Community-wide seed dispersal distances peak at low levels of specialisation in size-structured networks

Sorensen, Marjorie C.; Schleuning, Matthias; Donoso, Isabel; Neuschulz, Eike Lena; Mueller, Thomas

doi:10.1101/2020.02.23.958454

Cited by 4 publications

(30 citation statements)

References 72 publications

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“…These are broadly similar to studies that have previously undertaken allometric scaling of gut passage time on select groups of animals (e.g. Clauss et al., 2007; De Cuyper et al., 2020; Demment & Van Soest, 1985; Sorensen et al., 2020; Steuer et al., 2011; Warner, 1981; Yoshikawa et al., 2019). The raw data and derived scaling exponents from our database will help improve the output of ecological models that must rely on allometric scaling of gut passage time.…”

Section: Discussionsupporting

confidence: 83%

“…For birds, no statistical model was consistently best across markers. This may partly have arisen due to the stronger relationship between bird body mass and gut passage time (Robbins, 1993; Sorensen et al., 2020; Yoshikawa et al., 2019). However, there was also a large spread of RMSE results across statistical models for birds, suggesting that either the dataset is not large enough for the more complex models to become statistically different, or that important traits pertinent to TT and MRT in birds are missing from our analysis.…”

Section: Discussionmentioning

confidence: 99%

“…From this, we then calculated a mean TT and MRT across studies for each species from which to undertake our analysis. This procedure was undertaken to reduce individual study bias and has been practiced in other assessments of TT and MRT evaluation (Clauss et al., 2007; Sorensen et al., 2020; Steuer et al., 2011; Yoshikawa et al., 2019).…”

Section: Methodsmentioning

confidence: 99%

“…We then explored the allometric relationships between TT/MRT and body mass, both with and without consideration of the phylogenetic relatedness of the target species. These techniques have been undertaken before on select groups of animals (Clauss et al., 2007; De Cuyper et al., 2020; Robbins, 1993; Sorensen et al., 2020; Steuer et al., 2011; Yoshikawa et al., 2019). We performed simple generalised least squares (GLS) with log body mass as a single explanatory variable using the ‘ nlme ’ package (Pinheiro et al., 2014) and phylogenetic generalised least squares (PGLS) using the ‘ caper ’ package (Orme et al., 2013).…”

Section: Methodsmentioning

confidence: 99%

“…At present, dispersal models that assess biological dispersal of seeds, nutrients and microbes across a broad suite of taxa often use generalised mass‐based scaling parameters for gut passage time (e.g. Donoso et al., 2020; Doughty et al., 2020; Doughty, Roman, et al, 2016; Hempson et al., 2017; Pires et al, 2018; Sorensen et al., 2020; Viana et al., 2013; Wolf et al., 2013; Yoshikawa et al., 2019). The reasoning behind the choice of allometric scaling is based on theoretical grounds as gut capacity scales linearly to body mass (BM 1.00 ) and dry matter intake to the metabolic rate (BM 0.75 ; Demment & Van Soest, 1985).…”

Section: Introductionmentioning

confidence: 99%

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Improved estimation of gut passage time considerably affects trait‐based dispersal models

et al. 2021

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Animals are important vectors for transporting seeds, nutrients and microbes across landscapes. However, models that quantify the magnitude of these ecosystem services across a broad range of taxa often rely on generalised mass‐based scaling parameters for gut passage time. This relationship is weak and fundamentally breaks down when considering individual species, indicating that current models may incorrectly attribute or estimate the magnitude of dispersal. We collated a large dataset of gut passage time for endothermic animals measured using undigested markers (n = 391 species). For each species, we compiled trait data, including body mass, morphology, gut physiology, diet and phylogeny. We then compared the ability of five statistical models (constant, generalised least squares, phylogenetic generalised least squares, general linear model and random forest) to estimate the time of first marker appearance (transit time; TT) and mean marker retention time (MRT) for particle and solute markers in mammals and birds separately. For mammals, we found that the inclusion of additional traits appreciably reduced the median root‐mean squared error across all markers in a leave‐one‐out cross validation. For birds, however, additional traits did not significantly improve our ability to predict gut passage time across markers. This may have occurred due to the smaller number of bird species included in our analysis or the absence of important explanatory factors such as differences in gastrointestinal morphology. Using the MRTparticle random forest model from this study, we updated two trait‐based dispersal models for seed and nutrient movement by mammals. The magnitude of dispersal in our updated predictions ranged from 66% to 176% of the original model formulation for different scenarios, highlighting the importance of gut passage time for dispersal models. Furthermore, the contribution by individual or groups of species was found sizeably altered in our updated models. Future modelling studies of dispersal by mammals, for which empirical estimates of gut passage time are absent, will benefit from predicting gut passage time using statistical models that incorporate traits including animal morphology, diet and gut physiology. A free Plain Language Summary can be found within the Supporting Information of this article.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Improved estimation of gut passage time considerably affects trait‐based dispersal models

