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The niche construction paradigm in ecological time
John Vandermeer
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, United States
a r t i c l e
i n f o
a b s t r a c t
Article history:
Niche construction has emerged as a central focus for a variety of phenomena that operate
Received 22 August 2007
over evolutionary time. Although its importance in ecological time cannot be denied, an
Received in revised form
analysis of expected ecological dynamics of the concept has not yet appeared in the liter-
4 March 2008
ature. Using the concepts of necessary and sufficient population, an equilibrium approach
Accepted 7 March 2008
to the phenomenon is developed. The equilibrium theory states that there is a balance
Published on line 15 April 2008
between the need for a certain population to maintain the constructed niche and the size
of the population that can be sustained by that niche.
Keywords:
© 2008 Elsevier B.V. All rights reserved.
Niche
Equilibrium
Population dynamics
A recent literature in evolutionary theory emphasizes the idea
of niche construction (Olden-Smee et al., 2004; Lewontin, 2001;
Silver and Di Paolo, 2006; Kerr et al., 1999), in which the convention of a distinct separation between organism and its
environment is challenged. Rather, it is argued, the organism
has a profound effect on the very environment that generates the selective pressure to which the population of the
organism responds with genetic change, thus effecting evolution. This point of view is recognized as a new, if perhaps
controversial, idea in evolutionary biology (Vandermeer, 2004).
Application of the idea at the level of evolutionary theory is,
at least conceptually, evident. However, if environments are
being constructed by organisms, there must be ecological consequences in addition to the evolutionary ones (Vandermeer,
2004; Hui et al., 2004; Donohue, 2005). The purpose of the
present communication is to explore that idea.
At a most general level it has long been appreciated that
organisms affect their environment, and that the affected
environment can thus have a reciprocal effect on other organisms, creating an environment different from what it would
have been before having been changed. For example, Goldberg
(1990) provided an important framework for understanding
competition between plant species by noting that competi-
E-mail address: [email protected].
0304-3800/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ecolmodel.2008.03.009
tion could be divided into response and effect competition—a
species “effects” changes in the environment to which another
species must “respond”. To put this insight into the framework of constructivism, species A constructs the environment
to which species B must respond. Similarly, the literature
on “ecosystem engineers” (Berkenbusch and Rowden, 2003;
Flecker, 1996; Jones et al., 1997) implicitly incorporates the
same idea, that some species alter the physical environment
to such an extent that others are profoundly affected. And all
species interactions from predation to competition to mutualism, ultimately, although perhaps trivially, fall into this same
general framework. Despite this long history of appreciation of
the topic, if only indirectly, a theoretical framework for studying niche construction in ecological time has not appeared
in the literature, at least not explicitly. I here propose such
a framework based on two simple ideas, first the “necessary” population and second, the “sustainable” population.
The approach is only intraspecific, although implications for
interspecific applications (as in the examples in this paragraph) are obvious.
First, consider the concept of the necessary population.
Suppose that a given niche form is dictated by some critical factor—for example, the amount of fine leaf matter in a
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e c o l o g i c a l m o d e l l i n g 2 1 4 ( 2 0 0 8 ) 385–390
forest understory. As an artificial example consider a species
of milliped that on the one hand shreds leaves in the course
of eating, but, on the other hand, requires a bed of finely
shredded leaves for oviposition. Thus, the initial shredding
of leaves constructs a favorable environment for egg laying.
Since leaves are continually falling, it is necessary to continue
processing them to maintain a particular mixture of shredded
and non-shredded leaf material. Theoretically, if one knew the
rate at which leaves were falling, and the rate of shredding
which converts the leaves to fine matter, one could calculate
the number of millipeds necessary to maintain some particular fraction of fine leaf material in the leaf litter. This is the
first critical idea—the “necessary population”. It is the number
of individuals necessary to maintain a particular constructed
niche.
Second, consider the concept of the sustainable population. The niche affects the organism and effectively dictates
how many individuals can be sustained at a given level of
constructed niche. This number is the sustainable population.
Thus, for example, if the fine leaf matter in the above example
is only a small percentage of the total, the sustainable population of the millipeds will be very low, since oviposition sites
will be limited. If the fine organic matter is a high fraction, the
sustainable population of the millipeds will be very high.
1.
The equilibrium theory of constructivism
The relationship between the necessary and sustainable populations defines a clear dynamic for the population and its
niche. This dynamic is illustrated graphically in Fig. 1a. Consider a population that is located at N* with a niche of E* , in
Fig. 1a. That population will be above its sustainable level and
thus must decrease. However, that population will be below
the necessary population, which is to say, the population density necessary to maintain the niche level at E* , and thus the
niche level itself must decline. Following this reasoning for
the rest of the possible states of N and E, we see the overall dynamic behavior as illustrated in Fig. 1a, wherein any
population/niche combination will eventually come to lie at
the intersection of the two lines representing the necessary
and sustainable populations, indicated with a solid dot in the
figure.
