Assessing global warming vulnerability of restricted and common plant species in alpine habitats on two Oceanic Islands

Climate change is modifying plant communities and ecosystems around the world. Alpine ecosystems are of special concern on oceanic islands, due to their characteristic higher endemicity percentage, small area and undergoing severe climate change impact in the last few decades. During recent decades there has been increasing interest in the effects of climate change on biodiversity and a range of methods have been developed to assess species vulnerability. However, some new insights are necessary to obtain useful information for species management on oceanic islands. Here in the alpine area of two oceanic islands (Tenerife and La Palma) we evaluate the drivers that best explain the vulnerability of 63 endemic species along three scenarios, covering recent past to present and two future projections (2041–2060 and 2061–2080). The selected drivers were: loss of potential area, mismatch index between potential and occupied areas in different scenarios, and adaptive capacity constraints. We assess the influence of potential area size and whether the drivers of risk and the vulnerability for common, restricted and rare species are significantly different. Our results indicate that management must be widely distributed over the species, and not only focus on restricted species. Evidence for this was that drivers directly deriving from climate change showed no significant differences in their impact on the rarity groups identified. Vulnerability depends partially on the potential area size, showing a more complex picture where constraints on the adaptive capacity of the species have a strong enough influence to modify the effects of the characteristic drivers of climate change.


