Volcanic tephra deposition dataset based on interpolated field measurements following the 2021 Tajogaite Eruption on La Palma, Canary Islands, Spain.

In 2021, the Tajogaite Volcano erupted along the western slope of the Cumbre Vieja on the island of La Palma, Canary Islands, Spain. Volcanic tephra blanketed a substantial proportion of the island. By our estimations, approximately 23,000,000 m3 of pyroclastic ashes and more coarse-grained particles were deposited unto La Palma's land surface in addition to the lava flow. Five months following the initial eruption, we measured the depth of the new ash layer across the island. We combined this data with drone-based observations to compile a dataset comprising the point distribution of ash depth. A spatial interpolation was then performed using Inverse Distance Weighting (IDW) to estimate the ash depth across the island at a 2 m spatial resolution. The interpolation performed well, yielding a root mean squared error (RMSE) value of 0.34 and thus, the dataset offers immense reuse potential for spatial inquiries related to evolutionary traits, vegetation patterns, and vegetation response to disturbance on oceanic islands. In addition, the data can be used to test different spatial interpolation techniques in an effort to improve the accuracy achieved using IDW.

Identification of potential invasive alien species in Spain through horizon scanning.

Invasive alien species have widespread impacts on native biodiversity and ecosystem services. Since the number of introductions worldwide is continuously rising, it is essential to prevent the entry, establishment and spread of new alien species through a systematic examination of future potential threats. Applying a three-step horizon scanning consensus method, we evaluated non-established alien species that could potentially arrive, establish and cause major ecological impact in Spain within the next 10 years. Overall, we identified 47 species with a very high risk (e.g. Oreochromis niloticus, Popillia japonica, Hemidactylus frenatus, Crassula helmsii or Halophila stipulacea), 61 with high risk, 93 with moderate risk, and 732 species with low risk. Many of the species categorized as very high or high risk to Spanish biodiversity are either already present in Europe and neighbouring countries or have a long invasive history elsewhere. This study provides an updated list of potential invasive alien species useful for prioritizing efforts and resources against their introduction. Compared to previous horizon scanning exercises in Spain, the current study screens potential invaders from a wider range of terrestrial, freshwater, and marine organisms, and can serve as a basis for more comprehensive risk analyses to improve management and increase the efficiency of the early warning and rapid response framework for invasive alien species. We also stress the usefulness of measuring agreement and consistency as two different properties of the reliability of expert scores, in order to more easily elaborate consensus ranked lists of potential invasive alien species.

Time-calibrated phylogenies reveal mediterranean and pre-mediterranean origin of the thermophilous vegetation of the Canary Islands.

BACKGROUND AND AIMS: The Canary Islands have strong floristic affinities with the Mediterranean Basin. One of the most characteristic and diverse vegetation belts of the archipelago is the thermophilous woodland (between 200 and 900 m.a.s.l.). This thermophilous plant community consists of many non-endemic species shared with the Mediterranean Floristic Region together with Canarian endemic species. Consequently, phytogeographic studies have historically proposed the hypothesis of an origin of the Canarian thermophilous species following the establishment of the summer-dry mediterranean climate in the Mediterranean Basin around 2.8 million years ago. METHODS: Time-calibrated phylogenies for 39 plant groups including Canarian thermophilous species were primarily analysed to infer colonization times. In particular, we used 26 previously published phylogenies together with 13 new time-calibrated phylogenies (including newly generated plastid and nuclear DNA sequence data) to assess whether the time interval between stem and crown ages of Canarian thermophilous lineages postdates 2.8 Ma. For lineages postdating this time threshold, we additionally conducted ancestral area reconstructions to infer the potential source area for colonization. KEY RESULTS: A total of 43 Canarian thermophilous lineages were identified from 39 plant groups. Both mediterranean (16) and pre-mediterranean (9) plant lineages were found. However, we failed to determine the temporal origin for 18 lineages because a stem-crown time interval overlaps with the 2.8-Ma threshold. The spatial origin of thermophilous lineages was also heterogeneous, including ancestral areas from the Mediterranean Basin (nine) and other regions (six). CONCLUSIONS: Our findings reveal an unexpectedly heterogeneous origin of the Canarian thermophilous species in terms of colonization times and mainland source areas. A substantial proportion of the lineages arrived in the Canaries before the summer-dry climate was established in the Mediterranean Basin. The complex temporal and geographic origin of Canarian thermophilous species challenges the view of the Canary Islands (and Madeira) as a subregion within the Mediterranean Floristic Region.

