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Function in ecology: an organizational approach1

Nei Nunes-Neto

Address: History, Philosophy, and Biology Teaching Lab, Department of General

Biology, Institute of Biology, Federal University of Bahia. Rua Barão de Jeremoabo,

s/n, 40170-115, Campus Universitário de Ondina, Salvador, Brazil.

Email: nunesneto@gmail.com. Phone number: 00 55 71 88227238.

Fax number: 00 55 71 33627885.

Alvaro Moreno

Address: IAS-Research Centre for Life, Mind and Society, Department of Logic and

Philosophy of Science, University of the Basque Country, Avda. Tolosa 70, 20080,

Donostia - San Sebastián, Spain.

Charbel N. El-Hani

Address: History, Philosophy, and Biology Teaching Lab, Department of General

Biology, Institute of Biology, Federal University of Bahia. Rua Barão de Jeremoabo,

s/n, 40170-115, Campus Universitário de Ondina, Salvador, Brazil.

1 This is a pre-published version of the following paper:

Nunes-Neto, N.F.; Moreno, M.; El-Hani, C.N. (2014). Function in ecology: an organizational approach

Biology & Philosophy 29 (1), 123-141. DOI: 10.1007/s10539-013-9398-7

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Function in ecology: an organizational approach

Abstract Functional language is ubiquitous in ecology, mainly in the researches about

biodiversity and ecosystem function. However, it has not been adequately investigated

by ecologists or philosophers of ecology. In the contemporary philosophy of ecology we

can recognize a kind of implicit consensus about this issue: while the etiological

approaches cannot offer a good concept of function in ecology, Cummins’ systemic

approach can. Here we propose to go beyond this implicit consensus, because we think

these approaches are not adequate for ecology. We argue that a sound epistemological

framework to function in ecology is to be found in organizational approaches. In this

line, we define function in ecology as a precise effect of a given constraint on the

ecosystem flow of matter and energy performed by a given item of biodiversity, within

a closure of constraints. We elaborate on this definition by developing a case study of a

bromeliad ecosystem.

Keywords Function. Ecosystem. Biodiversity. BEF. Constraints. Organization

Introduction

Functional language is both ubiquitous and central in contemporary ecology,

mainly in the context of the research program on Biodiversity and Ecosystem Function

(BEF), which emerged in the 1990s amidst a growing social recognition of the

biodiversity crisis (Naeem 2002). Nevertheless, in spite of this strong presence, the

functional language has not been adequately investigated in ecology.

On the one hand, many ecologists seem simply to take the concept of function

for granted, regarding it as self-evident (as we find, for instance, in Díaz and Cabido

2001; Petchey and Gaston 2006; Nadrowski et al. 2010). However, this concept is far

from trivial.

On the other hand, few works in the philosophy of science has shown a special

interest in the epistemological problems associated to functional language in ecology

(Jax 2005; Almeida and El-Hani 2006; Sterelny 2006; Maclaurin and Sterelny 2008;

Caponi 2010; Nunes-Neto and El-Hani 2011). This becomes particularly clear when we

take into consideration the attention given to functional or teleological language in the

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philosophy of evolutionary biology, for instance, where the issue is much more

discussed (Allen et al. 1998; Ariew et al. 2002; Ayala and Arp 2010).

In the contemporary philosophical domain, we can recognize a kind of implicit

consensus (see, for instance, Almeida and El-Hani 2006; Sterelny 2006; Maclaurin and

Sterelny 2008; Caponi 2010; Nunes-Neto and El-Hani 2006, 2011) concerning

functional language in ecology, which can be put in the following terms: the etiological

approaches (e.g., Wright 1998[1973]) cannot offer an adequate concept of function for

ecology because they are strongly linked to a selectionist perspective and, consequently,

it would be necessary to adopt the idea of natural selection acting on ecological entities

above the population level in order to ascribe function. Nevertheless, the idea that

selection can act on species, guilds, functional groups or communities is still very

controversial in biology or in its philosophy. The selectionism of the etiological

approaches, as well as other problems related to them, well known in the literature (see,

for instance, Cummins 2002), seems to undermine an etiological concept of ecological

function. As a consequence, some authors suggested that an epistemological ground to

function in ecology is to be found in Cummins (1998[1975]) systemic approach,

because when explaining and ascribing function this approach is not committed to the

historical – and, more specifically, selectionist – assumptions that undermine the

application of the etiological one (Almeida and El-Hani 2006; Maclaurin and Sterelny

2008; Caponi 2010; Nunes-Neto and El-Hani 2006, 2011). However, as far as we know,

no fully-fledged systemic approach to ecological functions is found in the literature,

and, thus, those works simply propose a direct application of Cummins’ approach

without evaluating – among other important aspects – the limitations of his functional

analysis for ecology. This is the point where the contemporary literature stops.

In this paper we intend to move beyond this implicit consensus, through the

proposal of an epistemological framework to ground in a consistent way the concept of

function in contemporary ecology. To reach this goal our argumentative path will be the

following. In section “Function in the ecological literature” we will briefly describe

what we see as the main uses of the concept of function in the literature of the BEF.

