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Determinants of biodiversity regulate compositional stability of communities



The world is witnessing a decline in biodiversity which may be greater in magnitude than even previous mass-extinction events. This has rekindled interest in the relationships between biodiversity and the stability of community and ecosystem processes that have been reported in some empirical studies. Diversity has been linked with community and ecosystem processes, but disputes remain over whether it is diversity, environmental factors or the variety of functional groups in a community that drive these patterns. Furthermore, it remains unclear whether variation in diversity resulting from species loss within communities has similar effects on stability as natural variation in diversity associated with gradients in factors that regulate diversity. We believe that, across larger ecological scales, extrinsic determinants of biodiversity such as disturbance regimes and site history may be the primary determinants of certain measures of community stability. Here we use controlled field experiments in savanna grasslands in southern India to demonstrate and explain how low-diversity plant communities can show greater compositional stability when subject to experimental perturbations characteristic of their native environments. These results are best explained by the ecological history and species characteristics of communities rather than by species diversity in itself.
© 1999 Macmillan Magazines Ltd
VOL 401
14 OCTOBER 1999
| 691
letters to nature
Determinants of biodiversity
regulate compositional stability
of communities
Mahesh Sankaran & S. J. McNaughton
Biological Research Laboratories, Syracuse University, Syracuse,
New York 13210-1244, USA
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The world is witnessing a decline in biodiversity which may be
greater in magnitude than even previous mass-extinction
events1–3. This has rekindled interest in the relationships between
biodiversity and the stability of community and ecosystem
processes4that have been reported in some empirical studies5–7.
Diversity has been linked with community and ecosystem pro-
cesses8–14, but disputes remain over whether it is diversity, envir-
onmental factors or the variety of functional groups in a
community that drive these patterns15– 21. Furthermore, it remains
unclear whether variation in diversity resulting from species loss
within communities has similar effects on stability as natural
variation in diversity associated with gradients in factors that
regulate diversity. We believe that, across larger ecological scales,
extrinsic determinants of biodiversity such as disturbance
regimes and site history may be the primary determinants of
certain measures of community stability. Here we use controlled
field experiments in savanna grasslands in southern India to
demonstrate and explain how low-diversity plant communities
can show greater compositional stability when subject to experi-
mental perturbations characteristic of their native environments.
These results are best explained by the ecological history and
species characteristics of communities rather than by species
diversity in itself.
We studied the responses of natural savanna-grassland commu-
nities to disturbance within the Kalakad-Mundanthurai Tiger
Reserve (KMTR, 778159–778409E, 88259–88559N), along the
southern section of India’s Western Ghats Mountains. The stability
of species composition of three low-elevation grassland types
(200 m above sea level)—representing different positions along a
productivity, diversity and disturbance gradient (see Methods)
were measured in 72 plots (each 4 m 34 m) during 1997 –98
following experimental perturbations in the form of fires, herbivore
exclusion and simulated high-intensity grazing. The stability of
species composition was characterized with two indices: (1) resis-
tance to compositional change, R
, measured as the change in the
relative contribution of different species to the canopy between pre-
and post-disturbance states22; and (2) resistance to species turnover,
, calculated as the proportion of species common to pre- and
post-disturbance plots.
Across all communities, compositional stability as measured by
was negatively correlated with diversity (Fig. 1a, using arcsin
:r¼20:304, P¼0:009), and low-diversity communities
were more compositionally stable than high-diversity ones. In
contrast, more diverse communities were more stable as measured
by resistance to species turnover R
(Fig. 1b, using arcsin (R
r¼0:709, p,0:001).
As R
is influenced both by patterns of species colonization and
by loss from plots, each of these processes was analysed separately
(Fig. 2a and b). The number of new species recorded in plots
following the start of the experiment decreased as a function of
initial diversity (Fig. 2a; r¼20:482, P,0:001), while those lost
from plots increased with diversity (Fig. 2b; r¼0:617, P,0:001).
In most cases, the number of colonizing species outweighed those
lost from plots, resulting in the observed positive correlation
between diversity and R
(Fig. 1b). For communities that share a
common species pool, as was the case here, a negative relationship
between diversity and colonization can result, even in the absence of
specific ecological interactions, simply because fewer species remain
in the pool to colonize species-rich plots. A positive correlation
between species loss and diversity can result if high-diversity plots
contain a greater number of rare species, which are likely to be lost
due to purely stochastic processes. Across all plots, the number of
rare species (cover ,1%) initially present was positively correlated
with diversity (r¼0:387, P,0:05). Irrespective of whether these
observed trends were a consequence of an underlying ecological
mechanism or a statistical phenomenon23,24, low-diversity plots in
this study had a greater turnover of species than high-diversity plots.
Unlike the relationships that appear so evident when data are
pooled across communities, no consistent patterns were observed
between diversity and either measure of stability within individual
communities (arcsin (R
:Cymbopogon flexuosus:r¼0:03,
P.0:05; Aristida setacea:r¼20:44, P,0:05; mixture:
r¼20:20, P.0:05; arcsin (R
:C. flexuosus:r¼0:65,
P,0:05; A. setacea:r¼20:14, P.0:05; mixture: r¼0:29,
P.0:05). These results do not constitute evidence for lack of
significant effects of species diversity on the functioning of individ-
ual communities, as diversity was not specifically manipulated in
these experiments. However, when coupled with the contrasting
patterns observed between diversity and R
and R
across all
0.0 0.5 1.0 1.5 2.0 2.5 3.0
arcsin (R
arcsin (R
Initial species diversity, H'
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Figure 1 Compositional stability of communities as related to species diversity.
a, Resistance to compositional change (arcsinð
9þ0:813) and b,
resistance to species turnover (arcsinð
9þ0:585), both plotted against
initial species diversity (
9) of 72 experimental plots. Symbols identify communities
dominated by
C. flexuosus
(filled circles),
A. setacea
(open circles) and mixtures (dots).
