Taxonomic scale dependency of Bergmann’s patterns: a cross-scale comparison of hawkmoths and birds along a tropical elevational gradient

Abstract Bergmann’s rule predicts a larger body size for endothermic organisms in colder environments. The contrasting results from previous studies may be due to the differences in taxonomic (intraspecific, interspecific and community) and spatial (latitudinal vs elevational) scales. We compared Bergmann’s patterns for endotherms (Aves) and ectotherms (Lepidoptera: Sphingidae) along the same 2.6 km elevational transect in the eastern Himalayas. Using a large data spanning 3,302 hawkmoths (76 morpho-species) and 15,746 birds (245 species), we compared the patterns at the intraspecific (hawkmoths only), interspecific and community scales. Hawkmoths exhibited a positive Bergmann’s pattern at the intraspecific and abundance-weighted community scale. Contrary to this, birds exhibited a strong converse Bergmann’s pattern at interspecific and community scales, both with and without abundance. Overall, our results indicate that incorporation of information on intraspecific variation and/or species relative abundances influences the results to a large extent. The multiplicity of patterns at a single location provides the opportunity to disentangle the relative contribution of individual- and species-level processes by integrating data across multiple nested taxonomic scales for the same taxa. We suggest that future studies of Bergmann’s patterns should explicitly address taxonomic and spatial scale dependency, with species relative abundance and intraspecific trait variation as essential ingredients especially at short elevational scales.

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Taxonomic scale dependency of Bergmann's patterns: A cross-scale comparison of hawkmoths and birds along a tropical elevational gradient

10.1101/2021.03.29.437440 ◽

2021 ◽

Author(s):

Mansi Mungee ◽

Ramana Athreya ◽

Rohan Pandit

Keyword(s):

Body Size ◽

Large Data ◽

Elevational Gradient ◽

Scale Dependency ◽

Biological Organization ◽

Intraspecific Trait Variation ◽

Relative Contribution ◽

Single Location ◽

Species Abundances ◽

Patterns And Processes

Bergmann's rule predicts a larger body size for endothermic organisms in colder environments. The multiplicity of patterns and processes is expected because body size and temperature are two most fundamental factors on which many physiological, ecological and evolutionary processes depend, affecting all levels of biological organization, from individuals to communities. The confounding results from previous studies may be due to the differences in taxonomic (intraspecific, interspecific and community) and spatial (latitudinal vs elevational) scales. We compared Bergmann's patterns for endotherms (Aves) and ectotherms (Lepidoptera: Sphingidae) along a same 2.6 km elevational transect in the eastern Himalayas. Using a large data spanning 3,302 hawkmoths (76 morpho-species) and 15,746 birds (245 species), we compared the patterns at the intraspecific (hawkmoths only), interspecific and community scales. At the interspecific scale, we account for phylogenetic non-independence in body mass by using a heirarchical linear mixed effects model for hawkmoths, and a phylogenetic generalised least squares model for birds. We assess the importance of using abundance-weighted metrics at the community scales, after accounting for spatial auto-correlation in communities. Hawkmoths exhibited positive Bergmann's pattern at the intraspecific and abundance-weighted community scale. Intraspecific variation accounted for a substantial 33% variation at the community level. Contrary to this, birds exhibited a strong converse-Bergmann's pattern at interspecific and community scales, both with- and without-abundance. Overall, all metrics which incorporate local traits and/or species abundances show stronger correlations than when this information is lacking. The multiplicity of patterns at a single location provides the opportunity to disentangle the relative contribution of individual- and species-level processes by integrating data across multiple nested taxonomic scales for the same taxa. We suggest that future studies of Bergmann's patterns should explicitly address taxonomic- and spatial-scale dependency, with species relative abundance and intraspecific trait variation as essential ingredients especially at short elevational scales.

