| 1. |
- Albouy, Camille, et al.
(författare)
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The marine fish food web is globally connected
- 2019
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Ingår i: Nature Ecology & Evolution. - : NATURE PUBLISHING GROUP. - 2397-334X. ; 3:8, s. 1153-
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Tidskriftsartikel (refereegranskat)abstract
- The productivity of marine ecosystems and the services they provide to humans are largely dependent on complex interactions between prey and predators. These are embedded in a diverse network of trophic interactions, resulting in a cascade of events following perturbations such as species extinction. The sheer scale of oceans, however, precludes the characterization of marine feeding networks through de novo sampling. This effort ought instead to rely on a combination of extensive data and inference. Here we investigate how the distribution of trophic interactions at the global scale shapes the marine fish food web structure. We hypothesize that the heterogeneous distribution of species ranges in biogeographic regions should concentrate interactions in the warmest areas and within species groups. We find that the inferred global metaweb of marine fish-that is, all possible potential feeding links between co-occurring species-is highly connected geographically with a low degree of spatial modularity. Metrics of network structure correlate with sea surface temperature and tend to peak towards the tropics. In contrast to open-water communities, coastal food webs have greater interaction redundancy, which may confer robustness to species extinction. Our results suggest that marine ecosystems are connected yet display some resistance to perturbations because of high robustness at most locations.
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| 2. |
- Baiser, Benjamin, et al.
(författare)
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Ecogeographical rules and the macroecology of food webs
- 2019
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Ingår i: Global Ecology and Biogeography. - : Wiley-Blackwell Publishing Inc.. - 1466-822X .- 1466-8238. ; 28:9, s. 1204-1218
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Tidskriftsartikel (refereegranskat)abstract
- AimHow do factors such as space, time, climate and other ecological drivers influence food web structure and dynamics? Collections of well‐studied food webs and replicate food webs from the same system that span biogeographical and ecological gradients now enable detailed, quantitative investigation of such questions and help integrate food web ecology and macroecology. Here, we integrate macroecology and food web ecology by focusing on how ecogeographical rules [the latitudinal diversity gradient (LDG), Bergmann's rule, the island rule and Rapoport's rule] are associated with the architecture of food webs.LocationGlobal.Time periodCurrent.Major taxa studiedAll taxa.MethodsWe discuss the implications of each ecogeographical rule for food webs, present predictions for how food web structure will vary with each rule, assess empirical support where available, and discuss how food webs may influence ecogeographical rules. Finally, we recommend systems and approaches for further advancing this research agenda.ResultsWe derived testable predictions for some ecogeographical rules (e.g. LDG, Rapoport's rule), while for others (e.g., Bergmann's and island rules) it is less clear how we would expect food webs to change over macroecological scales. Based on the LDG, we found weak support for both positive and negative relationships between food chain length and latitude and for increased generality and linkage density at higher latitudes. Based on Rapoport's rule, we found support for the prediction that species turnover in food webs is inversely related to latitude.Main conclusionsThe macroecology of food webs goes beyond traditional approaches to biodiversity at macroecological scales by focusing on trophic interactions among species. The collection of food web data for different types of ecosystems across biogeographical gradients is key to advance this research agenda. Further, considering food web interactions as a selection pressure that drives or disrupts ecogeographical rules has the potential to address both mechanisms of and deviations from these macroecological relationships. For these reasons, further integration of macroecology and food webs will help ecologists better understand the assembly, maintenance and change of ecosystems across space and time.
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| 3. |
- 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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| 4. |
- Cirtwill, Alyssa, et al.
(författare)
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A review of species role concepts in food webs
- 2018
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Ingår i: Food Webs. - : Elsevier BV. - 2352-2496. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Many different concepts have been used to describe species' roles in food webs (i.e., the ways in which species participate in their communities as consumers and resources). As each concept focuses on a different aspect of food-web structure, it can be difficult to relate these concepts to each other and to other aspects of ecology. Here we use the Eltonian niche as an overarching framework, within which we summarize several commonly-used role concepts (degree, trophic level, motif roles, and centrality). We focus mainly on the topological versions of these concepts but, where dynamical versions of a role concept exist, we acknowledge these as well. Our aim is to highlight areas of overlap and ambiguity between different role concepts and to describe how these roles can be used to group species according to different strategies (i.e., equivalence and functional roles). The existence of “gray areas” between role concepts make it essential for authors to carefully consider both which role concept(s) are most appropriate for the analyses they wish to conduct and what aspect of species' niches (if any) they wish to address. The ecological meaning of differences between species' roles can change dramatically depending on which role concept(s) are used.
