Biology subjects

Kreft, H.

Publications and source records attributed to Kreft, H..

32 records · Page 2Linked to original sources

bioRxiv2022

Latitude influences stability via stabilizing mechanisms in naturally-assembled forest ecosystems at different spatial grains

Ecosystem stability reveals how ecosystems respond to global change over time. Yet, the focus of past research on small spatial grains and extents overlooks scale dependence and how broad-scale environmental gradients shape stability. Here, we use forest inventory data covering a broad latitudinal gradient from the temperate to the tropical zone to examine cross-scale variation in stability of aboveground biomass and underlying stabilizing mechanisms. While stability did not shift systematically with latitude at either spatial grain, we found evidence that species asynchrony increased towards the tropics at the small spatial grain while species stability decreased at both spatial grains. Moreover, latitude stabilized forest communities via its effects on both stabilizing mechanisms, which compensated for the weak and destabilizing effects of species richness. Yet, the trade-off in the relative importance of species stability and species asynchrony for stability was not mediated by latitude, suggesting that context-dependent factors - to a greater extent than macroecological ones - underlie large-scale patterns of stability. Our results highlight the crucial role of species asynchrony and species stability in determining ecosystem stability across broad-scale environmental gradients, suggesting that conserving biodiversity alone may not be sufficient for stabilizing naturally-assembled forest ecosystems.

ecology↗

bioRxiv2022

Landscape heterogeneity and soil biota are central to multi-taxa diversity for landscape restoration

How to enhance biodiversity in monoculture-dominated landscapes is a key sustainability question that requires considering the spatial organization of ecological communities (beta diversity). Here, we experimentally tested if increasing landscape heterogeneity - through tree islands - is a suitable landscape restoration strategy when aiming to enhance multi-taxa diversity. We found that multi-taxa diversity resulted from islands fostering unique species (turnover: between 0.18 - 0.73) rather than species losses and gains (nestedness: between 0.03 - 0.34), suggesting that tree islands enhance diversity at the landscape scale. Through partial correlation networks, we revealed that landscape heterogeneity is associated with multi-taxa diversity (strength = 0.84). Soil biota were also central to the overall community by connecting beta diversity patterns across taxa. Our results show that increasing landscape heterogeneity enhances multi-taxa diversity in monoculture-dominant landscapes. Furthermore, we highlight that strategies aiming to enhance multi-taxa diversity should consider that spatial distributions of above- and below-ground communities are associated.

ecology↗

bioRxiv2022

Climate and ant richness explain the global distribution of ant-plant mutualisms

Biotic interactions are known to play an important role in shaping species geographic distributions and diversity patterns. However, the role of mutualistic interactions in shaping global diversity patterns remains poorly quantified, particularly with respect to interactions with invertebrates. Moreover, it is unclear how the nature of different mutualisms interacts with abiotic drivers and affects diversity patterns of mutualistic organisms. Here, we present a global-scale biogeographic analysis of three different ant-plant mutualisms, differentiating between plants bearing domatia, extrafloral nectaries (EFNs), and elaiosomes, based on comprehensive geographic distributions of [~]15,000 flowering plants and [~]13,000 ant species. Domatia and extrafloral nectaries involve indirect plant defenses provided by ants, while elaiosomes attract ants to disperse seeds. Our results show distinct biogeographic patterns of different ant-plant mutualisms, with domatium- and EFN-bearing plant richness decreasing sharply from the equator towards the poles, while elaiosome-bearing plants prevail at mid-latitudes. Contemporary climate, especially mean annual temperature and precipitation, emerge as the most important predictor of ant-associated plant diversity. In hot and moist regions, typically the tropics, domatium- and EFN-bearing plant richness increases with related ant guild richness, while in warm regions plants with elaiosomes are strongly linked to interacting ants. Our results suggest that ant richness in combination with climate drives the spatial variation of plants bearing domatia, extrafloral nectaries, and elaiosomes, highlighting the importance of mutualistic interactions for understanding plant biogeography and its response to global change.