This will be important in order to fix precisely the use of the concept we propose to

ground in our philosophical work. In section “The organizational approach of biological

functions” we will briefly present this approach, which we see as more appropriate than

the etiological or the systemic approaches for ecology. In section “Towards an

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organizational framework of ecological”, then, we will propose one possible general

framework to function in ecology and apply it to a model ecosystem, by developing a

case study of a bromeliad ecosystem. Finally, in section “A possible objection: how is

this approach more adequate than a Cummins’ systemic approach to function in

ecology?” we will present a possible objection to our framework, which will lead to our

concluding remarks, in section “Final Remarks”.

Function in the ecological literature

Although important in ecology since the beginnings of the 20th

century (see, for

instance, Clements 2000[1916]), the concept of function has received increasing

attention in this science since the beginnings of the 1990s, in the context of the BEF.

Since then, the concept of function has been used in a loose way (as supported by

Petchey and Gaston 2006), that is, most of the papers (e.g., Lavorel and Garnier 2002;

Nadrowski et al. 2010), although strongly relying on a functional language, simply do

not define function.

In this research program – although in a somewhat implicit way – function plays

the role of a conceptual bridge between community ecology and ecosystem ecology,

two important but historically separated – in methods, concepts and ontology –

traditions of ecology. While community ecology is more focused on objects such as the

identity, variety, distribution and interactions of organisms, ecosystem ecology puts

more emphasis on the flow of matter and energy in the ecological systems (O’Neill et

al. 1986; Allen and Hoekstra 1992; Pickett et al. 2007).

Function plays an integrative role here because the ascription of function to the

biodiversity or to its components (such as the traits, populations, functional groups, etc.)

aims at explaining the maintenance of ecosystem properties (nutrient cycling, primary

productivity, etc.). To put it differently, the BEF recognizes that there is some

functional action of the objects of community ecology on the flow of matter and energy,

the object of ecosystem ecology. In this context, to consistently ground function in

ecology can contribute to the work of theoretical integration, which, by its turn, is

important to improve understanding and model building in this science (see Pickett et

al. 2007).

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We recognize three main uses of this concept in the BEF, each associated to

some item of functional ascription (ecosystem, biodiversity and components of

biodiversity). Let us examine in more detail these uses of the concept.2

The first mentioned use of function in the BEF is more directly linked to the

operation or dynamics of the ecosystem. For instance, Naeem (2002: 1539, emphases

added) states that: “… physical and chemical conditions of the environment are

increasingly recognized as driven, at least in part, by ecosystem function (e.g., nutrient

cycling and energy flow)”. Notice that in the exemplification of ecosystem function

through the reference to nutrient cycling and energy flow – which are phenomena at the

ecosystem level – Naeem makes it clear that he is not talking about functions in (or

inside) ecosystems, that is, activities of the biota or the organisms in separate, but rather

to activities at a different level of organization, which includes the biota as part.

In the second use of function in the BEF, biodiversity itself – that is, variety

(frequently measured as the diversity of genes, traits or species [Cardinale et al. 2012])

– plays a significant functional role on the dynamics of the ecosystem (nutrient cycling,

primary productivity, etc.). In this case, studies normally compare, in experimental

treatments, sites with low and high diversity, focusing on differences of the influence of

the latter on the ecosystem dynamics between those two situations. It is a strong thesis

of the BEF, highly supported along the last 20 years of research, that a high level of

biodiversity positively influences ecosystem dynamics (Altieri 1999; Mace et al. 2012;

Cardinale et al. 2012).3

The third, closely related to the second, use suggests that it is not biodiversity

itself, but instead the components of biodiversity (the entities or activities which are

biodiverse) that are the functional units in the ecosystem context. This use of the

concept of function will be our object in this paper. For the sake of the presentation of

our object here, this yet crude idea is enough. Below, in the context of the articulation of

our general framework and in the development of the application to a model ecosystem,

this idea will be more precisely elaborated.

2 We cannot elaborate too much about the issue of the use of function by ecologists here. We have done

this in another paper, which we recommend to the interested reader (see Nunes-Neto et al. 2013). 3 We must notice that there is a problem in assuming that biodiversity (which corresponds to variety) is

the functional entity: variety is something inferred (an unobservable) from the observation of the entities

that vary and, as a consequence, its status as a cause can be put into question. The same does not seem to

happen in the case of the components of biodiversity, which are observable entities.

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The organizational approach of biological functions

The organizational approaches constitute a group of philosophical accounts that

originated at the end of the 1990s with the goal of synthesizing in one framework the

two older, well established traditions in the treatment of function in the philosophy of

biology, namely, the etiological and systemic approaches (Schlosser 1998; Collier 2006;

Mossio et al. 2009; Saborido et al. 2011). The basic idea of the organizational

approaches is that functional ascriptions account for the explananda of both etiological

and systemic approaches. On the one hand, the organizational approaches explain the

existence of the items of functional ascription and, on the other, a systemic capacity to

which the function of this same item (a part of the system) contributes to. Here we will

focus only on the organizational approach proposed by Moreno, Mossio and Saborido

(see Mossio et al. 2009; Mossio and Moreno 2010; Saborido et al. 2011), since we are

particularly interested in the contribution of its distinction between two kinds of closure

– closure of constraints and closure of processes – to our proposal of a framework for

function in ecology. For the sake of simplicity we will hereafter refer to it simply as the

organizational approach, but this does not mean that this is the only or main

organizational approach or that a consistent ground for function in ecology could not be

developed based on other organizational approaches, or even on a non-organizational

one. In this paper, we are interested, however, in ascertaining the consequences of this

organizational approach to an interpretation of function in ecology.

