171
also shaped by the influx of new species that can compensate
(regarding the number of species) extinctions or even generate an overall increase of regional diversity. But, as mentioned previously in this section, species richness is not the
only dimension of biodiversity and the arrival of new species
does not necessarily guarantee the functional replacement of
extinct ones. In this context, it is crucial to better understand:
(i) which are the traits of extirpated and introduced species,
(ii) to what extent do they functionally overlap and (iii) if
introduced species will be able to keep the functioning of
ecosystems (Fig. 1).
Functional Diversity in Local Communities:
Are Species Lost Functionally Replaced
by Those Introduced?
As previously stated, human driven extinctions are not random, because certain species traits are favored or hampered
by anthropogenic pressures, which act as environmental filters (Hillebrand and Blenckner 2002; Fig. 1). Traits like
body size, fecundity, motility and physiological tolerance,
among others, have been identified as potential predictors of
both species’ extinction risk and capacity to spread and colonize new environments. In this sense, it has been suggested
that large body size, low fecundity, slow dispersal and
resource specialization are generally filtered out, while
small, fast reproducing, wide spreading, and generalist species are favored (McKinney and Lockwood 1999). According
to these observations, it has been proposed that in the spectrum of variability of these traits, threatened and successful
species must be in opposite extremes. Thus, those traits positively correlated with extinction risk must be negatively correlated with the probability of a species to get established
and successfully spread (Blackburn and Jeschke 2009). This
hypothesis, known as “two sides of the same coin”, has been
tested in terrestrial and aquatic environments for different
taxonomic groups (fish, crustaceans, birds, reptiles and
plants) (e.g., Murray et al. 2002; Marchetti et al. 2004;
Blackburn and Jeschke 2009; Larson and Olden 2010; van
Kleunen et al. 2010). The use of different definitions for
invasive, non-invasive, threatened and rare species across
articles, promoted the generation of contradictory evidence
(van Kleunen and Richardson 2007; Blackburn and Jeschke
2009). Despite the methodological inconsistencies observed
in the literature, it is still possible to draw some conclusions.
The assumption that for all functional traits analyzed, threatened and successful species will always exhibit contrasting
variants is an oversimplification (Tingley et al. 2016). The
majority of the traits evaluated in the bibliography show
small or no-difference among threatened and successful species (e.g., Jeschke and Strayer 2008; Tingley et al. 2016). It
is important to highlight that the still fragmentary nature of
the data for certain species could explain some of the
obtained results (van Kleunen and Richardson 2007).
The current “absence” of trends in multiple-trait analyses
questions the validity of the “two sides of the same coin”
hypothesis (Jeschke and Strayer 2008; Blackburn and
Jeschke 2009; Tingley et al. 2016). Available evidence makes
it extremely difficult to speak about a set of traits that
unequivocally predicts both extinction risk and species success, across environments and taxa. Nevertheless, results
become more consistent if we just focus on extinctions (a
process that has received much more attention in the last
decades) and some specific traits. In particular, ecological
and paleontological literature identified body mass as a
major predictor of extinctions, i.e., large-bodied species are
more likely to disappear. Body size tightly correlates with
different life history traits and demographic characteristics
determining the susceptibility of species to extinctionpromoting drivers (e.g., Purvis et al. 2000; Springer et al.
2003; Barnosky 2008).
8
Important functional traits like trophic position, diet width, and productivity scale with body
size. Thus, extinctions modify the size distribution of communities being able to alter the stability and functioning of
ecosystems (Woodward et al. 2005). Observational and
experimental examples have shown the consequences that
the loss of “big” species has on ecosystem processes. Solan
et al. (2004) showed that the loss of larger infaunal species
reduces bioturbation and sediment oxygenation, altering the
decomposition of organic matter and cycling of nutrients.
Articles showing cascading effects of large predator’s extinctions on overall ecosystems are probably those that better
exemplify the impacts of body size changes. Estes et al.
(2011) and Ripple et al. (2014) (and citations therein),
reviewed the literature highlighting the relevance of topdown controls in ecosystems. Carbon uptake in freshwater
and marine ecosystems, nutrients accumulation in soils and
waters or primary production in coastal areas are just some
examples of ecosystems processes affected by the extinction
of apex consumers.
The question that still remains to be answered is whether
the massive number of exotic species introduced worldwide
will be able to functionally replace those that are lost (Fig. 1).
Available data are insufficient to explain extinctions and
introductions in terms of species traits and to determine the
consequences of changes in those traits on ecosystem processes. Increasing research efforts on this topic are needed to
accurately predict how ecosystems will respond under global
change.
8 The single consideration of mean adult body size (as has been done in
most of the existing bibliography) in the mechanistic understanding of
ecological and evolutionary processes could be misleading, since species usually show dramatic ontogenetic changes in body size (see
Woodward et al. 2005 and Codron et al. 2012).
