What is conservation physiology? Perspectives on an increasingly integrated and essential science

1We define conservation physiology as: ‘An integrative scientific discipline applying physiological concepts, tools, and knowledge to characterizing biological diversity and its ecological implications; understanding and predicting how organisms, populations, and ecosystems respond to environmental change and stressors; and solving conservation problems across the broad range of taxa (i.e. including microbes, plants, and animals). Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales, and conservation includes the development and refinement of strategies to rebuild populations, restore ecosystems, inform conservation policy, generate decision-support tools, and manage natural resources.’

2The idea that physiological knowledge can inform conservation is not new. Although a search for the phrase ‘conservation physiology’ within Web of Science yields <30 papers, the pages of conservation journals include physiological content, while those of physiological journals include population management and conservation. Indeed, prior to the middle of the 20th century, ecology and physiology had largely been regarded as synonymous, resulting in frequent application of physiological approaches to investigations of population dynamics (e.g.;;; ). In many ways, the August Krogh principle for physiological adaptation, which was coined over a century ago (‘for … a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied’), is derived from the marvellous match of an animal's physiology with its environment. recognized six categories of effects (i.e. factors) for fish in which the environment and physiology interacted. Much earlier, provided a comprehensive treatment of environmental factors shaping plant and animal distributions, with much focus on physiological mechanisms, poorly explored as many of them were at that time.

3The discussion of physiology in a conservation context began to increase in the early 1990s, perhaps reflecting the growing appreciation for the significance of the field during and after the meeting organized by Wilcox and Soulé at which the term ‘conservation biology’ was first introduced. Although the journal Biological Conservation has existed since the late 1960s, and Conservation Biology since 1987, work with explicit reference to physiology in the abstract only began to appear in the 1990s. Likewise, in the fourth edition of his seminal book, argued the need for greater physiological information on stressed species given drastic environmental change and population reductions. A year later, in reviewing the iconoclastic 1987 volume by Feder et al., devoted his final section to the need for physiology to be concerned with human impacts. A parallel shift has also occurred in the field of toxicology and the sub-field of environmental toxicology. At one time, these areas were concerned with lethality as a measurement and regulatory end-point. Today, the importance of sub-lethal toxicity is well recognized, and books have been devoted to the mechanistic physiology that underlies toxicity (e.g. for fishes,, ). The reason for these shifts is simple; there is a much better appreciation of animal and plant physiology, especially in relationship to their environments.

4Such recognition of the significance of physiology for conservation has grown in primary research and in critical reviews (e.g.;;;;; ), but only recently has the discipline named ‘conservation physiology’ emerged. This discipline has expanded dramatically with the publication of synthetic papers, special issues (e.g.; ), and symposia [e.g. by the Society for Integrative and Comparative Biology and Society for Experimental Biology].

5In this overview, we briefly review what we mean by conservation physiology, developing a synthetic definition that reflects the current scope of the field. We then illustrate this scope with a range of examples, demonstrating that conservation physiology has much to offer to science and to those who find themselves with the considerable challenge of practising conservation in our rapidly changing world. In doing so, we provide the reasons for the launch of this new journal, Conservation Physiology. Echoing the words of the first editors of Biological Conservation, we offer no excuse for adding another journal to the world's burgeoning journal stable, but rather demonstrate that the need already exists and the time is ripe.

6‘Conservation physiology’ has been defined previously in several ways, each implying a somewhat different scope. To our knowledge, the first use of the phrase ‘conservation physiology’ was by, but several earlier phrases were conceptually similar. ‘Conservation physiology’ is more than the sum of its constituent words, though these words are powerful. Conservation is a movement or discipline focused on natural resource use, allocation, and protection. Physiology is focused on the mechanisms involved in how an organism works, including the anatomy and structure of organisms and organs, resource acquisition, metabolism and energy fluxes, regulation and homeostasis, acclimatization to changing environments and environmental tolerances, performance (such as growth, locomotion, and reproductive fitness), and impacts on the ecosystem. Physiology can be studied at the wide range of scales, from organisms, down to organ systems, organs, cells, and biomolecules and their chemical and/or physical functions.