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| 5. |
- Cirtwill, Alyssa, et al.
(författare)
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Between-year changes in community composition shape species' roles in an Arctic plant-pollinator network
- 2018
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Ingår i: Oikos. - : WILEY. - 0030-1299 .- 1600-0706. ; 127:8, s. 1163-1176
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Tidskriftsartikel (refereegranskat)abstract
- Inter-annual turnover in community composition can affect the richness and functioning of ecological communities. If incoming and outgoing species do not interact with the same partners, ecological functions such as pollination may be disrupted. Here, we explore the extent to which turnover affects species' roles - as defined based on their participation in different motifs positions - in a series of temporally replicated plant-pollinator networks from high-Arctic Zackenberg, Greenland. We observed substantial turnover in the plant and pollinator assemblages, combined with significant variation in species' roles between networks. Variation in the roles of plants and pollinators tended to increase with the amount of community turnover, although a negative interaction between turnover in the plant and pollinator assemblages complicated this trend for the roles of pollinators. This suggests that increasing turnover in the future will result in changes to the roles of plants and likely those of pollinators. These changing roles may in turn affect the functioning or stability of this pollination network.
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| 6. |
- Cirtwill, Alyssa, et al.
(författare)
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Feeding environment and other traits shape species roles in marine food webs
- 2018
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Ingår i: Ecology Letters. - : WILEY. - 1461-023X .- 1461-0248. ; 21:6, s. 875-884
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Tidskriftsartikel (refereegranskat)abstract
- Food webs and meso-scale motifs allow us to understand the structure of ecological communities and define species roles within them. This species-level perspective on networks permits tests for relationships between species traits and their patterns of direct and indirect interactions. Such relationships could allow us to predict food-web structure based on more easily obtained trait information. Here, we calculated the roles of species (as vectors of motif position frequencies) in six well-resolved marine food webs and identified the motif positions associated with the greatest variation in species roles. We then tested whether the frequencies of these positions varied with species traits. Despite the coarse-grained traits we used, our approach identified several strong associations between traits and motifs. Feeding environment was a key trait in our models and may shape species roles by affecting encounter probabilities. Incorporating environment into future food-web models may improve predictions of an unknown network structure.
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| 7. |
- Cirtwill, Alyssa, et al.
(författare)
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Host taxonomy constrains the properties of trophic transmission routes for parasites in lake food webs
- 2017
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Ingår i: Ecology. - : WILEY. - 0012-9658 .- 1939-9170. ; 98:9, s. 2401-2412
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Tidskriftsartikel (refereegranskat)abstract
- Some parasites move from one host to another via trophic transmission, the consumption of the parasite (inside its current host) by its future host. Feeding links among free-living species can thus be understood as potential transmission routes for parasites. As these links have different dynamic and structural properties, they may also vary in their effectiveness as trophic transmission routes. That is, some links may be better than others in allowing parasites to complete their complex life cycles. However, not all links are accessible to parasites as most are restricted to a small number of host taxa. This restriction means that differences between links involving host and non-host taxa must be considered when assessing whether transmission routes for parasites have different food web properties than other links. Here we use four New Zealand lake food webs to test whether link properties (contribution of a link to the predators diet, prey abundance, prey biomass, amount of biomass transferred, centrality, and asymmetry) affect trophic transmission of parasites. Critically, we do this using both models that neglect the taxonomy of free-living species and models that explicitly include information about which free-living species are members of suitable host taxa. Although the best-fit model excluding taxonomic information suggested that transmission routes have different properties than other feeding links, when including taxonomy, the best-fit model included only an intercept. This means that the taxonomy of free-living species is a key determinant of parasite transmission routes and that food-web properties of transmission routes are constrained by the properties of host taxa. In particular, many intermediate hosts (prey) attain high biomasses and are involved in highly central links while links connecting intermediate to definitive (predator) hosts tend to be dynamically weak.
