Chapter 2 – from the draft Conservation Biology: how nature works as a guide to conservation – Peter White 2019


A Concept Map: The 15 Threads of Conservation Biology 


Read this chapter to get your first exposure to cross-cutting themes (threads) that run throughout this book. I hope they deepen your understanding of nature and conservation biology.  They are grouped into five categories and form a concept map for major issues and approaches in conservation. The 15 threads are also the focus of a review in the next to last chapter in this book. 


Although we will proceed sequentially, starting with biodiversity and the theory of island biogeography and moving on to genetics, populations, metapopulations, communities, ecosystems, and landscapes, there are also cross-cutting themes that run through all the chapters.  The chapters are like the layers of a cake, the threads are like slices down through that cake.  In this chapter, I introduce you to a concept map for the field of conservation biology (Table 2-1):  15 threads grouped under five headings.  I will refer to the threads in the chapters to follow and will return in earnest to reexamine them in Chapter 36. The threads may seem mysterious at first, but bear with them for now.  


[Table 2-1.  Levels and threads of conservation biology] 


I defined these threads because I found that when I teach conservation biology, I make analogies across genetics, populations, metapopulations, communities, ecosystems and landscapes, and that the field itself was using the same abstract concepts across the levels of biodiversity.   


Some of the 15 threads are undoubtedly true, but others can be challenged.  I hope they are a guide to issues to think about and that they give an overall “shape” to the field and help to define those questions which are not yet answered.  The threads are also keys to being able to finish the sentence “the answer to conservation questions depends on…” 


The threads are grouped under five headings:  A. incomplete knowledge, B. diversity, C. the dancer and the dance, D. sampling problems, and E. time, space, and scale


A. Incomplete knowledge 


Nature is complex and we lack complete knowledge of biodiversity.  Our challenge is to find the keys to the puzzle, the essential features that that will help us understand the whole, and to allow us to refine our understanding as new discoveries are made.  Our first four threads deal with incomplete knowledge. 


1. Guidelines:  When specific knowledge is lacking, conservation biologists often use expert opinion to develop qualitative or semi-qualitative guidelines.  These can be formalized into decision trees that use sequential questions to arrive at a recommendation.  Since uncertainty is involved, advisory panels often revise the guidelines when new information is available.   


2. Surrogacy:  Some taxonomic groups (e.g., vertebrates) are much more thoroughly studied that others.  These groups are sometimes used to model general patterns and problems under the assumption they are adequate surrogates for the lesser known taxonomic groups.  When patterns are consistent among groups of organisms, the patterns are termed “congruent”.  Indicator, focal, umbrella, and flagship species are also forms of this thread—the response of one or a few species are used as a bellwether for other species.  Approach this thread with respectful skepticism!  There are cases when surrogacy doesn't work. 


3. Models for complexity:  There are many interacting causes of pattern in nature.  Models are used in three main ways: first, to depict the main causes and patterns see the consequences of our data in predicting future states (population viability analysis is an example, Chapter 17); second, to test management actions; and, third, to isolate and illustrate the effect one or a few important variables or processes by holding everything else constant (hence the frequent expression “all-else-being-equal” in these models).  This third use can feel frustrating in that the real world never behaves in ways that simple models depict—but try to learn from these attempts to isolate important factors so we can see their consequences and see those simple models as components of theory and of more complex models.  


4. Precaution and adaptive management:  In the face of uncertainty, the precautionary principle is to refrain from actions that have a high risk of causing harm and an unknown probability of success.  When in doubt, at least do no harm.  However, doing nothing in conservation is itself a decision that may have negative consequences--so doing nothing may violate the "do no harm" principle.  This suggests that our decisions and management actions are hypotheses that need to be tested, with management adapting based on monitoring results.   


B. Diversity of the elements: genes, species, and ecosystems 


Under this heading, I group five threads that have to do with diversity as a conservation goal.   


5. Discreteness and continuity:   Are the entities of conservation discrete and easily classified and tallied (the idea of diversity suggests we are enumerating entities)?  Part of the problem is that some entities have uncertain boundaries (e.g., subspecies within a species) or fluctuating boundaries (e.g., communities undergoing succession or responding to environmental change).  Some aspects of nature are impossible to classify because the underlying variation is continuous (e.g., compositional change along gradients, clinal variation in species).  Nonetheless, classification is used as a way of reducing complexity and for communication.  Classification is sometimes used under the assumption that the classes represent useful, if arbitrary, nodes along a gradient of continuous change.  Sometimes we abandon classification in favor of models of continuous change. 