7suggested that studies can be described as ‘conservation physiology’ when physiologists contribute knowledge, concepts, and perspectives to conservation decision-making. Such a definition is broad, but did not include a statement of the meaning of ‘conservation’. Although a zoologist, reminded readers of the threats that plants face given environmental change and pathogen emergence. In a paper titled ‘The importance of physiological ecology in conservation biology’, provided a case study on the nutritional ecology of desert tortoises and noted that ‘many of the threats to the persistence of populations of sensitive species have physiological or pathological mechanisms, and those mechanisms are best understood through the inherently integrative discipline of physiological ecology’. The authors noted that physiological ecology has become critical for understanding threats to the persistence of sensitive species and that physiological data can be used as part of ‘informed opinion’ (ideally, with theory and experiments to test hypotheses that form new syntheses of physiological and ecological knowledge), and eventually to guide management decisions.

8, both zoologists, coined the term ‘conservation physiology’ in a paper with that title. They explicitly defined it as ‘the study of physiological responses of organisms to human alteration of the environment that might cause or contribute to population declines’. The authors acknowledged that conservation physiology was relevant to all taxa, but their examples were entirely focused on vertebrates. One of the greatest limitations of that definition was its being framed only in terms of identifying problems rather than developing solutions. Also limiting is the focus on population declines as an end-point, which fails to recognize other relevant responses, such as range shifts, changes in genetic diversity, and alteration in the structure and function of populations, communities, and ecosystems. Although the authors did not provide a definition of conservation per se, they did provide a specific conservation-oriented metric (i.e. population decline), which is the basis for most regional, national, and international threat assessments (e.g. IUCN Red List; ). The definition provided by remained unchanged for some time despite its limited scope.

9Parallel developments were also focusing on the role of physiological studies in understanding the responses of organisms to anthropogenic change, the consequences thereof, and the scope for both mitigation of and adaptation to impacts. In particular, macrophysiology, defined as ‘the investigation of variation in physiological traits over large geographical and temporal scales and the ecological implications of this variation’, had focused on these conservation-related questions, as made explicit in a series of reviews. Subsequent macrophysiological work identified previously unappreciated conservation problems, such as climate-change-related threats to tropical and sub-tropical populations, illustrating its close links to conservation physiology (see also ).

10Following a brief hiatus in the discussion of conservation physiology, presented a revised definition; one that combined elements of earlier papers (e.g.; ) with that of. Conservation physiology became ‘the application of physiological theory, approaches and tools to elucidate and address conservation problems with the aim to provide a mechanistic understanding of how environmental disturbances and threatening processes impact physiological responses and thereby ecological function, population persistence, and species survival’. This definition was the first to use the word ‘mechanistic’, to refer to theory, approaches, and tools, and to expand the scope from populations to include a higher level of biological organization, namely ecological function and species survival. A key point in that paper was the value of conservation physiology in elucidating the ‘cause and effect’ that underpinned environmental impacts on organisms. This definition was taxon neutral, but there was little formal consideration of plants.

11In the same year, in a ‘conservation in practice’ paper focused on Pacific salmon, adopted the definition of, but showed that physiological knowledge has already been used not only to document problems, but also to generate management models to predict how organisms will respond to change, and to develop and test conservation strategies to generate desirable conservation outcomes (e.g. increases in population size, enabling sustainable use). A range of other studies has also demonstrated the specific conservation and management utility of physiological knowledge (e.g.;;;; ). Collectively, these examples show that conservation physiology can do more than document problems and elucidate mechanisms, which although important, are not always enough to assist population recovery. also noted that although conservation physiology is typically focused on anthropogenic stressors, rarely do stressors act alone, and stressors such as diseases can be moderated by human activities, consistent with ideas presented by. revised the previous definitions as follows: ‘We consider conservation physiology to be an applied subdiscipline within ecophysiology and define conservation physiology as the study of physiological responses of organisms to environmental changes and human-induced impacts, and their implications for population and ecosystem dynamics’. Their refined definition explicitly recognized that natural variations in the environment may alter the response of organisms to human impacts. A similar consideration also exists in the field of toxicology, where prior exposure to a toxicant can alter subsequent exposures, e.g. the induction of metallothionein-binding proteins in blood and detoxification enzymes in the liver. They also expanded the definition beyond population declines to ecosystem processes and emphasized scaling from physiological effects to community and ecosystem processes, though missing the overlap with macrophysiology. The authors noted that ‘conservation’ included conservation of biodiversity as well as the management of exploited living resources (presumably in a sustainable manner; ). used marine fish as a case study, but their definition certainly did not exclude plants. However, like previous definitions, they did not focus on the need for this science to solve conservation problems.

