title: authors: , arne strid , panayotis dimopoulos ...mar 01, 2020 · vulnerable species...
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Title: Management implications based on diversity patterns under climate change
scenarios in a continental island biodiversity hotspot
Authors: Konstantinos Kougioumoutzis1,2,3, Ioannis P. Kokkoris2, Maria Panitsa2,
Panayiotis Trigas3, Arne Strid4, Panayotis Dimopoulos2
Konstantinos Kougioumoutzis: [email protected] 1Department of Ecology and Systematics, Faculty of Biology, National and
Kapodistrian University of Athens, Panepistimiopolis, Greece, GR 15784 2Division of Plant Biology, Laboratory of Botany, Department of Biology, University
of Patras, Patras, Greece, GR 26504 3Laboratory of Systematic Botany, Department of Crop Science, Agricultural
University of Athens, Athens, Greece, GR 11855
Ioannis P. Kokkoris: [email protected] 2Division of Plant Biology, Laboratory of Botany, Department of Biology, University
of Patras, Patras, Greece, GR 26504
Maria Panitsa: [email protected] 2Division of Plant Biology, Laboratory of Botany, Department of Biology, University
of Patras, Patras, Greece, GR 26504
Panayiotis Trigas: [email protected] 3Laboratory of Systematic Botany, Department of Crop Science, Agricultural
University of Athens, Athens, Greece, GR 11855
Arne Strid: [email protected] 4Bakkevej 6, DK-5853 Ørbæk
Panayotis Dimopoulos: [email protected] 2Division of Plant Biology, Laboratory of Botany, Department of Biology, University
of Patras, Patras, Greece, GR 26504
Corresponding author: Konstantinos Kougioumoutzis; [email protected]
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Abstract
In the Anthropocene era, climate change poses a great challenge in environmental
management and decision-making for species and habitat conservation. To support
decision-making, many studies exist regarding the expected vegetation changes and the
impacts of climate change on European plants, yet none has investigated how climate
change will affect the extinction risk of the entire endemic flora of an island biodiversity
hotspot, with intense human disturbance. Our aim is to assess, in an integrated manner,
the impact of climate change on the biodiversity and biogeographical patterns of Crete
and to provide a case-study upon which a cost-effective and climate-smart conservation
planning strategy might be set. We employed a variety of macroecological analyses and
estimated the current and future biodiversity, conservation and extinction hotspots in
Crete, as well as the factors that may have shaped these distribution patterns. We also
evaluated the effectiveness of climate refugia and the NATURA 2000 network (PAs)
on protecting the most vulnerable species and identified the taxa that should be of
conservation priority based on the Evolutionary Distinct and Globally Endangered
(EDGE) index, during any environmental management process. The highlands of
Cretan mountain massifs have served as both diversity cradles and museums, due to
their stable climate and high topographical heterogeneity. They are also identified as
biodiversity hotspots, as well as areas of high conservation and evolutionary value, due
their high EDGE scores. Due to the ‘escalator to extinction’ phenomenon and the
subsequent biotic homogenization, these areas are projected to become diversity ‘death-
zones’ in the near future and should thus be prioritized in terms of conservation efforts
and by decision makers. In-situ conservation focusing at micro-reserves and ex-situ
conservation practices should be considered as an insurance policy against such
biodiversity losses, which constitute cost-effective conservation measures. Scientists
and authorities should aim the conservation effort at areas with overlaps among PAs
and climate refugia, characterized by high diversity and EDGE scores. These areas may
constitute Anthropocene refugia. Thus, this climate-smart, cost-effective conservation-
prioritization planning will allow the preservation of evolutionary heritage, trait
diversity and future services for human well-being and acts as a pilot for similar regions
worldwide.
Keywords: CANAPE; conservation; EDGE; environmental management; extinction
risk; Species Distribution Modelling
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Management implications based on diversity patterns under climate change
scenarios in a continental island biodiversity hotspot
1. Introduction
Earth has entered a new geological epoch, the Anthropocene (Zalasiewicz et al.,
2015), characterized by human-induced temperature, thus placing immense impacts
upon natural, atmospheric and hydrological processes. Consequently, global ecosystem
health is severely challenged, with shifts in biotic composition and ecological linkage
disruption being among the major threats of human activity worldwide. Species unable
to survive to such a novel adaptive matrix are on an inevitable path to extinction (Urban
et al., 2016), often causing a deadlock in nature management and protection practices.
Extinction threat might be more prominent on endemic species suffering from habitat
loss and fragmented populations (Warren et al., 2013), since they have narrower
geographical ranges and environmental niches. Climate change is projected to rapidly
change community structure in the near future, likely surpassing the land-use effects by
the 2070s (Newbold, 2018) and significantly altering terrestrial biodiversity (Warren et
al., 2013). On a global analysis of future climate change impacts, ca. 60% of plant
species examined were predicted to lose more than half of their current climatic range
in the coming decades, possibly leading to a substantial global biodiversity decrease
and ecosystem function degradation (Warren et al., 2013). Even though plants might be
more resistant to extinction compared to animals (Wing, 2004), climate change could
elevate the estimated extinction rates (Urban, 2015). Nearly 20-30% of species would
face high extinction risk if global temperature rises beyond 2-3 oC above pre-industrial
levels (Fischlin et al., 2007). In order to avoid a 1.5 oC rise in global temperature until
2052, unprecedented changes should be made at a global scale (IPCC, 2018). In this
context, it is important to follow a ‘climate-smart’ conservation planning strategy to
efficiently conserve as many species/communities as possible (Groves et al., 2012).