© 1999 Macmillan Magazines Ltd
communities (Fig. 1a and b), it does question the validity of
absolute measures of species diversity, in and of themselves, as
predictors of ‘stability’ in natural communities.
Species diversity in nature is an emergent property which results
from historic, biotic and abiotic interactions among different
constituent elements25,26. Consequently, we may expect diversity
in nature to co-vary with factors that regulate the distribution and
abundance of species, such as disturbances, site productivity or site
history (segregation of communities along the diversity axis in
Fig. 1a and b). These factors influence the identities of potential
member species in a community and can, therefore, affect its
stability properties. To determine how much of the observed
relationships in R
and R
were attributable to species and dis-
turbance characteristics rather than diversity in itself, a multiple
regression analysis was used on arcsin-transformed R
and R
separate effects of community type, diversity, disturbance type and
proneness to disturbance (see Methods). These variables cumula-
tively explained 42% of the observed variation in R
R2¼0:424; P,0:001), but only community type and proneness
to disturbance had significant effects (P,0:001). On the other
hand, 53% of the variation in R
was explained by variables
included in the regression (multiple R2¼0:529; P,0:01), but
only diversity was significant in this case (H9:P,0:001).
Greater species turnover in low-diversity communities in this
study did not translate into lowered stability as measured by R
most species that colonized (or were lost from) plots were rare and
did not contribute significantly to total cover. Compositional
stability as measured by R
depends on the sum total of shifts in
relative cover of individual species. Dominant species are likely to
have disproportionate effects on R
as they are capable of larger
absolute shifts in cover compared to rare species. Low-diversity
systems dominated by one or a few species can therefore show a
large range of variation in compositional stability, depending on the
response of the dominant species (triangular scatter of data points
in Fig. 1a). Similar patterns of greater variation in community
properties such as CO
flux13, biomass and density14 at lower
diversities have also been reported for synthesized microbial com-
munities. Even though low-diversity communities may show
greater variation in levels of stability, they may be more stable
than some higher-diversity communities when the dominant
species responds ‘favourably’ to the disturbances in question.
Given the role that disturbances play in structuring natural com-
munities, such patterns may be more common in nature than is
currently believed.
Previous studies investigating the biodiversity– stability relation-
ship have focused on aggregate community properties such as
biomass, productivity and nutrient cycling, while the relationship
between diversity and constancy of species composition has
received less attention22. Greater stability of aggregate community
properties with increasing diversity has been argued to result from
the increased probability of species or functional groups being
present that can adequately compensate for those harmed by the
disturbance4,6–8,11,14,27. However, compensation, by definition,
implies compositional change. As our data show, species and
dominance characteristics (collectively identified by community
type in this study) and disturbance history (as indexed by proneness
to disturbance) may better explain compositional stability patterns
across different community types.
These results have several implications for community, restora-
tion and conservation biologists. First, it is critical that different
aspects of the biodiversity– stability relationship arising from dif-
ferent choices of spatial and temporal scales not be confused.
Evidence for a negative effect of lowered species diversity on stability
resulting from species loss in a community in ecological time does
not imply that species-poor communities in nature, which have
evolved over evolutionary time, are necessarily less stable than
species-rich ones. Second, as our data indicate, and as has been
noted previously28, patterns of community stability vary depending
on the specific process measured. Third, disturbance regimes, site
productivity and other environmental factors that are currently
being modified can alter the stability properties of communities. In
situ declines in species diversity due to local extinctions can further
modify these patterns. Last, evidence for stability of aggregate
community properties such as nutrient cycling or above-ground
biomass does not preclude compositional shifts in communities6,7.
Communities and ecosystems are more than the biomass that
they support or the nutrients that they cycle. Even though
biomass or rates of nutrient cycling may remain unchanged, altered
abundance of food or host plants can change, and potentially
destabilize, herbivore and dependent predator populations.
Although high biodiversity may in some cases be associated with
‘desirable’ responses such as stability of nutrient cycling or produc-
tivity, we warn against concluding that species-rich ecosystems will
necessarily ‘cope’ better than species-poor ones in the face of
perturbations. M
Responses of three different community-types to disturbances were studied at KMTR
during 1997– 98. Communities dominated by C. flexuosus were the most productive, but
had low species richness and sustained low levels of herbivory. A. setacea-dominated
communities were the least productive, had intermediate species richness and suffered
highest levels of herbivory. Communities that had both species present were intermediate
in productivity and levels of herbivory sustained, and had the highest species richness.
Communities also differed in fire-proneness, with C. flexuosus communities the most fire-
prone, and A. setacea communities the least. The contribution of grass species to the
letters to nature
VOL 401
14 OCTOBER 1999
Number of new species recorded
Initial species diversity, H'
Number of species lost
Figure 2 Patterns of species colonization and loss from plots. a, The number of new
species that colonized plots (NEW ¼24:123
9þ23:58) and b, the number of species
that were lost from plots (LOST ¼3:856
9þ3:692) after 1 year, both plotted against
initial species diversity (
9) of experimental plots. Symbols as in Fig. 1.