12As evident from these previous definitions, the concept of ‘conservation physiology’ has evolved. We have reviewed the strengths and weaknesses of the previous definitions and considered additional properties required to embody the actual and potential capabilities of conservation physiology, as follows: Taxonomic inclusiveness.Interpretation of ‘physiology’ in the broadest sense to include functions and mechanisms at all scales, from the cellular to the organismal, to the community, ecosystem, and biosphere.Interpretation of ‘conservation’ in the broadest sense to include conservation of biodiversity as well as the sustainable management of biological resources.Inclusion of work not only on declines in populations of species of concern, but also on the broad range of problems facing conservation and management, e.g. how to control invasive species, how to maintain habitat, and how to manage fragmented and degraded systems.Recognition of the need to scale from physiological mechanisms and processes to the levels of interest to conservation practitioners (e.g. populations, species, communities, ecosystems).Focusing not only on the documentation and clarification of conservation problems, but also on identification and refinement of solutions.Extending from the core of basic knowledge to improve understanding and inform decision-making in a number of ways, such as incorporation of knowledge into models and other decision-support tools.Integration with the wide range of scientific sub-disciplines for maximal power and understanding.

13Taxonomic inclusiveness.

14Interpretation of ‘physiology’ in the broadest sense to include functions and mechanisms at all scales, from the cellular to the organismal, to the community, ecosystem, and biosphere.

15Interpretation of ‘conservation’ in the broadest sense to include conservation of biodiversity as well as the sustainable management of biological resources.

16Inclusion of work not only on declines in populations of species of concern, but also on the broad range of problems facing conservation and management, e.g. how to control invasive species, how to maintain habitat, and how to manage fragmented and degraded systems.

17Recognition of the need to scale from physiological mechanisms and processes to the levels of interest to conservation practitioners (e.g. populations, species, communities, ecosystems).

18Focusing not only on the documentation and clarification of conservation problems, but also on identification and refinement of solutions.

19Extending from the core of basic knowledge to improve understanding and inform decision-making in a number of ways, such as incorporation of knowledge into models and other decision-support tools.

20Integration with the wide range of scientific sub-disciplines for maximal power and understanding.

21Taking all these elements on board, we arrived at the definition of conservation physiology that is the epigraph of this paper. Consistent with this definition, we have outlined a series of topics that exemplify what conservation physiology encompasses (Box 1).

22From the days of Aldo Leopold (1920–40s) and his promotion of the land ethic (in A Sand County Almanac) and wildlife management (in Game Management) to Rachel Carson's candid assessment of the effects of pesticides on birds, the fate of the natural world and the recognition that we need to take better care of it and even attempt to repair the damage done has become a prevailing societal paradigm. How to do so, of course, remains a considerable challenge given increasing demands on the natural world. The global human population continues to expand rapidly, as does demand for resources. The human population has already doubled in the lifetime of one of the authors and is expected to exceed 9 billion by 2050. However, population size is not the sole problem, because affluence (or consumption) and technology also influence the relationship between humans and the environment. The actions and inactions of humans (e.g.; ) have led to widespread disturbance and environmental change, from local to global scales. In some cases, conservation problems have arisen from intensively managed and exploited species (e.g. Atlantic cod), such that what was once a management issue has since become a conservation problem. However, at the same time excellent targeted conservation actions have brought species back from the brink of extinction, fuelling optimism that the future of conservation is less bleak once we understand the mechanistic connections between and within organisms.