et al. 2021

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Downsizing of animal communities triggers stronger functional than structural decay in seed-dispersal networks

et al. 2020

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Downsizing of animal communities due to defaunation is prevalent in many ecosystems. Yet, we know little about its consequences for ecosystem functions such as seed dispersal. Here, we use eight seed-dispersal networks sampled across the Andes and simulate how downsizing of avian frugivores impacts structural network robustness and seed dispersal. We use a trait-based modeling framework to quantify the consequences of downsizing—relative to random extinctions—for the number of interactions and secondary plant extinctions (as measures of structural robustness) and for long-distance seed dispersal (as a measure of ecosystem function). We find that downsizing leads to stronger functional than structural losses. For instance, 10% size-structured loss of bird species results in almost 40% decline of long-distance seed dispersal, but in less than 10% of structural loss. Our simulations reveal that measures of the structural robustness of ecological networks underestimate the consequences of animal extinction and downsizing for ecosystem functioning.

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Specialists and generalists fulfil important and complementary functional roles in ecological processes

et al. 2021

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Species differ in their resource use and their interactions with other species and, consequently, they fulfil different functional roles in ecological processes. Species with specialized functional roles (specialists) are considered important for communities because they often interact with species with which few other species interact, thereby contributing complementary functional roles to ecological processes. However, the contribution of specialists could be low if they only interact with a small range of interaction partners. In contrast, species with unspecialized functional roles (generalists) often do not fulfil complementary roles but their contribution to ecological processes could be high because they interact with a large range of species. To investigate the importance of the functional roles of specialists versus generalists, we tested the relationship between species' degree of specialization and their contribution to functional‐role diversity for frugivorous birds in Andean seed‐dispersal networks. We used two measures for the specialization of birds—one based on the size, and one based on the position of their interaction niche—and measured their effect on the birds' contribution to functional‐role diversity and their functional complementarity, a measure of how much a species' functional role is complementary to those of the other species. In all networks, there were similar log‐normal distributions of species' contributions to functional‐role diversity and functional complementarity. Contribution to functional‐role diversity and functional complementarity increased with both increasing niche‐position specialization and increasing niche size, indicating that the composition of functional roles in the networks was determined by an interplay between specialization and generalization. There was a negative interaction between niche‐position specialization and niche size in both models, which showed that the positive effect of niche‐position specialization on functional‐role diversity and functional complementarity was stronger for species with a small niche size, and vice versa. Our results show that there is a continuum from specialized to generalized functional roles in species communities, and that both specialists and generalists fulfil important functional roles in ecological processes. Combining interaction networks with functional traits, as exemplified in this study, provides insight into the importance of an interplay of redundancy and complementarity in species' functional roles for ecosystem functioning. A free Plain‐Language Summary can be found within the Supporting Information of this article.

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Community-wide seed dispersal distances peak at low levels of specialisation in size-structured networks

Cited by 4 publications

References 72 publications

Improved estimation of gut passage time considerably affects trait‐based dispersal models

Improved estimation of gut passage time considerably affects trait‐based dispersal models

Downsizing of animal communities triggers stronger functional than structural decay in seed-dispersal networks

Specialists and generalists fulfil important and complementary functional roles in ecological processes

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