Introduction
Most species are represented by a few individuals or populations, while most individuals belong to some few common species (Rabinowitz 1981;Flather & Sieg 2007).The pattern of commonness and rarity of the biotas inhabiting the ecosystems may be natural (Martín 2009;Enquist et al. 2019).However, is frequently caused by human disturbances (Flather & Sieg 2007;Otto et al. 2020), which explains why many rare species are also vulnerable or even threatened (Gaston 2003;Ohlemüller et al. 2008).Due to scarce resources dedicated to ecosystem conservation, a common strategy for management has been to focus on threatened species (Flather & Sieg 2007), preventing integral management of the ecosystem.On the other hand, common species are often used for ecological restorations in deeply disturbed areas (del Arco et al. 1992).However, between rare and common species there is a wide species pool that is frequently forgotten in conservation plans.
Global warming has arrived as a driver that changes the rules of the game.Almost 40% of terrestrial plant species are categorized as very rare, and their risk of extinction is increasing due to climate change (Enquist et al. 2019).However, climate change can bene t some species (Somero, 2010), while common species can be threatened by both intrinsic and extrinsic factors (Périé & Blois, 2016;Dickson et al. 2019).Thus, there are losers and winners of climate change (Martín et al. 2020(Martín et al. , 2021) ) and common species may also become a priority (Cubas et al. 2022).The question is whether to continue with the same conservation management strategies or should the approaches be different.
Species differ naturally in their range-size and understanding its determinants is essential for identifying risks to species and habitats (Myers et al. 2000), and their sensitivity to anthropogenic climate change (Ohlemüller et al. 2008).Two main components may be distinguished to de ne the geographical space where a species can grow and expand (Soberon & Nakamura 2009).Firstly, the area where occur, mostly characterize by the climatic and other physical factors (fundamental niche), that allow the growth of a species population (Jackson & Overpeck 2000).Secondly, the area where biotic conditions would allow existence of viable populations (realized niche), determined mainly by Eltonian processes (Junker et al. 2019), ecological interactions and resource consumption (Jackson & Overpeck 2000).A third component is based on the limited area where the species can maintain effective dispersal or colonization over a sustained time interval (Soberon & Nakamura 2009).This factor is important due to the pressing need for migration as an adaptive response to global warming.Even though other factors can limit a species' distribution, it is generally assumed that climate remains a signi cant driver (Araújo & Peterson, 2012, Barber et al. 2016).However, assessment of climate change vulnerability must also include species sensitivity and adaptability (Paci ci et al. 2015; Foden et al. 2019).
Estimations of the speed of climate change (Burrows et al. 2014;Carroll et al. 2015; Barber et al. 2016) provide an idea of the rate at which species need to migrate to maintain an effective response to the climate change occurring over a given interval of time, as part of the adaptive capacity (Beever et al. 2015).However, there may be constraints that reduce or disable this capacity (Harter et al. 2015;Bello-Rodríguez et al. 2019).So, there is a need to consider both climate vulnerability and the stressor drivers that make the species more sensitive and explain the realized niche size and species distribution.In this way, the mechanisms underlying a nonlinear ecosystem response to climatic and anthropogenic stresses can be carefully explored (Martín et al. 2021;Wu et al. 2021).This requires considering what actions should be successful in enhancing the species' adaptive capacity, by reducing constraints and shifting the adaptive capacity from the realized niche to the fundamental niche (Beever et al. 2015).Oceanic islands are extremely fragile areas, with features that intensify the impact of global warming (Veron et al. 2019).In this context, alpine zones have been the focus of many research studies, due to their higher endemicity rate within a small surface area (Steinbauer et al. 2016).Indeed, they are undergoing some of the strongest climate change effects in just the last few decades (Pauli & Halloi 2019).In addition, mountaintop species are among the most vulnerable to climate change due to the "escalator effect" (Urban 2015), especially cold-adapted species (Rumpf et al. 2018).
There have been a great variety of methodological developments that aid in assessing the vulnerability of species to climate change (Felicísimo et al. 2012;Paci ci et al. 2015;Foden et al. 2019).These tools provide essential information on climate change vulnerabilities across different species and habitats and aid in conservation management of those species at highest risks (Heikkinen et al. 2021).However, some new drivers still currently require study on oceanic islands, since they show special characteristics such as their small size, greater rarity (endemicity rates) and an invasive herbivores stress sustained over time, even in the best-preserved areas (Nogales et al. 2006 (Chase et al. 2020).The fundamental niche is highly in uenced by island heterogeneity and habitat size (Whittaker & Fernández-Palacios, 2007) but realized niches on oceanic islands are frequently limited by invasive herbivores.After several hundred or thousands of years, the structure and composition of the plant communities mostly re ect differences in their palatability (Irl et al. 2014;Cubas et al. 2019).Thus, some fewer palatable species become dominant in the communities (Garzón et al. 2010; Cubas et al. 2018, González-Mancebo et al. 2019), even when more competitive species coexist as restricted (Irl et al. 2012).So, rarity and commonness in oceanic island habitats may be highly dependent on introduced herbivores, so the real niche may be the great unknown for many species.Many species could have unknown fundamental and realized niches, due to the low number of occurrences (observed niches) that have survived to our days because of various human activities.This not only affects restricted species; common species distributions may be the result of the loss of more competitive and highly palatable species.Characteristically, a consequence of anthropogenic activities is that narrow-ranged species become replaced by widespread species (Xu et al. 2019).
The Canary archipelago presents several interesting characteristics for testing vulnerability to climate change on islands.It has a good representation of the alpine ecosystem, which is even larger on Tenerife where it reaches 3715 m a.s.l., with a narrower area and a maximum elevation of 2426 m on La Palma.Furthermore, global warming in alpine zones on these islands is happening fast, notably on Tenerife (0.14 ± 0.07°C/decade in the area surrounding its summit (Martín et al. 2012).
Here, we evaluate the drivers (loss of fundamental niche area, persistence of fundamental and realized niche, and adaptive capacity constraints limiting the realized niche) that best explain the vulnerability of 63 endemic species in the alpine area of two oceanic islands (Tenerife and La Palma).Three scenarios are examined (present, and two future projections for the periods 2041-2060 and 2061-2080).We hypothesized that vulnerability for rare species depends more on the adaptive capacity constraints than on direct drivers of climate change.This could be expected to be consistent with rarity being highly dependent on human disturbance.We also expected negative correlations between the fundamental niche size and species vulnerability, resulting in greater vulnerability on the smaller island of La Palma, emphasizing a risk level related to its small size.