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| 8. |
- Cirtwill, Alyssa R., et al.
(författare)
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Building food networks from molecular data : Bayesian or fixed-number thresholds for including links
- 2021
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Ingår i: Basic and Applied Ecology. - : Elsevier BV. - 1439-1791 .- 1618-0089. ; 50, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- DNA metabarcoding of faeces or gut contents has greatly increased our ability to construct networks of predators and prey (food webs) by reducing the need to observe predation events directly. The possibility of both false positives and false negatives in DNA sequences, however, means that constructing food networks using DNA requires researchers to make many choices as to which DNA sequences indicate true prey for a particular predator. To date, DNA-based food networks are usually constructed by including any DNA sequence with more than a threshold number of reads. The logic used to select this threshold is often not explained, leading to somewhat arbitrary-seeming networks. As an alternative strategy, we demonstrate how to construct food networks using a simple Bayesian model to suggest which sequences correspond to true prey. The networks obtained using a well-chosen fixed cutoff and our Bayesian approach are very similar, especially when links are resolved to prey families rather than species. We therefore recommend that researchers reconstruct diet data using a Bayesian approach with well-specified assumptions rather than continuing with arbitrary fixed cutoffs. Explicitly stating assumptions within a Bayesian framework will lead to better-informed comparisons between networks constructed by different groups and facilitate drawing together individual case studies into more coherent ecological theory. Note that our approach can easily be extended to other types of ecological networks constructed by DNA metabarcoding of pollen loads, identification of parasite DNA in faeces, etc.
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| 9. |
- Cirtwill, Alyssa R., et al.
(författare)
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Flower-visitor and pollen-load data provide complementary insight into species and individual network roles
- 2024
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Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- Most animal pollination results from plant–insect interactions, but how we perceive these interactions may differ with the sampling method adopted. The two most common methods are observations of visits by pollinators to plants and observations of pollen loads carried by insects. Each method could favour the detection of different species and interactions, and pollen load observations typically reveal more interactions per individual insect than visit observations. Moreover, while observations concern plant and insect individuals, networks are frequently analysed at the level of species. Although networks constructed using visitation and pollen-load data have occasionally been compared in relatively specialised, bee-dominated systems, it is not known how sampling methodology will affect our perception of how species (and individuals within species) interact in a more generalist system. Here we use a Diptera-dominated high-Arctic plant–insect community to explore how sampling approach shapes several measures of species' interactions (focusing on specialisation), and what we can learn about how the interactions of individuals relate to those of species. We found that species degrees, interaction strengths, and species motif roles were significantly correlated across the two method-specific versions of the network. However, absolute differences in degrees and motif roles were greater than could be explained by the greater number of interactions per individual provided by the pollen-load data. Thus, despite the correlations between species roles in networks built using visitation and pollen-load data, we infer that these two perspectives yield fundamentally different summaries of the ways species fit into their communities. Further, individuals' roles generally predicted the species' overall role, but high variability among individuals means that species' roles cannot be used to predict those of particular individuals. These findings emphasize the importance of adopting a dual perspective on bipartite networks, as based on the different information inherent in insect visits and pollen loads.
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| 10. |
- Cirtwill, Alyssa R., et al.
(författare)
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Related plants tend to share pollinators and herbivores, but strength of phylogenetic signal varies among plant families
- 2020
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Ingår i: New Phytologist. - : WILEY. - 0028-646X .- 1469-8137. ; 226:3, s. 909-920
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Tidskriftsartikel (refereegranskat)abstract
- Related plants are often hypothesized to interact with similar sets of pollinators and herbivores, but this idea has only mixed empirical support. This may be because plant families vary in their tendency to share interaction partners. We quantify overlap of interaction partners for all pairs of plants in 59 pollination and 11 herbivory networks based on the numbers of shared and unshared interaction partners (thereby capturing both proportional and absolute overlap). We test for relationships between phylogenetic distance and partner overlap within each network; whether these relationships varied with the composition of the plant community; and whether well-represented plant families showed different relationships. Across all networks, more closely related plants tended to have greater overlap. The strength of this relationship within a network was unrelated to the composition of the networks plant component, but, when considered separately, different plant families showed different relationships between phylogenetic distance and overlap of interaction partners. The variety of relationships between phylogenetic distance and partner overlap in different plant families probably reflects a comparable variety of ecological and evolutionary processes. Considering factors affecting particular species-rich groups within a community could be the key to understanding the distribution of interactions at the network level.