6. Irreplaceability: genes, species, and ecosystems have unique histories and can’t be recreated exactly once gone.  Applied to species, this thinking underlies Leopold’s “first law of conservation biology”: “to save every cog and wheel is the first precaution of intelligent tinkering” (we will also encounter Janzen’s first law of intelligent repair, whether for watches or ecosystems, “save the design”).  The “irreplaceability” thread underlies one aspect of the precautionary principle: when faced with uncertainty about change that will be impossible to reverse, precaution is advised!   


Some scientists argue that, from a technological perspective, extinct species could be recreated by placing remnant or synthesized DNA in the right cellular context (Chapter 25).  This is termed “de-extinction”.  Scientists are contemplating bringing back woolly mammoths, passenger pigeons, and other extinct species.  This is a tall order!  But even after the technological problems are solved, remember that we need to restore not just the species, but also its genetic diversity and ecological relationships with other species, not to mention that we would have to remove the threats that caused extinction in the first place. Deextinction might eventually produce individuals of extinct species, but we need to figure out when this tool can achieve broader conservation goals.  To bring back all extinct species, great and small, is still in the realm of science fiction, but it is a dubious correction to the problem of extinctions, considering that the real problem is a sustainable balance between our species and all others.   


Since not all elements of diversity can be saved and some have already been lost, and given the impossibility of recreating the past, this thread leads to a question: to what degree can missing species or processes be replaced or simulated in a conserved ecosystem?  While species have unique roles, they also overlap in function so some lost functions might be replaceable.  In addition, the irreplaceability of a species does not mean that the loss of a particular species has large ecosystem effects—see the Fragility/Tolerance Thread next. 

7.  The fragility/tolerance of species and ecosystems, as a thread, poses these questions:  how fragile is an ecosystem or population, how robust is it to change?  How tightly connected and structured are the species interactions?  How endangered or tolerant are species to a given change?  How “right” do we have to get the environmental conditions and disturbance regimes to achieve restoration goals?  How tolerant are ecosystems to different management schemes?  Answers to these questions are rarely black and white and we often frame our questions with probabilistic terms—for instance, “how likely” is an extinction over a given period of time (Chapters 17 and 18)? 


Species vary in their functional contributions to ecosystems and those contributions can vary through time with species interactions, environmental change, and disturbances.  Some species play such important roles that their loss changes ecosystem dynamics and affects many other species.  In Chapter 7 we discuss “driver” versus “passenger” species, for example.  But species that seem to be passengers can become drivers when environment changes.  Even species that contribute little to overall function at large scales can be critical to smaller scales—the fern in the forest may not contribute much photosynthesis to the total carbon storage in the forest, but there are a host of invertebrates and fungi living in and on it nonetheless. 


8. The Goldilocks problem: Some species like it hot, some like it cold, and some like it in the middle. By this I mean that species have different optima and different ranges of tolerance for a host of environmental and habitat factors.  A species niche can be described by its performance across a range of physical conditions and by how it acquires resources.  If these responses are tested in the absence of other species, it is called the fundamental niche.  The realized niche is that set of conditions under which it is found in nature and therefore incorporates the effect of species that may contract its observed environmental niche through competition or expand it through mutualism. 


The differences among species are the results of trade-offs.  As a consequence, there is a limit to a species functional breadth—if a species is good at one thing, it must be poor at another because of the costs and benefits of adaptation, setting up the Goldilocks thread.  Species also differ, though, in niche breadth (not all niches are the same size, and not all optimum performances are of the same intensity).   


That uniqueness of species means that a particular environmental change or conservation action will be good for some species, bad for some, and neutral for others.  This is a major obstacle to generalization.  However, although species do have unique niches, they also have overlapping traits, too, and so generalization is possible.  Because species have different requirements, perhaps the greatest generalization of conservation biology is that, at large scales, heterogeneity of conditions supports diversity. 