For Mossio and colleagues, a trait T has a function in the organization O of a

system S if and only if:

C1: T contributes to the maintenance of the organization O of S;

C2: T is produced and maintained under some constraints exerted by O;

C3: S is organizationally differentiated (Mossio et al. 2009: 828)

While C1 and C2 constitute the general conditions of organizational closure, in a

loop between T and O, C3 is a condition for organizational differentiation. An example

can illustrate this definition. First, concerning organizational closure, notice that the

pumping of blood by the heart (its function) is a contribution to the maintenance of the

organization O of the organism, because it enables, for instance, the distribution of

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nutrients throughout the body. Moreover, the heart is produced and maintained by the

very organization of the body (which includes all other organs), whose integrity is

required to the existence of the heart. Concerning organizational differentiation, in turn,

the functional contribution of the heart in the organism is precise or differentiated, in the

sense that it is not conflated with the functional contributions of other organs (e.g., liver

or lungs) which are also necessary to the maintenance of the organization of the system

as a whole (for more details, see Mossio et al. 2009; Saborido et al. 2011).

Since, generally speaking, the organizational approach aims at overcoming

persistent problems in the more traditional perspectives on function, it can be

appropriately presented through a comparison with the etiological and systemic ones.

For this, we will consider the problem of the norms of the functional ascriptions.

The etiological approaches offer a clear answer to the problem of the normativity of

functional ascriptions, that is, the problem of the criteria against which one can evaluate

the norm a given trait should follow in order to be functional, so that one can separate

its functional from its accidental effects. The norm in this case is the right kind of

selective history. That is, what the trait should do is that for which it was selected for, in

its evolutionary history. Although this is a clear norm, it faces the problem of

selectionism. Natural selection is not the only important factor in the generation and

spread of biological traits. Frequently, other factors, such as genetic drift, changes in

developmental trajectories, developmental constraints, play more important roles than

natural selection in the generation and spread of traits. In sum, important problems with

the etiological approaches are related to the kind of norm appealed to and to the neglect

of other important norms to the generation and spread of traits.4

The organizational approach, in turn, seeks to overcome this problem through

the proposal of a different interpretation (inspired in Kant’s Third Critique; see Mossio

and Moreno 2010: 275) for the causal loop present in Wright’s formula. That is, while

from an etiological point of view function explains the existence (Wright 1998[1973])

or the current evolutionary maintenance (Godfrey-Smith 1998[1994]) of a functional

4 The changes caused by these factors can be seen as functional, but only through a non-historical

perspective, such as Cummins’ (1998[1975]). They cannot be functional from an etiological perspective.

Anyway, the central point here is that the origin and spread of traits can happen because of other

evolutionary factors, not only selection (Cummins 2002; Nunes-Neto and El-Hani 2011). Then, since the

traits originate and spread not only by natural selection, we cannot appeal always to the etiological

function as an explanation.

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item based on natural selection, in the organizational approach the existence of the item

is explained through the current organization in which it is embedded. This grounding

is performed by the first two elements of the definition of function in the organizational

approach, both constituting the condition of organizational closure. According to

Mossio and colleagues,

organizational closure justifies explaining the existence of a process by referring

to its effects: a process is subject to closure in a self-maintaining system when it

contributes to the maintenance of some of the conditions required for its own

existence. In this sense, organizational closure provides a naturalized grounding

for a teleological dimension: to the question ‘Why does X exist in that class of

systems?’, it is legitimate to answer ‘Because it does Y’. (Mossio et al. 2009:

825)

As an example, we can ground in different terms the following causal loop

applied to the heart: the heart is there because it pumps blood and pumping blood is a

consequence of the heart being there. Now, without any commitment to a selective

history we can appeal to an effect of the heart, say, pumping blood, in order to explain

its existence. The pumping of blood allows a series of other effects in the current

organization of the organism, such as the distribution of nutrients, the gas exchanges,

etc., in such a way that these conditions enable the very maintenance of the heart by the

organism. In contrast with etiological approaches, Cummins’ systemic approach does

not ground the normativity of the functional ascriptions. Because of its under-

specification of what a function should be, we can say that this systemic approach

proposes an excessively broad norm, which applies even to counterintuitive cases

(Wouters 2005), as we will see in more details below.

Constraints and closure of constraints

The idea of closure express that a sequence of processes forms a causal loop.

And here it is important to distinguish between closure of processes and closure of

constraints.

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Some purely physical or chemical systems are characterized by a closure of

processes, where one process influences another in a circular way. For instance,

consider the hydrologic cycle in prebiotic Earth. In simple terms, here, a set of

processes generates, under certain boundary conditions, a cycle of causal relations in

which each of these processes contributes to the maintenance of the whole, and is, in

turn, maintained by the whole: the sun evaporates the water of a lake, forming clouds.