© 1999 Macmillan Magazines Ltd
understory canopy varied from 85% in C. flexuosus communities, to 70% in A. setacea
communities, and 60% in mixture communities.
Experimental design
The experimental design was a 2 33 factorial experiment with two burning treatments
(burned and unburned) and three grazing treatments (natural levels of grazing, ungrazed
and experimentally clipped). All experimental plots were 4 m 34 m, located within an
area of ,1km
, subject to similar climate conditions and potentially shared a common
species pool. Overall, there were nine replicates for each unburned treatment and 18 for
treatment combinations involving burning (three and six in each of three community
types, respectively). Plots not experimentally manipulated (unburned, naturally grazed
treatments) were excluded from the analysis. At each sampling session, species richness
and cover was enumerated in eight and four 1-m
sub-plots, respectively, using a stratified
sampling scheme. Species cover in sub-plots was estimated using a 1m 31 m grid frame
subdivided into 100 units of 0.01 m
each. Data reported here are for one year following
experimental manipulations, and are therefore devoid of any seasonal biases. Where
necessary, they were transformed to fit the assumptions of normality.
Rc¼Sminimum ðpii;pofÞ, where p
and p
represent the relative cover of the ith species
in pre-disturbance and 1 year post-disturbance plots, respectively22.Rst ¼Ncom=Ntot,
where N
represents the total number of distinct species recorded in pre-disturbance and
1 year post-disturbance plots, and N
represents the number of species common to pre-
disturbance and 1 year post-disturbance plots. Diversity was calculated using the
Shannon– Weiner index29 as H9¼SpilnðpiÞ, where p
represents the proportional con-
tribution of the ith species to the canopy. Proneness of communities to different
disturbance combinations was calculated as Pbg ¼PbþPg, where the subscripts b and g
represent the specific burning and grazing treatments. Proneness to burning was
determined on the basis of the cover of C. flexuosus present initially in the plot (P
). Burned
treatments were assigned the value P
whereas unburned treatments were assigned a value
of (1 2Pc) for this index. We believe that this is a valid index because C. flexuosus
individuals are characteristic of the fire-prone environments, and also promote fires
because of the extent of litter and standing dead biomass they produce. For the grazing
treatments, grazed and clipped plots were assigned the value P
and ungrazed plots
(1 2Pg), where P
represents the fraction of species initially grazed in plots.
Received 27 July; accepted 16 August 1999.
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We thank the Tamil Nadu Forest Department for granting permission to work at KMTR,
and J. Ratnam for support and comments. Wealso thank L. L. Wolf, D.Frank, T. R. Shankar
Raman and D. Barua for comments; R. Ali, V. Vinatha, K. Kar Gupta, M. Katti,
D. Mudappa, N. M. Ishwar, K. Vasudevan and K. S. Gopi for their help; and C. Sankaran,
P. Kumar and C. Jayseelan for field assistance. This work was supported by the Wildlife
Conservation Society (India), NSF and the Sophie Danforth Conservation Biology Fund.
Correspondence and requests for materials should be addressed to M.S.
letters to nature
VOL 401
14 OCTOBER 1999
| 693
Symmetry in locomotor central
pattern generators and animal gaits
Martin Golubitsky*, Ian Stewart, Pietro-Luciano Buono& J. J. Collins§
*Mathematics Department, University of Houston, Houston,
Texas 77204-3476, USA
Mathematics Institute, University of Warwick, Coventry CV4 7AL, UK
Mathematics Institute, University of Warwick, Coventry CV4 7AL, UK
§Department of Biomedical Engineering, Center for BioDynamics,
Boston University, 44 Cummington Street, Boston, Massachusetts 02215, USA
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Animal locomotion is controlled, in part, by a central pattern
generator (CPG), which is an intraspinal network of neurons
capable of generating a rhythmic output1–4. The spatio-temporal
symmetries of the quadrupedal gaits walk, trot and pace5–8 lead
to plausible assumptions about the symmetries of locomotor
CPGs9–11. These assumptions imply that the CPG of a quadruped
should consist of eight nominally identical subcircuits, arranged
in an essentially unique matter. Here we apply analogous argu-
ments to myriapod CPGs. Analyses based on symmetry applied
to these networks lead to testable predictions, including a dis-
tinction between primary and secondary gaits, the existence of a
new primary gait called ‘jump’, and the occurrence of half-integer
wave numbers in myriapod gaits. For bipeds, our analysis also
predicts two gaits with the out-of-phase symmetry of the walk and
two gaits with the in-phase symmetry of the hop. We present data
that support each of these predictions. This work suggests that
symmetry can be used to infer a plausible class of CPG network
architectures from observed patterns of animal gaits.
The architecture of CPGs is seldom observable in vivo. Aspects of
CPG structure are therefore usually inferred from observable gait
features such as the phase of the gait cycle at which a given limb hits
the ground, and the ‘duty factor’—the proportion of the gait cycle
that a limb is in contact with the ground. It is usual to model CPGs
as networks of nominally identical systems of differential equations,
variously described9–17 as ‘units’, ‘oscillators’ or ‘cells’. We use the
term ‘cell’.
Here we discuss a schematic CPG network10 (Fig. 1) that has twice
as many cells as the animal has legs. For expository purpose we
assume that cells 1, ,2ndetermine the timing of leg movements,
and refer to the remaining cells as ‘hidden’.
