Full Text Full Text PDF PubMed Scopus (508) Google Scholar, 64.Darling E.S. Côté I.M. Seeking resilience in marine ecosystems.Science. 2018; 359: 986-987Crossref PubMed Scopus (38) Google Scholar, 65.Willis K.J. et al.What makes a terrestrial ecosystem resilient?.Science. 2018; 359: 988-989Crossref PubMed Scopus (40) Google Scholar]. Such bivariate frameworks incorporate resistance, representing the magnitude of change of the state variable, and recovery, a component of its recovery trajectory (recovery magnitude or rate) after the disturbance ends. Populations have stable demographic structures representing 'states' from which the population are displaced and then return to after disturbance. Such characteristics align demographic resilience to the general bivariate resilience [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,63.Oliver T.H. et al.Biodiversity and resilience of ecosystem functions.Trends Ecol. Evol. 2015; 30: 673-684Abstract Full Text Full Text PDF PubMed Scopus (508) Google Scholar, 64.Darling E.S. Côté I.M. Seeking resilience in marine ecosystems.Science. 2018; 359: 986-987Crossref PubMed Scopus (38) Google Scholar, 65.Willis K.J. et al.What makes a terrestrial ecosystem resilient?.Science. 2018; 359: 988-989Crossref PubMed Scopus (40) Google Scholar] and ecological stability [11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar,16.Pimm S.L. The complexity and stability of ecosystems.Nature. 1984; 307: 321Crossref Scopus (1595) Google Scholar,22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar] frameworks, which both have an engineering resilience perspective. We introduce a framework to define, quantify, and compare resilience across populations and species. The framework integrates resilience concepts from community ecology [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,17.Scheffer M. et al.Early-warning signals for critical transitions.Nature. 2009; 461: 53-59Crossref PubMed Scopus (2181) Google Scholar,18.Dakos V. et al.Resilience indicators: prospects and limitations for early warnings of regime shifts.Philos. Trans. R. Soc. B Biol. Sci. 2014; 370: 20130263Crossref Scopus (215) Google Scholar] and demographic theory [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar]. Following the conceptualizations of resilience in Hodgson et al. [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar], we define demographic resilience as the ability of populations to resist and recover (Box 1) from alterations in their demographic structure, usually with concomitant change in population size. We show that transient dynamics, as extensively described in [20.Neubert M.G. Caswell H. Alternatives to resilience for measuring the responses of ecological systems to perturbations.Ecology. 1997; 78: 653-665Crossref Scopus (253) Google Scholar,21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar], can be used to quantify demographic resilience and to anticipate the responses of the population and of species to disturbances. Thus, our framework marries two disciplines to define and quantify demographic resilience, and includes elements that draw from and are analogous to community resilience [11.Donohue I. et al.On the dimensionality of ecological stability.Ecol. Lett. 2013; 16: 421-429Crossref PubMed Scopus (189) Google Scholar,22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar]. Established resilience theories assume that natural systems can exist in alternative stable states [7.Holling C.S. Resilience and stability of ecological systems.Annu. Rev. Ecol. Syst. 1973; 4: 1-23Crossref Google Scholar], where the forces influencing the system are in balance [6.Parmesan C. Ecological and evolutionary responses to recent climate change.Annu. Rev. Ecol. Evol. Syst. 2006; 37: 637-669Crossref Scopus (5337) Google Scholar,20.Neubert M.G. Caswell H. Alternatives to resilience for measuring the responses of ecological systems to perturbations.Ecology. 1997; 78: 653-665Crossref Scopus (253) Google Scholar, 21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar, 22.Hillebrand H. et al.Decomposing multiple dimensions of stability in global change experiments.Ecol. Lett. 2018; 21: 21-30Crossref PubMed Scopus (76) Google Scholar]. When a disturbance displaces the system to an unstable state, these forces usually draw it back to stable state (Figure 1A ). However, if a disturbance forces the system beyond a domain of attraction, a tipping point, the system may transition to an alternative stable state [17.Scheffer M. et al.Early-warning signals for critical transitions.Nature. 2009; 461: 53-59Crossref PubMed Scopus (2181) Google Scholar,18.Dakos V. et al.Resilience indicators: prospects and limitations for early warnings of regime shifts.Philos. Trans. R. Soc. B Biol. Sci. 2014; 370: 20130263Crossref Scopus (215) Google Scholar]. This new system state is characterized by substantially different structures and is maintained by hysteresis processes or feedbacks [17.Scheffer M. et al.Early-warning signals for critical transitions.Nature. 