| 1. |
- Cirtwill, Alyssa, et al.
(författare)
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A quantitative framework for investigating the reliability of empirical network construction
- 2019
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Ingår i: Methods in Ecology and Evolution. - : WILEY. - 2041-210X. ; 10:6, s. 902-911
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Tidskriftsartikel (refereegranskat)abstract
- Descriptions of ecological networks typically assume that the same interspecific interactions occur each time a community is observed. This contrasts with the known stochasticity of ecological communities: community composition, species abundances and link structure all vary in space and time. Moreover, finite sampling generates variation in the set of interactions actually observed. For interactions that have not been observed, most datasets will not contain enough information for the ecologist to be confident that unobserved interactions truly did not occur. Here, we develop the conceptual and analytical tools needed to capture uncertainty in the estimation of pairwise interactions. To define the problem, we identify the different contributions to the uncertainty of an interaction. We then outline a framework to quantify the uncertainty around each interaction by combining data on observed co-occurrences with prior knowledge. We illustrate this framework using perhaps the most extensively sampled network to date. We found significant uncertainty in estimates for the probability of most pairwise interactions. This uncertainty can, however, be constrained with informative priors. This uncertainty scaled up to summary measures of network structure such as connectance and nestedness. Even with informative priors, we are likely to miss many interactions that may occur rarely or under different local conditions. Overall, we demonstrate the importance of acknowledging the uncertainty inherent in network studies, and the utility of treating interactions as probabilities in pinpointing areas where more study is needed. Most importantly, we stress that networks are best thought of as systems constructed from random variables, the stochastic nature of which must be acknowledged for an accurate representation. Doing so will fundamentally change network analyses and yield greater realism.
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| 2. |
- Cirtwill, Alyssa R., et al.
(författare)
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Species motif participation provides unique information about species risk of extinction
- 2024
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Ingår i: Journal of Animal Ecology. - : WILEY. - 0021-8790 .- 1365-2656.
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Tidskriftsartikel (refereegranskat)abstract
- Loss of species in food webs can set in motion a cascade of additional (secondary) extinctions. A species' position in a food web (e.g. its trophic level or number of interactions) is known to affect its ability to persist following disturbance. These simple measures, however, offer only a coarse description of how species fit into their community. One would therefore expect that more detailed structural measures such as participation in three-species motifs (meso-scale structures which provide information on a species' direct and indirect interactions) will also be related to probability of persistence. Disturbances affecting the basal resources have particularly strong effects on the rest of the food web. However, how disturbances branch out and affect consumer persistence depends on the structural pattern of species interactions in several steps. The magnitude, for example, the proportion of basal resources lost, will likely also affect the outcome. Here, we analyse whether a consumer's risk of secondary extinction after the removal of basal resources depends on the consumer's motif participation and how this relationship varies with the severity of disturbance. We show that consumer species which participate more frequently in the direct competition motif and less frequently in the omnivory motif generally have higher probability of persistence following disturbance to basal resources. However, both the strength of the disturbance and the overall network structure (i.e. connectance) affect the strength and direction of relationships between motif participation and persistence. Motif participation therefore captures important trends in species persistence and provides a rich description of species' structural roles in their communities, but must be considered in the context of network structure as a whole and of the specific disturbance applied. Like degree and trophic level, a species' participation in meso-scale motifs can affect its persistence after disturbance. We show that these relationships also depend strongly on the strength of disturbance.image
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| 3. |
- Laubmeier, A. N., et al.