9. The pure effects of diversity:  a central theorem in conservation biology is that diversity itself (the number of genes, species, and ecosystems or habitats) plays a functional role.  For genetics, the pure effects of diversity is represented by Fisher’s Fundamental Theorem.  It states that the rate of increase in fitness is equal to the variance in fitness.  In other words, the rate of evolution of a trait in a population is a function of the genetic diversity for that trait in the population, for a given intensity of selection.  As a characteristic of the population, diversity has a functional role in this case.  Can we extend that thinking to ecosystems, namely that there is ecosystem function correlated with species diversity? Can we extend the idea to the landscape level, namely that landscape function correlated with the diversity of ecosystem composition and structure in that landscape?  The general proposition of this thread is that more diverse aggregations have better short-term function and greater ability to adapt to changing conditions (Chapter 9). 


C. The dancer and the dance 


The “dancer and the dance” has four threads that concern the pattern of entities (for example, genes, species, and ecosystems) and the processes that cause ongoing change and dynamics in these entities.   


10. Pattern and process, balance and flux:  Nature consists of observable patterns (in genes, species, ecosystems)…but these patterns were created by dynamic processes…and processes continue and are driven by the elements of the pattern.  A Yeats poem captures this idea: 


O chestnut tree, great rooted blossomer, 

Are you the leaf, the blossom, or the bole? 

O body swayed to music, o brightening glance, 

How can we tell the dancer from the dance? 


You can hardly have a dancer, unless there is a dance.  You can’t have a dance unless there is a dancer.  We have to be concerned not just with the “thing” (the dancer) but also with the process (the dance) that produced it.  Thing and process forever interact, first one than the other occupying our attention. 


In 1949, A.S. Watt published a paper that articulated the concept of “pattern and process” at the community level, using that phrase to describe vegetation as made up of dynamic patches.  A patch could be created by the death of dominant individuals or disturbances.  Each patch, after disturbance, goes through a developmental sequence.  Mortality, disturbance, and succession are the processes; the patches are the composition and structure of the vegetation.   


Pattern and process occurs at all levels of biological diversity—genes, populations, metapopulations, ecosystems, and landscapes—and Watt’s phrase has been much repeated in ecology and evolutionary biology.  For instance, we can describe the pattern of distribution of genes within and between the populations of a particular species, but there are also dynamic processes of gene change (gene flow, genetic drift, evolution).  The nature we are interested in has the intertwined properties of dancer and dance. 


Because of dynamic process, nature is in flux, at least at small scales. But at broader scales there may be an overall balance and so there may be a dynamic equilibrium at that scale.  Conservationists would naturally be interested in this sort of dynamic stability—and finding the right scale of stability—despite local flux.  Does it occur?  At what scales?   


One paradigm for nature is represented by the phrase “the balance of nature”.  This has been replaced by a second paradigm “nature in flux” (drifting continents, changing climates, natural disturbances, evolution) (Pickett et al. 1992, Fieldler et al. 1997).  But dynamic equilibrium may also hold at least for some time periods at some spatial scales.  Small scale changes may be compensatory, resulting in a dynamic equilibrium (“balance”) at a larger scale, even for the “nature in flux” paradigm.  The relation of small scale to large scale change becomes a critical issue.  The idea of larger scale persistence in the face of local change will appear in areas as diverse as metapopulations and disturbance ecology.  For example, in disturbance ecology, the idea of qualitative or persistence equilibrium describes a large scale stability made up of smaller scale patches that undergo the dynamics of succession and disturbance (Chapter 31).  Thus, the balance and flux describes the overall dynamic state of the pattern and process concept—it addresses whether the elements and processes produce a dynamic stability or overall trajectories of change.   


A corollary of dynamic equilibrium is that conservation success increases and management costs decrease (per unit area) as the size of the conservation tract increases because larger tracts would be more likely to be dynamically stable (Pickett and Thompson 1978).  However, some ecosystem threats, such as disease, invasive species, climate change, and pollution are not respecters of natural area size per se.   


The paradigm of flux poses a further challenge in conservation biology: if change is natural, why not accept all change, including human induced change?  If nature is in flux, what is our benchmark for conservation goals?  What we really want to know is this: what is the relation of human induced change to the ability of an ecosystem to go on functioning and adapting (see chapters 3, 4, 31, and 32)?  In the face of flux, we need to conserve the very ability to change and adapt.   


