| 1. |
- 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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| 2. |
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| 3. |
- Åkesson, Anna, 1985-
(författare)
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Disturbances in food webs : Importance of species interactions from an ecological and evolutionary perspective
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biodiversity loss is occurring globally at an unprecedented pace. This is not only followed by ethical concerns; it also affects all levels of an ecosystem, with wide-spread implications for ecosystem functioning, services and human well-being. The severe extinction risk for many species is a result of human activities, such as habitat destruction and land-use change, overexploitation and introduction of invasive species. During the past decades, climate change has additionally become an important human-induced driver, causing biodiversity loss and altered species interactions.To mitigate the negative impact on ecosystems, we need to understand how the species building up the systems respond to disturbances. Several structural properties, both at species- and network-level, are known to affect species vulnerability. At the species-level, a species position in the food web, as well as its distribution of prey items, are important factors. At the network-level, diversity and structure of feeding interactions are important measurements related to stability. Additionally, species may both directly and indirectly affect other species, as species are entangled in complex network structures. The loss of a single species could set in motion a cascade of secondary extinctions that may not be predictable based on species’ performance in isolation. Particularly, disturbances of primary producers have a high risk to propagate and augment through the network. Moreover, species interactions have the potential to affect several other ecological processes. For example, altered environmental conditions force species to disperse to more suitable habitats, or to stay and adapt to the new local condition. Such processes can be significantly altered by species interactions. Another example concerns ecosystem service provisioning. Even if a species not being a service provider goes extinct, the event can via direct and indirect effects cause secondary extinctions of service providing species, causing loss of the services.Despite the recognition of the importance of a network context and of species interactions, such aspects are in many cases modeled in a simplified manner or not considered. In this thesis, I use mathematical models to study how species embedded in an ecological network respond to disturbances. I have two primary focus areas. First, I analyze how the interplay between evolution, dispersal and species interactions affect how species respond to climatic change. In paper I, I studied the effects of these eco-evolutionary processes under increasing temperatures, using empirically-motivated parameterizations of a suite of community models with increasing ecological interaction complexity. Second, I analyze how several structural properties affect species persistence following a disturbance. In Paper II, I focus on how network-level properties as well as species-level properties affect consumer species persistence following basal level disturbances. In Paper III, I disentangle the most influential characteristics of groups of basal species, causing a negative impact on consumer species when disturbed. I use the Serengeti savanna food web as case study. In Paper IV, I connect ecosystem services to the species providing them, and analyze how ecosystem service provisioning is affected by anthropogenic threats. I use the Baltic Sea as a case study.In summary, the results of this thesis underscore the importance of studying disturbances within a network context. Species interactions highly influenced the eco-evolutionary dynamics in Paper I, and mitigated some of the negative impacts following climatic change. Several structural network properties, both of the species being disturbed and of the species being affected, influenced species’ vulnerability following disturbance in Paper II-IV. The interplay between species influenced how disturbances percolated through the network. Moreover, Paper IV found that indirect effects mediated by the network of species interactions were of substantial importance for how anthropogenic threats are affecting ecosystem service delivery. in this thesis, I have developed novel methods, as well as extended and showcased new applications for existing ones. As such, this thesis has a broad applicability and expands our basic understanding of the interplay between ecological and evolutionary processes, as well as our understanding of the mechanisms behind how networks of interacting species are affected by disturbances. Further, the results have important implications for conservation efforts.
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| 4. |
- Åkesson, Anna, et al.
(författare)
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The importance of species interactions in eco-evolutionary community dynamics under climate change
- 2021
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Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Eco-evolutionary dynamics are essential in shaping the biological response of communities to ongoing climate change. Here we develop a spatially explicit eco-evolutionary framework which features more detailed species interactions, integrating evolution and dispersal. We include species interactions within and between trophic levels, and additionally, we incorporate the feature that species interspecific competition might change due to increasing temperatures and affect the impact of climate change on ecological communities. Our modeling framework captures previously reported ecological responses to climate change, and also reveals two key results. First, interactions between trophic levels as well as temperature-dependent competition within a trophic level mitigate the negative impact of climate change on biodiversity, emphasizing the importance of understanding biotic interactions in shaping climate change impact. Second, our trait-based perspective reveals a strong positive relationship between the within-community variation in preferred temperatures and the capacity to respond to climate change. Temperature-dependent competition consistently results both in higher trait variation and more responsive communities to altered climatic conditions. Our study demonstrates the importance of species interactions in an eco-evolutionary setting, further expanding our knowledge of the interplay between ecological and evolutionary processes. Understanding the dynamics of species interactions can help predict community responses to climate change. A spatially explicit model finds that species interactions and competition mitigate the harmful impacts of climate change, and that temperature-dependent competition makes communities more variable and responsive to changing climates.