(författare)
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From theory to experimental design : Quantifying a trait-based theory of predator-prey dynamics
- 2018
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 13:4
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Tidskriftsartikel (refereegranskat)abstract
- Successfully applying theoretical models to natural communities and predicting ecosystem behavior under changing conditions is the backbone of predictive ecology. However, the experiments required to test these models are dictated by practical constraints, and models are often opportunistically validated against data for which they were never intended. Alternatively, we can inform and improve experimental design by an in-depth pre-experimental analysis of the model, generating experiments better targeted at testing the validity of a theory. Here, we describe this process for a specific experiment. Starting from food web ecological theory, we formulate a model and design an experiment to optimally test the validity of the theory, supplementing traditional design considerations with model analysis. The experiment itself will be run and described in a separate paper. The theory we test is that trophic population dynamics are dictated by species traits, and we study this in a community of terrestrial arthropods. We depart from the Allometric Trophic Network (ATN) model and hypothesize that including habitat use, in addition to body mass, is necessary to better model trophic interactions. We therefore formulate new terms which account for micro-habitat use as well as intra-and interspecific interference in the ATN model. We design an experiment and an effective sampling regime to test this model and the underlying assumptions about the traits dominating trophic interactions. We arrive at a detailed sampling protocol to maximize information content in the empirical data obtained from the experiment and, relying on theoretical analysis of the proposed model, explore potential shortcomings of our design. Consequently, since this is a "pre-experimental" exercise aimed at improving the links between hypothesis formulation, model construction, experimental design and data collection, we hasten to publish our findings before analyzing data from the actual experiment, thus setting the stage for strong inference.
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| 4. |
- Wootton, Kate, et al.
(författare)
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Beyond body size-new traits for new heights in trait-based modelling of predator-prey dynamics
- 2022
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 17:7 July
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Tidskriftsartikel (refereegranskat)abstract
- Food webs map feeding interactions among species, providing a valuable tool for understanding and predicting community dynamics. Using species' body sizes is a promising avenue for parameterizing food-web models, but such approaches have not yet been able to fully recover observed community dynamics. Such discrepancies suggest that traits other than body size also play important roles. For example, differences in species' use of microhabitat or non-consumptive effects of intraguild predators may affect dynamics in ways not captured by body size. In Laubmeier et al. (2018), we developed a dynamic food-web model incorporating microhabitat and non-consumptive predator effects in addition to body size, and used simulations to suggest an optimal sampling design of a mesocosm experiment to test the model. Here, we perform the mesocosm experiment to generate empirical timeseries of insect herbivore and predator abundance dynamics. We minimize least squares error between the model and time-series to determine parameter values of four alternative models, which differ in terms of including vs excluding microhabitat use and non-consumptive predator-predator effects. We use both statistical and expert-knowledge criteria to compare the models and find including both microhabitat use and non-consumptive predatorpredator effects best explains observed aphid and predator population dynamics, followed by the model including microhabitat alone. This ranking suggests that microhabitat plays a larger role in driving population dynamics than non-consumptive predator-predator effects, although both are clearly important. Our results illustrate the importance of additional traits alongside body size in driving trophic interactions. They also point to the need to consider trophic interactions and population dynamics in a wider community context, where non-trophic impacts can dramatically modify the interplay between multiple predators and prey. Overall, we demonstrate the potential for utilizing traits beyond body size to improve traitbased models and the value of iterative cycling between theory, data and experiment to hone current insights into how traits affect food-web dynamics. © 2022 Wootton et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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| 5. |
- Wootton, Kate
(författare)
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Disentangling ecological and taphonomic signals in ancient food webs
- 2021
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Ingår i: Paleobiology. - : Cambridge University Press (CUP). - 0094-8373 .- 1938-5331. ; 47, s. 385-401
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of ancient food webs reveal important paleoecological processes and responses to a range of perturbations throughout Earth's history, such as climate change. These responses can inform our forecasts of future biotic responses to similar perturbations. However, previous analyses of ancient food webs rarely accounted for key differences between modern and ancient community data, particularly selective loss of soft-bodied taxa during fossilization. To consider how fossilization impacts inferences of ancient community structure, we (1) analyzed node-level attributes to identify correlations between ecological roles and fossilization potential and (2) applied selective information loss procedures to food web data for extant systems. We found that selective loss of soft-bodied organisms has predictable effects on the trophic structure of "artificially fossilized" food webs because these organisms occupy unique, consistent food web positions. Fossilized food webs misleadingly appear less stable (i.e., more prone to trophic cascades), with less predation and an overrepresentation of generalist consumers. We also found that ecological differences between soft- and hard-bodied taxa-indicated by distinct positions in modern food webs-are recorded in an early Eocene web, but not in Cambrian webs. This suggests that ecological differences between the groups have existed for >= 48 Myr. Our results indicate that accounting for soft-bodied taxa is vital for accurate depictions of ancient food webs. However, the consistency of information loss trends across the analyzed food webs means it is possible to predict how the selective loss of soft-bodied taxa affects food web metrics, which can permit better modeling of ancient communities.