Study area and target species
The study area consisted of the summit areas of La Palma and Tenerife in the Canary Islands (Fig. 1).On La Palma they include the highest part of Caldera de Taburiente National Park in the north of the island, and the Cumbre Vieja (1949 m) ridge in the south.On Tenerife, mostly coincides with Teide National Park.The alpine ecosystem on both islands (supra-, and oromediterranean thermotypes) is characterized by shrubby vegetation communities: Spartocytisetum supranubii (Tenerife) and Genisto benehoavensis-Adenocarpetum spartioidis (La Palma) (del Arco & Rodriguez-Delgado 2018).On Tenerife it harbours 37 endemic species (56% single-island endemics) and on La Palma 33 species (40% single-island endemics).Among these, 31.74% are threatened (Bañares et al. 2004).Target species in this study included 63 endemic species: 17 restricted to Tenerife and 14 to La Palma, 16 being common to both islands.
Although the alpine ecosystems on both islands are included within protected areas, they are subject to several types of disturbances.Invasive herbivore impact maintained over time has greatly contributed to the alpine ecosystem of La Palma being dominated now by Adenocarpus viscosus, the less palatable species in this habitat (Irl et al. 2012).Fortunately, over the last 30 years, a successful management action sowing restricted species within herbivore exclusion fences revealed a different potential community structure and composition of this ecosystem (Irl et al. 2012, González-Mancebo et al. 2019).On Tenerife, the establishment of Teide National Park in 1954 halted shrub harvesting and the grazing.However, in 1968 the Corsican mu on was introduced (Ovis mu on), which is still present, but controlled by the National Park wardens.The European rabbit was introduced on these islands about 500 years ago, but its population has increased in the

Rarity Index
All 63 species studied are rare at a global level, because we are working with endemic plants in a small habitat.Even so, habitat range size varies between species.Among target species, 80% occur exclusively above 1800 m, while others (La Palma nine species and Tenerife four) showed a wider distribution area including lower elevations, although with higher frequency higher up.We analyzed species rarity using two quantitative approaches: a) number of occurrence cells (500 x 500m) (observed niche) and b) percentage of occurrence cells occupied by each species in its known fundamental niche (F.N.).In a third approach (rarity index) three groups were distinguished with a combination of the two previous approaches, including rare, restricted and common species.Rare species include those with a highest frequency of 50 occurrence cells and a percentage of cells in their F.N. no higher than 35%.Restricted species refers to those with a frequency between 51-150 cells, and a percentage of F.N. cells no higher than 55%.Common species have a frequency of more than 150 cells or a percentage of occurrence cells higher than 75% in their F.N. Additionally, the sizearea of the fundamental niche (F.N. size) was also evaluated.Occurrence data were compiled from the valuable data bases of the National Parks and our own prospections and completed for the species located at lower elevations by referring to the Canary Islands Biodiversity Databank (Gobierno de Canarias 2021).

Species Vulnerability
Three types of vulnerability were considered, to obtain the mean vulnerability of the species in each scenario.The rst two refer to direct exposure to local climate change: 1) loss of suitable fundamental niche area (F.N. loss), 2) persistence index (Felicísimo et al. 2012), including both persistence (%) of F.N. area and persistence of cells of the realized niche, and 3) adaptive capacity constraints (ACC), including only stressors/drivers.We follow a speci c combination of factors used by other researchers (Felicísimo et

Species Distribution Models And Loss Of Suitable Fundamental Niche Area
Most vulnerability studies have been conducted at a rather coarse scale (Heikkinen et al. 2021) and smallscale results are completely necessary on small islands (Segal et al. 2021).To evaluate the climatic vulnerability of the species, we obtained data about the F.N. area they occupy through distribution models, using MaxEnt 3.4.1 (Phillips et al. 2006).As dependent variable, we introduced the presence of the selected species and as predictor variables the mean, maximum and minimum temperature and annual precipitation, which were calculated through interpolations from weather stations data provided by the Spanish National Meteorological Agency (AEMET), which we homogenized with the R package 'climatol' (Guijarro 2019) for the period 1959-2019.Those data were divided into a rst period from 1959 to 1989 and a second one from 1990 to 2019, so it was possible to evaluate both present and recent past scenarios.Interpolations were performed in R Studio 1.3.1093,using multiple linear regression algorithms for temperature and random forest (randomForest package, RColorBrewer & Liaw 2018) for precipitation, as they resulted to be the best tting models in each case.For the future scenarios, we adapted the anomalies from international layers to the Canary Islands (Karger et  With the species distribution models obtained we estimated the F.N. size occupied by each species in hectares (ha), selecting the threshold of the 10th percentile to generate presence-absence maps because it showed less restrictive or permissive values than other parameters offered by MaxEnt.Fundamental niche was calculated in ESRI ArcGIS 10.1 considering the areas with pixel values above the 10th percentile of each species.With those presence-absence maps we calculated the increases or decreases in F.N. size for each species as a measure of response to climate change.

