Dagmar Martina Hanz

The discipline of functional island biogeography and studies on plant ecological strategies shaping island assemblages have emerged only recently. Due to volcanic activity, primary succession is an important natural process driving ecosystem dynamics on oceanic islands. However, our knowledge about plant functional traits in explaining the mechanism of ecological succession on these islands characterized by impoverished and disharmonic, but endemic‐rich floras, is limited. We investigated the distribution of plants with respect to nine functional traits related to resource use, reproduction, and growth as well as their overall functional diversity during primary succession using a chronosequence on 10 lava flows of La Palma, Canary Islands. We analysed changes of single traits with age using community‐weighted trait means and applied ordination techniques to evaluate changes in trait composition. Based on ecological succession theory, we tested several hypotheses for changes of functional traits along the successional gradient. We also analysed the role of endemic and introduced plants in structuring successional communities. Both the single‐trait and trait compositional approach revealed that the composition of plants displaying core traits related to leaf economics and dispersal ability shifted with substrate age showing a change from acquisitive to conservative traits and from anemochory to zoochory along the gradient. These shifts were entirely driven by endemic shrubs, while other growth forms contributed to the increase in species and functional richness with lava age but little to vegetation structure. Introduced species were almost absent in successional trajectories. Functional dispersion increased whereas trait turnover was constant and low during succession. Synthesis. Our island system reflects a directional succession governed by the selection of functional traits related to environmental conditions and acquisitive‐conservative strategies as well as to dispersal capacity in early stages followed by a gradual modification of the environment and an expansion of the niche space linked to functional divergence in later stages. Major changes in functional traits occurred five hundred years after the eruptions indicating that primary succession in this dry environment is very slow. The dominance of endemic shrubs and the lack of introduced plants at all successional stages highlight the importance of evolutionary processes in shaping species ecological strategies linked to disturbances like volcanism on this oceanic archipelago.

Aim: Oceanic islands possess unique floras with high proportions of endemic species. Island floras are expected to be severely affected by changing climatic conditions as species on islands have limited distribution ranges and small population sizes and face the constraints of insularity to track their climatic niches. We aimed to assess how ongoing climate change affects the range sizes of oceanic island plants, identifying species of particular conservation concern.Location: Canary Islands, Spain.Methods: We combined species occurrence data from single‐island endemic, archipelago endemic and nonendemic native plant species of the Canary Islands with data on current and future climatic conditions. Bayesian Additive Regression Trees were used to assess the effect of climate change on species distributions; 71% (n = 502 species) of the native Canary Island species had models deemed good enough. To further assess how climate change affects plant functional strategies, we collected data on woodiness and succulence.Results: Single‐island endemic species were projected to lose a greater proportion of their climatically suitable area (x ̃ = −0.36) than archipelago endemics (x ̃ = −0.28) or nonendemic native species (x ̃ = −0.26), especially on Lanzarote and Fuerteventura, which are expected to experience less annual precipitation in the future. Moreover, herbaceous single‐island endemics were projected to gain less and lose more climatically suitable area than insular woody single‐island endemics. By contrast, we found that succulent single‐island endemics and nonendemic natives gain more and lose less climatically suitable area.Main Conclusions: While all native species are of conservation importance, we emphasise single‐island endemic species not characterised by functional strategies associated with water use efficiency. Our results are particularly critical for other oceanic island floras that are not constituted by such a vast diversity of insular woody species as the Canary Islands.

Current models of island biogeography treat endemic and non‐endemic species as if they were functionally equivalent, focussing primarily on species richness. Thus, the functional composition of island biotas in relation to island biogeographical variables remains largely unknown. Using plant trait data (plant height, leaf area and flower length) for 895 native species in the Canary Islands, we related functional trait distinctiveness and climate rarity for endemic and non‐endemic species and island ages. Endemics showed a link to climatically rare conditions that is consistent with island geological change through time. However, functional trait distinctiveness did not differ between endemics and non‐endemics and remained constant with island age. Thus, there is no obvious link between trait distinctiveness and occupancy of rare climates, at least for the traits measured here, suggesting that treating endemic and non‐endemic species as functionally equivalent in island biogeography is not fundamentally wrong.

Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.Location: Canary Islands, Spain.Major taxa studied: Spermatophytes.Time period: Present day.Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non‐endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non‐endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.Results: Trait space of endemic and non‐endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non‐endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.Main conclusions: We found that endemic and non‐endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.

Aim: Trait‐based approaches are increasingly important in ecology and biogeography, but progress is often hampered by the availability of high‐quality quantitative trait data collected in the field. Alternative sources of trait information include scientific floras and taxonomic monographs. Here we test the reliability and usefulness of trait data acquired from scientific floras against trait values measured in the field, and those in TRY, the most comprehensive global plant trait database.Location: Tenerife and La Palma, Canary Islands, Spain.Methods: We measured leaf area and specific leaf area (SLA) in the field for 451 native vascular plant species and compared them with equivalent trait data digitised from the most recent and comprehensive guide of the Canarian flora, and data sourced from TRY. We regressed the field‐measured traits against their equivalents estimated from the literature and used the regression models from one island to predict the trait values on the other island.Results: For leaf area, linear models showed good agreement between values from the scientific flora and those measured in the field (r² = 0.86). These models were spatially transferable across islands. In contrast, for SLA we found a weak relationship between field‐measured values and the best estimates from the scientific flora (r² = 0.11). Insufficient data were available in the TRY database for our study area to calculate trait correlations with other data sources.Conclusions: Scientific floras can act as useful data sources for quantitative plant trait data for some traits but not others, whilst the TRY database contains many traits, but is incomplete in species coverage for our study region, and oceanic islands in general.

Aim: It is not yet clear whether similar mechanisms influence the assembly of ecological communities across different continents. Here, we investigated the functional and phylogenetic diversity of bird assemblages along elevational gradients in two biogeographic regions in order to identify how these are driven by biotic factors, such as food resources and vegetation structure, and abiotic factors, such as ambient temperature and precipitation.Location: Two 2,000‐m elevational gradients in the Ecuadorian Andes and on Mount Kilimanjaro, Tanzania.Taxon: Forest‐dwelling bird species.Methods: We recorded bird species abundances on 18 and 30 plots in the Ecuadorian Andes and on Mount Kilimanjaro respectively. We measured 10 functional morphological traits, related to bird feeding and movement, and utilized bird phylogenies to compare observed values and null‐model corrected effect sizes of functional and phylogenetic diversity along elevational gradients and between biogeographic regions. Furthermore, we assessed how observed values and effect sizes of functional and phylogenetic diversity were associated with the underlying gradients in available food resources, vegetation structure, temperature and precipitation.Results: Functional and phylogenetic diversity were generally higher in species assemblages in the Ecuadorian Andes than on Mount Kilimanjaro. Both observed values and effect sizes of functional and phylogenetic diversity decreased significantly with increasing elevation in both biogeographic regions. Functional diversity consistently increased with increasing resource availability, whereas phylogenetic diversity increased with increasing vegetation heterogeneity and canopy closure in both biogeographic regions. Temperature and precipitation were not significantly associated with functional and phylogenetic diversity.Main conclusions: Our results suggest that in both mountain systems the diversity of functional traits in bird species assemblages is the result of environmental filtering by available food resources, whereas phylogenetic diversity is primarily limited by vegetation structure. These findings suggest important differences in the main drivers of functional and phylogenetic diversity. We conclude that biotic factors might be more important for driving bird diversity patterns than abiotic factors and that a loss of resource availability and vegetation structure, e.g., through human impacts, is likely to trigger changes in community assembly on tropical mountains.