The structure of the CPG network for a quadruped shown in
Fig. 1b can be deduced from six assumptions: (1) the abstract CPG
network is composed of identical cells, and the signal from each
cell goes to one leg; (2) different gaits are generated by the same
... where pii represents the relative cover of the ith species in September 2007 (before the disturbance) and pif represents the relative cover of the ith species after the disturbance (October, November and December 2007) (Sankaran & McNaughton 1999). The closer to 1.0 this index becomes, the more resistant the community is. ...
... The closer to 1.0 this index becomes, the more resistant the community is. Before analyses, R values were transformed in arcsin square root (as suggested by Frank & McNaughton 1991;Sankaran & McNaughton 1999). ...
... we found that richer (or more diverse) plots are more resilient than the poorer or less diverse ones. Thus, our results are in line with other studies showing that increase in species richness enhances stability (McGrady-Steed et al. 1997;Sankaran & McNaughton 1999) and productivity (Tilman et al. 1996;Bouchard et al. 2007;Flombaum & Sala 2008). However, the diversity-stability hypothesis is still a controversial subject in community ecology (Maltchik et al. 2005;Zhang & Zhang 2006;Schultz et al. 2011). ...
Full-text available
In the last two decades, the relationship between diversity and stability/ecosystem functioning has been widely discussed and has become a central issue in ecology. Here, we assessed the relationship between wetland plant diversity and community resilience after a disturbance. Our study area was located in the Upper Paraná River floodplain (Brazil). An experiment was carried out in situ (18 1 m ¥ 1 m plots with richness varying from 1 to 18 species). In each plot, we recorded the number of species, total per cent vegetation cover and per cent age cover of each species. The above-ground biomass of wetland plants was removed, simulating a disturbance by animal trampling or an extreme flood. The recovery of vegetation was monitored over 3 months. According to a linear regression, the recovery of wetland plants was positively correlated with diversity. Comparisons with plots containing monocultures of one of the dominant species (Polygonum stelligerum) suggested that this species did not overyield in mixed cultures. Thus, our experiments indicate that the higher resilience in richer plots after a disturbance is mainly due to the fact that species have different resource use requirements (complementarity effect) and not due to the presence of a single, more productive species. Our experiment carried out in a more real condition (in situ) showed that biodiversity is important to wetland functioning and stability, paralleling the results obtained in laboratory and mesocosms experiments.These results also suggest that the loss of plant diversity in our study area could compromise community recovery following strong disturbances.
... The extent of change in community composition and function caused by stresses is highly related to community stability, a property reported governed by several biotic and abiotic factors (de Vries and Ashley, 2013). Species richness composing the community and the nutrients surround the community are reported in uential to the stability of a certain community (Sankaran and McNaughton, 1999; de Vries and Ashley, 2013; Bastida et al., 2017;O'Brien et al., 2017). However, unfortunately, there have been contradictory conclusions and opinions as to whether richness and environmental factors bene t community stability, or reduce it, when facing climatic stresses. ...
... A tropical forest study showed that plant community resistance to heat stress was enhanced by higher richness as the higher richness of plant neighbours in the surrounding area signi cantly enhanced the number of seedlings that survived under drought conditions (O'Brien et al., 2017). While a eld control experiment of savanna grassland in India reported that the composition of a plant community with higher richness was easier to change when exposed to drought stress and showed lower resistance (Sankaran and McNaughton, 1999). Su cient nutrients and favorable moisture could increase individual resistance of microorganisms to drought stress and thus might enhance community compositional stability (Bastida et al., 2017). ...
... Thus, if richness and environmental factors show different effects on resistance and resilience, while at the same time the communities studied rely mainly on either resistance or resilience, contradictory results may be observed. However, current research on compositional stability to climate stresses is mainly focused on arti cial communities composed of speci c species (Pennekamp et al., 2018), or focused on communities from a single ecosystems (Sankaran and McNaughton, 1999;Bastida et al., 2017;O'Brien et al., 2017). And it's quite necessary to explore the differences of community stability components from different ecosystems and resolve their relationship to richness and nutrient conditions, to get deeper understanding on community response and stability to climate stresses. ...
Full-text available
Soil microbial communities play irreplaceable roles in regulating environment. However, global climate change induced extreme weather events were reported capable reshape microbial community composition, which exert possible influences on the environment regulation function. Unfortunately, the compositional response of microbial community to extreme weather events and the potential factors regulating this response were still scarcely explored up to date. To fill the gap, here we sampled soils from 5 different type ecosystems and conducted a simulated extreme high-temperature stress experiment. The results showed that the complex ecosystems (like forests) had higher richness reduction than simple ecosystems (like bare land) during stress stage, most bacterial community richness kept decreasing while most fungal community richness were relatively unchanged during recovery stage. Despite the fungal communities in different types of ecosystems showed different and specific changes in the face of stress during the stress and recovery stage, the relative abundances of α- Proteobacteria were enhanced by stress in simple ecosystems but decreased in complex ecosystems, and the recovery stage of simple ecosystems were characterized by the trade-off between α-, β- and γ- Proteobacteria while complex ecosystems were by Firmicutes . Further analysis showed that the simple ecosystems tend to possess higher resistance and lower resilience while the complex ecosystems displayed the opposite trend. Resistance and resilience were significantly negatively correlated. Structural equation modeling showed that richness provided a higher contribution to bacterial and fungal resistance than to resilience while nutrients provided a higher contribution to resilience than to resistance. This research explored the influence of extreme high temperature stress on soil microbial community and the resistance and resilience of microbial community different types ecosystems to the stress, highlighted the respectively greater relative contribution of richness and nutrients offered to resistance and resilience, which provided valuable information for future prediction on microbial community response to climatic stresses.