Persistence Of The Fundamental Niche Area And Present Occurrences
With the maps obtained in the previous section, we also calculated several parameters used in the general vulnerability index presented in this study, following Felicísimo et al. (2012).Firstly, we calculated the percentage of coincident distribution area of each species between the present scenario and the different climate change projections.Secondly, we obtained the percentage persistence that shows the actual presences in the potential distribution areas, according to the different projections.
With that data, after transforming the percentages to a 0-1 scale, we obtained an objective parameter that addresses the climatic vulnerability of the studied species, synthesized through an index (IV) (Felicísimo et al.

2012) using the following formula:
IV = 1 -(Intersection between past/future fundamental niche area and current occurrences) × (Intersection between past/future and present fundamental niche area) To interpret the index, lower values mean that the two chosen parameters overlap more between the present and future scenarios, so the species is more likely to maintain its niche despite climate change.These values provided a vulnerability approximation for each species, related to the persistence of habitat and cells.

Adaptive Capacity Constraints
Indirect climate exposure: (b) Habitat speci city.Species with a low tolerance range (specialized niche requirements) tend to migrate less easily.This constraint was considered for species restricted to habitats underrepresented in the entire F.N., such as lithological or freshwater requirements.(c) Small size fundamental niche.The fragility of islands due to their characteristically small size may involve an extreme risk in smaller potential habitats (Simberloff 2000).Here, size of fundamental niche was considered as a constraint to species expansion, when its area did not exceed 5% that of the entire island in question.
Species sensitivity: sheep and domestic sheep-goats), an exhaustive eld analysis was carried out.For this purpose, three localities of each species were selected, with a great effort to ensure they were as climatically or ecologically contrasting as possible.For species present on both islands, independent work has been already done.Rabbit damage is easily distinguishable from that caused by other mammalian species (rats and mice) because fresh droppings are frequently found around damaged plants.Characteristic rabbit damage marks are also left on herbaceous plants and shrubs, such as oblique cuts on branches and twigs, gnawed bark and a foliage height-line at 40-50 (70) cm above ground level (Cooke et al. 2008).Intensity of damage by rabbits, mou ons, goal-antelope and feral goats was assessed by applying the index (0-5) of Cooke et al. (2008).
(e) Small populations refer to when the species has few populations or subpopulations (< 20 occurrence cells) or a low number of individuals per subpopulation (< 250 individuals).
(f) Drought was considered as a migration constraint when detected in more than 50% of the individuals selected for productivity analysis (see later) in any of the 3 locations assessed on each island.Individuals were considered as suffering from drought when they had more than 50% dry branches, or their owering rate was less than 25% and attributable to drought stress.
(g) Potential dispersal ability to adapt to climate change.Dispersal interacts with the adaptive capacity to facilitate niche evolution and range expansion of the species (Sheth et al. 2020).Biotic velocity of climate change (m/year) was analysed in combination with the type of potential dispersal of each species, as a migration barrier.This is because some species are not expected to respond fast enough to maintain suitable abiotic conditions, according to the potential distribution models for the different scenarios.This parameter was the mean distance in meters the species needs to migrate in each scenario to maintain the same climate conditions, calculated from past to present and from the present to the different futures, dividing by the time that separates each period from the present.A modi ed version of the Hamann et al. (2015) algorithms provided distance maps for each species in each scenario, only considering the pixel values in which there was movement, from presence to absence and from absence to presence.These maps served as a measure of the sensitivity the species showed to climate shifts in each time interval.Species adaptability was evaluated by assessing whether its potential dispersal capacity allowed it to cover this mean distance (m/year).Three aspects were considered: seed productivity, potential seed dispersal and regeneration rate.This latter rate was estimated through a population structure analysis based on 15 individuals measured per locality and the number of juveniles (non-reproductive individuals) counted, compared to adults (reproductive).
The same three localities and individuals used to estimate herbivory damage (see above) were also used to evaluate seed productivity.At each, the numbers of owers were estimated on 15 randomly selected individuals of each species (see supplementary material for methods).Efforts were always made to visit the populations at the peak of blooming or seed production.To estimate the reproductive effort/success (number of owers, fruits and seeds) at each plant, their height and two perpendicular diameters from each other were measured.All owers per individual were counted in the eld for small-sized species, but when the number of owers/in orescences was high (e.g.Asteraceae, Boraginaceae) these were collected and counted in the laboratory (15 in orescences/locality).For large shrubs, 5 quadrats/individual were selected (100-2500 cm 2 ) to count the number of owers.A mean of these numbers was then extrapolated to the total number of quadrats in bloom.For the species with heterogeneous fruit/seed production, 15 fruits/locality were collected, counting seed numbers to obtain mean seed production/fruit.When we detected substantial losses of owers without fruit production, a correction factor was applied to estimate seed production.