When rising at higher levels these clouds get colder and generate rain; the rain, in turn,

contributes to generate a spring, which gives rise to a river, which contributes to

generate a lake, which regenerates clouds and so on.5

Closure of constraints, however, is a specific mode of dependence between a set

of constraints, in which a system that produces some of the constraints harnessing its

underlying dynamics realizes closure. This means that not only the constrained

processes form a causal loop, but that this loop is achieved because the constraints

generated in the system influence each other so as to achieve closure. In formal terms, a

set of constraints C realises closure if, for each constraint Ci belonging to C, (i) Ci

depends directly on at least one other constraint of C (Ci is dependent) and (ii) there is at

least one other constraint Cj belonging to C which depends on Ci. For instance, a living

cell is maintained because of the constraining action of constraints like enzymes and

membranes, which harness chemical reactions inside the cell in a cyclic way. But, in

turn, each of these constraints contributes to the generation (and re-generation) of the

other constraints.

More specifically, very often the action of an enzyme allows a particular

chemical reaction to happen (or at least to be performed in a rate that is adequate to the

self-maintenance of the cellular system). Then, in a loop, the enzyme and its

constraining action are necessary conditions to the result of the reaction. This result, in

turn, is a necessary condition to the production and maintenance of adequate

concentrations of the enzyme itself, because the result of the reaction generates a

cascade of products (such as other enzymes) that will act on the very production of the

mentioned enzyme. In other words, there is a closure in this system made possible by

the constraints, and the result of the adequate action of these constraints is the

instantiation of functions.

5 Other examples can be find in Mars’ cycle of CO2 (Centler and Dittrich 2007) or in Titan’s cycle of

methane (Lunine and Hörst 2011).

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It is worth noticing that closure of constraints is not synonymous with

homeostasis. The notion of homeostasis implies that the organization of the system is

maintained by homeostatic mechanisms, which are not necessarily produced by the

system itself; instead, the idea of closure of constraints means that the system is

maintained by constraints generated by the very organization of the system. In sum, the

notion of closure of constraints is a more detailed representation (or elaboration) of self-

maintenance than homeostasis.

Constraints are particularly important in integrated systems (Bechtel and

Richardson 2010). In these systems, the organization of the whole is significantly

involved in the determination of the constituent functions (Bechtel and Richardson

2010: 26). Integrated systems are minimally decomposable systems (Simon 1981) in the

sense that they cannot be adequately understood only through reference to the

decomposition of the system into component parts and the concomitant ascription of

functions to the parts. In other words, in these systems the functions of the parts are less

governed by their respective intrinsic properties and more by the embedment of the

components in a complex and integrated organization. Ecological systems can be

included in this category.

In integrated systems, constraints can be conceived, then, as changing the

dynamics, distribution, and magnitude of the parts of the system and their interactions

due to their embedment in the system itself, in which different entities play a general

constraining role. Due to a multinested series of constraints on the possible interactions

of the system’s components (Emmeche et al. 2000), these components have a much

more ordered distribution in spacetime than they would have in its absence, and the

behavior of the system itself is constrained to a particular region of its space of possible

states (e.g., Emmeche et al. 2000; El-Hani and Emmeche 2000).6

As we will see in our example below in more details, the distribution and

biogeochemical pathways of the nutrients in self-maintained ecosystems are ordered

6 It is important to build a distinction concerning two possible ways of understanding constraint, which

are related to the hierarchical frame into which they are embedded: (i) in a nested hierarchy, constraint is

a whole-part relationship: it is a restriction of the whole system organization on the component parts of

the system and (ii) in a control hierarchy, constraint is a restriction from higher-level entities on lower-

level ones, but the higher-level entities do not necessarily contain the lower-level ones. The general

framework and the case presented here follow this second interpretation of constraint, although it could

also be further interpreted according to the first one.

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because of the constraining actions of the organisms on these nutrients. This is related to

a central idea in our arguments, namely that a constraint reduces the degrees of freedom

of the processes in an integrated system. To put it differently, there is a “selective

activation of lower-level causal processes by higher-level boundary conditions” (van

Gulick 1993: 268), that is, the probability that a given lower-level causal process is

instantiated is affected by the harnessing action of the constraints. A similar idea was

advanced much earlier by Pattee (1972: 377), according to which, a general problem of

theoretical biology is “to explain the origin and operation (including the reliability and

persistence) of the hierarchical constraints which harness matter to perform coherent

functions”. Consequently, only one or a few of all the possibilities of interactions

among the constrained processes get instantiated within its integrated organization, and

it is also because of this constraining action that the system as a whole is able to

maintain its own stability or organization.

Towards an organizational framework of ecological functions

A general proposal

The organizational approach (as virtually any approach to function in the

philosophy of biology) was initially designed to account only for organismic functions.

Actually these are the paradigmatic cases of functional ascriptions and naturally became

the focus of primary philosophical attention. However, as Saborido and colleagues

(2011: 597) pointed out, the organizational approach could possibly be extended to

ecosystems. Given this background, a first, tentative definition of function in ecology7

could be put in the following terms:

An ecological function is a precise (differentiated) effect of a given constraining

action on the flow of matter and energy (process) performed by a given item of

biodiversity, in an ecosystem closure of constraints.

7 Our definition here converges with the theoretical perspective of O’Neill and colleagues (1986), Allen

and Hoekstra (1992) and Ulanowicz (2000). However, in spite of this convergence, we should point that,

these authors did not explicitly intend to develop an approach to function for ecology, and much less they

take into account the concept of organizational closure of constraints, which is crucial in ecological

systems, in our understanding.

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Now we need to explain the main components in this definition: (i) the flow of

matter and energy (process) and the items of biodiversity entangled in the closure of

constraints of the ecosystem; and (ii) the notion that the function is a precise,

differentiated effect.