This strategy relies on the identification of climate refugia, i.e., relatively climatically
stable regions for many species of high conservation value which are characterised by
high endemic and genetic diversity (Sandel et al., 2011).
The Mediterranean Basin is a biogeographically complex area, with high levels of
endemism and diversification, due to its high topographic and climate heterogeneity
(Médail, 2017). It constitutes the second largest terrestrial biodiversity hotspot in the
world (Médail and Myers, 2004) with nearly 12500 plant species endemic to the region,
most of which have an extremely narrow geographical range (Médail, 2017). The
Mediterranean islands have high overall and endemic species richness (Médail, 2017).
Plant endemism varies between 9-18% on the largest islands and reaches up to 40% in
the high-altitude zone of their mountain ranges (Médail, 2017). Several of these islands
constitute biodiversity hotspots and climate refugia (Médail and Diadema, 2009). Crete
(S Greece) is rendered the hottest endemism hotspot of the Mediterranean Basin, owing
its high species number and endemism levels to long-term geographical isolation and
climate stability, as well as to its high environmental and topographical heterogeneity
(Médail, 2017).
The current global temperature will probably continue to rise (IPCC, 2018) and has
already forced species to migrate into higher altitudes, changed flowering
period/duration and in some cases, leading species to extinction (e.g., Thackeray et al.,
2016). These impacts will most likely accelerate (Urban, 2015) and are expected to be
more severe for species occurring on mountain ranges, due to the ‘escalator to
extinction’ phenomenon (Urban, 2018). The Mediterranean is a global hotspot of
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vulnerable species (Pacifici et al., 2015) and among the regions expected to experience
the largest changes in climate (e.g., Giorgi and Lionello, 2008), possibly leading to a
ca. 545 m upward vegetation shift and a 50-80 km northward shift in latitude, with these
impacts being more prominent on islands and mountain summits (Médail, 2017).
However, the Mediterranean Basin has experienced few plant species extinctions (22
taxa – 0.17% of the total; Domina et al., 2015). Most Mediterranean countries have
their own Red List of threatened plants. Nevertheless, regarding Crete ca. 30% (58 taxa)
of the Cretan single island endemics (SIEC) have been assessed and only five are
considered facing imminent extinction (Phitos et al., 2009). Several SIEC occur on the
island’s mountain ranges and comprise small and isolated populations, thus being prone
to climate change impacts.
New light can be shed upon the mechanisms underlying species’ possible extinction
and their subsequent conservation needs when integrating phylogenetic diversity
metrics into conservation-centred analyses (Morelli and Møller, 2018). Evolutionary
distinct species usually have unusual phenotypes, rare ecological roles and increased
functional importance (e.g., Cadotte et al., 2008). As such, they have great conservation
value, since their loss cannot be readily replaced. Thus, if evolutionary isolated species
are to become extinct, this would result into great evolutionary loss. Therefore, any
conservation plan needs to take into account the advantage of the conservation
prioritization of evolutionary distinct species, as it allows the preservation of
evolutionary heritage, trait diversity and future services for human well-being (Veron
et al., 2018).
Correlative species distribution models (SDMs) are widely used to identify which
species are most vulnerable, as well as to answer how, why, where and when these
species are vulnerable (Foden et al., 2019). There is ample evidence that the
expectations from correlative SDMs have matched recent population trends focusing
on birds, mammals and plants, in decreasing order and they provide appropriate results
when the aim is to estimate a species’ extinction risk (Pacifici et al., 2015). To our
knowledge, even though continental-wide studies exist regarding the expected
vegetation changes and the impacts of climate change on European plants (e.g., Berry
et al., 2017), none has investigated how climate change will affect the extinction risk
of the entire endemic flora of an island biodiversity hotspot, such as Crete. Our aim is
to assess, in an integrated manner, the impact of climate change on the biodiversity and
biogeographical patterns of the endemic plants of Crete and to provide a case-study
upon which a cost-effective and climate-smart conservation planning strategy might be
set.
2. Material and Methods
2.1 Study area
We focus on Crete (Fig. 1), the fifth largest island in the Mediterranean Basin and
the richest island hotspot of Europe in terms of endemic plant species (Médail, 2017).
Crete is the largest (8836 km2) and most topographically complex island in the
Aegean archipelago with more than 50 mountain peaks exceeding 2000m a.s.l. The
island is climatically compartmentalized in a W-E axis and is characterized by a sharp
altitudinal gradient (0-2456 m a.s.l.). There are three main mountain massifs present on
Crete (Lefka Ori, Idi and Dikti), with an entirely different climate than the warm and
dry lowland plains.
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Figure 1. The island of Crete, along with the altitudinal contours at a 100m
increment.
Geologically, Crete comprises mostly limestones, is part of the Hellenic Arc and was
formed in response to the subduction of the African plate beneath the Aegean (Higgins,
2009).