Statistical methods.
To evaluate whether there were signi cant differences between the analyzed variables of common, restricted and rare species, we performed a Kruskal-Wallis test and a Dunn post-hoc test (Oksanen et al. 2018).
Boxplots were used with the function () applying the statistical software R (R Core Team, 2020).
Principal Component Analysis (PCA) was implemented for each scenario (present, FI and FII) and species group (all combined, common, rare, restricted, Tenerife and La Palma) in R software (R Core Team, 2020) using 'prcomp' function.All variables analyzed (vulnerability drivers, rarity approaches and migration barriers) were included as input dataset.The lowest signi cant variables were removed until the explained variance of principal components 1 and 2 stabilized, ensuring a minimum of ve input variables for each PCA.Spearman's correlation tests were also applied to the relationship between the principal component factors, input variables and vulnerability indices.
Generalized lineal models using XLSTAT program were used to analyze the relationship between the rarity approaches (number of occurrence cells and % fundamental niche area occupied) and the drivers (fundamental niche loss and persistence index).

Results
Among the 63 endemic owering plant species assessed in the alpine zone of the Canary Islands there were currently 65.07% at low risk (vulnerability index 1 and 2), 33.33% at high risk (vulnerability index 3 and 4) and 1.59% at critical risk (vulnerability index 5 or 6).A progressive increase in risk occurs in 55 Assessing all three rarity groups, common and restricted species showed 80% of species currently at low risk (Table 1).High risk was detected in common and restricted species (16% and 17% respectively).However, rare species showed only 28.57% of species at low risk and 66.67% with high risk.Critical risk at present was found only for rare species (4.76%).Examining the changes through the studied period to FI (1990-2019) to (2041-2060) and FII (2041-2060) to (2061-2080), it is noteworthy that for common species the high risk in FI may soon be twice as much as today (32%), increasing up to 23% for restricted species (Table 1).For rare species, an increase in critical risk (23.81%) was forecasted for the near FI, indicating a higher priority for management of many species in this group, which in FII show nearly 50% of species at critical risk.Herbivore damage acted as a constraint for 66% of the species, being highly signi cant for all rarity groups and both islands in at least one or two scenarios (Fig. 3).Potential dispersal ability to adapt to climate change was a constraint for 23.80% of the species and highly signi cant when all species were considered, for rare species, and for Tenerife.Contrastingly, small populations (26.98%) were signi cant when all species were combined, for rare and restricted species, and for Tenerife.Island area < 5% (23.98% of the species) was signi cant for common and rare species in the present day and in futures I and II on La Palma.Drought (20.63% of the species) was only signi cant for restricted species (19.04%).
Among the rarity approaches, number of occurrence cells was signi cant only at present, when all groups were included and common species, La Palma and Tenerife when each was analyzed separately.In contrast, % F.N. niche occupied was only highly signi cant (p < 0.0001) at present for restricted and Tenerife species, and for common species in futures I and II.