ecology↗

bioRxiv2022

Machine learning improves global models of plant diversity

Despite the paramount role of plant diversity for ecosystem functioning, biogeochemical cycles, and human welfare, knowledge of its global distribution is incomplete, hampering basic research and biodiversity conservation. Here, we used machine learning (random forests, extreme gradient boosting, neural networks) and conventional statistical methods (generalised linear models, generalised additive models) to model species richness and phylogenetic richness of vascular plants worldwide based on 830 regional plant inventories including c. 300,000 species and predictors of past and present environmental conditions. Machine learning showed an outstanding performance, explaining up to 80.9% of species richness and 83.3% of phylogenetic richness. Current climate and environmental heterogeneity emerged as the primary drivers, while past environmental conditions left only small but detectable imprints on plant diversity. Finally, we combined predictions from multiple modelling techniques (ensemble predictions) to reveal global patterns and centres of plant diversity at multiple resolutions down to 7,774 km2. Our predictive maps provide the most accurate estimates of global plant diversity available to date at grain sizes relevant for conservation and macroecology.

ecology↗

bioRxiv2022

Assembly of functional diversity in an oceanic island flora

Oceanic island floras are well-known for their morphological peculiarities and exhibit striking examples of trait evolution1,2. These morphological shifts are commonly attributed to insularity and thought to be shaped by biogeographical processes and evolutionary histories of oceanic islands1,3. However, the mechanisms through which biogeography and evolution have shaped the distribution and diversity of plant functional traits remain unclear. Here, we describe the functional trait space of an oceanic island flora (Tenerife, Canary Islands, Spain) using extensive field and laboratory measurements, and relate it to global trade-offs in ecological strategies. We find that the island trait space is concentrated around a functional hotspot dominated by shrubs with a conservative life-history strategy. By dividing the island flora into species groups with distinct biogeographical distributions and diversification histories, our results reveal that long-distance dispersal, and the interplay between inter-island dispersal and archipelago-level speciation processes drive functional divergence and expand trait space. Conversely, speciation via cladogenesis has overall led to functional convergence, densely packing trait space around shrubbiness. Our approach combines ecology, biogeography and evolution and opens avenues for new trait-based insights into how dispersal and speciation shape the assembly of native island floras.

ecology↗

bioRxiv2022

Plant longevity, drought and island isolation favoured rampant evolutionary transitions towards insular woodiness

Insular woodiness (IW)--the evolutionary transition from herbaceousness towards woodiness on islands--is one of the most iconic features of island floras. Since pioneering work by Darwin and Wallace, five IW drivers have been proposed: (i) favourable aseasonal climate and (ii) lack of large native herbivores promote plant longevity that (iii) results in prolonged flowering favouring outcrossing. Alternatively, (iv) competition for sunlight requires taller and stronger stems, and (v) drought favours woodiness to safeguard root-to-shoot water transport. However, information on the occurrence of IW is fragmented, hampering tests of these potential drivers. Here, we identify 1,097 insular woody species (IWS) on 375 islands, and infer at least 175 evolutionary transitions on 31 archipelagos, concentrated in six angiosperm families. Structural equation models reveal that the IWS richness on oceanic islands correlates with aseasonal favourable climate, followed by increased drought and island isolation (approximating competition). When continental islands are included, reduced herbivory pressure by large native mammals, increased drought and island isolation are most relevant. The repeated evolution of IW opens promising avenues to disentangle the variation in gene regulatory networks triggering wood formation, and emphasize individual archipelagos as laboratories of evolution, where similar environmental conditions replicate convergent evolution of similar traits.

evolutionary biology↗

bioRxiv2021

Trash-basket epiphytes as secondary foundation species: a review of their distribution and effects on biodiversity and ecosystem functions

BackgroundSecondary foundation species (FS) are organisms that inhabit ecosystems structurally defined by a primary foundation species, providing additional structure to habitats and communities. Trash-basket epiphytes (TBE) are secondary FS that enhance arboreal soil accumulation, providing shelter to animals, and rooting sites for plants. While their importance may vary across biomes, TBE have been overlooked as drivers of biodiversity and ecosystem functions. Here, we discuss the prevalence of TBE across biomes, their effects on biodiversity and ecosystem functions, and future research directions. MethodsWe performed a systematic literature review of articles, books and theses and collated and synthesised information about the taxonomic distribution of TBE, their effects on ecosystem functions, and reports of plant-animal and plant-plant interactions. Then, we analysed the global distribution of TBE using a generalized linear model and summarised two studies to assess their effects on soil invertebrates. ResultsWe identified 120 publications describing 209 species of TBE. Most TBE belong to Araceae (43%), Polypodiaceae (23%), and Orchidaceae (14%) and occur in all tropical and southern temperate forests. TBE richness peaks in the South-American Pacific mangroves, Eastern Cordillera Real, and the Napo moist forests. TBE effects on ecosystem functions include arboreal soil accumulation, water retention and temperature regulation in the canopy, and nutrient leaching through stem-flow. TBE provide shelter to species in more than 97 animal families, including from invertebrates to mammals, while 72 vascular plants have been reported to root in arboreal soil of TBE. ConclusionsTBE are a compelling group of model organisms that can be used to study ecological processes such as facilitation cascades, niche construction, extended phenotypes, or the effects of secondary FS on biodiversity and ecosystem functioning. TBE should also be included in forest management plans to enhance the availability of microhabitats in the canopy supporting its associated flora and fauna.

