168
consensus on the following set of statements, trends and
potential underlying mechanisms:
Biodiversity Increases Stability at the Ecosystem
Level The diversity-stability debate is probably one of the
most relevant — given its implications in light of the
anthropogenic- induced loss of biodiversity — and long
standing ones in Ecology (McCann 2000). The pioneering
observational works of Odum (1953) and Elton (1958),
awakened this discussion by acknowledging that simplified
terrestrial communities (e.g., in agricultural systems) exhibit
stronger fluctuations and are more vulnerable to biological
invasions. Blindly accepted until the beginning of the 1970s,
these statements were questioned by a series of thoughtful
mathematical essays developed by Robert May (May 1971,
1972, 1973). The linear stability analysis of constructed random communities
1
showed that the higher complexity is (in
terms of connectance, strength of interaction and number of
interacting species) the more unstable
2
population dynamics
will be. May’s arguments, and beyond the unrealistic
assumptions of the proposed models (i.e., communities are
randomly structured and exhibit stable equilibrium dynamics, McCann 2000), highlighted the absence of a mechanistic
understanding of existing empirical evidence. In other words,
if more diverse natural ecosystems tend to be more stable but
those randomly constructed are not, natural ecosystems must
be structured by a set of non-random principles that determine their stability. The challenge raised by May’s results
triggered the search for a set of properties capable of conferring stability to complex ecological systems. The accumulated evidence by the analysis of empirical ecological
networks highlighted, for example, the role of weak interactions and modularity as properties that prevent the spread of
disturbances (Paine 1992; McCann et al. 1998; Neutel et al.
2002; Olesen et al. 2007; Gilarranz et al. 2017).
3
A large
body of empirical evidence supporting the diversity-stability
relationship has been generated in the last four decades
(McNaughton 1977; Stachowicz et al. 2007; Tilman et al.
2014). The manipulation of species or functional richness
has shown that diversity reduces the temporal variability in
the structure and functioning of communities (e.g., measured
as biomass production). A remarkable conclusion of the syn1 Theoretical communities where the type and magnitude of the interactions are defined using statistical distributions (see May 1972 for a brief
but enlightening summary).
2 Original works of Robert May define stability in terms of resilience,
assuming that stable systems are those able to return to the equilibrium
after a perturbation (see McCann 2000).
3 The list of features mentioned for ecological networks is far from
being exhaustive, but a detailed presentation of described topological
patterns and underlying mechanisms is out of the scope of the present
chapter. In this sense, we recommend Montoya et al. (2006) and Ronney
and McCann (2012) for a general overview of the state of the art in food
webs theory.
theses of these results is that the positive correlation between
diversity and stability at the community level cannot necessarily be extended to single populations (Gross et al. 2014;
Tilman et al. 2014). Alternative hypotheses have been proposed to account for these results (Yachi and Loreau 1999;
Lehman and Tilman 2000). The averaging and covariance
effects predict that the variability of the overall community
will be dampened due to the balance between contrasting
single species dynamics (Lehman and Tilman 2000). These
hypotheses assume that the higher the diversity, the higher
the probability of observing species that respond differentially to conditions and disturbances (McCann 2000).
Furthermore, the insurance hypothesis added the idea that
the higher the diversity, the higher the probability of having
functionally redundant species. Thus, the loss of species with
particular functions can be replaced by others, increasing the
temporal stability of ecosystems’ functioning (Yachi and
Loreau 1999). All in all, existing theoretical and experimental evidence provided a potential solution to the diversitystability debate: the stabilizing effects of biodiversity at the
ecosystem level (i.e., the observations of Odum and Elton)
can occur at the expenses of decreasing single species stability (i.e., the theoretical conclusions of May) (Lehman and
Tilman 2000).
Biodiversity Increases the Efficiency and Productivity of
Ecosystems The number of observational and experimental
studies analyzing how changes in biodiversity impact the
functioning of ecosystems has rapidly increased since the
1990s. Research across ecosystems (from terrestrial to
marine) and considering diversity at different levels of biological organization (from genes to functional groups) has
been developed worldwide. Recent meta-analyses have summarized available bibliography, obtaining conclusive evidence that, on average, the decrease of biodiversity is
translated into altered ecosystem functions (e.g., a lower
capacity of communities to use resources and produce biomass, see Cardinale et al. 2012 and citations therein).
Regardless of the clarity of these findings, a consensus on the
responsible mechanisms is still elusive. The selection effect
(i.e., the prevalence of species with certain traits in the determination of ecosystem processes) and/or the complementarity effect (i.e., a better performance of the community due to
an efficient partitioning of resources or facilitation among
species) have been proposed for the explanation of
biodiversity- functioning relationships (Loreau and Hector
2001). A sampling process
4
is involved in both mechanisms,
which means that the higher the diversity, the higher the odds
4 In light of the existing literature, it is important to draw the attention of
the readers on the fact that the sampling and selection effects, sometimes, are incorrectly used as interchangeable concepts. Please see
Loreau and Hector (2001) for a clear explanation of the differences.