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| 11. |
- 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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| 12. |
- Hambäck, Peter A., et al.
(författare)
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More intraguild prey than pest species in arachnid diets may compromise biological control in apple orchards
- 2021
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Ingår i: Basic and Applied Ecology. - : Elsevier BV. - 1439-1791 .- 1618-0089. ; 57, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the full diet of natural enemies is necessary for evaluating their role as biocontrol agents, because many enemy species do not only feed on pests but also on other natural enemies. Such intraguild predation can compromise pest control if the consumed enemies are actually better for pest control than their predators. In this study, we used gut metabarcoding to quantify diets of all common arachnid species in Swedish and Spanish apple orchards. For this purpose, we designed new primers that reduce amplification of arachnid predators while retaining high amplification of all prey groups. Results suggest that most arachnids consume a large range of putative pest species on apple but also a high proportion of other natural enemies, where the latter constitute almost a third of all prey sequences. Intraguild predation also varied between regions, with a larger content of heteropteran bugs in arachnid guts from Spanish orchards, but not between orchard types. There was also a tendency for cursorial spiders to have more intraguild prey in the gut than web spiders. Two groups that may be overlooked as important biocontrol agents in apple orchards seem to be theridiid web spiders and opilionids, where the latter had several small-bodied pest species in the gut. These results thus provide important guidance for what arachnid groups should be targets of management actions, even though additional information is needed to quantify all direct and indirect interactions occurring in the complex arthropod food webs in fruit orchards.
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| 13. |
- Hambäck, Peter A., et al.
(författare)
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Species composition of shoreline wolf spider communities vary with salinity, but their diets vary with wrack inflow
- 2022
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- Wolf spiders are typically the most common group of arthropod predators on both lake and marine shorelines because of the high prey availability in these habitats. However, shores are also harsh environments due to flooding and, in proximity to marine waters, to toxic salinity levels. Here, we describe the spider community, prey availabilities, and spider diets between shoreline sites with different salinities, albeit with comparatively small differences (5‰ vs. 7‰). Despite the small environmental differences, spider communities between lower and higher saline sites showed an almost complete species turnover. At the same time, differences in prey availability or spider gut contents did not match changes in spider species composition but rather changed with habitat characteristics within a region, where spiders collected at sites with thick wrack beds had a different diet than sites with little wrack. These data suggest that shifts in spider communities are due to habitat characteristics other than prey availabilities, and the most likely candidate restricting species in high salinity would be saline sensitivity. At the same time, species absence from low-saline habitats remains unresolved.
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| 14. |
- Kortsch, Susanne, et al.