The fate of terrestrial biodiversity during an oceanic island volcanic eruption.

Volcanic activity provides a unique opportunity to study the ecological responses of organisms to catastrophic environmental destruction as an essential driver of biodiversity change on islands. However, despite this great scientific interest, no study of the biodiversity at an erupting volcano has yet been undertaken. On La Palma (Canary archipelago), we quantified the main species affected and their fate during the 85-day eruption (September-December 2021). Our main objective consisted of monitoring the biodiversity subjected to critical stress during this volcanic eruption. We found that all biodiversity within a 2.5 km radius was severely affected after the first two weeks. It is challenging to assess whether volcanism can drive evolutionary traits of insular organisms. Examples are the adaptation of an endemic conifer to high temperatures, selection of functional plant types-secondary woodiness-, effects of the disappearance of invertebrates and their influence in trophic nets and vertebrate trophic plasticity. However, our data suggest that such previous evolutionary changes might continue to favour their resilience during this eruption. Lastly, it is a very good opportunity to assess the extent to which these periodic volcanic catastrophes may constitute temporary windows of repeated opportunities for the evolution and speciation of oceanic island biota.

Interpopulation Plasticity in a Darkling Beetle Life-History along a Whole Oceanic Island Altitudinal Gradient.

Insects show remarkable phenotypic plasticity in response to changing environmental conditions. The abiotic factors that determine their phenotypes often vary in time and space, and oceanic islands harbour ideal environments for testing predictions on this matter. The ubiquitous beetle Pimelia laevigata costipennis Wollaston, 1864 (Tenebrionidae) is distributed over the entire altitudinal gradient of the island El Hierro (Canary archipelago), from 0 to 1501 m above sea level. Here, we examine how environmental factors (i.e., rainfall and temperature), associated with the altitudinal gradient, affect the body size, reproductive phenology, clutch size and egg volume, and population dynamics of this ectothermic flightless insect. Pimelia l. costipennis populations inhabiting upland localities, typified by lower temperatures, and greater precipitation and vegetation cover, were larger in body size and laid larger clutches with smaller eggs than those in the lowlands. Moreover, reproduction occurred earlier in the year at lower sites and later at higher sites, whereas activity density was highest in the uplands where it increases with temperature. This study first explores the changes in life history patterns along a whole insular altitudinal gradient, and finds interpopulation plasticity. It confirms that environmental factors associated with species spatial distribution act additively as drivers of phenological and phenotypic expression.

Could climate change benefit invasive snakes? Modelling the potential distribution of the California Kingsnake in the Canary Islands.

The interaction between climate change and biological invasions is a global conservation challenge with major consequences for invasive species management. However, our understanding of this interaction has substantial knowledge gaps; this is particularly relevant for invasive snakes on islands because they can be a serious threat to island ecosystems. Here we evaluated the potential influence of climate change on the distribution of invasive snakes on islands, using the invasion of the California kingsnake (Lampropeltis californiae) in Gran Canaria. We analysed the potential distribution of L. californiae under current and future climatic conditions in the Canary Islands, with the underlying hypothesis that the archipelago might be suitable for the species under these climate scenarios. Our results indicate that the Canary Islands are currently highly suitable for the invasive snake, with increased suitability under the climate change scenarios tested here. This study supports the idea that invasive reptiles represent a substantial threat to near-tropical regions, and builds on previous studies suggesting that the menace of invasive reptiles may persist or even be exacerbated by climate change. We suggest future research should continue to fill the knowledge gap regarding invasive reptiles, in particular snakes, to clarify their potential future impacts on global biodiversity.