The ecosystem closure of constraints: items of biodiversity harnessing the flow of matter

and energy in the ecosystem

In our definition, function is embedded in a control hierarchy, with two levels:

the level of the items of biodiversity which constrain the flow of matter and energy, and

the level of the flow of matter and energy itself, to which we refer here as processes. We

can ascertain what level is lower and what is higher by considering the frequency of

behavior of the entities at each level. Parts behave at a higher frequency than wholes,

what happens also in the relationship between different entities in a control hierarchy. In

fact, this is one of the reasons why nested or control hierarchies are established (Ahl and

Allen 1996: 101). In the levels we are considering here, the flow of matter and energy

shows a frequency of behavior that is higher than that of the items of biodiversity, as we

will see along this section.

These levels are entangled, but we can describe them separately for the sake of

clarity. Let us begin by considering the flow of matter and energy, that is, the process.

For the sake of the argument we need to restrict the process, from now on, to the flow of

matter only.8 And by matter we will mean the atoms of carbon, nitrogen, phosphorus,

sulphur, etc. (that is, the essential elements to the biological metabolism), which can be

followed through radioactive methods in an ecosystem, just as biochemists follow

radioactive atoms or substances in the cell (Allen and Hoekstra 1992). Although the

atoms of these elements obviously exist (in the Earth’s reservoirs, such as the

atmosphere, the oceans, the soils, etc.) without the constraining role of biological or

ecological entities (notice that prebiotic Earth’s atmosphere already contained these

elements), the specific flow that recycles matter, in current ecosystems, is very much

dependent on these biological or ecological entities. In other words, the level of the

processes – after the appearance of life on Earth – should not be understood as a level of

8 Nevertheless, we think that our approach can account also for the flow of energy in the ecosystem. We

think, however, that to consider the energy now would make our analysis much more complicated.

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merely physicochemical events; they are instead metabolically or ecologically generated

flows. These flows simply would not exist as such if there were not the biological or

ecological entities, which perform a constraining action on them (Wilkinson 2006). This

suggests something about the constraining role of life on flows of matter. To use our

terminology, the items of biodiversity harness (constrain) the matter in the ecosystem in

a way that the coordinated action of all these items makes ecosystem properties

possible, such as the adequate cycling of the main elements.

We use a very broad definition of “items of biodiversity”. Something is an item

of biodiversity if it is a biological entity or activity directly relevant for the maintenance

of an ecosystem, by actively participating in, at least, one constraining action within this

same ecosystem. For us, the concept includes in its domain (sensu Pickett et al. 2007)

the following items: morphological or physiological traits, organisms, populations,

species and functional groups. Although a clear definition of this domain is yet an open

issue for ecology, these seem to be the most important functional units in the BEF.9

Such a broad class of items of biodiversity implies that we need pragmatic

considerations in order to make use of this concept in a meaningful way. The context of

research, including the specific research question, the explanandum and the biome being

studied, all together determine the item(s) of biodiversity participating in the

explanation. Let us briefly examine some examples. In spite of the limitation of the

concept of species diversity (Tilman and Lehman 2002), species (or better: populations

of a given species) can be good candidates for items of biodiversity. For instance,

generally speaking, in species-poor environments, such as tundras and hotsprings, or in

environments with keystone species (O’Neill et al. 1986: 207), the ecological role of an

individual population of a given species is crucial to the dynamics or operation of the

whole ecosystem, since no functionally equivalent population of another species is

likely to be present. In these cases it makes sense to assume that the species or the

populations of a given species are items of biodiversity. In turn, when seeking to

explain the decomposition of organic matter in megadiverse environments, such as the

soil of a tropical rainforest, the species or the populations of a given species are not

good loci for the functional ascriptions, since there is high functional redundancy. The

9 For the heterogeneity of ecological entities that can be functional see, for instance, Díaz and Cabido

(2001), Lavorel and Garnier (2002), Nadrowski et al. (2010), Mace et al. (2012) and Cardinale et al.

(2012).

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existence of functional redundancy requires that we look at a higher level, particularly

to the functional groups (Brussaard et al. 2007).

Function is a precise, differentiated effect of the constraint

Let’s begin to show this point with a simple case. The enzyme DMSP-lyase in

marine algae metabolism is specific to the conversion of DMSP into DMS, a relevant

component of the sulphur cycle; that is, this conversion cannot be done by other

enzyme, say, malate dehydrogenase, which, in turn, participates in the oxidation of

malate to oxaloacetate, as part of the Krebs cycle, in the biochemical process of

respiration. That is, the two enzymes are part of different, specific organizational

patterns, even if they occur in the same organism (e.g., the algae cell). At the same time,

both are general: while the class of the DMSP-lyase can act on all marine algae, the

class of the malate dehydrogenase is a broader one, operating in all organisms

exhibiting the Krebs cycle.

This means that, in general, each constraint is specific to the particular

interaction between the constrainer and the constrained. We have to notice, however,

that this specificity of the constraint is not in tension with its general nature. The

constraint is general in the sense that it applies to all or (statistically) to most of the

elements of a given class x, but it is also precise in the sense that it can be distinguished

from other constraints, from classes y or z, for instance.