Discussion
Despite the restricted vulnerability evaluation method used here, our assessment revealed that the ora of alpine ecosystems in the Canary Islands is at signi cant risk due to climate change.According to the vulnerability index applied here, even at present 16% of the species are at risk (high mean vulnerability), and this percentage will increase to 32% in the high-risk category in 2040-2060 (future I) and to 60% in 2061-2080 (future II), including also the critical category.Species vulnerability depends on a trade-off between the F.N. size and the A.C.C. of the species.These two drivers vary according to the rarity group under assessment.
The speci c drivers associated with global warming (F.N. loss and persistence index) were not the main components explaining species vulnerability, although their signi cance increases in the future scenarios for all groups and islands (Fig. 4).The A.C.C. hindering the species responses is an important driver in all scenarios on both islands (Fig. 4) and for rare and restricted species.Rare species show signi cantly higher vulnerability than common and restricted species.However, this difference is not due to a stronger signi cant effect of climate change drivers, but rather to the current state of the populations and their threats.The vulnerability pattern during all three scenarios was different on the two islands (Fig. 4).While on La Palma it was notably dependent on F.N. size, on Tenerife it depended mainly on the constraints and rarity.Tenerife, where the alpine ecosystem occupies a larger zone, shows a delay in climate change impact compared to La Palma, resulting in lower vulnerability at present (intermediate on Tenerife with an index of 0.34 and high on La Palma, 0.47).However, this vulnerability will probably increase according to the future scenarios, due to shrinkage in fundamental niche area attributable to island topography and in the persistence of the currently suitable areas for plants to survive.
In this study we are working with very small areas (mean F.N. size for all species was 18,306ha at present, 15,215ha in future I and 11,998ha in future II).The F.N. size of the species showed a signi cant negative correlation with species vulnerability (p < 0.0001) throughout our assessment periods, but no correlation was found with the percentage area occupied in this niche (p > 0.05).In fact, rare species showed no signi cant differences from common species in F.N. size (p > 0.05), which along with their signi cant higher percentage of constraints points to anthropogenic rarity.Thus, constraints are limiting the area of the realized niches within the fundamental niches ( The emerging picture is that species with large ranges may have small populations, and that there are common species in small sized fundamental niches.Thus, two types of rarity are combined in the species of this alpine ecosystem: habitat rarity (dependent on F.N. size) and species rarity, mostly related to stressor factors (R.N.).This appears to reduce the ecological signi cance of F.N. size to climate change and highlights the importance of identifying and understanding the drivers that most constrain the realized niche.In fact, the widely established close relationship between rarity and extinction risk (e.g.Schwartz et al. 2006) has been long questioned because of the existence of natural rarity in small habitats (Gaston 1994;Martín 2009).Indeed, the use of the UICN absolute presence thresholds to evaluate the risk species face has been discouraged on small oceanic islands (Martín et al. 2009; González-Mancebo et al. 2012), since it can lead to overestimating the threat in smaller habitats.Nevertheless, current climate change has arrived as a factor that increases the risk level of small populations, whether the rarity is due to natural or anthropic causes.Thus, small natural habitats may be also in risk even for common species, because climatic stability is particularly essential to species survival in small areas and populations (Morueta-Holme et al. 2013).This is of special concern regarding geographically isolated habitats subjected to sustained stress over time, as occurs on oceanic islands with undergoing introduced herbivore damage (Caujapé-Castells et al. 2010).
Although rare species show signi cantly higher vulnerability than common and restricted species, these latter two groups include species under high risk at present and even critical in the future.Rare species with large F.N. size included some with a high dispersal potential, but highly threatened, like Cicer canariense (Tenerife and La Palma).This small legume can grow at from 445 m to 2000m in elevation, is also quite drought tolerant and regenerates quickly but is highly palatable to invasive herbivores.Its fundamental niche is 21,290 ha with 12% occupied on La Palma, 50741ha on Tenerife (1% occupied).Sixty-one % of the species we classi ed as rare occupy a maximum 5% of their fundamental niche and are threatened on their native island, while those that occupy more are expanding currently, such as Cheirolophus teydis on Tenerife, or threatened species with new populations resulting from National Parks management.Knowledge is greatly lacking about the fundamental and realized niches of these species, even though some are well studied.
However, there are also species whose rarity derives from their small F.N. size, as for instance Viola palmensis (64% of 648 ha occupied, in 46 occurrence cells).
Climate change is affecting plant communities and ecosystems around the world.Managing communities so that they can resist requires speci c measures with precise methods for assessing vulnerability.Such supportive aids can prioritize actions within the framework of comprehensive management.Our results indicate that conservation management nowadays must be widely distributed among all native species, and not only focus on threatened or restricted ones.Drivers of vulnerability vary strongly between species, and therefore understanding and including them in climate change vulnerability assessments is essential for e cient allocation of nite management resources (Beever et al. 2015).Our results highlight the need for urgent management of rare and restricted species, to gauge the possibilities of enlarging their realized niches to enhance and prolong their adaptive capacity (Thurman et al. 2021).In other words, to reduce the constraints on the adaptability of these species through the removal or mitigation of threats, and to strengthen and better understand the realized niche by means of experimental translocations.Common species also need management since are inhabiting habitats that are already disappearing around the summits of the islands, so management must be addressed to preserving them in the best possible conditions.Notably, removal or effective control of invasive herbivores will help to achieve this, since they are the strongest constraint on all the groups analyzed.This study emphasizes the need to further assess the climate change vulnerability of species and the drivers of their responses, to achieve better management of these unique ecosystems.