(författare)
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Landscape composition and pollinator traits interact to influence pollination success in an individual-based model
- 2023
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Ingår i: Functional Ecology. - 0269-8463. ; 37:7, s. 2056-2071
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Tidskriftsartikel (refereegranskat)abstract
- The arrangement of plant species within a landscape influences pollination via changes in pollinator movement trajectories and plant–pollinator encounter rates. Yet the combined effects of landscape composition and pollinator traits (especially specialisation) on pollination success remain hard to quantify empirically. We used an individual-based model to explore how landscape and pollinator specialisation (degree) interact to influence pollination. We modelled variation in the landscape by generating gradients of plant species intermixing—from no mixing to complete intermixing. Furthermore, we varied the level of pollinator specialisation by simulating plant–pollinator (six to eight species) networks of different connectance. We then compared the impacts of these drivers on three proxies for pollination: visitation rate, number of consecutive visits to the focal plant species and expected number of plants pollinated. We found that the spatial arrangements of plants and pollinator degree interact to determine pollination success, and that the influence of these drivers on pollination depends on how pollination is estimated. For most pollinators, visitation rate increases in more plant mixed landscapes. Compared to the two more functional measures of pollination, visitation rate overestimates pollination service. This is particularly severe in landscapes with high plant intermixing and for generalist pollinators. Interestingly, visitation rate is less influenced by pollinator traits (pollinator degree and body size) than are the two functional metrics, likely because ‘visitation rate’ ignores the order in which pollinators visit plants. However, the visitation sequence order is crucial for the expected number of plants pollinated, since only prior visits to conspecific individuals can contribute to pollination. We show here that this order strongly depends on the spatial arrangements of plants, on pollinator traits and on the interaction between them. Taken together, our findings suggest that visitation rate, the most commonly used proxy for pollination in network studies, should be complemented with more functional metrics which reflect the frequency with which individual pollinators revisit the same plant species. Our findings also suggest that measures of landscape structure such as plant intermixing and density—in combination with pollinators' level of specialism—can improve estimates of the probability of pollination. Read the free Plain Language Summary for this article on the Journal blog.
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| 15. |
- Liénart, Camilla, et al.
(författare)
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A sprinkling of gold dust : Pine pollen as a carbon source in Baltic Sea coastal food webs
- 2022
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 67:1, s. 53-65
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Tidskriftsartikel (refereegranskat)abstract
- Allochthonous subsidies to marine ecosystems have mainly focused on biogeochemical cycles, but there has also been recent interest in how terrestrial carbon (C) influences marine food webs. In the Baltic Sea, pine (Pinus sylvestris) pollen is found in large amounts in shallow bays in early summer. Pollen is a significant C-source in freshwater ecosystems and may also be important in coastal food webs. We examined the consumption of pollen and autochthonous resources by benthic invertebrates in shallow bays of the Baltic Sea. We used stable isotopes to estimate diets and reconstructed consumer-resource networks (food webs) for grazers and particulate organic matter (POM)-feeders to compare how these different guilds used pollen. We found that P. sylvestris pollen was consumed in small amounts by a variety of animals and in some cases made up a sizeable proportion of invertebrates' diets. However, invertebrates generally depended less on pollen than other resources. The degree of pollen consumption was related to feeding traits, with generalist invertebrate grazers consuming more pollen (> 10% of diet) than the more specialist POM-feeders (< 5% of diet contributed by pollen). POM-feeders may consume additional microbially-degraded pollen which was not identifiable in our model. We suggest that pollen is a small but substantial allochthonous C-source in shallow bay food webs of the Baltic Sea, with the potential to affect the dynamics of these ecosystems.
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| 16. |
- Simmons, Benno I., et al.
(författare)
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Motifs in bipartite ecological networks: uncovering indirect interactions
- 2019
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Ingår i: Oikos. - : WILEY. - 0030-1299 .- 1600-0706. ; 128:2, s. 154-170
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Tidskriftsartikel (refereegranskat)abstract
- Indirect interactions play an essential role in governing population, community and coevolutionary dynamics across a diverse range of ecological communities. Such communities are widely represented as bipartite networks: graphs depicting interactions between two groups of species, such as plants and pollinators or hosts and parasites. For over thirty years, studies have used indices, such as connectance and species degree, to characterise the structure of these networks and the roles of their constituent species. However, compressing a complex network into a single metric necessarily discards large amounts of information about indirect interactions. Given the large literature demonstrating the importance and ubiquity of indirect effects, many studies of network structure are likely missing a substantial piece of the ecological puzzle. Here we use the emerging concept of bipartite motifs to outline a new framework for bipartite networks that incorporates indirect interactions. While this framework is a significant departure from the current way of thinking about bipartite ecological networks, we show that this shift is supported by analyses of simulated and empirical data. We use simulations to show how consideration of indirect interactions can highlight differences missed by the current index paradigm that may be ecologically important. We extend this finding to empirical plant-pollinator communities, showing how two bee species, with similar direct interactions, differ in how specialised their competitors are. These examples underscore the need to not rely solely on network- and species-level indices for characterising the structure of bipartite ecological networks.
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