ecology↗

bioRxiv2021

Vascular epiphytes contribute disproportionately to global centres of plant diversity

AimVascular epiphytes are ubiquitous features of wet tropical forests where they contribute substantially to local and regional plant diversity. While some basic epiphyte distribution patterns are relatively well studied, little effort has been made to understand the drivers responsible for constraining their global distribution. This study quantifies the substantial contribution of epiphytes to global gradients and centres of vascular plant diversity and explores whether epiphytes vary from terrestrial plants in relation to contemporary and historical environmental variables. LocationGlobal. Time periodPresent. Major taxa studiedVascular epiphytes. MethodsWe integrated EpiList 1.0, a comprehensive list comprising > 30,000 vascular epiphyte species, and species distributions derived from the GIFT database to describe the global biogeography of epiphytes. We used generalized linear mixed effects models to assess the relationship between epiphytic and terrestrial plant diversity, and contemporary and historical environmental predictors. ResultsWe find that epiphytes substantially contribute to global centres of vascular plant diversity, accounting for up to 39% of the vascular flora in the Neotropics. Epiphytes decrease in species numbers with increasing latitude at a rate three times faster than terrestrial plants, a trend that is driven mainly by the distribution of tropical forests and precipitation. Further, large regional differences emerge that are explained by several large endemic angiosperm families (e.g., Neotropical Bromeliaceae) that are absent in other tropical regions. Main conclusionsOur results show that epiphytes are disproportionately diverse in most global centres of plant diversity and play an important role in driving the global latitudinal diversity gradient for plants. The distribution of precipitation and tropical forests emerge as major drivers of the latitudinal diversity gradient in epiphyte species richness. Finally, our findings demonstrate how epiphyte floras in different biogeographical realms are composed of different families and higher taxa revealing an important signature of historical biogeography.

ecology↗

bioRxiv2021

Differential responses of amphibians and reptiles to land-use change in the biodiversity hotspot of north-eastern Madagascar

Large expanses of tropical rainforest have been converted into agricultural landscapes cultivated by smallholder farmers. This is also the case in north-eastern Madagascar; a region that retains significant proportions of forest cover despite slash-and-burn hill rice cultivation and vanilla agroforestry expansion. The region is also a global hotspot for herpetofauna diversity, but how amphibians and reptiles are affected by land-use change remains largely unknown. Using a space-for-time study design, we compared species diversity and community composition across seven prevalent land uses: unburned (old-growth forest, forest fragment, and forest-derived vanilla agroforest) and burned (fallow-derived vanilla agroforest, woody fallow, and herbaceous fallow) land-use types, and rice paddy. We conducted six comprehensive, time-standardized searches across at least ten replicates of each land-use type and applied genetic barcoding to confirm species identification. We documented an exceptional diversity of herpetofauna (119 species; 91% endemic). Plot-level amphibian species richness was significantly higher in old-growth forest than in all other land-use types. Plot-level reptile species richness was significantly higher in unburned land-use types compared to burned land-use types. For both amphibians and reptiles, the less-disturbed land-use types showed more uneven communities and the species composition in old-growth forest differed significantly from all other land-use types. Amphibians had higher forest dependency (38% of species occurred exclusively in old-growth forest) than reptiles (26%). Our analyses thus revealed that the two groups respond differently to land-use change: we found less pronounced losses of reptile species richness especially in unburned agricultural habitats, suggesting that reptiles are less susceptible to land-use change than amphibians, possibly due to their ability to cope with hotter and drier microclimates. Overall, old-growth forest harboured a unique diversity, but some species also thrived in vanilla agroforestry systems, especially if these were forest-derived. This highlights the importance of conserving old-growth forests and non-burned land-use types within agricultural landscapes.

