Biology subjects

Helsen, K.

Publications and source records attributed to Helsen, K..

4 recordsLinked to original sources

bioRxiv2021

Extending the CWM approach to intraspecific trait variation: how to deal with overly optimistic standard tests?

Community weighted means (CWMs) are widely used to study the relationship between community-level functional traits and environment. For certain null hypotheses, CWM-environment relationships assessed by linear regression or ANOVA and tested by standard parametric tests are prone to inflated Type I error rates. Previous research has found that this problem can be solved by permutation tests (i.e. the max test). A recent extension of the CWM approach allows the inclusion of intraspecific trait variation (ITV) by the separate calculation of fixed, site-specific, and intraspecific CWMs. The question is whether the same Type I error rate inflation exists for the relationship between environment and site-specific or intraspecific CWM. Using simulated and real-world community datasets, we show that site-specific CWM-environment relationships have also inflated Type I error rate, and this rate is negatively related to the relative ITV magnitude. In contrast, for intraspecific CWM-environment relationships, standard parametric tests have the correct Type I error rate, although somewhat reduced statistical power. We introduce an ITV-extended version of the max test, which can solve the inflation problem for site-specific CWM-environment relationships and, without considering ITV, becomes equivalent to the "original" max test used for the CWM approach. We show that this new ITV-extended max test works well across the full possible magnitude of ITV on both simulated and real-world data. Most real datasets probably do not have intraspecific trait variation large enough to alleviate the problem of inflated Type I error rate, and published studies possibly report overly optimistic significance results.

ecology↗

bioRxiv2021

Do forest over- and understory respond to the same environmental variables when viewed at the taxonomic and trait level?

While the relative importance of climate filtering is known to be higher for woody species assemblages than herbaceous assemblage, it remains largely unexplored whether this pattern is also reflected between the woody overstory and herbaceous understory of forests. While climatic variation will be more buffered by the tree layer, the understory might also respond more to small-scale soil variation, next to experiencing additional environmental filtering due to the overstorys effects on light and litter quality. For (sub)tropical forests, the understory often contains a high proportion of fern and lycophyte species, for which environmental filtering is even less well understood. We explored the proportional importance of climate proxies and soil variation on the species, functional trait and (functional) diversity patterns of both the forest overstory and fern and lycophyte understory along an elevational gradient from 850 to 2100 m a.s.l. in northern Taiwan. We selected nine functional traits expected to respond to soil nutrient or climatic stress for this study and furthermore verified whether they were positively related across vegetation layers, as expected when driven by similar environmental drivers. We found that climate was a proportionally more important predictor than soil for the species composition of both vegetation layers and trait composition of the understory. The stronger than expected proportional effect of climate for the understory was likely due to fern and lycophytes higher vulnerability to drought, while the high importance of soil for the overstory seemed driven by deciduous species. The environmental drivers affected different response traits in both vegetation layers, however, which together with additional overstory effects on understory traits, resulted in a strong disconnection of community-level trait values across layers. Interestingly, species and functional diversity patterns could be almost exclusively explained by climate effects for both vegetational layers, with the exception of understory species richness. This study illustrates that environmental filtering can differentially affect species, trait and diversity patterns and can be highly divergent for forest overstory and understory vegetation, and should consequently not be extrapolated across vegetation layers or between composition and diversity patterns.

ecology↗

bioRxiv2021

Comparing trait syndromes between Taiwanese subtropical terrestrial and epiphytic ferns and lycophytes at the species and community level

Background and AimsWhile functional trait-trait and trait-environment relationships are well studied in angiosperms, it is less clear if similar relationships, such as the leaf economics spectrum (LES), hold for ferns, and whether they differ between terrestrial and epiphytic fern communities. We used vegetation data collected along an elevation gradient in Taiwan to explore these relationships. MethodsWe measured nine leaf traits for 47 terrestrial and 34 epiphytic fern species across 59 vegetation plots along an elevation gradient in the subtropical forest of Northern Taiwan. We explored trait-trait and trait-environment relationships at both the species and community levels for both growth habits, while accounting for phylogenetic relationships. Key ResultsEpiphytes differed from terrestrial ferns in species- and community-level trait values, mainly reflecting responses to higher drought and nutrient stress. The angiosperm LES was reflected in the trait-trait correlations of terrestrial ferns and less expressively in epiphytes. This pattern suggests that mainly water rather than nutrient availability shapes epiphytic trait patterns. Trait-trait analysis on raw trait data and on independent contrasts vary in some ways. Trait-environment relationships were similar for several drought-related traits across both species groups. ConclusionsThis study illustrates that fern trait patterns are not entirely equivalent for epiphytic and terrestrial species or communities and should not be extrapolated across growth habits or between the species and community levels. Phylogenetic constraints may influence the trait-environment response of epiphytic species.

ecology↗

bioRxiv2019

Pre-adaptation to climate change through topography-driven evolution of traits and their plasticity

Climate change is expected to increase the level of drought stress experienced by many plant populations, yet the spatial distribution of changes in dryness remains highly uncertain. Species can, to some extent, adapt to climate uncertainty through evolving increased trait plasticity. Biodiversity conservation could capitalize on such natural variation in the ability of populations to cope with climate variability. Yet, disentangling evolution of trait means vs. trait plasticity is challenging, as it requires a sampling design with genetic replicates grown under distinct environmental conditions. Here, we applied different soil moisture treatments to clones of Fragaria vesca plants that were raised from seeds that were sampled in distinct mountainous topographical settings, to study adaptive trait and plasticity divergence in response to drought. We demonstrate that various fitness traits evolved along topographical gradients, including increased specific leaf area (SLA) with increasing slope, and increased growth plasticity with increasing altitude. Our results indicate that traits and their plasticity can evolve independently in response to distinct topographical stressors. We further show that trait heritability varies considerably among traits and topographical settings. Heritability of phenotypic plasticity tended to increase with altitude for all traits, with populations from high altitudes harboring more than twice the heritability for growth and SLA plasticity compared to populations from low altitudes. We conclude that (i) low altitudinal populations, which are expected to be least vulnerable to climate change, may only withstand limited increases in drought stress, while (ii) populations that evolved to thrive under more heterogeneous mountain conditions are pre-adapted to climate change through high plasticity and heritability. Highly heterogeneous landscapes may thus represent invaluable sources of quantitative genetic variation that could support conservation under climate change across the globe.

ecology↗