... Compared with functional stability, community compositional stability, which considers changes in community membership and species relative abundance (Micheli et al., 1999;Sankaran & McNaughton, 1999), has received considerably less attention. Several earlier studies have examined compositional stability in relation to species diversity and documented various relationships between the two (Foster et al., 2002;Frank & McNaughton, 1991;Sankaran & McNaughton, 1999;Shurin et al., 2007;Wang et al., 2010). ...
... Compared with functional stability, community compositional stability, which considers changes in community membership and species relative abundance (Micheli et al., 1999;Sankaran & McNaughton, 1999), has received considerably less attention. Several earlier studies have examined compositional stability in relation to species diversity and documented various relationships between the two (Foster et al., 2002;Frank & McNaughton, 1991;Sankaran & McNaughton, 1999;Shurin et al., 2007;Wang et al., 2010). These results suggest varied importance of species diversity for regulating community compositional stability. ...
Full-text available
Anthropogenic nutrient enrichment is known to alter the composition and functioning of plant communities. However, how nutrient enrichment influences multiple dimensions of community‐ and ecosystem‐level stability remains poorly understood. Using data from a nitrogen (N) and phosphorus (P) addition experiment in a temperate semi‐arid grassland that experienced a natural drought, we show that N enrichment, not P enrichment, decreased grassland functional and compositional temporal stability, resistance and recovery but increased functional and compositional resilience. Compositional stability and species asynchrony, rather than species diversity, were identified as key determinants of all dimensions of grassland functional stability, except for recovery. Whereas grassland functional recovery was decoupled from compositional recovery, N enrichment altered other dimensions of functional stability primarily through changing their corresponding compositional stability dimensions. Our findings highlight the need to examine ecological stability at the community level for a more mechanistic understanding of ecosystem dynamics in the face of environmental change.
... Resilience has become an increasingly popular concept in the past decades within the field of ecology (Bellwood et al., 2006;Isbell et al., 2015;Leps et al., 1982;Macgillivray & Grime, 1995;Sankaran & McNaughton, 1999;Wardle & Jonsson, 2014) and well beyond (Carpenter et al., 2001;Zell & Hubbart, 2013). Despite this growing interest, studies quantitatively documenting resilience in the field are still uncommon (e.g. ...
... Despite this growing interest, studies quantitatively documenting resilience in the field are still uncommon (e.g. López et al., 2013;Macgillivray & Grime, 1995;Sankaran & McNaughton, 1999). This lack of empirical evidence is especially true for arid and semi-arid woody ecosystems, where slow dynamics and high spatial heterogeneity make the study of temporal trends highly time-consuming, often exceeding the typical duration of research grants (Li et al., 2015;Lindenmayer et al., 2012;Meserve et al., 2003). ...
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Resilience—the capacity of an ecosystem to recover from disturbance—is a popular concept but quantitative empirical studies are still uncommon. This lack of empirical evidence is especially true for semi‐arid ecosystems in the face of the combined and often confounding impacts of land use and climate changes. We designed a methodology to disentangle vegetation responses to land‐use exclusion and weather variability, and piloted it at the southern extreme of the Gran Chaco forest, the most extensive seasonally dry forest in South America. We established 16 pairs of neighbouring fenced and unfenced plots in four ecosystem types resulting from different long‐term land‐use regimes under the same climate and on highly similar soil parental material. From lower to higher land‐use intensity, related with logging and livestock grazing and trampling, these types were: primary forest (no land use in the last 50 years), secondary forest, closed species‐rich shrubland and open shrubland. In each plot we monitored plant species composition during the first 5 years following land‐use exclusion, and evaluated the resilience as the rate of change of vegetation towards the primary forest, considered as the reference ecosystem. We found that during the first 5 years of exclusion and despite the high rainfall, only grass cover in the secondary forest showed positive resilience (recovery towards the reference ecosystem). The rest of the variables in the other ecosystem types showed either no significant change (null resilience) or even transitioned away from the reference state (negative resilience). Synthesis . The lack of detectable recovery after 5 years of exclusion suggests that (a) long‐term land use, even at lower intensities, has affected the sources of resilience of this ecosystem; (b) rainy periods do not necessarily speed up recovery as suggested in the literature; and (c) study designs should incorporate the variation of the reference ecosystem in order to differentiate the effect of land use from other factors in a context of climate change. Although still confined to the early post‐disturbance stages, our findings suggest that recovery of these systems may be slower and more complicated than predicted in the literature on the basis of space‐for‐time substitutions.
... Resistance (the capability of an ecosystem to retain its original state during an environmental disturbance) and recovery (the capacity to recover following an extreme event) are two important aspects of ecosystem temporal stability (White et al., 2020;Xu et al., 2022). However, previous studies concerning ecological stability have principally concentrated on the resistance and/or recovery of ecosystem functions (particularly biomass) (He et al., 2022;Ma et al., 2023), paying less attention to the structural resistance and recovery of ecological communities, i.e., variations in community component species and species relative abundance (Micheli et al., 1999;Sankaran & McNaughton 1999). This has likely constrained the development of a comprehensive understanding of ecological stability across various levels of ecological organization. ...