If the relationship between the sustainable and necessary
functions is reversed (Fig. 1b), the dynamic reverses itself and
the intersection of the two functions becomes an unstable
point. Thus, any combination of N and E will result in either
the extinction of the population or a continuously increasing
population and niche. The latter is obviously impossible in the
real world, so some constraining force must be involved, as
discussed below. However, the basic principle of either a stable or unstable relationship between N and E is clear at this
level of abstraction.
Two categories of non-linearities are likely to be involved
in this formulation. First, it is most likely that increases in
the necessary population at high levels of niche will increase
more dramatically than at low levels, which is to say that it is
impossible to increase niches without limit. Second, it is likely
that increases in sustainable levels will saturate at high levels
of niche. Given these two likely non-linearities, we obtain the
Fig. 1 – Basic relationship between sustainable and
necessary population as a function of the ecological niche.
Fig. 2 – Incorporating non-linearities in the basic unstable
situation of construction dynamics.
picture illustrated in Fig. 2. The basic pattern, then, from a
constructivist approach is that a population may either form a
globally stable situation (Fig. 1a), or it may form a bistable case
with a higher stable state for both N and E, and a zero state for
either N or E (Fig. 2). Thus, we see the generation of an Allee
effect, where a critical population density is necessary (along
with a critical niche) for the population to be successful.
2.
Exploring the dynamics of
constructivism
The above equilibrium approach is a first approximation presented largely for heuristic purposes. Here a more analytical
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e c o l o g i c a l m o d e l l i n g 2 1 4 ( 2 0 0 8 ) 385–390
avenue is explored. In devising a dynamic framework we
immediately face the fundamental question of facultative versus obligate construction. In a facultative constructive niche
the organism survives even in the absence of niche construction, nevertheless benefits further from the construction. In an
obligate constructive niche the organism dies in the absence of
construction. Similarly, a facultative organism survives even
in a non-constructive niche, but benefits further from the
construction, whereas an obligate organism does not survive
unless a constructed niche becomes available. Given this formulation there are four distinct cases to be considered, based
on the orthogonal classification of facultative versus obligate
niche crossed with facultative versus obligate organism. The
following more analytical development will clarify these ideas.
Let the dynamics of the population be represented by the
coupled equations,
dN
(K + kE − N)
= rN
dt
K + kE
(1a)
dE
= aN + m − bE
dt
(1b)
where the basic formulation for the organism is the logistic
equation, with K as the carrying capacity, r the intrinsic rate of
natural increase, k the conversion factor with which the environmental measure (E) is converted to organism equivalents,
a the rate of niche construction (the amount of E produced
by an individual organism), m the inherent production of E
(independent of the organism) and b the rate of decay of the
niche.
Isoclines are,
N = K + kE
N=
b
m
E− .
a
a
Both K and r may be either positive or negative, imposing a
facilitative/obligate dichotomy on both the niche and population dimension. Based on these two dichotomies, a four-fold
classification results, as mentioned above and as presented in
Table 1.
The equilibrium solutions for each of these four cases are
elementary and are displayed graphically in Fig. 3. In Fig. 3 are
the four qualitatively distinct outcomes for both homotypic
(either both facilitative or both obligate) cases. In the facilitative homotypic case (Fig. 3a) the system either moves toward
a stable equilibrium point or increases without limit, much
like the simple case presented in Section 1. In the obligate
homotypic case (Fig. 3b) the system either declines to zero
Fig. 3 – The four distinct homotypic cases. Isoclines for
niche dynamics bold, for population dynamics regular.
or has an Allee effect in which a minimum population number and niche quantity is required for a successful population,
but if successful, the population increases without limit. In
Fig. 4 are the four qualitatively distinct outcomes for each of
the two heterotypic cases (i.e., either niche obligate and consumer facilitative or consumer obligate and niche facilitative).
Basically four qualitatively distinct outcomes are observed for
each of the two heterotypic cases—(1) an Allee effect with ever
increasing population and niche at higher values, (2) a stable equilibrium point, (3) decomposition of the system, and (4)
increasing without limit. These outcomes, in both Figs. 3 and 4,
are equivalent, with complications, to the graphical equilibrium theory presented in Section 1.
The niche construction framework is reminiscent of earlier suggestions, such as the “community effect” (the effect
of all species on the species of concern) versus the “species
effect” (the effect of that species on all the other species)
(Vandermeer, 1972) or the response and effect framework
Table 1 – The four distinct cases of niche construction based on facultative versus obligate relationships
K≤0
K>0
m≤0
Obligate organism
Obligate niche construction
Facultative organism
Obligate niche construction
m>0
Obligate organism
Facultative niche construction
Facultative organism
Facultative niche construction
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e c o l o g i c a l m o d e l l i n g 2 1 4 ( 2 0 0 8 ) 385–390
Fig. 4 – The two heterotypic cases. Isoclines for niche dynamics bold, for population dynamics normal.