23Although human impact on the environment can be measured in many ways, loss of biodiversity is commonly understood to be important. Biodiversity, in its most simple form, is the variety (at all scales) of life on earth, and is by most accounts in decline. A recent report revealed that despite some local successes, and considerable efforts to slow the decline, the rate of biodiversity loss is not slowing. Amphibians, freshwater fish, and tropical forests, as well as their resident biota, show particularly high rates of biodiversity loss and extinction. Loss of biodiversity is often first noted as declines in population sizes, a common metric used for regional, national, and international threat levels. Population declines are pervasive, with examples in nearly every region and taxon (e.g. sea grasses,; coral reefs, ). Vertebrate imperilment status (as measured by the IUCN Red List) continues to be dire, although the deterioration in species status would have been worse in the absence of conservation efforts. Alarmingly, declines in the abundance of species and the loss of biodiversity have direct and indirect effects on human well-being. Although there is some debate regarding the ecosystem consequences of biodiversity loss (e.g. ), in general it is recognized that there is real potential to alter ecosystem properties and the goods and services they provide to society. Effective conservation of biodiversity is essential for human survival and the maintenance of ecosystem processes and services. Understanding the influences of anthropogenic disturbance and variation in habitat quality on organism condition, health and survivalProviding a mechanistic/functional understanding of the effect of anthropogenic environmental change on organisms; using physiological knowledge to develop mechanistic models for species distributionsEvaluating stress responsiveness and environmental tolerances relative to environmental change (including global climate change and ocean acidification)Developing mechanistic relationships between population declines and physiological processesUnderstanding the relevance of acclimatization and adaptation of physiological processes to environmental variation (e.g. studies of thermal adaptation among populations and species) to management and conservationUnderstanding the physiological mechanisms involved in changes in community, ecosystem and landscape structure, as well as individual species, in response to environmental changeApplications of contemporary genomic and post-genomic technologies to conservation physiologyIntegration of physiology with conservation behaviour, conservation medicine, conservation toxicology, conservation genetics, and other relevant sub-disciplines (Table 1)Understanding the relevance of ecology and evolution of physiological diversity to conservationExploiting knowledge of organismal physiology to control invasive species and restore threatened habitats and populationsUnderstanding the optimal environmental conditions for ex situ preservation of endangered species (captive breeding, seed bank protocols for storage and regeneration, tissue culture for plant species or genotypes that are difficult to regenerate from seeds)Evaluating and improving the success of various management and conservation interventionsApplying physiological biomarkers as part of long-term environmental monitoring programmsDeveloping predictive models in conservation practices that include physiological parametersIntegrating physiological knowledge into ecosystem management and development of tools to solve complex conservation problemsUnderstanding the policy implications of conservation physiology research

24Understanding the influences of anthropogenic disturbance and variation in habitat quality on organism condition, health and survival

25Providing a mechanistic/functional understanding of the effect of anthropogenic environmental change on organisms; using physiological knowledge to develop mechanistic models for species distributions

26Evaluating stress responsiveness and environmental tolerances relative to environmental change (including global climate change and ocean acidification)

27Developing mechanistic relationships between population declines and physiological processes

28Understanding the relevance of acclimatization and adaptation of physiological processes to environmental variation (e.g. studies of thermal adaptation among populations and species) to management and conservation

29Understanding the physiological mechanisms involved in changes in community, ecosystem and landscape structure, as well as individual species, in response to environmental change

30Applications of contemporary genomic and post-genomic technologies to conservation physiology

31Integration of physiology with conservation behaviour, conservation medicine, conservation toxicology, conservation genetics, and other relevant sub-disciplines (Table 1)

32Understanding the relevance of ecology and evolution of physiological diversity to conservation

33Exploiting knowledge of organismal physiology to control invasive species and restore threatened habitats and populations

34Understanding the optimal environmental conditions for ex situ preservation of endangered species (captive breeding, seed bank protocols for storage and regeneration, tissue culture for plant species or genotypes that are difficult to regenerate from seeds)

35Evaluating and improving the success of various management and conservation interventions

36Applying physiological biomarkers as part of long-term environmental monitoring programms

37Developing predictive models in conservation practices that include physiological parameters

38Integrating physiological knowledge into ecosystem management and development of tools to solve complex conservation problems

39Understanding the policy implications of conservation physiology research

40In the 1980s, scientists such as Michael Soulé began to consider the need for a new multi-disciplinary field dedicated to the science of scarcity and diversity. Conservation biology was born, with a focus on providing principles and tools for preserving biological diversity. The field matured and evolved, and eventually adopted an even more holistic perspective and moniker (i.e. conservation science). This field contributed new approaches to conservation practice, such as conceptual frameworks (e.g.;,; ) for scientists to provide information relevant to conservation practitioners (e.g. managers, policy-makers). The recognition grew that evidence, rather than anecdote, was essential for meaningful conservation action, and especially to move beyond arbitrary or ad hoc approaches.

41Within the sphere of conservation science several sub-disciplines have emerged, including conservation genetics, conservation medicine, and conservation social science (see Table 1). Many of these sub-disciplines have become recognized specialty areas in their own right, beyond their integration within the broader realm of conservation science. All of these sub-disciplines are focused on generation of knowledge to understand problems as well as to develop solutions. Indeed, modern conservation science is as much about restoring ecosystems and rebuilding populations (e.g. ) as it is about documenting responses to stressors. The exception, perhaps, is in terms of predicting the future (e.g.;; ) such that it is possible to develop adaptation strategies for environmental change. Clearly, given the multitude of threats facing biodiversity, population persistence, and ecosystem structure and function, conservation science plays an essential role. Likewise, resource management, even of exploited populations, has at its heart conservation and the science behind it (see; note that this was also recognized by ), because management activities were intended to be based on sustainable use within an ecosystemic context. International policy instruments, laws, agreements, and initiatives, such as the Convention on Biological Diversity, the Convention on the International Trade of Endangered Species, and the Millennium Ecosystem Assessment and Development Goals, provide institutional guidance for addressing some of the larger-scale conservation issues, although in reality most successes have been based on more localized activities.