Its palaeogeographical history is rather complex and determined by two main
geological events that created important dispersal barriers (for a thorough review of the
Aegean’s palaeogeographical history see Sakellariou and Galanidou, 2016): i) the
isolation of Crete from Karpathos’ and Cyclades’ island groups 12 Mya and ii) the
isolation of Crete from Peloponnese after the Messinian salinity crisis (Manzi et al.,
2013).
2.2 Environmental data
An initial set of 43 predictors has been constructed (see Appendix A in Supporting
Information), all at a 30 arc-sec resolution, including:
a. sixteen climatic variables based on the 19 bioclimatic variables from
WorldClim for current and future climate conditions.
b. three Global Circulation Models (GCMs) that are rendered more suitable and
realistic for the study area’s future climate.
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c. two different IPCC scenarios from the Representative Concentration Pathways
(RCP) family: the mild RCP2.6 and the severe RCP8.5.
d. seven soil variables providing predicted values for the surface soil layer at
varying depths.
e. elevation data from the CGIAR-CSI data-portal (Jarvis et al., 2008) aggregated
and resampled to match the resolution of the other environmental variables.
From this set of predictors, only seven were not highly correlated (Spearman rank
correlation < 0.7 and VIF < 5 – see Appendix A).
2.3 Climate refugia We located sites in Crete that are climatically stable (sensu Owens and Guralnick, 2019)
for the past 4 My, using paleoclimatic data obtained from Brown et al. (2018) and
Gamisch (2019), the framework of Owens and Guralnick (2019) and the
`climateStability´ 0.1.1 package (Owens, 2019). Climate refugia as designated here
refer to macro-refugia according to Ashcroft (2010).
2.4 Species Occurrence Data
Crete hosts 2240 native plant species, 183 of which are single island endemics (SIEC)
(Dimopoulos et al., 2013, 2016; Strid, 2016). Based on the most extensive and detailed
database [Flora Hellenica Database, Strid (ongoing)], we compiled a dataset of all the
SIEC (8773 occurrences). The final dataset includes 172 SIEC, since we modelled only
those SIEC with at least three locations (following van Proosdij et al., 2016).
Data cleaning and organizing procedure follows Robertson et al. (2016 – see
Appendix A).
2.5 Phylogenetic tree
Since molecular data are not available for many of the SIEC, we used a “supertree”
approach to generate our phylogenetic tree (see Appendix A). We subsequently
calculated evolutionary distinctiveness (ED) and EDGE (Evolutionary Distinct and
Globally Endangered) scores for each taxon, as well as the standardized effect size
scores of phylogenetic diversity (PD) for each grid cell (see Appendix A).
2.6 Species distribution models
2.6.1 Model parameterization and evaluation
The realized climatic niche of each taxon was modelled by combining the available
occurrence data to current environmental predictors in an ensemble modelling scheme
(Araújo and New, 2007 - see Appendix A).
2.6.2 Model projections
Calibrated models with a TSS score > 0.8 (to avoid poorly calibrated ones) were used
to project the suitable area for each taxon under current and future conditions through
an ensemble forecast approach (Araújo and New, 2007 - see Appendix A).
2.6.3 Area range change
We assessed whether the 172 SIEC will experience range contraction or expansion
under future conditions (see Appendix A). Taxa were not assumed to have unlimited
dispersal capability, since this assumption could be overoptimistic.
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2.7 IUCN measures
We followed the Preliminary Automated Conservation Assessment (PACA) framework
(Stévart et al., 2019), calculated the IUCN measures EOO (Extent of Occurrence) and
AOO (Area of Occupancy) and assigned each SIEC to a preliminary IUCN threat
category according to the Criteria A and B under current and future conditions (see
Appendix A). After taxa were assigned to an IUCN and a PACA category, the total
number of taxa recorded and the proportion of taxa assessed under each category were
estimated, by combining Criteria A and/or B.
2.8 Niche breadth
Levins’ inverse concentration measure of niche breadth (Levins, 1968) was computed
for each taxon (see Appendix A). Niche breadth values range from 0 (specialists) to 1
(generalists) being thus comparable among taxa (Levins, 1968). Difference of niche
breadth between the different IUCN threat categories, was investigated via a Kruskal-
Wallis non-parametric test (KWA), as well as the difference of area range change
between SIEC with broad or narrow environmental niches (see Appendix A).
2.9 Hotspot analysis
For each climate scenario, we stacked the final binary maps of all 172 SIEC. From this
overlay, we calculated for each 30-sec grid-cell the number of taxa that would find
suitable environmental conditions there. We defined potential SIEC hotspots as the 20%
of cells that provide suitable environmental conditions to the highest number of taxa.
2.10 Generalized Dissimilarity Modelling analysis
We used Generalised Dissimilarity Modelling (GDM) to model pairwise plant
community compositional dissimilarity (Sorensen’s dissimilarity) within map grid cells
across Crete. We used the same environmental variables as in the SDM analyses, with
the significance of all variables assessed through a Monte Carlo permutation test (see
Appendix A).
2.11 Significant Differences
To identify sites where predictions of hotspot location differed significantly between
current and future environmental conditions, we applied the methodology proposed by
Januchowski et al. (2010 - see Appendix A).
2.12 Biodiversity indices We performed Categorical Analyses of Neo- and Paleo-Endemism (CANAPE), using
the methods and reasoning described in Mishler et al. (2014) and Thornhill et al. (2016
– see Appendix A).