Declarations
Teide National Park during the last few decades (Martin et al. 2021), in accordance with the rising minimum temperatures due to global warming (Martin et al. 2012).During recent decades these factors are causing a striking new change in the species composition of this ecosystem (Martin et al. 2020).
al. 2011; Barber et al. 2016; Young et al. 2015) but adding some speci c factors for island habitats.Intrinsic and extrinsic parameters associated with the exposure, sensitivity and adaptive capacity (AC) of each species to climate change were covered (Foden et al. 2019).The sensitivity and adaptive capacity of the species were analyzed according to the rate of exposure to climate change and adaptive constraints (Foden et al. 2019; Comer et al. 2019).The vulnerability index included 6 levels of risk with values between 0-1: low (< 0.25), intermediate (0.25-0.45), high (0.45-0.60), very high (0.60-0.75), critical (0.75-0.90) and very critical (> 0.90), and was the mean value obtained for the three drivers considered (A = fundamental niche loss (%), B = persistence index and C = adaptive capacity constraints (%).
al. 2017), including different feasible climate change scenarios for the periods 2041-2060 and 2061-2080.We considered several Representative Concentration Pathways (RCP), but focusing on only the most pessimistic (RCP 8.5), since the responses of governments and their practical implementation of climate change actions is ridiculously slow.
(a) Habitat fragmentation was considered when there is habitat discontinuity, either due to natural causes (e.g.orographic, including climate discontinuity) or anthropic (e.g.agricultural, agricultural or urbanized areas).To assess the role of human uses as constraint we overlapped the CORINE Land Cover 2018 layer (Copernicus Program 2018) with the potential distribution models (F.N.) in ESRI ArcMap 10.1 and calculated the percentage of the present area occupied.
(d) Index of herbivory damage.Invasive herbivores are a great threat to species expansion and consequently the ability to migrate in response to climate change (Bello-Rodríguez et al. 2019; Martin et al. 2020; Kappes et al. 2021).To assess the impact of introduced and feral herbivores (European rabbit, Corsican mou on, Babary