42Conservation physiology is a latecomer relative to the other sub-disciplines that have become trusted and recognized components of conservation science (e.g. conservation genetics, conservation behaviour). While physiology was identified as relevant (see Fig. 1; ) in the early days of conservation biology, one must look quite hard to find even a mention of physiology in any of the introductory conservation biology textbooks (e.g.;;;; ). It is almost as if the relevance of physiology was forgotten or dismissed for some time. evaluated publication trends in conservation science and revealed that most research was focused on species and populations, rather than the broader suite of scales from molecules to ecosystems, demonstrating that physiology was poorly represented within at least key conservation science journals. In the field of ecological restoration, some have even expressed doubt that a general mechanistic approach is necessary at all (e.g. ), while others have vigorously argued that it is essential (e.g.;;; ). We believe that this oversight, intentional or not, reflected the difficulty of easily connecting physiology with its application. With the expanded knowledge in the mechanistic aspects of environmental physiology and environmental toxicology, this is no longer the case. The growth of physiology back towards ecology and application to conservation has been deliberate, albeit perhaps somewhat stealthy.

43Why is conservation physiology needed? In answering this question, we must go beyond the bland statement that linkages between physiology and conservation have become possible. Therefore, more specifically, what does conservation physiology contribute to conservation science, resource management, and policy? In fact, many roles can be outlined for the importance of conservation physiology within the broader sphere of conservation science. These roles can be targeted specifically towards current needs, as recommended by. Indeed, there have been several syntheses that have outlined priority research topics (via horizon scanning and collaborative prioritization exercises) and needs in conservation science in general (see;,,, ), as well as for specific regions (e.g. the UK,; USA,; Canada,; Antarctica, ), taxa (e.g. turtles,; birds,; insects,; pollinators,; metallophytes, ), and pressing problems (e.g. pharmaceuticals in the environment,; coastal and marine management, ). Such research priority documents can be mined to identify potential ways in which conservation physiology can be relevant to practitioners. For example, in the 2012 horizon scan of emerging global conservation issues, listed a number of issues that are in desperate need of mechanistic physiological studies to understand and solve problems (e.g. warming of the deep sea, mining in the deep ocean, climate-driven colonizations in Antarctic waters, increases in pharmaceutical discharges as human populations age, and the potential consequences of graphene on organisms). In addition, a group of physiologists (i.e. ) suggested that physiology had the potential to inform and address a variety of conservation issues and emphasized the need to transform such science into information and tools that other constituencies can process and use. Clearly, there is no shortage of opportunity for the nascent field of conservation physiology.

44It is not possible to review all of the possible applications here, so we refer the reader to other syntheses, including,,, and, as well as to Table 2, for examples of the potential ways in which various research areas within physiology can contribute to plant and animal conservation physiology and conservation science. For all examples provided, a core strength of physiology, i.e. the mechanistic approach, is to identify and confirm cause-and-effect relationships through experimentation. Indeed, suggested that physiologists could be helpful in setting standards for the type of evidence that would constitute compelling proof of a cause-and-effect relationship. Given that physiology moves beyond correlation to seeking causation, it arrives at robust information that would be compelling in legal proceedings, such as are common for conservation and environmental issues (e.g. ), as well as toxicological ones.

45Here we provide a brief overview of key ways in which conservation physiology can contribute in an important manner to conservation science. As noted by, there remain challenges in ensuring that conservation physiology is relevant to policy-makers and conservation practitioners, and thus we aim to demonstrate with concrete examples where successes have been achieved in conservation physiology (see ).

46Physiological diversity is the variation in function and tolerances among individuals, populations, and species, and arises due to a combination of genetic, developmental, and environmental influences. At the most basic level, physiological assessments can identify and characterize functional biodiversity, a necessary requisite to biodiversity conservation. For example, substantial efforts in characterizing physiological diversity in insects (reviewed by ) have revealed that as a consequence of limited upper thermal tolerances and the form of the metabolic rate–temperature relationship, tropical and sub-tropical populations are likely to be much more at risk from changing climates than their more temperate counterparts (;;; Hoffmann et al., in press). Likewise, it appears that responses to changing environments might differ substantially between the hemispheres, and that winter warming may be especially problematic for temperate species. In this respect, point out that the austral marine flora may be more sensitive to global warming than their boreal counterparts. Algal reproduction is extremely sensitive to temperature and, for instance, predicted significant changes, due ocean warming, in coastal community structure associated with the northward shift in the southern boundaries of the major canopy-forming kelps of the genus Laminaria.