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| 6. |
- Wootton, Kate
(författare)
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How species traits influence trophic interaction strength
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An organism's traits affect how it interacts with the world and with other species. In a predator-prey interaction both the predator's and prey's traits affect the likelihood that a given predation attempt will be successful. Together multiple predation events determine the strength of the trophic interaction between these two species. A number of traits can be important in determining interaction strength. For trophic interactions, one of the best-studied traits is body size - which has proven so important that a significant portion of interactions within a food web can be predicted from this one trait alone. Beyond body size, other traits, such as prey defenses, mobility, feeding preference, and diet breadth also shape interactions between species. Abiotic conditions shape and alter the relationship between species traits and interaction strength. This impact can be direct, where abiotic conditions change traits or their effectiveness, or indirect, where a species' ability to thrive in that environment - and thus interact with predators or prey - depends on its traits. Species respond to changes in abiotic conditions in different ways, potentially changing interaction strength. For example, temperature affects species at different rates depending on their body size, affecting interaction strength through changes in consumption rate, growth rate etc. Disturbances and changes in climate also affect species unequally, leading to mismatches in relative abundance, phenology or ranges. Such mismatches may lead to novel interactions, or the strengthening or weakening of interactions by altering overlap and encounter rates. Together these trait-mediated interactions shape ecological communities. With a wealth of species interacting at the same time, the sum total of direct and indirect interactions determine community dynamics. Many traits and interactions have been studied, but there are still gaps in our understanding of how these interactions combine. A closer investigation of the mechanisms underpinning the relationship between traits and interaction strength will allow for more efficient quantification of food webs and predictions of how communities will respond to disturbances.
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| 7. |
- Wootton, Kate L., et al.
(författare)
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Food webs coupled in space : Consumer foraging movement affects both stocks and fluxes
- 2023
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Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 104:8
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Tidskriftsartikel (refereegranskat)abstract
- The exchange of material and individuals between neighboring food webs is ubiquitous and affects ecosystem functioning. Here, we explore animal foraging movement between adjacent, heterogeneous habitats and its effect on a suite of interconnected ecosystem functions. Combining dynamic food web models with nutrient-recycling models, we study foraging across habitats that differ in fertility and plant diversity. We found that net foraging movement flowed from high to low fertility or high to low diversity and boosted stocks and flows across the whole loop of ecosystem functions, including biomass, detritus, and nutrients, in the recipient habitat. Contrary to common assumptions, however, the largest flows were often between the highest and intermediate fertility habitats rather than highest and lowest. The effect of consumer influx on ecosystem functions was similar to the effect of increasing fertility. Unlike fertility, however, consumer influx caused a shift toward highly predator-dominated biomass distributions, especially in habitats that were unable to support predators in the absence of consumer foraging. This shift resulted from both direct and indirect effects propagated through the interconnected ecosystem functions. Only by considering both stocks and fluxes across the whole loop of ecosystem functions do we uncover the mechanisms driving our results. In conclusion, the outcome of animal foraging movements will differ from that of dispersal and diffusion. Together we show how considering active types of animal movement and the interconnectedness of ecosystem functions can aid our understanding of the patchy landscapes of the Anthropocene.
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| 8. |
- Wootton, Kate, et al.