Potential role of lava lizards as pollinators across the Galápagos Islands.

Lizards have been reported as important pollinators on several oceanic islands. Here we evaluate the potential role of Galápagos lava lizards (Microlophus spp.) as pollinators across their radiation. Over 3 years, we sampled pollen transport by 9 lava lizard species on the 10 islands where they are present, including 7 single-island endemics. Overall, only 25 of 296 individuals sampled (8.4%) transported pollen of 10 plant species, the most common being Prosopis juliflora, Exodeconus miersii, Sesuvium sp. and Cordia leucophlyctis. At least 8 of these plant species were native, and none were confirmed as introduced to the archipelago. Despite the low overall proportion of individuals carrying pollen, this was observed in 7 of the nine lizard species, and on 8 of the ten main islands (Española, Fernandina, Floreana, Isabela, Marchena, Pinta, Santa Cruz and Santiago), suggesting that this is a widespread interaction. The results reported here support the potential role of lava lizards as pollinators across their radiation, although they may represent a relatively modest contribution when compared with birds and insects. However, we cannot discard that lizards may be ecologically significant for particular plant species and ecosystems given the specific climatic condition and functional diversity of each island.

Environmental temperatures shape thermal physiology as well as diversification and genome-wide substitution rates in lizards.

Climatic conditions changing over time and space shape the evolution of organisms at multiple levels, including temperate lizards in the family Lacertidae. Here we reconstruct a dated phylogenetic tree of 262 lacertid species based on a supermatrix relying on novel phylogenomic datasets and fossil calibrations. Diversification of lacertids was accompanied by an increasing disparity among occupied bioclimatic niches, especially in the last 10 Ma, during a period of progressive global cooling. Temperate species also underwent a genome-wide slowdown in molecular substitution rates compared to tropical and desert-adapted lacertids. Evaporative water loss and preferred temperature are correlated with bioclimatic parameters, indicating physiological adaptations to climate. Tropical, but also some populations of cool-adapted species experience maximum temperatures close to their preferred temperatures. We hypothesize these species-specific physiological preferences may constitute a handicap to prevail under rapid global warming, and contribute to explaining local lizard extinctions in cool and humid climates.

Small size does not restrain frugivory and seed dispersal across the evolutionary radiation of Galápagos lava lizards.

Frugivory in lizards is often assumed to be constrained by body size; only large individuals are considered capable of consuming fruits, with the potential of acting as seed dispersers. However, only one previous study has tested the correlation of frugivory with body and head size at an archipelago scale across closely related species. All nine lava lizards (Microlophus spp.) were studied on the eleven largest Galápagos islands from 2010 to 2016 to investigate whether frugivory is related to body and head size. We also tested whether fruit abundance influences fruit consumption and explored the effect of seed ingestion on seedling emergence time and percentage. Our results showed that across islands, lava lizards varied considerably in size (64-102 mm in mean snout-vent length) and level of frugivory (1-23%, i.e., percentage of droppings with seeds). However, level of frugivory was only weakly affected by size as fruit consumption was also common among small lizards. Lava lizards consumed fruits throughout the year and factors other than fruit abundance may be more important drivers of fruit selection (e.g., fruit size, energy content of pulp). From 2,530 droppings, 1,714 seeds of at least 61 plant species were identified, 76% of the species being native to the Galápagos. Most seeds (91%) showed no external structural damage. Seedling emergence time (44 versus 118 days) and percentage (20% versus 12%) were enhanced for lizard-ingested seeds compared to control (uningested) fruits. De-pulping by lizards (i.e., removal of pulp with potential germination inhibitors) might increase the chances that at least some seeds find suitable recruitment conditions. We concluded that lizards are important seed dispersers throughout the year and across the whole archipelago, regardless of body size.

Divergence in floral trait preferences between nonflower-specialized birds and insects on the Galápagos.