Climate warming, often accompanied by extreme drought events, could have profound effects on both plant community structure and ecosystem functioning. However, how warming interacts with extreme drought to affect community‐ and ecosystem‐level stability remains a largely open question. Using data from a manipulative experiment with three warming treatments in an alpine meadow that experienced one extreme drought event, we investigated how warming modulates resistance and recovery of community structural and ecosystem functional stability in facing with extreme drought. We found warming decreased resistance and recovery of above‐ground net primary productivity (ANPP), and structural resistance, but increased resistance and recovery of belowground net primary productivity (BNPP) and overall net primary productivity (NPP), and structural recovery. The findings highlight the importance of jointly considering above‐ and belowground processes when evaluating ecosystem stability under global warming and extreme climate events. The stability of dominant species, rather than species richness and species asynchrony, was identified as a key predictor of ecosystem functional resistance and recovery, except for BNPP recovery. Besides, structural resistance of common species contributed strongly to the resistance changes in BNPP and NPP. Importantly, community structural resistance and recovery dominated the resistance and recovery of BNPP and NPP, but not for ANPP, suggesting the different mechanisms underlie the maintenance of stability of above‐ versus belowground productivity. This study is among the first to elaborate that warming modulates ecosystem stability in facing extreme drought, and lay stress on the need to investigate ecological stability at community level for a more mechanistic understanding of ecosystem stability in response to climate extremes. This article is protected by copyright. All rights reserved.
... Another aspect of pasture functionality that was not measured in this study was pasture stability. Pasture stability has also been shown to be related to the growth of plant with specific stress-tolerant traits (Sankaran & McNaughton, 1999;Tracy & Sanderson, 2004), and not necessarily total species diversity. As was explained in Section 4.2, the functional groups that were promoted in kānuka pasture had different survival strategies, with D. glomerata having stress tolerant traits, and the HFAs not growing through summer. ...
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Silvopastoral systems have great potential for forming multifunctional landscapes that provide a range of economic and environmental benefits to pastoral land. However, pasture production–diversity relationships in silvopastures require further exploration. This study measures how pasture functional group production, pasture species diversity and pasture functional diversity (FD) are impacted by trees in a novel native silvopastoral system in New Zealand hill country with kānuka (Kunzea spp.). Silvopastoral trees facilitated the growth of fast‐growing competitor functional groups (Lolium perenne, Dactylis glomerata and high fertility annuals: Bromus hordeaceus and Critesion murinum), because of positive impacts on soil fertility, organic matter and porosity. Shannon diversity, species richness and species evenness were significantly less in the more productive pastoral environment under the trees, but functional richness, functional evenness and functional dispersion were similar between kānuka pasture and open pasture. These results show that silvopastures can increase pasture production by promoting the growth of competitive pasture functional groups, and that reduced species diversity under silvopastoral trees does not necessarily impact FD in the context of production. Moreover, species indices overestimated diversity reductions under the trees compared to functional indices. Thus, considering FD in silvopastoral systems is integral for not misinterpreting diversity outcomes.
... Efforts to determine the relationship between biodiversity and the stability o f ecological function are at the heart o f a long-standing debate in ecology (McCann 2000). While demonstration o f the diversity-stability link has been elusive (Grime 1997;Naeem 2002aNaeem , 2002b, mounting evidence supports the hypothesis that biodiversity loss could Sankaran and McNaughton 1999;Tilman 1996;Tilman and Downing 1994). Therefore, in this era o f rapid climate change, increasing natural resource exploitation, and accelerating species extinctions Smith et al. 1993;Vitousek et al. 1997 Northern forestry and carabids: the case for concern about old-growth species. ...
Boreal forests of Canada, and elsewhere, are increasingly stressed by multiple, potentially interacting disturbances. In addition to natural disturbances like wildfire, anthropogenic stressors associated with increasing demands for natural resources have become critical elements of the disturbance regime in many areas. Thus, biodiversity conservation and sustainable forest management will increasingly depend on our understanding of the cumulative ecological consequences of disturbance. I examined the combined effects of wildfire and industrial forestry practices on boreal mixed-wood ground beetles and saproxylic beetles, and on the ecological function of one saproxylic species. Ground beetle responses to the individual and combined effects of wildfire, forest harvesting and herbicide-use were species-specific, but disturbance combinations led to a greater decrease in the compositional variability of the entire ground beetle assemblage. For saproxylic beetle assemblages, the combination o f wildfire and forest harvesting (postfire salvage logging) reduced species richness and altered species composition to a greater extent that either disturbance alone. Postfire salvage logging also altered the trophic structure o f the saproxylic beetle assemblage and was particularly detrimental for wood- and bark boring species. Through a series of experiments, the abundance of one such species, Monochamus scutellatus scutellatus, was linked to decomposition processes in burned forests. Together, the results of these studies suggest that disturbance combinations should be avoided whenever possible because they may impact not only beetle diversity, but also decomposition processes in forests recovering from wildfire.
... Recognizing the determinants of diversity and distribution of fauna at the global and regional scales is one of the important themes of ecological research, especially in the context of recent changes in the climate (Sankaran and McNaughton, 1999;Willig et al., 2003). The study of biodiversity is heavily dominated by the terrestrial ecosystem although the number of higher taxa is substantially greater in the marine realm than on land (Grassle et al., 1991). ...