Figure 1 Location
Figure 1

Figure 3 Principal
Figure 3 ; Caujapé et al. 2010; González-Mancebo et al. 2019).Together with climate conditions and island area, habitat size is one of the most important factors explaining both richness (Whittaker & Fernández-Palacios 2007; González-Mancebo et al. 2011) and species range sizes (Ohlemüller et al. 2008; Morueta-Holme et al. 2013) on oceanic islands.Habitat size may be correlated with species rarity on islands, but especially in disturbed habitats .56% of species through the period assessed (from present to 2061-2080), while 41.27% of them remained at a similar risk (27% low, 13% high, and 2% at critical risk).There are two species (3.17%) on La Palma whose maximum vulnerability is at present and the risk decreases through the assessed periods.Currently on Tenerife, 72.73% of species are at low risk and 24.24% at high risk, while on La Palma there are only 56.67% at low risk and high risk reaches 43.33%.In contrast, future soon (FI) La Palma may show more low vulnerability (63.33%) than Tenerife (51.51%).This tendency increases in future II (FII) (Tenerife: 18.18% of species at low risk, and La Palma: 43.33%).Critical species have similar percentages (20% and 21.21%) in F II on both islands, while high risk species are much more numerous on Tenerife (60.60%) than La Palma (36.66%).
(Bellis et al. 20215Garzón et al. 2010;Irl et al. 2012) species dispersal capacity, an important trait in their response to climate change(Estrada et al. 2015).These results are clearly related to the high degree of anthropogenic disturbance of the alpine ecosystem on both islands (Rodríguez-Delgado &Elena-Roselló, 2006;Garzón et al. 2010;Irl et al. 2012).Human impacts are signi cantly more intense on islands than in mainland areas(Kier et al. 2009), which might explain both, the large fundamental niches of rare species and the non-correlation with the selected drivers (F.N. loss or the persistence index).Mostly due to invasive herbivores, many rare species occupy only a small area within the fundamental niche.Consequently, their ecological requirements are unknown, since reduced populations do not always show the true ecological requirements of the species.Sometimes, they are even preserved in areas where they are doomed to extinction, because the climatic conditions there are not the most suitable for them (Marrero-Gómez et al. 2007).For these species, experimental translocations, close monitoring and modelling are essential to estimate the fundamental and realized niche size necessary to manage them in the face of climate change(Bellis et al. 2021).Fundamental niche size was positively correlated with drivers directly related to climate change: F.N. loss (p < 0.0001) and persistence index (p < 0.0001), and with the persistence of the number of occurrence cells (p < 0.0001).Therefore, we should expect that vulnerability of common species (those occupying a greater proportion of the fundamental niche), would be more dependent on the above drivers.However, F.N. size prevents establishing this relationship, since the common species are also highly vulnerable in very small habitats that are disappearing with global warming.Small habitat size is itself a notable risk(Enquist etal.2019; Horváth et al. 2019), and vulnerability of the studied alpine ecosystem is probably strongly underestimated due to habitat loss.Moreover, the characteristic isolation of insular alpine ecosystems, islands within islands (Fernández-Palacios et al. 2014) makes them more vulnerable because of limitations to spatial processes (Rybicki & Hanski 2013; Horváth et al. 2019).
(Martín et al. 2021 under the pressure of abiotic and biotic changes, the rapidity of current climate change may cancel advantages for this species group, depending on the constraints to their adaptability and loss of their fundamental niches.Other common species at high risk at present on La Palma include Arrhenatherum calderae, the dominant member of poaceae currently present in this ecosystem, Genista benehoavensis and Echium gentianoides.The latter two are threatened species managed for the last 30 years by the Caldera de Taburiente National Park.They now occupy respectively 89.15% and 83.03% of their fundamental niche, which however is currently very small (4708 ha and 6109 ha respectively).The near future also holds high risk for some common species on Tenerife: A. calderae, Argyranthemum teneriffae, Descurainia bourgeauana, Nepeta teydea and Tolpis webbii.Some of these species are currently in expansion: A. teneriffae, T. webbii and A. calderae(Martín et al. 2021), which supports a delay in their reaching high risk in the alpine zone of this island.A greater area and elevation (more than 1000 meters higher than La Palma) mean without doubt more time to extend their survival of climate change in this zone.Although some species are already starting to recoil in southern areas, such as D. bourgeauana, N. teydea or C. supranubius (Martin et al. 2020, 2021, Cubas et al. 2022).
Common species may play an important role in ecosystem functioning and their decline can even lead towards ecosystem collapse, as recently detected for Cytisus supranubius on Tenerife (Cubas et al. 2022).Although common species may have a greater