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TURNOVER OR INTRASPECIFIC TRAIT VARIATION: EXPLAINING FUNCTIONAL VARIABILITY IN A NEOTROPICAL ANURAN METACOMMUNITY

10.1101/2020.03.04.977397 ◽

2020 ◽

Author(s):

Diego Anderson Dalmolin ◽

Alexandro Marques Tozetti ◽

Maria João Ramos Pereira

Keyword(s):

Body Mass ◽

Intraspecific Variation ◽

Environmental Gradients ◽

Interspecific Variation ◽

Limb Length ◽

Head Shape ◽

Trait Variation ◽

Intraspecific Trait Variation ◽

Relative Contribution ◽

Eye Size

ABSTRACTTrait variation across environmental gradients results from two processes: intraspecific variation (ITV) and turnover. Tadpoles are known to exhibit phenotypic plasticity in several traits in response to the environment, resulting from intra or interspecific variation. Here we evaluate patterns of intraspecific variation in functional traits of adult anurans (head shape, eye size and position, limb length and body mass) and their relationship with environmental variables in an anuran metacommunity in southern Brazil. From anurans sampled from 33 ponds, we decomposed trait variation into ITV and turnover and modelled trait-environment relationships. We predict that the contribution of ITV and turnover to trait variation and trait-environment relationships should vary according to the preferred habitat of the species and the analysed traits. Intraspecific variation accumulated the highest rate of trait variation for arboreal species, while interspecific variation was greater for aquatic-terrestrial species and for the whole set of species. The contributions of turnover and ITV to shifts in community mean trait values were similar between traits, but differed between species sets. Depth, distance between ponds, area of Pinus surrounding the ponds, and types of pond vegetation and substrate strongly influenced trait variation, but their relative contribution depended on the analysed traits and species sets. The great contribution of ITV for head shape and eye size and position suggests the existence of intraspecific adaptations to microhabitats, while turnover dominance in the variation of body mass and limb length suggests differences in dispersal and trophic segregation between species.

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Intraspecific trait variability and community assembly in hawkmoths (Lepidoptera: Sphingidae) across an elevational gradient in the eastern Himalayas, India

10.1101/768705 ◽

2019 ◽

Cited By ~ 1

Author(s):

Mansi Mungee ◽

Ramana Athreya

Keyword(s):

Community Assembly ◽

Environmental Gradients ◽

Species Turnover ◽

Elevational Gradient ◽

Functional Ecology ◽

List Type ◽

Environmental Response ◽

Trait Variation ◽

Eastern Himalayas ◽

Response Traits

AbstractRecent progress in functional ecology has advanced our understanding of the role of intraspecific (ITV) and interspecific (STV) trait variation in community assembly across environmental gradients. Studies on plant communities have generally found STV as the main driver of community trait variation, whereas ITV plays an important role in determining species co-existence and community assembly. However, similar studies of faunal taxa, especially invertebrates, are very few in number.We investigated variation of hawkmoth (Lepidoptera: Sphingidae) traits along an environmental gradient spanning 2600 m in the eastern Himalayas and its role in community assembly, using the morpho-functional traits of body mass (BM), wing loading (WL) and wing aspect ratio (AR).We employ the recently proposed T-statistics to test for non-random assembly of hawkmoth communities and the relative importance of the two opposing forces for trait divergence (internal filters) and convergence (external filters).Community-wide trait-overlap decreased for all three traits with increasing environmental distance, suggesting the presence of elevation specific optimum morphology (i.e. functional response traits). Community weighted mean of BM and AR increased with elevation. Overall, the variation was dominated by species turnover but ITV accounted for 25%, 23% and <1% variability of BM, WL and AR, respectively. T-statistics, which incorporates ITV, revealed that elevational communities had a non-random trait distribution, and that community assembly was dominated by internal filtering throughout the gradient.This study was carried out using easily measurable morpho-traits obtained from calibrated field images of a large number (3301) of individuals. That these also happened to be important environmental response traits resulted in a significant signal in the metrics that we investigated. Such studies of abundant and hyperdiverse invertebrate groups across large environmental gradients should considerably improve our understanding of community assembly processes.

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