An application of the concept of function

In order to illustrate how to apply this concept of function in ecology we take the

case of one bromeliad and its associated organisms. Bromeliads are plants of the family

Bromeliaceae, frequent in tropical environments, which possess a reservoir delimitated

by their leaves – called phytotelmata – in which they accumulate water from rain. In the

phytotelmata and in the aerial part of the plant, there is a huge diversity of organisms,

forming a complex network of interactions (see Fig. 1). Moreover, bromeliad

ecosystems are good candidates for ecosystem studies because of their size, the relative

physical delimitation of the system given by the bromeliad leaves and the spider web at

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the top, and the relatively fast life cycles of the organisms that inhabit them (Srivastava

et al. 2004).

Fig. 1 General view of the bromeliad Quesnelia arvensis (brom) and its associated organisms. The dotted

line indicates the place where the spider Aglaoctenus castaneus builds its web (sp), while in the zoom,

there are, the phytotelmata (phyt), the microorganisms (mic) and the larvae (larv) of Culicidae, and in the

aerial part, the adults (ad) of Culicidae. Drawn by Edu Moraes and Nei Nunes-Neto, inspired in Romero

and Srivastava (2010)

We cannot account here for all the details and complexity found in real

bromeliad ecosystems. Our strategy will be, rather, to build a simple model of a possible

(idealized) ecosystem, and we refer the readers to the original works for more details

(Romero and Srivastava 2010, Srivastava et al. 2004). The most important feature of

this model system is that it allows us to think clearer about function in ecological terms,

by applying the organizational definition offered above.

An explanation of the case, in our terminology, would be as follows (see also

Fig. 2). First of all, notice that the boundary conditions of the ecosystem are those that

influence the ecosystem dynamics from outside, such as solar radiation, temperature,

rain, direction and strength of winds, etc.10

According to the general framework

presented above, we consider that two levels, in a control hierarchy, compose this

10

Notice that in our approach, these factors are not functions, but can be interpreted instead as limiting

factors. This is a restriction of the domain of functional language in ecology that seems necessary to

exclude cases like the following: “the altitude difference caused by hills functions to create divergent

communities of animals and plants”.

16

ecosystem. At the upper level, we find the constraints, instantiated by the items of

biodiversity (the bromeliad Quesnelia arvensis, microorganisms, larvae and adults of

mosquitoes of the family Culicidae, and, finally, a top predator, the spider A.

castaneus). And, at the lower level, we find the process at stake here, the cycling of

matter in the ecosystem, more specifically, the route followed by the nitrogen atoms

within it.

Fig. 2 Graphic scheme of the epistemological framework with a functional treatment of one bromeliad

ecosystem. The inner circle, level 1 (L1), represents the process at stake, namely the flow of matter (more

specifically, nitrogen, in three different hypothetical states, N1, N2, N3). The larger, dotted circle, level 2

(L2), represents the level of the constraints, instantiated by the items of biodiversity. The larger, bold

arrows represent the constraining actions on the process, performed by each item of biodiversity. The

small arrows in the inner circle show the possible routes of the nitrogen, one of which is selected through

the constraining action. The boundary conditions act from outside the system

Our central focus should be on the actions of the constraints in the ecosystem

(that is, the actions of the items of biodiversity). We can begin with the top predator, the

spider A. castaneus. This spider lives at the top of the plant where it builds its web (see

Fig. 1). It predates on adults (in the aerial part of the plant) and larvae (in the surface of

the water) of Culicidae insects. The actions of the spider can be seen as constraints on

the flow of the nitrogen in the ecosystem. This happens through the biochemical (and

also ecological) transference of the nitrogen found in the biomass of Culicidae

17

organisms to the spider itself. This obeys generalized organizational principles, strictly

associated to particular traits of the organism at stake (say, for this spider, to its sit-and-

wait hunting mode, associated, in turn, with its metabolism as well as web construction

and architecture). It is worth noticing that these organizational principles are general but

at the same time specific, as pointed out above; for instance, it is known that the

bromeliad Q. arvensis can be occupied by a different species of spider belonging to the

genus Corina, which shows an active hunting behavior, directed towards different prey

species (see Romero and Srivastava 2010). This means that the generalized

organizational principles that guide Corina’s constraining actions on the flow of matter

are different from those guiding A. castaneus’ actions.

Then, through the influence of these specific constraints, what would be

indeterminate possible states of the nitrogen atoms in the ecosystem turn into a

determinate state; this can be seen as a kind of channeling or modulation of those

indeterminate states (reducing the degrees of freedom, as explained above). In other

words, in the absence of that particular spider, the nitrogen of the Culicidae would be

free in ecological terms, it would be not constrained, or, more realistically, it would be

differently constrained by different items of biodiversity. The spider instantiates, in

sum, a specific kind of constraint on the flow of nitrogen, depending on its behavior,

morphology, etc., which obeys generalized organizational principles (being general to

that species of spider, or more broadly, depending on the trait at stake, to a genus of

spider or to the class Arachnida as a whole, etc.). The nitrogen found in the biomass of

the Culicidae will become – after the action of predation and digestion by the spider –

part of the biomass of the spider itself and will also compose the guanine-rich feces of

the predator. The spider carcass (after its death), its feces and the carcasses of its preys

will constitute the raw material for the decomposition of organic matter by the

functional group of the microorganisms in the phytotelmata. They will use the nitrogen

in form of guanine and in the form of aminoacids and proteins (which contain nitrogen)

of, say, the spider’s body to their own metabolism. The plant will also absorb part of

this nitrogen in the phytotelmata through its specialized leaf trichomes in the water

column (Benzing 2000; Romero and Srivastava 2010). In turn, the Culicidae organisms

capture the nitrogen from the microorganisms’ biomass through its filter-feeding

behavior, through which they incorporate the nitrogen of the ecosystem. And the

nitrogen of the Culicidae is captured by the predation of the spider, closing the cycle.