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The global pattern of shallow marine biodiversity is constructed primarily using the data from extra-tropical sites. A severe knowledge gap in the shallow benthic diversity exists for the tropical Indian Ocean, especially along the coastline of peninsular India. Latitudinal biodiversity gradient (LBG)—a poleward decrease in diversity, even though accepted as a pervasive global pattern, often differs from regional trends. Although several oceanographic variables are known to influence regional patterns, their relative effect in shaping the shallow benthic community in tropical seas remains unclear. The east coast of India bordering the Bay of Bengal (BoB) presents a 2,500 km stretch (8–22°N) of tropical coastline with a spatial variation in oceanographic parameters including freshwater mixing, primary productivity, temperature, and shelf area. Here, we documented the marine bivalve distribution using spatially-temporally averaged beach samples and evaluated their relationship with the oceanographic variables. Our data reveal the existence of a highly diverse fauna, comparable to other tropical shallow marine sites. Overall species composition reflects a typical assemblage of the Indian Ocean, dominated by Veneridae but shows an uncharacteristically low proportion of Tellinidae and Lucinidae. The latitudinal variation in diversity shows a mid-latitude drop at around 14°N—a pattern inconsistent with the prediction of latitudinal biodiversity gradient (LBG). The functional groups are dominated by infauna (65%), unattached groups (69%), and suspension feeders (87%). There is only a slight difference in species composition between southern and the northern sites pointing to a predominantly continuous circulation and considerable mixing within the BoB. Productivity range, shelf area, and salinity emerge as best predictors of the species richness. All environmental variables together explain the species composition across the latitudinal bins satisfactorily. The species composition of the east coast shows no distinct nature in comparison to the Indo-Malayan biodiversity hotspot; the proximity to this hotspot and biological exchange with it may have contributed to the high diversity of the east coast fauna. Our study highlights the complex interplay between multiple oceanographic variables in determining the distribution and diversity of tropical shallow marine benthos at a regional scale generating biodiversity patterns that are at odds with global trends such as LBG.
Three hypotheses regarding relationships between community diversity and occurrences of rare and non-native species and community stability include: (1) diverse communities contain the greatest numbers of rare species, (2) hotspots of native species richness and abundance also support many non-native species, and (3) community diversity promotes stability. We explored these hypotheses by sampling plant communities during two years (2018, 2021) in 151, 0.05-ha plots across a landscape of temperate forests and open habitats (e.g., prairies) in Ohio, USA. Occurrence of rare plant species corresponded with the most species-rich and diverse (Shannon diversity index) communities in one or both study years. Species richness of native and non-native plants was positively associated both years but cover was not. Stability of species composition between 2018 and 2021 was unrelated to 2018 species richness and was negatively related to community diversity and evenness. The most diverse sites were not the most compositionally stable. Although statistically significant relationships occurred between community diversity measures and rare and non-native species distributions and community compositional stability, the relationships were often weak or mainly only evident at the extremes. Moreover, variance partitioning indicated that occurrences of rare and non-native species and community compositional stability were more closely associated with location effects within the landscape and community type than they were to community diversity. Nevertheless, when especially high or low, community diversity measures may facilitate predicting levels of other community components of conservation priority, such as rare species occurrences.
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We evaluated the effects of plant functional group richness on seasonal patterns of soil nitrogen and phosphorus cycling, using serpentine grassland in south San Jose, California. We established experimental plots with four functional types of plants: early-season annual forbs (E), late-season annual forbs (L), nitrogen-fixers (N), and perennial bunchgrasses (P). These groups differ in several traits relevant to nutrient cycling, including phenology, rooting depth, root:shoot ratio, size, and leaf C:N content. Two or three species of each group were planted in single functional group (SFG) treatments, and in two-, three-, and four-way combinations of functional groups. We analyzed available nutrient pool sizes, microbial biomass nitrogen and phosphorus, microbial nitrogen immobilization, nitrification rates, and leaching losses. We used an index of “relative resource use” that incorporates the effects of plants on pool sizes of several depletable soil resources: inorganic nitrogen in all seasons, available phosphorus in all seasons, and water in the summer dry season. We found a significant positive relationship between increasing relative resource use (including both plant and microbial uptake) and increasing plant diversity. The increase in relative resource use results because different functional groups have their maximum effect on different resources in different seasons: E’s dominate reduction of inorganic nitrogen pools in winter; L’s have a stronger depletion of nitrogen in spring and a dominant reduction of water in summer; P’s have a stronger nitrogen depletion in summer; N-fixers provide additional nitrogen in all seasons and have a significant phosphorus depletion in all seasons except fall. Single functional group treatments varied greatly in relative resource use; for example, the resource use index for the L treatment is as high as in the more diverse treatments. We expected a reduction of leaching losses as functional group richness increased because of differences in rooting depth and seasonal activity among these groups. However, measurements of nitrate in soil water leached below the rooting zone indicated that, apart from a strong reduction in losses in all vegetated treatments compared to the bare treatment, there were no effects of increasing plant diversity. While some single functional group treatments differed (P ≤ L, N), more diverse treatments did not. Early- and late-season annuals, but not perennial bunchgrasses, had significant positive effects on microbial immobilization of nitrogen in short-term (24 h) ¹⁵N experiments. We conclude that: (1) total resource use, across many resource axes and including both plant and microbial effects, does increase with increasing plant diversity on a yearly timescale due to seasonal complementarity; (2) while the presence of vegetation has a large effect on ecosystem nitrogen retention, nitrogen leaching losses do not necessarily decrease with increasing functional group richness; (3) indirect effects of plants on microbial processes such as immobilization can equal or exceed direct effects of plant uptake on nutrient retention; and (4) plant composition (i.e., the identity of the groups present in treatments) in general explains much more about the measured nutrient cycling processes than does functional group richness alone (i.e., the number of groups present).