We assessed the impact of climate change on the distribution of the endemism
hotspots by repeating the CANAPE analysis for every GCM/RCP combination
included in our study.
We tested the relationships among phylogenetic endemism (PE) and relative
phylogenetic endemism (RPE) with elevation, pH, mean diurnal range (MDR) and
climate stability by employing spatial autoregressive models with spatially
autocorrelated errors (SARerr - see Appendix A).
2.13 Future diversity and biogeographical patterns We derived species composition in each grid cell under current and future climatic
conditions by stacking the presences from the individual species models. We followed
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the framework outlined in Menéndez-Guerrero et al. (2019) regarding the assessment
of the spatial biodiversity and biogeographical patterns under future climate scenarios
(see Appendix A).
2.14 Protected areas network and climate refugia overlap
We overlapped current and future CANAPE and hotspot results with the areas
recognised as climate refugia, as well as with the protected areas (PA) network retrieved
from the World Database on Protected Areas (see Appendix A). Based on each species’
current and future EOO, we calculated the irreplaceability of each PA and climate
refugium in Crete for the current and future climate conditions. The irreplaceability
index represents biotic uniqueness and quantifies the degree of overlap between each
PA/climate refugium and the range of SIEC (Le Saout et al., 2013). We investigated
whether the degree of overlap differed between the current and future conditions via a
Kruskal-Wallis non-parametric test.
3. Results
3.1 Model performance
The models for most SIEC had sufficient predictive power (TSS ≥ 0.7 – mean TSS:
0.94; Table S1 in Appendix B). The resulting habitat suitability maps were converted
into binary maps and then compared to the binary maps obtained for each GCM, RCP
and time-period for each SIEC. Precipitation-related variables had the highest
contribution among the response variables for most SIEC (53.5%), while temperature-
related variables and soil pH were important for a smaller fraction of SIEC (42.4% and
4.1%, respectively). Full details and analyses of model performance are given in Table
S1.
3.2 Area range change
All SIEC species will experience range contraction, with varying magnitude across taxa,
GCMs and RCPs (11.7% - 100.0%; Table S1), but the median range contraction was
98.3% (see Table S2 for the median values for each GCM and RCP).
3.3 IUCN measures
For the first time, we provide a preliminary assessment of every SIEC occurring in Crete
according to the IUCN Criteria A and B (Fig. 2; Table S1). At present, 58.7% of SIEC
are facing imminent extinction (Fig. 2) and 87.8% are characterised as Likely
Threatened (LT) under the PACA categories (Table S1). This phenomenon could be
greatly deteriorated, since under any GCM and RCP included in our analyses, many of
these species are projected to become extinct (median EX%: 48.85% - Fig. 2, Table
S1). The distribution and the proportion of taxa assessed as Threatened either under the
IUCN or the PACA categories under both Criteria A and B are not uniform across Crete
(Fig. 3). These taxa are mostly concentrated at the Cretan mountain massifs, with the
highest proportion of them occurring in Lefka Ori (Fig. 3). These high-altitude areas
are predicted to become extinction hotspots under any GCM/RCP (Fig. S1).
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Figure 2. Proportion of the Cretan Single Island Endemics included in our analysis
under the IUCN threat categories for the current conditions according to both
Criterion A and B, as well as for every GCM and RCP considered in the present
study.
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Figure 3. (a) Proportion of species and (b) number of species preliminary assessed as
Threatened (either Critically Endangered, Endangered or Vulnerable) following
Criteria A and B.
3.4 Niche breadth
The median niche breadth was 0.41 for the SIEC and 25% of the SIEC are considered to
have a narrow niche breadth (Table S1). Niche breadth differed significantly between
all the IUCN categories (KWA: H = 56.6, d.f. = 3, p < 0.05) and species with narrow
niches have higher extinction probability for every GCM/RCP (Table S1).
3.5 EDGE
Based on both Criteria A and B, the SIEC have EDGE scores in the range 3.57-8.74,
with most species (75%) falling in an EDGE score class of 3.57-6.39. Eleven species
(Table S1) have an EDGE score exceeding 7.0, belonging to eleven different families
and all are considered as CR taxa (Table S1).
3.6 Hotspot analysis
The eastern, central and high-altitude parts of Crete are more likely to lose most of the
SIEC occurring there (Figs. S2-8). The SIEC hotspots are currently located above 1500
m a.s.l. in Crete (Fig. S2), but all of them are expected to shift downwards – even below
1000 m a.s.l. under any GCM/RCP (Fig. S3-8) and these shifts are significantly
different in absolute or relative terms (Figs. S9-20).
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3.7 GDM analysis
GDM helped disentangle the relative contribution of geographic and environmental
drivers of SIEC community composition across time and space. Our model explained
26.6% of deviance in SIEC composition (Figs. S21-22). Under any GCM/RCP, the low-
elevation area in W Crete is predicted to exhibit the greater floristic turnover than any
other region, followed by the high-altitude Cretan mountain ranges (Figs. S23-28). The
most important gradient for determining SIEC turnover was annual potential
evapotranspiration (PET), followed by geographical distance (Fig. S21). Soil pH was
the weakest predictor of SIEC turnover. The fitted functions describing the turnover rate
and magnitude along each gradient were nonlinear, with turnover rate varying with
position along gradients (Fig. S21). An acceleration zone in SIEC turnover was evident
for PET and short geographical distances, while a sharp compositional transition was
apparent along the precipitation of the wettest month gradient (Fig. S21).