Biodiversity and the Functioning of Ecosystems in the Age of Global Change: Integrating Knowledge Across Scales
also shaped by the influx of new species that can compensate
(regarding the number of species) extinctions or even generate an overall increase of regional diversity. But, as mentioned previously in this section, species richness is not the
only dimension of biodiversity and the arrival of new species
does not necessarily guarantee the functional replacement of
extinct ones. In this context, it is crucial to better understand:
(i) which are the traits of extirpated and introduced species,
(ii) to what extent do they functionally overlap and (iii) if
introduced species will be able to keep the functioning of
ecosystems (Fig. 1).
Functional Diversity in Local Communities:
Are Species Lost Functionally Replaced
by Those Introduced?
As previously stated, human driven extinctions are not random, because certain species traits are favored or hampered
by anthropogenic pressures, which act as environmental filters (Hillebrand and Blenckner 2002; Fig. 1). Traits like
body size, fecundity, motility and physiological tolerance,
among others, have been identified as potential predictors of
both species’ extinction risk and capacity to spread and colonize new environments. In this sense, it has been suggested
that large body size, low fecundity, slow dispersal and
resource specialization are generally filtered out, while
small, fast reproducing, wide spreading, and generalist species are favored (McKinney and Lockwood 1999). According
to these observations, it has been proposed that in the spectrum of variability of these traits, threatened and successful
species must be in opposite extremes. Thus, those traits positively correlated with extinction risk must be negatively correlated with the probability of a species to get established
and successfully spread (Blackburn and Jeschke 2009). This
hypothesis, known as “two sides of the same coin”, has been
tested in terrestrial and aquatic environments for different
taxonomic groups (fish, crustaceans, birds, reptiles and
plants) (e.g., Murray et al. 2002; Marchetti et al. 2004;
Blackburn and Jeschke 2009; Larson and Olden 2010; van
Kleunen et al. 2010). The use of different definitions for
invasive, non-invasive, threatened and rare species across
articles, promoted the generation of contradictory evidence
(van Kleunen and Richardson 2007; Blackburn and Jeschke
2009). Despite the methodological inconsistencies observed
in the literature, it is still possible to draw some conclusions.
The assumption that for all functional traits analyzed, threatened and successful species will always exhibit contrasting
variants is an oversimplification (Tingley et al. 2016). The
majority of the traits evaluated in the bibliography show
small or no-difference among threatened and successful species (e.g., Jeschke and Strayer 2008; Tingley et al. 2016). It
is important to highlight that the still fragmentary nature of
the data for certain species could explain some of the
obtained results (van Kleunen and Richardson 2007).
The current “absence” of trends in multiple-trait analyses
questions the validity of the “two sides of the same coin”
hypothesis (Jeschke and Strayer 2008; Blackburn and
Jeschke 2009; Tingley et al. 2016). Available evidence makes
it extremely difficult to speak about a set of traits that
unequivocally predicts both extinction risk and species success, across environments and taxa. Nevertheless, results
become more consistent if we just focus on extinctions (a
process that has received much more attention in the last
decades) and some specific traits. In particular, ecological
and paleontological literature identified body mass as a
major predictor of extinctions, i.e., large-bodied species are
more likely to disappear. Body size tightly correlates with
different life history traits and demographic characteristics
determining the susceptibility of species to extinctionpromoting drivers (e.g., Purvis et al. 2000; Springer et al.
2003; Barnosky 2008).
8
Important functional traits like trophic position, diet width, and productivity scale with body
size. Thus, extinctions modify the size distribution of communities being able to alter the stability and functioning of
ecosystems (Woodward et al. 2005). Observational and
experimental examples have shown the consequences that
the loss of “big” species has on ecosystem processes. Solan
et al. (2004) showed that the loss of larger infaunal species
reduces bioturbation and sediment oxygenation, altering the
decomposition of organic matter and cycling of nutrients.
Articles showing cascading effects of large predator’s extinctions on overall ecosystems are probably those that better
exemplify the impacts of body size changes. Estes et al.
(2011) and Ripple et al. (2014) (and citations therein),
reviewed the literature highlighting the relevance of topdown controls in ecosystems. Carbon uptake in freshwater
and marine ecosystems, nutrients accumulation in soils and
waters or primary production in coastal areas are just some
examples of ecosystems processes affected by the extinction
of apex consumers.
The question that still remains to be answered is whether
the massive number of exotic species introduced worldwide
will be able to functionally replace those that are lost (Fig. 1).
Available data are insufficient to explain extinctions and
introductions in terms of species traits and to determine the
consequences of changes in those traits on ecosystem processes. Increasing research efforts on this topic are needed to
accurately predict how ecosystems will respond under global
change.
8 The single consideration of mean adult body size (as has been done in
most of the existing bibliography) in the mechanistic understanding of
ecological and evolutionary processes could be misleading, since species usually show dramatic ontogenetic changes in body size (see
Woodward et al. 2005 and Codron et al. 2012).
Biodiversity and the Functioning of Ecosystems in the Age of Global Change: Integrating Knowledge Across Scales