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!
Synthesis
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.