PREMISE OF THE STUDY: The characteristic scarcity of insects on remote oceanic islands has driven nonflower-specialized vertebrates to broaden their trophic niches and explore floral resources. From our previous studies in the Galápagos, we know that native insectivorous and frugivorous birds visit a wide range of entomophilous flowers and can also act as effective pollinators. Here, we tested whether opportunistic Galápagos birds show any preference for specific floral traits, and if so, this preference differs from that of insects. METHODS: Sixteen floral morphology and nectar traits of 26 native species were studied, as well as the frequency with which they are visited by birds and insects. Nonmetric multidimensional scaling (NMDS) was used to evaluate the distribution of flower traits values along two main dimensions and measure the similarity between the plants visited mostly by birds versus those by insects. KEY RESULTS: NMDS of floral traits resulted in two species groups: (1) bell-shaped, white flowers with wider corollas at nectary level and higher nectar volume, associated with high bird visitation rates; and (2) bowl and tubular-shaped flowers with narrower corollas at nectary level and lower nectar volume, associated with high insect visitation rates. CONCLUSIONS: Despite the divergence in floral trait preferences between opportunistic Galápagos birds and insects, bird-visited flowers display mixed traits not fitting the classical ornithophilous syndrome. This finding is compatible with the existence of a transitional or bet-hedging phenotype between insect and bird visitors and underscores the importance of coevolution and floral diversification in nonspecialized plant-visitor interactions.

Disclosing the double mutualist role of birds on Galápagos.

Life on oceanic islands deviate in many ways from that on the mainland. Their biodiversity is relatively poor and some groups are well-represented, others not, especially not insects. A scarcity of insects forces birds to explore alternative food, such as nectar and fruit. In this way, island birds may pollinate and disperse seed to an extent unseen on any mainland; they may even first consume floral resources of a plant species and then later harvest the fruit of the same species. Through this biotic reuse, they may act as double mutualists. The latter have never been studied at the level of the network, because they are traditionally considered rare. We sampled pollination and seed-dispersal interactions on Galápagos and constructed a plant-bird mutualism network of 108 plant (12% being double mutualists) and 21 bird species (48% being double mutualists), and their 479 interactions, being either single (95%) or double mutualisms (5%). Double mutualists constitute the core in the pollination-dispersal network, coupling the two link types together. They may also initiate positive feedbacks (more pollination leading to more dispersal), which theoretically are known to be unstable. Thus, double mutualisms may be a necessary, but risky prerequisite to the survival of island biodiversity.

Species-environment interactions changed by introduced herbivores in an oceanic high-mountain ecosystem.

Summit areas of oceanic islands constitute some of the most isolated ecosystems on earth, highly vulnerable to climate change and introduced species. Within the unique high-elevation communities of Tenerife (Canary Islands), reproductive success and thus long-term survival of species may depend on environmental suitability as well as threat by introduced herbivores. By experimentally modifying the endemic and vulnerable species Viola cheiranthifolia along its entire altitudinal occurrence range, we studied plant performance, autofertility, pollen limitation and visitation rate and the interactive effect of grazing by non-native rabbits on them. We assessed the grazing effects by recording (1) the proportion of consumed plants and flowers along the gradient, (2) comparing fitness traits of herbivore-excluded plants along the gradient, and (3) comparing fitness traits, autofertility and pollen limitation between plants excluded from herbivores with unexcluded plants at the same locality. Our results showed that V. cheiranthifolia performance is mainly affected by inter-annual and microhabitat variability along the gradient, especially in the lowest edge. Despite the increasingly adverse environmental conditions, the plant showed no pollen limitation with elevation, which is attributed to the increase in autofertility levels (≥ 50% of reproductive output) and decrease in competition for pollinators at higher elevations. Plant fitness is, however, extremely reduced owing to the presence of non-native rabbits in the area (consuming more than 75% of the individuals in some localities), which in turn change plant trait-environment interactions along the gradient. Taken together, these findings indicate that the elevational variation found on plant performance results from the combined action of non-native rabbits with the microhabitat variability, exerting intricate ecological influences that threaten the survival of this violet species.