18

It is important to say a bit more about the role of the plant in this model, because

in some sense it acts like a huge membrane for the other constraints. The plant itself is

not prey for the animals inhabiting it, as normally happens with plants (which are

typically consumed by herbivorous animals). Instead, it acts on the flow of nitrogen

through its consumption of the nitrogen that falls in the phytotelmata (included in

carcasses, feces, etc.), leading to the production of its own leaves, which, in turn, are

important to the support of the whole ecosystem. The plant has, then, a kind of

supportive importance, because it offers the conditions for – through its particular

consumption of nitrogen and production of nitrogen-based compounds – the persistence

of the other constraints in the system. This means that the constraining action of the

plant – through its generalized organizational principles, say, the typical disposition of

its rosette leaves – is not so specific (that is, it is less localized, to use the terminology

of Bechtel and Richardson 2010) as the action of the other constraints (the spider, the

insects and the microorganisms).

In identifying the items of biodiversity, it is important to assume again a pluralist

perspective: while, by one hand the bromeliad and the spider are individual organisms,

by the other, the insects of the Culicidae family and the microorganisms form functional

groups. An outcome of this will be that particular epistemological models of the

relationship between items of biodiversity and ecosystem properties will be likely to

contain a unique combination of items of biodiversity with different ecological natures.

Each constraint itself is produced by the complex set of interactions in which it

is embedded. Take again the example of the spider. Nitrogen flows through the spider’s

predation of the Culicidae, which means that it incorporates the biomass of these insects

into its own biomass. At least in part, the spider is produced by the cascade of effects of

its own action on the predation of the Culicidae. That is to say, when it predates the

larvae and adults of the Culicidae, the spider contributes to the maintenance of the

internal conditions of operation of the ecosystem as a whole, avoiding, for instance, a

cascade of events that could destabilize the system (low predation of the Culicidae

might cause, for instance, a decrease in the production of guanine-rich feces by the

spider and, consequently, a decrease in nutrient uptake by the bromeliad, which might

eventually be unable to keep its leaves, which are an important support for the spider

web). In sum, at least in part, the whole organization of the ecosystem ensures the

existence of the spider itself.

19

It is worth considering the issue of the individuality or identity of the ecological

systems in general (and of the idealized bromeliad ecosystem, in particular). Differently

from organisms, which show a strong individuality because they are designed by natural

selection (Caponi 2010), ecosystems show only a weak individuality (Huneman 2011).

This concept of weak individuality is based on Simon’s (1981) quasi-independence

idea. Quasi-independence defines individual systems in a weak sense. Notice that in a

set of many different elements it is possible to find many interactions among them, in

such a manner that there are subsets (or modules), each of which depends upon all the

other subsets. It is possible to identify a quasi-independent system to a given subset if

the interactions among the elements within this particular subset are stronger than those

with the external elements, that is, of other subsets. From this point of view, ecosystems

in general are quasi-independent systems, showing a weak individuality. This

characterization shows that ecosystems are not individuals in the same sense as

organisms, which avoids the problems of conceiving them as Clementsian

superorganisms, for instance.

Yet concerning the individuality of the system, it is important to draw

distinctions among the functional effects (the functions themselves), the items of

biodiversity (the objects of functional ascription), and the system itself. In our

framework, the identity of the (eco)system as a whole is somewhat independent of the

species or groups of species that comprise the system, due to functional redundancy. In

other words, the components (the items of biodiversity) of the system can change and

yet the latter can preserve its identity because the organization of the system can be

maintained by different components that perform the same functional effect (for

instance, pollination, in general, can be performed by different animal species, among

bats, bees, etc.). What determines which component or item of biodiversity can perform

the functional effect is the evolutionary history of lineages, which restricts the

possibilities of traits and ecological interactions that will persist in a given ecosystem.

Consequently, we can say that the system as a whole breaks down (or changes its

identity) when a function is lost, not necessarily when a given component or item of

biodiversity is lost.

To finish, we can summarize our organizational approach to ecological function

as follows: the items of biodiversity, when acting as constraints on the biologically

generated flow of matter, functionally modulate (channel) these rates in such a manner

20

that a global self-maintaining (ecological) cycle is ensured. This harnessing action of

the items of biodiversity can be treated as being analogical to the constraining action of

enzymes in metabolism. As with the enzymes – which catalyze biochemical reactions in

cell metabolism – the items of biodiversity harness the ecological transformations of

nutrients, which otherwise would happen only at a very slow rate or would not occur at

all.

A possible objection: how is this approach more adequate than a Cummins’

systemic approach to function in ecology?

We maintain that the organizational approach is more adequate than Cummins’

precisely to the extent that it avoids both reductionism and excessive liberality. Let’s

appreciate now these two issues.