F. R. Barboza et al.
consensus on the following set of statements, trends and
potential underlying mechanisms:
Biodiversity Increases Stability at the Ecosystem
Level The diversity-stability debate is probably one of the
most relevant — given its implications in light of the
anthropogenic- induced loss of biodiversity — and long
standing ones in Ecology (McCann 2000). The pioneering
observational works of Odum (1953) and Elton (1958),
awakened this discussion by acknowledging that simplified
terrestrial communities (e.g., in agricultural systems) exhibit
stronger fluctuations and are more vulnerable to biological
invasions. Blindly accepted until the beginning of the 1970s,
these statements were questioned by a series of thoughtful
mathematical essays developed by Robert May (May 1971,
1972, 1973). The linear stability analysis of constructed random communities
1
showed that the higher complexity is (in
terms of connectance, strength of interaction and number of
interacting species) the more unstable
2
population dynamics
will be. May’s arguments, and beyond the unrealistic
assumptions of the proposed models (i.e., communities are
randomly structured and exhibit stable equilibrium dynamics, McCann 2000), highlighted the absence of a mechanistic
understanding of existing empirical evidence. In other words,
if more diverse natural ecosystems tend to be more stable but
those randomly constructed are not, natural ecosystems must
be structured by a set of non-random principles that determine their stability. The challenge raised by May’s results
triggered the search for a set of properties capable of conferring stability to complex ecological systems. The accumulated evidence by the analysis of empirical ecological
networks highlighted, for example, the role of weak interactions and modularity as properties that prevent the spread of
disturbances (Paine 1992; McCann et al. 1998; Neutel et al.
2002; Olesen et al. 2007; Gilarranz et al. 2017).
3
A large
body of empirical evidence supporting the diversity-stability
relationship has been generated in the last four decades
(McNaughton 1977; Stachowicz et al. 2007; Tilman et al.
2014). The manipulation of species or functional richness
has shown that diversity reduces the temporal variability in
the structure and functioning of communities (e.g., measured
as biomass production). A remarkable conclusion of the syn1 Theoretical communities where the type and magnitude of the interactions are defined using statistical distributions (see May 1972 for a brief
but enlightening summary).
2 Original works of Robert May define stability in terms of resilience,
assuming that stable systems are those able to return to the equilibrium
after a perturbation (see McCann 2000).
3 The list of features mentioned for ecological networks is far from
being exhaustive, but a detailed presentation of described topological
patterns and underlying mechanisms is out of the scope of the present
chapter. In this sense, we recommend Montoya et al. (2006) and Ronney
and McCann (2012) for a general overview of the state of the art in food
webs theory.
theses of these results is that the positive correlation between
diversity and stability at the community level cannot necessarily be extended to single populations (Gross et al. 2014;
Tilman et al. 2014). Alternative hypotheses have been proposed to account for these results (Yachi and Loreau 1999;
Lehman and Tilman 2000). The averaging and covariance
effects predict that the variability of the overall community
will be dampened due to the balance between contrasting
single species dynamics (Lehman and Tilman 2000). These
hypotheses assume that the higher the diversity, the higher
the probability of observing species that respond differentially to conditions and disturbances (McCann 2000).
Furthermore, the insurance hypothesis added the idea that
the higher the diversity, the higher the probability of having
functionally redundant species. Thus, the loss of species with
particular functions can be replaced by others, increasing the
temporal stability of ecosystems’ functioning (Yachi and
Loreau 1999). All in all, existing theoretical and experimental evidence provided a potential solution to the diversitystability debate: the stabilizing effects of biodiversity at the
ecosystem level (i.e., the observations of Odum and Elton)
can occur at the expenses of decreasing single species stability (i.e., the theoretical conclusions of May) (Lehman and
Tilman 2000).
Biodiversity Increases the Efficiency and Productivity of
Ecosystems The number of observational and experimental
studies analyzing how changes in biodiversity impact the
functioning of ecosystems has rapidly increased since the
1990s. Research across ecosystems (from terrestrial to
marine) and considering diversity at different levels of biological organization (from genes to functional groups) has
been developed worldwide. Recent meta-analyses have summarized available bibliography, obtaining conclusive evidence that, on average, the decrease of biodiversity is
translated into altered ecosystem functions (e.g., a lower
capacity of communities to use resources and produce biomass, see Cardinale et al. 2012 and citations therein).
Regardless of the clarity of these findings, a consensus on the
responsible mechanisms is still elusive. The selection effect
(i.e., the prevalence of species with certain traits in the determination of ecosystem processes) and/or the complementarity effect (i.e., a better performance of the community due to
an efficient partitioning of resources or facilitation among
species) have been proposed for the explanation of
biodiversity- functioning relationships (Loreau and Hector
2001). A sampling process
4
is involved in both mechanisms,
which means that the higher the diversity, the higher the odds
4 In light of the existing literature, it is important to draw the attention of
the readers on the fact that the sampling and selection effects, sometimes, are incorrectly used as interchangeable concepts. Please see
Loreau and Hector (2001) for a clear explanation of the differences.
F. R. Barboza et al.