Galápagos land iguana (Conolophus subcristatus) as a seed disperser.

The role of the most common land iguana (Conolophus subcristatus) in the Galápagos Islands as an effective seed disperser is explored in this study. A total of 5705 seeds of 32 plant species were identified from 160 scats, 4545 of which (80%) appeared visually undamaged. Germination trials of 849 seeds from 29 species revealed that at least 10 species remained viable after passing through the iguana's gut, although only a small proportion of those seeds (4%) germinated. In any case, we argue that C. subcristatus exerts an important role on the 7 Galapagos islands where it occurs because of its abundance and capacity to ingest and disperse seeds at long distances. Our results strongly suggest that the Galápagos C. subcristatus plays an important role as a seed disperser of not only of native species but also some introduced plants in the Galápagos Islands.

Comparing seed dispersal effectiveness by frugivores at the community level.

Seed dispersal effectiveness (SDE) is the contribution of dispersers to plant recruitment and is estimated as the product of the number of seeds dispersed (quantity) and the probability of recruitment of each dispersed seed (quality). Although SDE is a key concept in seed dispersal ecology, few studies estimate SDE and none has a community approach. Oceanic islands, with simple communities, are ideal for this purpose. In this study, we compared the SDE of the main types of dispersers (lizards and passerine birds) at the community level in a given habitat. We estimated SDE using a stochastic simulation model parameterized with empirical data on quantity and quality components measured throughout the recruitment process. Although lizards are highly frugivorous and their density was approximately 20 times higher than that of birds, lizards and birds dispersed a similar quantity of seeds. This may be due to lower intake of seeds by lizards due to their slower metabolism (approximately 20 times lower than birds). This low metabolic rate limits the importance of lizards as seed dispersers, but it is compensated by extraordinarily high lizard densities in the study area (approximately 9600 individuals/km2). High densities of lizards are typical of islands, and this helps to explain why dispersal by lizards seems mainly an island phenomenon. Birds and lizards showed functional complementarity, especially regarding seed dispersal distribution patterns. In fact, lizards dispersed more seeds in shrublands and open sites, and birds in woodlands and beneath canopies, with their joint contribution helping to maximize recruitment. Lizards provided higher SDE than birds for 7 out of 11 plant species. The disperser with a higher quantity for a given plant generally had the higher quality, and plants could be classified as bird- or lizard-dependent for dispersal. This dependence increased when considering SDE instead of dispersal quantity only. Moreover, quality was a better predictor of SDE than quantity, which should be considered when parameterizing interaction networks, as this might affect inferences about their architecture.

Long-distance dispersal to oceanic islands: success of plants with multiple diaspore specializations.

A great number of scientific papers claim that angiosperm diversification is manifested by an ample differentiation of diaspore traits favouring long-distance seed dispersal. Oceanic islands offer an ideal framework to test whether the acquisition of multiple sets of diaspore traits (syndromes) by a single species results in a wider geographic distribution. To this end, we performed floristic and syndrome analyses and found that diplochorous species (two syndromes) are overrepresented in the recipient flora of the Azores in contrast to that of mainland Europe, but not to mainland Portugal. An additional analysis of inter-island colonization showed a general trend of a higher number of islands colonized by species with a single syndrome (monochorous) and two syndromes than species with no syndrome (unspecialized). Nevertheless, statistical significance for differences in colonization is meagre in some cases, partially due to the low proportion of diplochorous species in Europe (244 of ∼10 000 species), mainland Portugal (89 of 2294 species), and the Azores (9 of 148 species), Canaries (17 of 387 lowland species) and Galápagos (18 of 313 lowland species). Contrary to expectations, this first study shows only a very marginal advantage for long-distance dispersal of species bearing multiple syndromes.

Historical isolation of the Galápagos carpenter bee (Xylocopa darwini) despite strong flight capability and ecological amplitude.