The web of life means that change in one part of that web ramifies in complex ways across the web.  Indirect effects can amplify, dampen, or reverse the direction of change.  We have to consider indirect effects when try to predict or generalize the effects of an environmental change or management action.   


The objects of conservation, whether gene pool, species, ecosystems, or landscapes, not only respond to change in the short-term, the objects themselves also change in ways that affect their future reaction to the same or new changes.  This process of adaptation is itself dependent on the attributes of the entities.  The working hypothesis is that the best predictor of this response is diversity itself (see above, under the pure effects of diversity). 


D. Sampling problems 


Under “sampling problems” I present two threads that represent the consequences of having conservation areas that are subsets or pieces of some original larger entity. 


11. Conservation as sampling:  By definition, conservation areas area a subset of some original larger whole.  What are the consequences of this subsetting?  Keep an eye on process here:  sometimes we successfully conserve a pattern only to find that pattern was dependent on processes at larger scales that we didn’t conserve.  Or we don’t know the process and lose the pattern within protect areas.  What is the best conservation subset or sample?   


Sampling involves two effects.  First, we begin with a sample (subset) of the original and, by virtue of being smaller, that sample is already poorer than the original, like taking one piece of a larger tapestry. This can be a nonrandom sample at that—humans take the highest productivity and easiest to use sites first leaving conservation areas that are colder, rockier, steeper, or swampier than a random sample!  The second sampling effect is that the sample itself changes or decays through time simply because it is now removed from a larger whole.  The sampling effect is on both pattern and process.   


12. The either/or dilemma under fixed resources and the bigger/many dilemma:  If resources are fixed, would we rather protect one large (fill in the blank with:  park, population) or several small (fill in the blank again: parks, populations) of the same total (fill in the blank: area, number of individuals)?  This debate has been defined by acronyms in a series of applications: 


SLOSS (“Single Large or Several Small”).  Given a fixed amount of land to conserve, should we conserve one large tract or several small tracts of the same total area? 


SLOPP (“Single Large or Plentifully Patchy”).  Given a fixed number of individuals to conserve, should we conserve one large population or several smaller populations of the same total number of individuals? 


FLOSS (“Few Large or Several Small”).  Given a fixed number of individuals to release, in order to reestablish a wild population or introduce a biocontrol agent, should we release all  individuals in one large release or should release several smaller sets of individuals across time or space?   


GLOSS (“Genetic Large or Several Small”).  Should we sample genetic diversity for a genebank from one large population, or should we sample the same number of individuals spread across several populations?  


In each case, we are asking, “what is the best conservation design?”, given that we have a fixed set of resources for executing our design.  For instance, if we can conserve 1000 acres, would we be better off with one tract of 1000 acres or 10 tracts of 100 acres or 100 tracts of 10 acres?  If we can conserve 1000 individuals, would we be better off with one population of 1000, 10 populations of 100, or 100 populations of 10?  The answer to these questions may seem obvious (isn’t bigger always better?) but hold your judgment.  There are situations when “many” is better!  And the science behind the advantages of “big” and “many” is fascinating and important for you to understand. 


Conservationists often find themselves trying to decide between alternative actions (like the big/many dilemma, but including many other choices).  Often this is because we can’t do BOTH alternatives, the underlying cause of which is that we don’t have enough time, money, or political will.  Sometimes it is better to increase the time, money, and political will, than accept the constraint that forces the choice.   


E. Time, space, and scale 


The last group contains three threads that treat the spatial and temporal patterns of biodiversity.  Processes within populations and ecosystems may be understandable from data collection at small scales of time and space.  For example, we could analyze population dynamics in a 10 by 10 meter plot over a single season.  Sometimes, locally measured phenomena don’t tell the whole story because there are legacies of past events or interactions over large spatial scales that are also important 


13. The two pillars of ecological explanation:  Ecologists generally explain why a species is where it is by referring either to (1) a niche-environment based explanation or (2) a dispersal-spatial configuration based explanation (Nekola and White 2001).  These two pillars have different implications for conservation.  The niche-environment pillar suggests that we need to get the environment (habitat quality) right and often means we need to select the largest conservation area with the best habitat quality.  The dispersal-spatial configuration pillar suggests that we need a network of multiple conservation areas (even if they have similar environments) and need to think about connectivity between these areas.  The two pillars argue that the underpinnings of conservation are the fields of ecology (to support habitat quality and ecosystem completeness and integrity) and geography (to support geographic uniqueness unrelated to environment).  We discuss ecological and geographical appropriateness when considering genetic diversity (including germplasm sources for restoration), species diversity, and ecosystem restoration. 