47Understanding what such diversity means for the organization and function of ecosystems is also a growing and necessary topic. The recognition that inter-individual variation in physiological diversity can generate intra-population diversity has important implications for conservation (e.g. population reintroduction programmes). Several approaches to explain broad-scale patterns in biodiversity have incorporated elements of physiological diversity (e.g.;; ). As noted by, attempts to derive such relationships between physiological diversity and distribution and/or abundance should be based, where possible, on hypothesis-driven manipulative examinations, not only to document patterns, but also to understand their mechanistic basis. Such examples now exist. For instance, used both ecological and evolutionary physiology to document herpetological diversity along altitudinal gradients in the Andes. Likewise, greater animal diversity at cold seeps vs. hydrothermal vents appears to be related to the greater physiological barriers to invasion of hydrothermal vents. As shown for Hawaiian Plantago species, studies of the physiology of rare plant species within a genus can indicate traits that make them distinctive as conservation priorities, and additionally, reflect their differentiated habitat preferences.

48Habitat is the foundation of functional ecosystems. It is therefore not surprising that many conservation and management efforts relate to identifying and protecting critical habitats from human alteration. Studies of animals have used behavioural information to study their spatial ecology; however, there is increasing interest in documenting the fitness benefits of occupying different habitats and niches, particularly in a bioenergetics context. Niche theory, encompassing both the fundamental niche, where species are able to survive, and the realized niche, where species are actually found, provides a useful framework to examine the influence of abiotic and biotic factors on the distribution of organisms and to predict the impact of environmental change. Physiology plays a fundamental role in setting a fundamental niche, and a secondary role to expressed behaviours in setting a realized niche. Without such physiological knowledge, therefore, niche descriptions become limited. Furthermore, described the concept of ‘energy landscapes’ as a means to consider how animals may make decisions about how they select various habitats or movement paths. Given that landscapes and their constituent habitats vary in composition, such habitats will be of different value to different taxa. In some cases, organisms will be excluded due to environmental thresholds that exceed their tolerances (e.g. light, temperature, moisture), but in other cases organisms may persist in areas of lower habitat quality although they suffer fitness consequences for doing so. Thus, for rare species, as well as for populations of common species at the edge of their ranges, and subject to the influence of climate change, detailed quantification of habitat and physiological responses is necessary. Indeed, advocate ensuring that the nutritional requirements for reptiles are met within protected habitats if they are to benefit reptile conservation. In one study, estuarine habitat quality was evaluated using fish condition as a proxy. Conservation physiology can also be used to inform habitat-related management actions. For example, evaluated energy use in endangered salmon during their spawning migration in different reaches of a regulated river to identify areas where energy use was elevated and thus could represent areas in need of restoration as well as to inform minimal flows. In a unique case, information on the thermal physiology of an endangered Australian snake was used to predict its critical habitat needs from a thermoregulatory perspective. Given that protecting all habitats is unrealistic, physiological tools could be useful for identifying areas that are functionally (rather than structurally) important and that serve as critical habitats.

49Changes in the abiotic environment affect the physiology of organisms at multiple levels, which is problematic given the level of anthropogenically mediated environmental change currently underway. From ocean acidification to global climate change and from the Arctic to the Amazon, we need to predict how organisms will respond to such changes. suggested that increased growth and competitive ability of non-calcareous marine macroalgae, alongside negative impacts of acidification on calcifying species, could have major implications for the functioning of coastal reef systems at elevated CO2 concentrations. Studies on microalgae, with their short generation times, have provided insights regarding adaptive responses to global change (see ). Human ‘adaptation’ or adjustments to resource availability and risk are necessary to protect livelihoods. The perceived importance of environmental change and the associated motivation for human response depends largely on the rate and magnitude of environmental change and the projected degree to which humans will be affected. Physiological approaches can be used in experimental tests of the response of individual organisms to different types of environmental change (individual and multiple stressors), thereby enabling predictions for future environmental scenarios. For example, used aerobic scope models and biotelemetry data to predict the success of spawning migrations relative to warming river conditions. Phenotypic plasticity enables the persistence of organisms within a species across a range of environmental conditions to a point; however, it is understood that there is also a limit to physiological compensation for environmental variability such that if conditions exceed the tolerances or capacities of a species, it will be extirpated from a given location. As reviewed by and, compensatory responses occur at different time scales, including between generations (genetic adaptation) and during development (developmental plasticity) so that phenotypes are matched to prevailing environmental conditions, and within the adult lifespan as reversible plasticity (acclimation and acclimatization; ). Individual physiological acclimatization capacity will define the winners and losers relative to different types and extents of environmental change which will be driven. Also relevant are the suite of options available to humans in order to respond to environmental change, something that could be clarified by conservation physiology (e.g. which species are likely to be capable of surviving in a given environment and should we attempt to introduce them to replace the function of species that are extirpated?). In some cases, knowledge of how organisms respond to environmental change could help to identify potential mitigation strategies.