ecology↗

bioRxiv2020

Modeling the long-term dynamics of tropical forests: from leaf traits to whole-tree growth patterns

Tropical forests are the most diverse terrestrial ecosystems and home to numerous tree species with diverse ecological strategies competing for resources in space and time. Functional traits influence the ecophysiological performance of tree species, yet the relationship between traits and emergent long-term growth pattern is poorly understood. Here, we present a novel 3D forest stand model in which growth patterns of individual trees and forest stands are emergent properties of leaf traits. Individual trees are simulated as 3D functional-structural tree models (FSTMs), considering branches up to the second order and leaf dynamics at a resolution of one m3. Each species is characterized by a set of leaf traits that corresponds to a specific position on the leaf economic spectrum and determines light-driven carbon assimilation, respiration and mortality rates. Applying principles of the pipe model theory, these leaf scale-processes are coupled with within-tree carbon allocation, i.e., 3D tree growth emerges from low-level processes. By integrating these FSTMs into a dynamic forest stand model, we go beyond modern stand models to integrate structurally-detailed internal physiological processes with interspecific competition, and interactions with the environment in diverse tree communities. For model calibration and validation, we simultaneously compared a large number of emergent patterns at both the tree and forest levels in a pattern-oriented modeling framework. At the tree level, varying specific leaf area and correlated leaf traits determined the maximum height and age of a tree, as well as its size-dependent growth rate and shade tolerance. Trait variations along the leaf economic spectrum led to a continuous transition from fast-growing, short-lived and shade-intolerant to slow-growing, long-lived and shade-tolerant trees. These emerging patterns resembled well-known functional tree types, indicating a fundamental impact of leaf traits on long-term growth patterns. At the forest level, a large number of patterns taken from lowland Neotropical forests were reproduced, indicating that our forest model simulates structurally realistic forests over long time spans. Our ecophysiological approach improves the understanding of how leaf level processes scale up to the tree and the stand level, and facilitates the development of next-generation forest models for species-rich forests in which tree performance emerges directly from functional traits.

ecology↗

bioRxiv2019

GIFT - A Global Inventory of Floras and Traits for macroecology and biogeography

To understand how traits and evolutionary history shape the geographic distribution of plant life on Earth, we need to integrate high-quality and global-scale distribution data with functional and phylogenetic information. Large-scale distribution data for plants are, however, often restricted to either certain taxonomic groups or geographic regions. For example, range maps only exist for a small subset of all plant species and digitally available point-occurrence information is strongly biased both geographically and taxonomically. An alternative, currently rarely used resource for macroecological and botanical research are regional Floras and checklists, which contain highly curated information about the species composition of a clearly defined area, and which together virtually cover the entire global land surface. Here we report on our recent efforts to mobilize this information for macroecological and biogeographical analyses in the GIFT database, the Global Inventory of Floras and Traits. GIFT integrates plant distributions, functional traits, phylogenetic information, and region-level geographic, environmental and socioeconomic data. GIFT currently holds species lists for 2,893 regions across the whole globe including ~315,000 taxonomically standardized species names (i.e. c. 80% of all known land plant species) and ~3 million species-by-region occurrences. In addition, GIFT contains information about the floristic status (native, endemic, alien and naturalized) and takes advantage of the wealth of trait information in the regional Floras, complemented by data from global trait databases. Based on a hierarchical and taxonomical derivation scheme, GIFT holds information for 83 functional traits and more than 2.3 million trait-by-species combinations and achieves unprecedented coverage in categorical traits such as woodiness (~233,000 spp.) or growth form (~213,000 spp.). Here we present the structure, content and automated workflows of GIFT and a corresponding web-interface (http://gift.uni-goettingen.de) as proof of concept for the feasibility and potential of mobilizing aggregated biodiversity data for global macroecological and biogeographical research.