3.8 Biodiversity indices
Higher and lower PD than expected was found in 21 and 86 sites, respectively (Fig.
S29). These sites did not differ significantly in terms of elevation or pH preferences
(both occur above 850 m a.s.l.), but the non-significant sites were located in lower
elevation areas with higher pH (KWA: H = 261.93, d.f. = 5, p < 0.05; Table S3).
The CANAPE analyses revealed 208 sites as containing more PE than expected (Fig.
4a), which are mainly concentrated within and at the periphery of the four Cretan
mountain massifs. Areas of mixed-endemism are the most common, followed by paleo-
and neo-endemism areas (156, 26 and 21, respectively). Centres of paleo- and mixed-
endemism occur in significantly higher altitude than not-significant sites (KWA: H =
15.73, d.f. = 4, p < 0.01; Table S4). Most paleo-endemism areas occur in western Crete
and on the mountain massifs of eastern Crete (Fig. 4a). Overall results are congruent,
regardless the grid resolution (Fig. S30).
The occurrence of the centres of endemism is projected to shift downwards (except
for the super-endemism centres) in the future under any GCM/RCP (Figs. S31-36;
Table S5) and these changes are significantly different for the mixed- and paleo-
endemism centres mainly (KWA: H = 344.17, d.f. = 9, p < 0.01).
The SARerr models indicate that elevation is the most important predictor of both PE
and RPE (GR2 = 16.1% and 5.9%, respectively; Table S6), followed by MDR and CS,
respectively.
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Figure 4. (a) Map of significant phylogenetic endemism (PE) identified by the
Categorical Analysis of Neo- And Paleo-Endemism (CANAPE) analysis for 172
Cretan Single Island Endemics. Red squares: centres of mixed-endemism (i.e. mix of
neo- and paleo-endemism). Blue squares: centres of neo-endemism; Purple squares:
centres of paleo-endemism. Orange squares: centres of super-endemism. (b) Map of
Crete showing predicted distribution of areas of biotic homogenization with respect to
Cretan SIE species diversity, according to the CCSM4 26 GCM/RCP. Red areas
indicate a decrease in beta-diversity (biotic homogenization). Blue areas indicate an
increase in beta-diversity (biotic heterogenization). Analyses were performed under
the assumption that a species cannot have unlimited dispersal capability, since this
assumption could be overoptimistic.
3.9 Future diversity and biogeographical patterns
3.9.1 Changes in ΔEDGE
Patterns of change regarding the EDGE index show that the high-altitude areas of Crete
are currently identified as hosting assemblages of great evolutionary distinctiveness
facing immediate extinction risk (Fig. S37). These areas are projected to become
extinction hotspots under any GCM/RCP (Figs. S38-39). In the future, the mid-altitude
areas are predicted to take up their place (Figs. S38-39).
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3.9.2 Changes in ΔBD
Areas with high SIEC βsim are currently concentrated in high altitudes, mainly across
the four Cretan mountain massifs (Fig. 5a). On the other hand, βsim is relatively low
over most of the lowlands and especially in the coastal area of northern Crete (Fig. 5a).
βsim is projected to generally increase in western Crete and in the mid-elevation areas
(1000-1500 m a.s.l. – a trend towards biotic heterogeneity) and this pattern is projected
to be greatest in a small coastal area of SW Crete (Fig. 4b). An entirely different pattern
emerged mainly in the Cretan highlands, where βsim is predicted to decrease (i.e., a trend
towards biotic homogenization – Figs. 4b-5).
Figure 5. Bivariate maps depicting relative changes in biodiversity measures for
Cretan SIE between the present and the CCSM4 26 GCM/RCP. Colours indicate the
relative amount of change. The red and blue end of the spectrum indicate reductions
and increases, respectively. Each transition in colour shading indicates a 10% quantile
shift in the value of the variables. (a) beta-Diversity, (b) species richness (SR), (c)
average level of ecological generalism (EG), (d) phylogenetic diversity (PD). Yellow
areas indicate sites with high current beta-diversity that will continue to have
proportionally high beta-diversity. Blue areas indicate sites that beta-diversity is
predicted to increase in the future. Green areas indicate sites where beta-diversity will
remain largely unchanged. We used a function generated by José Hidasi-Neto to
generate the map (http://rfunctions.blogspot.ca/2015/03/bivariate-maps-bivariatemap-
function.html).
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The most parsimonious model for all GCMs/RCPs was the full GAM including
ΔEG, ΔPD, ΔSR and elevation (Table S7, ΔAIC < 2), which explained 71.2-96.6% of
the total variance in βsim (Table S7). Both ΔPD and ΔSR were negatively correlated
with βsim change, while ΔEG was positively correlated with βsim change (Fig. 7; Figs.
S40-44). Here we focus on the results obtained for the CCSM4 2.6 GCM/RCP, as it
shows the highest similarity with the current conditions (see Changes in
biogeographical patterns below) and the patterns and trends do not deviate between the
different GCMs and RCPs. The increasing heterogeneity of western Crete and mid-
elevation areas (Figs. 4b-5) is mainly driven by range expansion and local extinction of
generalist and specialist species, respectively (Fig. 6; see also red areas in Fig. 5b-c).