50Disturbance is pervasive as a result of human activities. Physiological tools can be used to identify the sources and consequences of stressors on plants and animals. Of particular importance is the ability to identify thresholds which either do not elicit stress or which do so at a level that is not maladaptive. Novel ways now exist to assess stress without having to handle animals repeatedly (e.g. use of faecal glucocorticoid monitoring, biotelemetry, and biologging) in large part due to a desire to apply such measurements to conservation problems. Two of the earliest of such studies on vertebrates showed that logging and snowmobile activity can increase glucocorticoid stress hormone release in Spotted Owl and elk (Cervus canadensis), respectively, and these discoveries assisted with reserve zoning to restrict such activity in some areas. Similar work has occurred with a range of other taxa and in response to a variety of other stressors (e.g. fisheries interactions, ecotourism, urbanization, aircraft noise). Physiological knowledge has also been used to identify regulatory thresholds for various pollutants for plants (e.g. ) and animals. Another important aspect of such work has been to identify how stress responses vary relative to differences in habitat quality (e.g.; ), as well as determining when and how such stressors affect fitness and population-level processes (for discussion see ). Various stressors also have the potential to promote or mediate disease development and, given high-profile problems such as chytrid fungus and amphibians, conservation physiology approaches are being used to understand disease dynamics. With human populations expected to continue to grow and our footprint to expand, it is certain that organisms will face more disturbance and pollutants in the future.

51Ex situ conservation activities related to highly endangered species remain important safeguards for plants and animals. In many ways, such efforts represent the last resort and are undesirable in that they are resource intensive and expensive, not to mention that there are limitations with such programmes (see ). However, there have been some remarkable successes, and in many of those instances, success has occurred because of a strong understanding of the reproductive biology of the organism (e.g.; ). In fact, much of the earliest work in conservation physiology was directly related to reproduction (see ). In vertebrates, knowledge of endocrine function is typically exploited to monitor and manipulate the reproductive state of captive animals (e.g.;; ). In the field of stress physiology and environmental toxicology, the interactions of cortisol and estrogen mimics are well documented at the physiological and biochemical levels, e.g. sex reversal of fishes by estrogen mimics. Although many of these efforts are directly related to understanding reproductive function and how to manage and maximize reproductive output, other elements of physiology have proved to be valuable. For example, understanding the nutritional physiology of organisms is key when feeding animals in captivity, to ensure that they have the necessary energy and nutrients to engage in reproduction and produce viable offspring (e.g.; ). Also important is minimizing stress during captivity and translocation of animals (e.g.; ) and ensuring that the appropriate environmental conditions are provided. For plants, knowledge of seed dormancy has enabled the development of seed storage for germplasm conservation, and knowledge of habitat requirements and plant–animal interactions continues to improve the outlook for preserving species from extinction and restoring ecosystems.