First, let us consider reductionism. In Cummins’ approach, the parts’ capacities

are used to explain a global capacity of the system (Cummins 1998[1975]). To put it in

another way, causality is only bottom-up, that is, the capacities of the parts as well as

the interactions among them are responsible for the generation of the systemic global

capacity. There is no room in Cummins’ approach to the constraining action of some

entities on the underlying processes (be them component parts of the system or not).

However, this idea of a constraining action is quite important in understanding the role

of biodiversity in relation to ecosystem properties, a general claim of the BEF. Although

in different ways, emphasis to this general idea of constraints or top-down influences in

ecology, is advanced by several works (such as Mikkelson 2004; Brussaard et al. 2007;

Maclaurin and Sterelny 2008: 116; Mace et al. 2012). As a consequence, Cummins’

approach cannot adequately account for the way that current ecology and philosophy of

ecology propose that ecological systems operate. In turn, the organizational approach

defines function as a result of the top-down action of constraints on the ecosystem

processes, and as a consequence captures more adequately the spirit of BEF’s functional

language.

Second – and related to the first feature – Cummins’ approach is too liberal

(Wouters 2005). That is to say, it allows us to ascribe functions to parts of systems that

do not have functions. Kitcher (1998[1993]), for instance, claimed that Cummins’

approach allows the ascription of functions to mutant DNA sequences involved in the

21

formation of tumors, a case where a functional explanation is not adequate at all. The

organizational approach on function, by its turn, is less liberal, because function is

defined as a precise, differentiated effect of the constraints on the processes.

We suspect that because of this liberality it is always possible to complement

Cummins’ approach with concepts or criteria outside it, as it is done by Maclaurin and

Sterelny in the following passage:

… phenomenological communities are organized systems only if they are stable,

bounded, and with enduring global features of biological importance to which

particular components make a regular contribution. Arguably, they are organized

systems in this sense if they are regulated, that is, constrained in membership

and numbers by their Cummins-functional organization, or if they have causally

important emergent properties (Maclaurin and Sterelny 2008: 116, emphases

added).

We agree with the content of what is said by Maclaurin and Sterelny, but we

have to point out that, since they are talking about constraints, organization, regulation

and emergent properties, this is no more Cummins’ philosophical project! They are, in

fact, ascribing some features of the organizational approaches in general to Cummins’

systemic approach. As Craver (2001: 56-7) noticed, although Cummins mentioned

organization in his criteria to ascribe function, he did not say enough about this concept

in his work. After all, it seems that a good way to see Cummins’ work is as a kind of

first proposal of a philosophical research agenda to understand the concept of function

within the framework of a systemic worldview (see Nunes-Neto and El-Hani 2011). As

a first attempt, the ideas were not well developed. However, they offered insights to

future works, including the organizational approaches to function.

Based on these considerations it is clear that we need a different label for this

perspective shed on ecological systems (as it is illustrated by Maclaurin and Sterelny).

And, more importantly than just claiming that we need a new label: we should explicitly

move towards the organizational approach in order to ground the use of function in

ecology. In the proper context of an organizational approach we can appeal to

constraints, organization and associated concepts, as Maclaurin and Sterelny are indeed

doing.

22

Final Remarks

In this paper we presented some steps towards one possible epistemological

framework for function in ecology based on a recent organizational approach to

function from the general philosophy of biology. We suggest that this approach can

ground the ascription of function to the items of biodiversity in an ecosystem context,

an important claim of the BEF in contemporary ecology. Instead of assuming that this is

a complete and singular framework, we think that it is an initial proposal in need of

further developments. However, it seems clear to us that to take into consideration ideas

from the organizational approach to function – such as closure of constraints and

organization – constitute a promising way for future investigations in philosophy of

ecology.

As further developments of this work we see three main roads. First, it seems

necessary hereafter to concentrate on the other uses of function in ecology, only briefly

discussed in this paper, ecosystem function and the function of biodiversity itself.

Perhaps the abstract concept advanced here can ground – with some adaptation – these

other uses too. Second, it seems interesting to examine the implications of the new

philosophy of mechanism to function and organization in ecology (Craver 2001;

Bechtel and Richardson 2010). And finally, third, to examine the ethical

presuppositions or foundations of the functional language in ecology, which seems to be

aligned with a kind of anthropocentric ethics and is nowadays very influent in the

management of natural resources (De Groot et al. 2002). These – among others – are

important issues to be tackled by future philosophy of ecology, with urgent scientific

and social consequences.

Acknowledgements Nei Nunes-Neto acknowledges to CAPES (Ministry of Education of Brazil) for a

PDSE grant (nº 6084/11-7) and to the Information and Autonomous System Research Group (University

of Basque Country) for all the support to the realization of this work. Alvaro Moreno acknowledges the

aid of the Research Project IT 505-10 of the Gobierno Vasco and FFU2009-12895-CO2-02 and FFI2011-

25665 of the Spanish Ministerio de Economıa y Competitividad. Charbel N. El-Hani thanks the Brazilian

National Council for Scientific and Technological Development (CNPq) for a productivity research grant

(no 301259/2010-0) and both CNPq and the Research Support Foundation of the State of Bahia

(FAPESB) for research funding (Project PNX0016_2009). We are indebted to Sergio Martinez and

23

Maximiliano Martinez for thoughtful discussions of a previous version of the paper. Finally, we

acknowledge an anonymous reviewer and Kim Sterelny for their valuable comments, which helped to

significantly improve the paper.

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