Range expansions and local extinctions tend to drive species richness decreases,
resulting in phylogenetic clustering (Fig. 6d). Hence, future SIEC assemblages will tend
to be species-poor and comprised of taxa that are more closely related than current
assemblages (Fig. 6d; see also blue areas in Fig. 5d). The same processes are largely
responsible for the predicted biotic homogenization of the higher elevation areas in
Crete, even though these areas are predicted to host more specialist species.
Figure 6. Biplots showing the predicted relationships between βsim change and the
four environmental predictors included in the best generalized additive model (GAM)
a b
c d
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for the CCSM4 26 GCM/RCP. (a) Change in species richness (ΔSR). (b) Change in
phylogenetic diversity (ΔPD). (c) Change in elevation. (d) Change in the average
level of ecological generalism (ΔEG). Fitted lines show the univariate GAMs with
95% confidence interval (dark grey). Rugs on the x-axes show the predictor values
and how they are distributed. Labels on the y-axes indicate the smooth functions for
the term of interest (ΔSR, ΔPD, ΔEG and elevation) and the estimated degrees of
freedom (following the term). Values above and below the horizontal dashed line
indicate heterogenization and homogenization, respectively. Values left and right of
the vertical dashed line indicate in (a) species loss and gain, (b) PD decrease and
increase and (d) assemblages composed by specialists and generalists, respectively.
3.10 Climate refugia and protected areas network overlap
Six areas were identified as climate refugia and are located along a W-E axis in Crete
(Fig. S60). The largest and most species-rich climate refugium is located in the wider
area of Lefka Ori in W Crete, while the smallest and species-poor is near the Asterousia
mountain range in SC Crete (Fig. S60; Table S9). One and two of the climate refugia
are significantly phylogenetically overdispersed and clustered, respectively (Table S9).
In the future, all these areas are predicted to continue to serve as climate refugia, with
different trends: the species-poor and species-rich refugia show a trend towards
phylogenetic dispersion (PD increases) and clustering (PD decreases), respectively
(Table S9).
The overlap between the PA network in Crete and endemism centres detected by
CANAPE is rather high and ranges between 52-65% (Table S10; Fig. S61). The overlap
between the areas recognised as climate refugia and endemism centres detected by
CANAPE is lower than that reported for the PA network and ranges between 0-22%
(Table S10; Fig. S62). Under any GCM/RCP, the predicted overlap for both the PA
network and the climate refugia is lower than the one currently observed for most
GCMs/RCPs and CANAPE categories (Table S10). The overlap between the PA
network and the climate refugia ranges between 13.3-97.0% (Table S11). The percent
overlap based on the recognised climate refugia of at least the neo-endemism centres is
predicted to increase in the future, while the opposite trend is predicted for all the other
CANAPE types (Tables S11-12). The mean irreplaceability index differs significantly
between PAs and climate refugia (KWA: H = 56.6, d.f. = 1, p < 0.01; Fig. S63), as well
as between PAs and any GCM/RCP (KWA: H = 103.3, d.f. = 6, p < 0.01). Regarding
climate refugia, the mean irreplaceability index is significantly different only between
the current and the HadGEM2 RCP 8.5 climate projection (KWA: H = 14.6, d.f. = 6, p
< 0.05; Fig. S63). When taking out the effect of area, the mean irreplaceability index
does not differ significantly between PAs and climate refugia, except for the current
and the HadGEM2 RCP 8.5 climate conditions (KWA: H = 2.79, d.f. = 1, p = 0.09; Fig.
S64).
4. Discussion
Climate change is projected to alter biodiversity and biogeographical patterns all over
the globe (e.g., Enquist et al., 2019). The Mediterranean Basin is expected to face the
largest changes in climate worldwide (e.g., Giorgi and Lionello, 2008), with these
impacts being more prominent on islands and mountain summits (Médail, 2017). Here,
we used the hottest endemic Mediterranean hotspot, Crete, as a case-study for
management scenario building and decision making, based on an integrated assessment
of climate-change impacts on biodiversity, biogeographical and conservation patterns.
Our results highlight an augmented extinction risk for the majority of the SIEC, while
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pinpointing areas of high conservation and evolutionary value; they should alert
conservation practices and management to take measures for biodiversity loss restrain
and halt of further deterioration.
4.1 Diversity hotspots
The high-altitude areas of Crete are identified as species richness hotspots, with Lefka
Ori, the western mountain massif, hosting the most SIEC (Fig. S1). These areas are
predicted to experience a sharp decline in species richness under any GCM/RCP and
will no longer constitute biodiversity hotspots, as a result of the ‘escalator to extinction’
phenomenon (e.g., Urban, 2018). Due to upward species’ range shift and the extinction
of high-altitude SIEC, mid-altitude areas will host an increasing number of species, thus
intensifying the observed mid-domain effect of the SIEC (Trigas et al., 2013). Most of
the upward migrating species will probably be neo-endemic species, since neo-
endemism centres occur at lower altitudes than paleo-endemism centres in Crete (Table
S4).