2009; 461: 53-59Crossref PubMed Scopus (2181) Google Scholar,23.Folke C. et al.Regime shifts, resilience, and biodiversity in ecosystem management.Annu. Rev. Ecol. Evol. Syst. 2004; 35: 557-581Crossref Scopus (2227) Google Scholar]. Populations show similar properties to those in classical views of ecological resilience. Similarly to communities, populations are structured [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar]. Like distinct species in a community contribute differently to community dynamics [24.Levin S.A. Paine R.T. Disturbance, patch formation, and community structure.Proc. Natl. Acad. Sci. 1974; 71: 2744-2747Crossref PubMed Scopus (544) Google Scholar], individuals of distinct ages, sizes, or developmental stages in a population contribute differently to population dynamics [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar]. In a constant environment, a population will attain a stable demographic structure with stable population growth [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar,21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar]. Therefore, as in classical resilience views, populations are systems with a stable state defined by their demographic structure and growth. Disturbances change the size and structure of a population, displacing it from a stable structure (e.g., a fire affects younger rather than older tree individuals [25.Enright N.J. et al.Interval squeeze: altered fire regimes and demographic responses interact to threaten woody species persistence as climate changes.Front. Ecol. Environ. 2015; 13: 265-272Crossref Scopus (208) Google Scholar]). Such alterations to structure and size are akin to changes in community composition and biomass. Disturbances result in short-term dynamics that can differ from those at demographic stability, leading to either faster or slower growth than at stability (amplification and attenuation respectively [21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar]). These transient dynamics [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar,21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar], which depend on population structure, are generated by a relative over- or under-representation of individuals with high survival and/or reproduction. The largest extents of population amplification and attenuation after a disturbance represent the transient bounds, that are akin to resistance in classic resilience theory (Figure 1). As under-represented individuals are repopulated, the population is drawn back towards demographic stability, that is akin to recovery in classic resilience theory (Figure 1). Transient dynamics are thus ideal to estimate the intrinsic ability of populations to respond to disturbances. Population ecology has a panel of tools to measure demographic resilience, thus overcoming a key criticism of many resilience frameworks in communities, which lack operationalization [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,14.Donohue I. et al.Navigating the complexity of ecological stability.Ecol. Lett. 2016; 19: 1172-1185Crossref PubMed Scopus (206) Google Scholar]. Structured population models facilitate explicit simulations of disturbances that impact on different life-cycle stages [26.Stearns S.C. The Evolution of Life Histories. Oxford University Press, 1992Google Scholar], and enable calculation of the consequent transient responses [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar,21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar]. Bivariate resilience frameworks [10.Hodgson D. et al.What do you mean, 'resilient'?.Trends Ecol. Evol. 2015; 30: 503-506Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar,15.Ingrisch J. Bahn M. Towards a comparable quantification of resilience.Trends Ecol. Evol. 2018; 33: 251-259Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar,27.Nimmo D.G. et al.Vive la résistance: reviving resistance for 21st century conservation.Trends Ecol. Evol. 2015; 30: 516-523Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar] decompose resilience into two components, resistance and recovery (Figure 1 and Box 1). We distinguish resistance into two different processes, demographic compensation and demographic resistance (Figure 2; details below). In addition, we provide a distinction between recovery to a particular population size and recovery to a particular structure and growth (Figure 2). Demographic compensation incorporates amplifications in population size after disturbance (Box 2 and Figure 2), which compensate for post-disturbance reductions in population size. We advocate the use of reactivity, maximal amplification, and amplification inertia [21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar] to estimate changes in population size at various times after a disturbance, relative to stable growth (Figure 2). Reactivity quantifies the immediate, short-term response to a disturbance; maximal amplification is the highest density that the population can reach at any time-step, and inertia measures the total displacement of the population in the long-term, after the transient period. Reactivity, therefore, quantifies immediate compensation of a population, whereas maximal amplification measures the overall ability of the population to compensate, and inertia quantifies how far away from the stable state the population ends up following disturbance (Box 2).Box 2Transient CalculationsIn Table I we present a compendium of equations to estimate the aforementioned transient metrics using the most common structural population models used in demography – matrix population models [19.Caswell H. Matrix Population Models: Construction, Analysis, and Interpretation.2nd edn. Sinauer Associates, 2001Google Scholar]. However, the estimation of transient dynamics can be done using different structured population models (e.g., integral projection models [66.Ellner S.P. Rees M. Integral projection models for species with complex demography.Am. Nat. 2006; 167: 410-428Crossref PubMed Scopus (359) Google Scholar]) and other approaches [21.Stott I. et al.A framework for studying transient dynamics of population projection matrix models.Ecol. Lett. 2011; 14: 959-970Crossref PubMed Scopus (80) Google Scholar]. Transient dynamics can be measured by estimating the absolute changes in the population size, which combine the transient rat