(författare)
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Layer-specific imprints of traits within a plant-herbivore-predator network - complementary insights from complementary methods
- 2024
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Ingår i: Ecography. - 0906-7590 .- 1600-0587. ; 2024
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Tidskriftsartikel (refereegranskat)abstract
- Who interacts with whom is a key question in community and network ecology. The concept that these interactions may be driven by a match between the traits of consumer and resource species is known as trait-matching. If trait-matching would allow for general predictions of interaction structure based on sufficiently few and easily-measurable traits, then this approach could replace the laborious description of each individual pairwise interaction. To resolve imprints of trait-matching in a species-rich tri-trophic Salix-galler-parasitoid network, and to identify the most relevant traits, we applied five different methods, each approaching the same phenomenon from a different perspective. As traits, we used, body sizes, gall type (position on plant, structure of gall) and phenology, among others, as well as phylogenetic proxies. When jointly applied, the methods demonstrate distinctly different imprints of traits within the two bipartite network elements (Salix-galler versus galler-parasitoid interactions). Of the galler-parasitoid sub-network's interactions, approximately half were explainable by the species traits used; of the Salix-galler sub-network's interactions, traits explained at most two-fifths. Gall type appeared to be the most important structuring trait in both networks. Phylogeny explained as much, or more than did our tested traits, suggesting that traits may be conserved and phylogeny therefore an effective proxy. Overall, the more specialized structure of the Salix-galler network versus the more nested structure of the galler-parasitoid network meant that different methods were more effective at capturing interactions and interaction structure in the different sub-networks. Thus, our analysis reveals how structuring impacts may vary even between levels within the same multitrophic network, and calls for comparative analyses of trait matching across a wide set of systems and methods.
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| 9. |
- Wootton, Kate
(författare)
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Love (eating) thy neighbour? Understanding and predicting food-web structure and dynamics
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Food webs are networks of feeding interactions that provide the backbone of ecological communities. The structure - who eats whom - and dynamics - how population abundances fluctuate as a result - of food webs depend on the traits of the species present. The exchange of individuals or material between food webs can have further consequences for the structure and dynamics of both the donor and recipient communities. Increasing our insight into how species traits constrain both structure and dynamics of food webs, and how this is affected by exchanges with other communities, will advance both the theory and predictive capacity of food-web ecology. In this thesis, I make a multifaceted foray into the factors behind food-web structure and dynamics. To provide a general framework for selecting and applying traits to food-web interactions, I show how a trophic interaction can be broken into steps and, combined with traits, used to parameterize dynamic food-web models. The resulting framework is sufficiently general and flexible to be applied to any community and to guide comparison across diverse interaction types and ecosystems. Using this framework, I developed a dynamic model parameterized by body size and microhabitat use and applied it in a mesocosm experiment. I found that different versions of the model fit the data equally well, but generated vastly different predictions for interactions with a hypothetical new species. With data from a tritrophic Salix-galler-parasitoid network, I used a suite of statistical approaches to reveal different facets of the relationship between traits and network structure, finding that traits explained more of the galler-parasitoid than Salix-galler network, and that the relationship between traits and network structure was non-linear. Finally, I returned to dynamic models to address the question of how coupled food webs affect each other. I simulated food-web and soilnutrient dynamics in adjacent habitats differing in fertility and plant diversity. The foraging movement of consumers between habitats affected all elements of ecosystem function. This was especially evident in low fertility habitats coupled to high fertility habitats, with considerable applied and theoretical implications. In total, I show that a trait-based approach to food webs has great promise for understanding food-web structure and dynamics and our ability to make accurate predictions, but that there are still a number of challenges to address. I lay out a framework and ground-work experiments for addressing some of these challenges, and show how the iteration between theory, empirical experiments, and analysis is ultimately required to reach the promise that trait-based approaches hold.
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| 10. |
- Wootton, Kate
(författare)
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Stable motifs delay species loss in simulated food webs
- 2022
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 2022
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Tidskriftsartikel (refereegranskat)abstract
- Some three-species motifs (unique patterns of interactions between three species) are both more stable when modelled in isolation and over-represented in empirical food webs. This suggests that these motifs may reduce extinction risk for species participating in them, ultimately stabilising the food web as a whole. We test whether a species' time to extinction following a perturbation is related to its participation in stable and unstable motifs and assess how motif roles co-vary with a species' degree or trophic level. We found that species' motif roles are related to their times to extinction following a disturbance. Specifically, having a larger proportion of the motif role made up by the omnivory motif was associated with longer times to extinction, even though the omnivory motif is less stable than the others when modelled in isolation. While motif roles were associated with extinction risk, they also varied strongly with degree and trophic level. This means that these simpler measures of a species' role may be sufficient to roughly predict which species are most vulnerable to disturbance (though motif roles can be used to refine these predictions), but that studies of species' motif participation can also reasonably comment on vulnerability to extinction.
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