Colonization across the Galápagos Islands by the carpenter bee (Xylocopa darwini) was reconstructed based on distribution of mitochondrial haplotypes (cytochrome oxidase II (COII) sequences) and haplotype lineages. A total of 12 haplotypes were found in 118 individuals of X. darwini. Distributional, phylogenetic and phylogeographic analyses suggest early colonization of most islands followed by historical isolation in two main groups: eastern and central-western islands. Evidence of recurrent inter-island colonization of haplotypes is largely lacking, despite strong flight capability and ecological amplitude of the species. Recent palaeogeographic data suggest that several of the current islands were connected in the past and thus the isolation pattern may have been even more pronounced. A contrast analysis was also carried out on 10 animal groups of the Galápagos Islands, and on haplotype colonization of seven animal and plant species from several oceanic archipelagos (the Galápagos, Azores, Canary Islands). New colonization metrics on the number of potential vs. inferred colonization events revealed that the Galápagos carpenter bee shows one of the most significant examples of geographic isolation.

Relative importance of phenotypic trait matching and species' abundances in determining plant-avian seed dispersal interactions in a small insular community.

Network theory has provided a general way to understand mutualistic plant-animal interactions at the community level. However, the mechanisms responsible for interaction patterns remain controversial. In this study we use a combination of statistical models and probability matrices to evaluate the relative importance of species morphological and nutritional (phenotypic) traits and species abundance in determining interactions between fleshy-fruited plants and birds that disperse their seeds. The models included variables associated with species abundance, a suite of variables associated with phenotypic traits (fruit diameter, bird bill width, fruit nutrient compounds), and the species identity of the avian disperser. Results show that both phenotypic traits and species abundance are important determinants of pairwise interactions. However, when considered separately, fruit diameter and bill width were more important in determining seed dispersal interactions. The effect of fruit compounds was less substantial and only important when considered together with abundance-related variables and/or the factor 'animal species'.

Bird-flower visitation networks in the Galápagos unveil a widespread interaction release.

Owing to food scarcity and to the high densities that vertebrates often reach on islands, typical insect- and seed-eaters widen their feeding niche and interact with a greater fraction of species than their mainland counterparts. This phenomenon, coined here 'interaction release', has been previously reported for single species but never for an entire community. During 4 years, we gathered data on bird-flower visitation on 12 Galápagos islands. We show that all sampled land birds exploit floral resources and act as potential pollinators across the entire archipelago, in all major habitats and all year round. Although species and link composition varies among islands, strong interaction release takes place on all islands, making their bird-flower network highly generalized. Interaction release is crucial to the survival of native birds but simultaneously threatens the unique biodiversity of this archipelago, as the birds also visit invading plants, likely facilitating their integration into pristine native communities.

How important are seabirds in the diet of black rats on islands with a superpredator?

This study assessed the impact of introduced black rats (Rattus rattus) on Cory's shearwater (Calonectris diomedea borealis) in a multi-invaded insular ecosystem where rats are mesopredators. We hypothesized that black rats should have little impact on Cory's shearwaters in the presence of cats as superpredators. Stomach contents and stable isotope analysis (SIA) in tissues of black rats were analyzed to assess the trophic ecology and the importance of Cory's shearwater in their diet. We also studied the isotopic signature in tissues of house mouse (Mus domesticus) to confirm previous data showing no predation of this species on Cory's shearwaters. For both rodent species, temporal variation in diet composition in response to the availability of seabird prey was evaluated, and short- and long-term consistency in diet was tested using different tissues from the same individual. For black rats a Bayesian isotope mixing model (SIAR) was applied to determine the relative contribution of each prey to the individual diet. SIA of mouse tissues varied between the Cory's shearwater breeding and non-breeding periods. However, no significant differences were found in diet and SIA for black rats. In contrast, individuals of both species showed a strong consistency in diet which apparently benefited their body condition index. Although black rats supplement their diet with Cory's shearwater eggs and chicks (8.3% in stomach contents and 10.6% in the SIAR model), their current impact on the Cory's shearwater population appears to be small, probably due to several factors including the small size of the rat population and a high level of rat predation by cats.