4.2 Conservation assessment We evaluated the potential conservation status of SIEC using the IUCN Criteria A and
B. Most of the SIEC are potentially threatened by extinction (Table S1; Fig. 2). These
potential extinctions were not randomly distributed among evolutionary groups, when
accounting for mean future area loss (Cmean = 0.12; p < 0.01), a phenomenon observed
in mammals as well (Davies and Yessoufou, 2013). The SIEC will be highly vulnerable
in the future, since up to 154 taxa are projected to become extinct (Table S1; Fig. 2).
The high-altitude areas that now serve as diversity and conservation hotspots (due to
high EDGE scores - Figs. S2 and S37) are projected to become extinction hotspots (due
to very low ΔEDGE scores - Figs. S1 and S38-39) and should thus be prioritized in
terms of conservation efforts. Eleven taxa (Table S1) should also be given high
conservation priority, since they have a very high EDGE score. However, none of them
is included in the IUCN Top-50 Mediterranean Island Plants initiative (de Montmollin
and Strahm, 2005). Identifying conservation priorities and implementing effective
actions are urgently needed and will become increasingly important, since human
activities and land use are exerting unprecedented pressure on natural environments,
leading to severe biodiversity changes (IPCC, 2018; Veron et al., 2016). In this context,
locating areas with high EDGE and low ΔEDGE scores could help prioritize areas of
high conservation and evolutionary importance and high extinction risk.
4.3 CANAPE A fundamental block for understanding biodiversity patterns and consequently for
conservation prioritization is to determine where species diversify (centres of neo-
endemism – cradles) and persist (centres of paleo-endemism – museums) over
evolutionary time. By this, we can decide whether or not PAs are indeed sheltering
different aspects of biodiversity (Tucker and Cadotte, 2013) and improve conservation
management in the unprecedented biodiversity decline setting which is currently
underway (Humphreys et al., 2019). By incorporating evolutionary history and
randomization processes, we were able to identify new areas of high evolutionary and
conservation value. In total, 107 sites had PD higher or lower than expected by chance
(Fig. S29), scattered across a W-E axis. Phylogenetically overdispersed sites of high
conservation importance (Swenson et al., 2007) occur at higher altitudes in Crete and
this may be related to a variety of reasons, such as the competitive exclusion of closely
related taxa with high niche overlap, the colonization of phylogenetically distinct
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lineages (e.g., Campanula/Roucela species) or the high topographical heterogeneity of
the Cretan mountain massifs that harbour distinctly adapted plant lineages (e.g., Edh et
al., 2007).
In Crete, mixed-endemism centres occurring in higher altitude than the other types
of endemism centres, prevail (Fig. 4). It seems that in Crete, montane regions do not
act just as diversity cradles, but also as diversity museums – a pattern observed in other
parts of the world as well (e.g., Dagallier et al., 2019). Most paleo-endemism centres
occur in or near ravines/gorges in western Crete and on the mountain massifs of eastern
Crete (Fig. 4a); these areas may have functioned as biogeographical museums (Chown
and Gaston, 2000). Neo-endemism centres tend to occur in sub-montane altitude in
Crete, rather near mixed-endemism centres (Fig. 4a); their recent diversification may
have hindered their expansion. In the future, the occurrence of almost all types of
endemism centres are projected to shift downwards under any GCM/RCP (Figs. S31-
36; Table S5), suggesting that montane areas that have served as both diversity cradles
and museums for a very long time, will probably become diversity ‘death-zones’ in the
near future.
Climatic stability and high topographical/environmental heterogeneity may act in
conjunction to provide the conditions needed for the simultaneous persistence of paleo-
endemics and the diversification of neo-endemics (e.g., Azevedo et al., 2019). In this
context, altitude – a proxy of environmental heterogeneity (e.g., Cabral et al., 2014)
emerged as the most important predictor of PE and RPE in Crete, followed by MDR,
pH and CS. Niche-related processes thus seem to play a minor role in generating
endemism patterns in Crete, which is in line with previous studies at a coarser scale
(Lazarina et al., 2019). Distinct endemism patterns may be found in sites with
phylogenetically distinct assemblages, even if environmental similarity is high, due to
phylogenetically conserved niche breadth and dispersal ability (Wiens and Graham,
2005). This could be the case in Crete, since SIEc’s niche breadth has a significant,
though weak phylogenetic signal (Cmean = 0.11, p < 0.05). Our results lend weight to
the suggestion that the interplay between topographical heterogeneity and climate may
be linked with the configuration of centres of paleo- and neo-endemism on mountain
massifs (Rangel et al., 2018), a phenomenon also recorded in the Neotropics (Azevedo
et al., 2019). However, the low GR2 for both RE and RPE limits the scope of
conclusions we can draw from these results, and so they should be regarded as
informative rather than conclusive.
4.4 Future diversity and biogeographical patterns
We predict a trend towards biotic homogenization in the Cretan highlands, whereas an
opposite trend towards biotic heterogenization will probably occur in low- and mid-
elevation areas in Crete (Figs. 4b-5). Biotic homogenization is driven by the range
expansion of generalists and the consequent local extinction of specialists, resulting in
overall lower local species richness and phylogenetic diversity (Figs. 6 and S40-44).