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THE functioning and sustainability of ecosystems may depend on their biological diversity1-8. Elton's9 hypothesis that more diverse ecosystems are more stable has received much attention1,3,6,7,10-14, but Darwin's proposal6,15 that more diverse plant communities are more productive, and the related conjectures4,5,16,17 that they have lower nutrient losses and more sustainable soils, are less well studied4-6,8,17,18. Here we use a well-replicated field experiment, in which species diversity was directly controlled, to show that ecosystem productivity in 147 grassland plots increased significantly with plant biodiversity. Moreover, the main limiting nutrient, soil mineral nitrogen, was utilized more completely when there was a greater diversity of species, leading to lower leaching loss of nitrogen from these ecosystems. Similarly, in nearby native grassland, plant productivity and soil nitrogen utilization increased with increasing plant species richness. This supports the diversity-productivity and diversity-sustainability hypotheses. Our results demonstrate that the loss of species threatens ecosystem functioning and sustainability.
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Humans are modifying both the identities and numbers of species in ecosystems, but the impacts of such changes on ecosystem processes are controversial. Plant species diversity, functional diversity, and functional composition were experimentally varied in grassland plots. Each factor by itself had significant effects on many ecosystem processes, but functional composition and functional diversity were the principal factors explaining plant productivity, plant percent nitrogen, plant total nitrogen, and light penetration. Thus, habitat modifications and management practices that change functional diversity and functional composition are likely to have large impacts on ecosystem processes.
We test the hypothesis that the responses of vegetation to extreme events is a function of the nutrient stress tolerance of species present. The nutrient stress tolerance of a range of species was defined by a formalized procedure in which traits measured by screening in the laboratory were synthesized using principle components analysis. 2. Results were then compared with the results from a large-scale field experiment which examined the responses of five herbaceous plant communities in Derbyshire, UK to three extreme events (frost, drought and fire). 3. Nutrient stress tolerance was positively correlated with resistance to initial damage and negatively correlated with resilience (speed of recovery). The results illustrate the use of laboratory data to predict the field responses of plants to extreme events and demonstrate that the axis from high to low nutrient stress tolerance can play an effective role in predicting these responses.
Naeem and Li present the results of a microcosm study in which species diversity of organisms within trophic groups was varied. They conclude that the existence of multiple species within these groups enhanced the ``reliability'' of these systems, that is, the increased likelihood of a consistent level of performance over a given unit of time. But there are problems with their study. For the least diverse communities, one predator species was randomly selected from a selection of two, one autotroph from a selection of three, one consumer of bacteria from a selection of five, and one omnivore from a selection of six. Meanwhile, with the most diverse communities, both predator species and all three autotroph species were used, three consumer bacteria were chosen from the five and three omnivores from the six.
One of the tenets of the conservation movement has been that areas containing many species--those of high biodiversity--are particularly worth saving, since ecosystems of high diversity show improved ecosystem function. As Grime explains in his Perspective, this tenet is being replaced by another view, which is bolstered by three reports in this week's issue (pages 1296, 1300, and 1302). These studies all show that it is actually the specific features of the species in an ecosystem that determine its function--not their number.
We compared the distribution of historical bird and mammal species extinctions across genera and families with the distribution we would expect if these extinctions had occurred at random with respect to taxonomy. We then repeated the comparison for species listed in various categories of threat according to the 1996 Red List of the World Conservation Union. We found the distributions of extinctions and threat classifications to be almost always nonrandom—“selective”—with clustering in certain genera and families. Furthermore, extinctions tended to be clustered in taxa that contain few species; species in smaller genera tended to have higher probabilities of extinction. This tendency was strong for historical extinctions but was reduced or absent for some categories of threat. We attribute this to a change in the causes of extinction whereby predation and introduced species have been joined or superseded by widespread habitat loss. We then assessed the implications of this variable selectivity for the past and likely future losses of genera and families. In most cases, the number of lost taxa rises. Finally, we made predictions about minimum losses of taxa at specific dates in the future and showed that, despite the reduction in some forms of selectivity, we will still lose more taxa than if species extinctions were random. Selectividad Taxonómica Presente y Futura Extinciones de Aves y Mamíferos Se comparó la distribución de las extinciones históricas de especies de aves y mamíferos con la distribución que se esperaría si las extinciones hubieran ocurrido al azar con respecto a la taxonomía. La comparación fue repetida para las especies incluidas en distintas categorías de riesgo en la Lista Roja de la UICN. En casi todos los casos se encontró que las distribuciones de las extinciones y de las categorías de riesgo no estaban distribuidas al azar, sin que fueron ‘selectivas,’ con distribución agrupada en ciertos géneros y familias. Se observó, además, que las extinciones tendieron a estar agrupadas en taxones que contienen pocas especies; las especies en géneros más pequeños tienden a tener mayores probabilidades de extinción. Esta tendencia fue fuerte para las extinciones históricas, pero reducida o ausente para algunas categorías de riesgo. Esto se atribuyó a un cambio en las causas de extinción, donde la predación y las especies introducidas se han sumado o han sido reemplazadas por la gran destrucción de hábitat. Se evaluaron luego las consecuencias de esta selectividad variable para las extinciones de géneros y familias en el pasado y en un futuro probable. En la mayoría de los casos el número de taxones extinguidos aumenta. Finalmente, se hicieron predicciones acerca de las extinciones mínimas de taxones en el futuro, demostrándose que, a pesar de la reducción en algunas formas de selectividad, se extinguirán más taxones que si las extinciones fueran al azar.