52Conservation practitioners, resource managers and policy-makers often make decisions regarding conservation actions to undertake in order to address given objectives. They are often guided by various plans (e.g. conservation plans, recovery plans, wildlife management plans, forest management plans; ) and the suite of options available to them is ideally based on scientific evidence. In addition, actions are ideally implemented in an active, adaptive way such that monitoring will lead to revision of plans and refinement of actions as appropriate. Conservation physiology can be used as an integral part of such monitoring programmes (see below; ), and furthermore, to assist the identification of actions likely to be most successful. For example, bycatch reduction strategies for sea turtles have benefited greatly from knowledge of sensory physiology (e.g. to develop repellents; ). In addition, physiological knowledge has been useful in elucidating the chemical ecology of natural enemies, herbivores, and host plants such that biological control programme efforts can focus on the most successful strategy. In general, however, physiology is perhaps most useful in parameterizing ecological and management models to support decision-making. For example, describe how various models (e.g. population models, individual-based models, species distribution models, and mass- or energy-balanced models) can incorporate information on the relationship between physiology and the environment to inform management actions. As part of a risk assessment, used species-distribution models populated with physiological data to assess the invasion potential of buffel grass in Mexico to inform management actions related to preventing such an invasion. Likewise, used degree-day information for flowering plant species being transported to Antarctica, along with explicit information on visitor numbers and current and future climates to predict areas of most risk for the establishment of invasive alien species. These assessments are now directing conservation management in the region. emphasized the need for ecophysiological experiments to improve the precision of such models. As modelling techniques become more sophisticated, physiology will play an important role in ensuring that these decision-support tools are appropriately parameterized and calibrated through careful experimentation.

53One of the strengths of conservation physiology is its ability to provide objective scientific information to permit evaluation of the extent to which various conservation and management activities are successful. For example, restoration of degraded habitats is a common conservation action that is presumed to have benefits at a variety of biological levels. Traditional measures of community structure to assess success can be slow to respond to changes and often take longer than the period for which monitoring is set to occur (if any monitoring at all; ). Physiological tools can be used to understand whether there are individual-level benefits associated with restoration (e.g. reduced stress, improved growth, or nutritional condition) on a shorter time frame. For example, contrasted the response of two eucalypts to seasonal drought at restored sites and determined that although the plants were in the same functional group, they responded differently to resource limitation. Success of restoration plans can be improved by using physiological knowledge about environmental thresholds of different species to identify the types of species or which populations (usually plants) might be likely to succeed, particularly in highly degraded sites (e.g.; ). Translocation of animals is another conservation strategy that has benefited from physiological knowledge. Research has revealed the best practices for relocating wildlife (e.g. ) and plants (e.g. ), while minimizing stress and maximizing survival. Conversely, a recent ecosystem-level decision by the salmon-farming industry in British Columbia, Canada voluntarily to relocate salmon net pens away from the migration path of juvenile Pacific salmon during the migration window was based in part on physiological studies of swimming and osmoregulatory performance of pink salmon that characterized the critical role of fish size in tolerating parasitic sea lice.

54To date, various definitions of conservation physiology have existed, but all possessed limitations. In particular, some were not sufficiently inclusive in recognizing the role and full potential of conservation physiology. Here, we have refined the definition of conservation physiology by reflecting on past definitions and identifying the key requirements of the definition. As a result, the definition we have generated is, in many ways, an integration of previous definitions. Moreover, the definition was generated by a diverse authorship team covering plants and animals (from insects to vertebrates), as well as different topical expertise. To reiterate, conservation physiology is an integrative scientific discipline applying physiological concepts, tools, and knowledge to characterizing biological diversity and its ecological implications; understanding and predicting how organisms, populations, and ecosystems respond to environmental change and stressors; and solving conservation problems across the broad range of taxa, including microbes, plants, and animals. Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales, and conservation includes the development and refinement of strategies to rebuild populations, restore ecosystems, inform conservation policy, generate decision-support tools, and manage natural resources.

55We are confident that this new definition will be embraced by the broader scientific community. However, when dealing with biodiversity crises, and in the face of immense management and policy challenges, we recognize that action is more important than the definition. We hope, therefore, that the new definition and journal will galvanize further action. Conservation physiology is certainly needed, and it has great potential to be effective by broadly contributing to conservation science in many ways (; Box 1). In addition, given that physiology embraces a variety of topical sub-disciplines and types of expertise (Table 2), there are many ways in which physiology can contribute. We cannot possibly identify all of the ways in which conservation physiology is needed, but the examples that we provide here represent ways in which tangible and rapid progress can be made (see ). Indeed, it is our view that the creativity of those working on conservation physiology will identify new ways in which it can become even more relevant to conservation practitioners. Moreover, because of the ability of conservation physiology to generate cause-and-effect relationships, we anticipate a rapid expansion of its use in support of evidence-based conservation. Indeed, evidence-based conservation is likely to run a parallel course to that taken by medical science, where mechanistic experimentation is currently the primary way in which the evidence base is established.

56For conservation science to reach its full potential will require true integration, which means that physiologists will need to collaborate with scientists with other expertise (i.e. integration; ), as well as directly with conservation practitioners. The success of conservation science requires building on strengths and foundations of existing sub-disciplines, both basic and applied; physiology certainly provides such a foundation.