(Goldberg, 1990), both of which were designed to apply to
the situation of interspecific competition. However, with the
constructivist framework presented here, such dichotomous
schema are relevant also to a single population. That is, the
population has an “effect” on its niche and must “respond”
to that niche. Given this framework, the parameters a and
k take on the meanings of effect and response, respectively. All the various cases in Figs. 3 and 4 can thus be
interpreted as stemming from particular balances between
the obligate/facilitative dichotomy and the effect/response
dichotomy. However, the tacit assumption made thus far is
that the effect on the niche is a positive one, corresponding
to the use of the word “constructive”. Casting the problem in
terms of an organism’s “effect” on its niche, it is clear that
the effect could be either positive or negative, indeed is usually thought to be negative in the context of competition.
Thus, it makes sense to relax the assumption that parameter a must be positive. If parameter a is negative, the isocline
of the niche dynamics has a negative slope and all cases
that include an obligate niche become uninteresting. Only
with a facilitative niche can there be a solution in the positive quadrant [i.e., if (K/k) < (m/b)], and that solution must be
oscillatory, indeed it must be a stable focus, as illustrated in
Fig. 5.
Fig. 5 – The two distinct cases of niche “destruction”.
e c o l o g i c a l m o d e l l i n g 2 1 4 ( 2 0 0 8 ) 385–390
Fig. 6 – Obligate population and facilitative niche in the
context of a construction/destruction switch as a function
of population density (i.e., a system composed of Eq. (1a)
and Eq. (2)).
With the strictly linear approach of system 1, we are
forced into a choice between niche construction (a > 0) or niche
“destruction” (a < 0). More likely is the case in which a small
population will engage in niche construction but a larger population be characterized by niche destruction, in which case
the parameter a will be a decreasing function of N. Thus, equation (1b) becomes,
dE
= (f − gN)N + m − bE
dt
(2)
with isocline,
E=
1
(fN − gN2 + m)
b
which is curvilinear and represents one solution to the continuously expanding populations in various cases of Figs. 2–4,
as illustrated in Fig. 6 (compare with Fig. 2).
3.
Discussion
The concept of niche construction, while gaining influence in
evolutionary biology, has hardly been mentioned in its ecological time frame, even though concepts such as response/effect
(Goldberg, 1990), or community/species effect (Vandermeer,
1972), or ecological engineering (Berkenbusch and Rowden,
2003; Flecker, 1996; Jones et al., 1997) are very closely related
to the general idea. Yet one would be hard-pressed to find an
ecologist that would deny the importance of the phenomenon.
Here, the idea is developed in very general terms, proposing that the niche construction itself will be of a density
dependent form, and thus there will be a certain popula-
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tion density that will be necessary to maintain the niche at
a particular level, what is termed the “necessary” population. And, the parallel idea is that the population responds
to the constructed niche, reaching a sustainable level but
not beyond. Thus, the two key ideas are the necessary population and the sustainable population. Casting these two
ideas in dynamic relationship to one another, we arrive at a
simple equilibrium framework for studying their equilibrium
properties.
The overall qualitative dynamics that naturally emerge
(Figs. 1 and 2) are reflected in the more analytical approach
(Figs. 3–6), with some added complications. Namely, it will
obviously be the case that some niche construction simply
adds to a population’s well-being, in which case that population can be said to respond to niche construction in a
facultative way, while other niche construction will be clearly
necessary for the survival of the species, in which case that
population is obliged to construct its niche. This is similar to
the facultative/obligate dichotomy well-known in mutualisms
(Vandermeer and Boucher, 1978). However, the niche itself is
subject to the same analysis. Some niche measures simply
exist in the absence of any constructive activity of the population and thus are facultatively increased by the population,
others do not exist at all in the absence of the population, and
are thus obligate.
Not explicitly treated in the current paper, yet certainly
important in a more general formulation of the niche construction idea is its application at an interspecific level. Indeed,
conceptual frameworks such as the response/effect competition framework of Goldberg (1990) are by nature interspecific
and conceptually fall within the same sort of framework. The
“effect” competition is essentially a negative niche construction. Ecological engineering by one species to the benefit of
another would also fall within this general framework. While
a treatment of this interspecific effect is certainly warranted,
it is beyond the intended scope of the present paper, even
though the initial motivating examples were actually interspecific.
There also exists an evident case of niche construction that
cannot really be included in the present formulation, that in
which an individual manufactures some aspect of its own
niche that has relatively no effect on other individuals of the
population. Nests, burrows and webs, for example, are clearly
examples of constructed environments, but they do not translate into population-level density dependent effects and are
more akin to other individual traits such as skin color, toxicity or flight ability. The current theoretical formulation is
not intended to incorporate such individual-level constructive
activities.
Furthermore, while niches are constructed by organisms,
they are also “destructed” by organisms. There is thus an evident dichotomy in which niche destruction parallels niche
construction. While niche destruction has been taken as a
foundation of competition theory, it is rarely considered as
happening within the same population. Here, the idea of a
continuum of niche destruction to niche construction, based
on the population density of the population is presented. A
key non-linearity emerges from such a consideration (Fig. 6),
that provides a mechanistic basis for the obviously necessary
control of the population at higher densities.
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e c o l o g i c a l m o d e l l i n g 2 1 4 ( 2 0 0 8 ) 385–390
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