The same processes drive biotic heterogenization in Crete, however these assemblages
will probably have higher species richness, due to the higher migration rate from the
lowlands. The prominent homogenization of the Cretan highlands suggests that
climate-driven extinctions of specialists may have greater impact on beta-diversity
patterns than the generalists’ range expansion. After all, the most important gradient for
determining SIEC turnover is PET, followed by geographical distance (Figs. S21-22)
and niche-based processes were found to exert some influence in the distribution of
species occurring in Crete (Lazarina et al., 2019). These regional variation shifts in beta
diversity could disrupt ecosystem functioning and provisioning of ecosystem services
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(Cardinale et al., 2012). To properly assess and predict future projections of landscape
fragmentation, changes in demand, use and supply of ecosystem services should be
taken into account, using a climate-change, management scenario-based approach (e.g.
Kokkoris et al. 2019) and is particularly important for policy and decision-making
related to land and resource use (Geijzendorffer et al., 2017). Our results are in line
with the emergence of the ‘Homogenocene’ era, observed in other regions and
organisms as well (e.g., Menéndez-Guerrero et al., 2019).
Currently Crete, a speciation centre (Panitsa et al., 2018) and a distinct Aegean
phytogeographical region (Kougioumoutzis et al., 2017) is biogeographically
subdivided into 14 different regions (Figs. S45-46), a result probably of
paleogeographical history and local climate differentiation. This unique
biogeographical compartmentalization seems to be at peril, since under any GCM/RCP
it will drastically change (Figs. S47-58; Table S8), showing a trend towards biotic
homogenization in a W-E axis, along Crete’s altitudinal range. This phenomenon seems
to have a greater impact on the SIEC of the Cretan highlands, since most of the habitat
specialists occurring there, will probably be among the first to become extinct in the
next decades.
4.5 Conclusions – Conservation and management implications
Incorporating climate-change projections is critically important for management
strategies. Identifying climate refugia is an integral part of the ‘climate-smart’
conservation planning framework, since they constitute taxonomic and genetic
diversity centres (e.g., Sandel et al., 2011), with macro-refugia – areas that sustain
climatic suitability along broad spatiotemporal gradients (Ashcroft, 2010) – being
generally more easily captured by GCMs. In the Mediterranean basin, where land-use
change and the occurrence of fire events are expected to intensify (e.g., Turco et al.,
2018), having a resilient PA system should be a priority. However, the current
conservation strategy and management agenda for future conservation projects in Crete
is based on the obligations of Dir. 92/43/EEC and especially for habitats and species of
Annex I and II, respectively. These obligations include reporting for the conservation
status and future trends for only a few species identified as under extinction risk by the
present study. It is also evident that hesitancy toward anything but conventional
conservation actions persists (Hagerman and Satterfield, 2013). Considering the worst-
case scenario (i.e. extinction of the highest number of species by climate-change
impact), in-situ conservation focusing at micro-reserves and ex-situ conservation
practices should be considered, as an insurance policy against such losses of plant
biodiversity (Hawkes et al., 2012), which constitute cost-effective conservation
measures (Kadis et al., 2013). By this, our study urges scientists and authorities to aim
the conservation effort at areas with overlaps among PAs and climate refugia,
characterized simultaneously by high diversity and EDGE scores (including the 11 taxa
with the highest EDGE score), as well as serving as mixed-endemism centres. These
areas are qualified as future climate refugia and may actually constitute Anthropocene
refugia (Monsarrat et al., 2019). By doing so, this ‘climate-smart’, cost-effective
conservation prioritization planning will allow the preservation of evolutionary
heritage, trait diversity and future services for human well-being (Veron et al., 2019).
Landscape connectivity as a prerequisite for successful migration is an important
management issue. The current scale of habitat fragmentation is likely to hamper the
potential success of migration that relies heavily upon the connectedness of populations
across suitable environments (Hoffmann and Sgro 2011). Thus, measures to mitigate
landscape fragmentation, as an active conservation strategy, should be included in
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprintthis version posted March 3, 2020. ; https://doi.org/10.1101/2020.03.01.971143doi: bioRxiv preprint
ongoing and future Action Plans for habitats and species, based on climate-change
projections and management scenarios. To properly assess and predict future
projections of landscape fragmentation, changes in demand, use and supply of
ecosystem services should be taken into account, using a climate-change, management
scenario-based approach (e.g. Kokkoris et al. 2019). This procedure is important for
policy and decision-making related to land and resource use (Geijzendorffer et al.,
2017).
Future climatic projections can trigger the interest of the scientific community and
the conservation society. However, to reach decision and policy making, raw scientific
information is not always the appropriate mean of communication. All information
produced by the present study should be transformed into tangible material using the
ecosystem services approach and by this communicate the loss (via plant species
extinction) of various ecosystem services and the related impacts into the socio-
economic environment. In EU the MAES concept encapsulates this idea and acts as a
management- and dissemination- tool among scientists and policy makers.
Acknowledgments: This project has received funding from the Hellenic Foundation
for Research and Innovation (HFRI) and the General Secretariat for Research and
Technology (GSRT), under grant agreement No [2418].
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Appendix A. Extended Materials and Methods
Appendix B. Supplementary Tables and Figures
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprintthis version posted March 3, 2020. ; https://doi.org/10.1101/2020.03.01.971143doi: bioRxiv preprint