The two pillars suggest a contrast between space-free ecology vs. spatial constraint and universality vs. temporal constraint.  When can we measure a pattern or process without worrying about spatial position—and when does spatial position become as important as local ecological interactions?  Spatial constraint can be an obstacle to generalization because what we find is dependent on the spatial context rather than locally measurable attributes.  When is a pattern or process the result of interactions that are universal and independent of when in time they are measured?  When is what we observe the result of historical influences (that is, interactions that can no longer be measured)?  Temporal constraint can be an obstacle to generalization because what we find is dependent on temporal context (history) rather than locally measurable attributes.  Temporal constraint also leads to the notion of “set points” for such biodiversity features as genetic diversity, species diversity, and ecosystem function.  For instance, the amount of genetic diversity is not the same in all species and the amount of species diversity is not the same for all ecosystems…the conservation goal is not to maximize genetic or species diversity, but it to establish and manage for a unique set point for that species and ecosystem. 


One reason that a common phrase in conservation biology is that “it depends…” derives from the simple fact that the properties of nature are spatially and temporally contingent—the context in time and space matters. 


14.  History for history, history for continuity:  Conservation is often a response to the changes of the last 150 years—increases in the human population and increases in the impact per person (especially industrialization) have pushed species and ecosystems to the brink of loss.  Our target for restoration and the gold standard for the quality of natural areas is often informed by reference information from the past or from areas presumed to have very low human impact.  But what do we do with that information?  We could manage for that historic state, but environments change and those ecosystems and species populations may not even have been stable historically, let alone under the conditions of a different contemporary environment…to manage only for history borders on pure nostalgia.  Another way to conceptualize the value of history is to see historical states and less disturbed sites as the springboard for future change, so that our restoration is aimed at creating continuity with the past, rather than static preservation of the past.   


Thus, history can give us an important description of past conditions—and conditions of an ecosystem under different human impacts.  That is “history for history” and there are times when our goal is to restore historical conditions.  But we can also view the importance of the historical state, not just as setting a goal for conservation, but also as the describing the state from which potential future states emerge.  That is “history for continuity”. 


History is also important in the sense that species that have interacted for long periods have had their interactions shaped by coevolution.  We may not understand the details of this until some change has occurred, but we can conjecture that continuity of species interactions does embed this coevolution.  When we discuss invasive species we will discuss the coevolutionary hypothesis that a host and its specialized diseases come into a long term balance of increased resistance and decreased virulence and that the absence of that coevolutionary history explains the great susceptibility of species to introduced pests and diseases (coevolutionary balance is an hypothesis, though, and be wary of expecting it to apply in all cases). 


[Figure 2-1.  The components of scale: grain and extent.] 


15. Grain, extent, and scale dependence:  What we see in nature depends on the scale of the observations.  We will operationalize scale by talking repeatedly about its two components: Grain and Extent (Figure 2-1).  One of the dangers is that small spatial scales and the immediate present will dominate our thinking and our choices, when the larger scale and longer time perspective lead to different conclusions. 


Grain and extent arise repeatedly in conservation biology:  for example, in island biogeography, minimum dynamic area, genetic diversity, population viability, metapopulations, invasive species, disturbance ecology, ecological restoration, landscape ecology, and fragmentation.  I even see the importance of grain and extent in our search for a conservation ethic in Chapters 3 and 4! 




Conservation biology can be seen as a layer cake: genes, populations, metapopulations, ecosystems, and landscapes.  We can also cut this layer cake vertically—these are the threads that run through the chapters.  Using a tapestry as the image instead of the cake, I’ve called the cross-cutting themes the 15 threads of conservation biology.  They form a concept map for the book and they are critical to explaining what the answers to conservation dilemmas and problems depend on.  Let’s move forward and stay curious.  We return to the 15 threads at the end.