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| 5. |
- Alger, Susanne, 1967-
(författare)
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Licence to drive : the importance of reliability for the validity of the Swedish driving licence test
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The Swedish driving licence test is a criterion-referenced test resulting in a pass or fail. It currently consists of two parts - a theory test with 65 multiple-choice items and a practical driving test where at least 25 minutes are spent driving in traffic. It is a high-stakes test in the sense that the results are used to determine whether the test-taker should be allowed to drive a car without supervision. As the only other requirements for obtaining a licence is a few hours of hazard education (and a short introduction if you intend to drive with a lay instructor) it is important that the test result, in terms of pass or fail, is reliable and valid. If this is not the case it could have detrimental effects on traffic safety. Examining all relevant aspects is beyond the scope of this licentiate thesis so I have focused on reliability.Methods Reliability for both the theoretical and practical test results was examined. As these are very different types of tests the types of reliability examined also differed. In order to examine inter-rater reliability of the driving test 83 examiners were accompanied by one of five selected supervising examiners for a day of tests. All in all 535 tests were conducted with two examiners assessing the same performance. At the end of the day the examiners compared notes and tried to determine the reason for any inconsistencies. Both examiners and students also filled in questionnaires with questions about background and preparation. As for studying decision consistency and decision accuracy of the theory test, three test versions (a total of around 12,000 tests) were examined with the help of methods devised by Subkoviak (Subkoviak, 1976, 1988) and Hanson & Brennan (Brennan, 2004; Hanson & Brennan, 1990).Results The results from two research studies concerning reliability were presented. Study I focused on inter-rater reliability in the driving test and in 93 per cent of cases the examiners made the same assessment. For the tests where their opinions differed there was no correlation to any of the background variables or other variables examined except for three, which had logical explanations and did not constitute a problem. Although there were cases where the differences were due to different stances on matters of interpretation the most common suggested cause was the placement in the car (back seat vs. front seat). Although the supervising examiners gave both praise and criticism as to how the test was carried out the study does not answer the question whether the tests were equal in terms of composition and difficulty.In Study II the focus was on decision consistency and decision accuracy in the theory test. Three versions of the theory tests were examined and, on the whole, found to be fairly similar in terms of item difficulty and score distribution, but the mean was so close to the cut-score (i.e. the score required to pass) that the pass rate differed somewhat between versions. Agreement coefficients were around .80 for all test versions (between .79 and .82 depending on method). Classification accuracy indicated an .87 probability of a correct classification.Conclusion It is important to examine the reliability and validity of the driving licence test since a misclassification can have serious consequences in terms of traffic safety. In the studies included here the rate of agreement between examiners is deemed as satisfactory. It would be preferable if the classification consistency and classification accuracy, as estimated by the methods used, were higher for the theory test, given its importance.While reliability in terms of agreement between raters/examiners or consistency and accuracy of classification are routinely examined in other contexts, such as large-scale educational testing, this is not often done for the driving licence tests. At the same time, the methods used here can be transferred to contexts where such properties are generally not examined. Collecting information about test-takers and examiners, like in Study I, can provide evidence concerning possible bias.Examining to what extent decisions are consistent is one important aspect of collecting evidence that shows that test results can be used to draw conclusions about driver competence. Still, regardless of outcome, validation is a process that never ends. There is always reason to examine various aspects and make further improvements. There are also many other relevant aspects to examine. A prerequisite for the validity of the score interpretation of a criterion-referenced test like this one is that the cut-score is appropriate and the content relevant. This should therefore be the subject of further research as the validation process continues.