ecology↗

bioRxiv2019

Disharmony of the world’s island floras

Disharmony is a key concept in island biology that describes the biased representation of higher taxa on islands compared to their mainland source regions. Although differential colonization success of taxa is predicted by selective dispersal, environmental and biotic filtering, the empirical evidence for disharmony remains largely anecdotal. Here, we develop a novel method for delineating island source regions and present the first global quantitative assessment of island disharmony. We analyzed the overall compositional bias of 320 island floras and examined the over- or under-representation on islands for 450 plant families. We found that the compositional bias of island floras is strongly predicted by geographical and climatic island characteristics (isolation, area, geologic origin, temperature, precipitation), whereas the representation of individual families is only weakly related to family-specific characteristics (family size, family age, taxonomic group, functional traits), indicating that the taxonomic scope of the disharmony concept has historically limited its wider applicability. Our results provide a strong foundation for integrating disharmony with quantitative functional and phylogenetic approaches in order to gain a deeper understanding of assembly processes on islands.

ecology↗

bioRxiv2017

Interactions between ecological, evolutionary, and environmental processes unveil complex dynamics of island biodiversity

AimsUnderstanding how biodiversity emerges and varies in space and time is central to ecology and biogeography. Multiple processes affect biodiversity at different scales and organizational levels, hence progress in understanding biodiversity dynamics requires the integration of these underlying processes. Here we present BioGEEM (BioGeographical Eco-Evolutionary Model), a spatially-explicit, process-based model that integrates all processes hypothesized to be relevant for biodiversity dynamics and that can be used to evaluate their relative roles.\n\nLocationHypothetical oceanic islands\n\nMethodsThe model is stochastic, grid-based, and integrates ecological (metabolic constraints, demography, dispersal, and competition), evolutionary (mutation and speciation), and environmental (geo-climatic dynamics) processes. Plants on oceanic islands served as model system. We used the full model to test hypotheses about emergent patterns at different spatio-temporal scales and organizational levels (populations, species, communities, and assemblages), switching off processes to assess the importance 1) of competition for realistic population and range dynamics; 2) metabolic constraints for endemism and community composition; 3) environmental dynamics and 4) speciation for biogeographical patterns.\n\nResultsThe full model generated multiple patterns matching empirical and theoretical expectations. For example, populations were largest on young, species-poor islands. Species, particularly endemics, were better able to fill their potential range on small, species-poor islands. Richness gradients peaked at mid-elevations. The proportion of endemics was highest on old, large, and isolated environments within the islands. Species and trait richness showed unimodal temporal trends. Switching off selected processes affected these patterns, and we found most of our hypotheses supported.\n\nMain conclusionsIntegrating ecological, evolutionary, and environmental processes is essential to simultaneously generate realistic spatio-temporal dynamics at population, species, community, and assemblage level. Finally, large-scale biodiversity dynamics emerged directly from biological processes which make this mechanistic model a valuable virtual long-term field station to study the linkages between biogeography and ecology.

ecology↗

bioRxiv2017

Effects of time and isolation on plant diversity: testing island biogeography theory with an eco-evolutionary model

AimsThe General Dynamic Model of oceanic island biogeography (GDM) predicts how biogeographical rates, species richness, and endemism vary depending on island age, area, and isolation, based on the interplay of colonization, extinction, and speciation. Here, we used a simulation model to test whether GDM predictions may arise from individual- and population-level processes.\n\nLocationHypothetical hotspot islands.\n\nMethodsOur model (i) considers an idealized island ontogeny, (ii) metabolic constraints, and (iii) stochastic, spatially-explicit, and niche-based processes at the level of individuals and populations (plant demography, dispersal, competition, mutation, and speciation). Isolation scenarios involved varying dispersal ability and distances to mainland.\n\nResultsHumped temporal trends were obtained for species richness, endemic richness, proportion of cladogenetic endemic species, number of radiating lineages, number of species per radiating lineage, and biogeographical rates. The proportion of anagenetic endemics and of all endemics steadily increased over time. Extinction rates of endemic species peaked later than for non-endemic species. Species richness and the number of anagenetic endemics decreased with isolation as did rates of colonization, anagenesis, and extinction. The proportion of all endemics and of cladogenetic endemics, the number of cladogenetic endemics, of radiating lineages, and of species per radiating lineage, and the cladogenesis rate all increased with isolation.\n\nMain conclusionsThe results confirm most GDM predictions related to island ontogeny and isolation, but predict an increasing proportion of endemics throughout the experiment: a difference attributable to diverging assumptions on late island ontogeny. New insights regarding the extinction trends of endemics further demonstrate how simulation models focusing on low ecological levels provide tools to test biogeographical-scale predictions and to develop more detailed predictions for further empirical tests.

ecology↗