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| 6. |
- Binzer, Amrei, et al.
(författare)
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The susceptibility of species to extinctions in model communities
- 2011
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Ingår i: Basic and Applied Ecology. - : Elsevier. - 1439-1791 .- 1618-0089. ; 12:7, s. 590-599
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Tidskriftsartikel (refereegranskat)abstract
- Despite the fact that the loss of a species from a community has the potential to cause a dramatic decline in biodiversity, for example through cascades of secondary extinctions, little is known about the factors contributing to the extinction risk of any particular species. Here we expand earlier modeling approaches using a dynamic food-web model that accounts for bottom-up as well as top-down effects. We investigate what factors influence a species’ extinction risk and time to extinction of the non-persistent species. We identified three basic properties that affect a species’ risk of extinction. The highest extinction risk is born by species with (1) low energy input (e.g. high trophic level), (2) susceptibility to the loss of energy pathways (e.g. specialists with few prey species) and (3) dynamic instability (e.g. low Hill exponent and reliance on homogeneous energy channels when feeding on similarly sized prey). Interestingly, and different from field studies, we found that the trophic level and not the body mass of a species influences its extinction risk. On the other hand, body mass is the single most important factor determining the time to extinction of a species, resulting in small species dying first. This suggests that in the field the trophic level might have more influence on the extinction risk than presently recognized.
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| 7. |
- Brose, Ulrich, et al.
(författare)
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Predicting the consequences of species lossusing size-structured biodiversity approaches
- 2017
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Ingår i: Biological Reviews. - : Wiley-Blackwell. - 1464-7931 .- 1469-185X. ; 92:2, s. 684-697
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Forskningsöversikt (refereegranskat)abstract
- Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait-free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size-spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re-assess three classic debates on the relationships between biodiversity and (i) food-web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size-structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body-mass distributions maintaining food-web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock-on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size-structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss.
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| 8. |
- Brose, Ulrich, et al.
(författare)
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Spatial aspects of food webs
- 2005
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Ingår i: Dynamic Food Webs. - London, UK : Elsevier. - 9780120884582 - 0120884585 ; , s. 463-469
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Konferensbidrag (refereegranskat)abstract
- Aspects of spatial scale have until recently been largely ignored in empirical and theoretical food web studies (e.g., Cohen & Briand 1984, Martinez 1992, but see Bengtsson et al. 2002, Bengtsson & Berg, this book). Most ecologists tend to conceptualize and represent food webs as static representations of communities, depicting a community assemblage as sampled at a particular point in time, or highly aggregated trophic group composites over broader scales of time and space (Polis et al. 1996). Moreover, most researchers depict potential food webs, which contain all species sampled and all potential trophic links based on literature reviews, several sampling events, or laboratory feeding trials. In reality, however, not all these potential feeding links are realized as not all species co-occur, and not all samples in space or time can contain all species (Schoenly & Cohen 1991), hence, yielding a variance of food web architecture in space (Brose et al. 2004). In recent years, food web ecologists have recognized that food webs are open systems – that are influence by processes in adjacent systems – and spatially heterogeneous (Polis et al. 1996). This influence of adjacent systems can be bottom-up, due to allochthonous inputs of resources (Polis & Strong 1996, Huxel & McCann 1998, Mulder & De Zwart 2003), or top-down due to the regular or irregular presence of top predators (e.g., Post et al. 2000, Scheu 2001). However, without a clear understanding of the size of a system and a definition of its boundaries it is not possible to judge if flows are internal or driven by adjacent systems. Similarly, the importance of allochthony is only assessable when the balance of inputs and outputs are known relative to the scale and throughputs within the system itself. At the largest scale of the food web – the home range of a predator such as wolf, lion, shark or eagle of roughly 50 km2 to 300 km2 –the balance of inputs and outputs caused by wind and movement of water may be small compared to the total trophic flows within the home range of the large predator (Cousins 1990). Acknowledging these issues of space, Polis et al (1996) argued that progress toward the next phase of food web studies would require addressing spatial and temporal processes. Here, we present a conceptual framework with some nuclei about the role of space in food web ecology. Although we primarily address spatial aspects, this framework is linked to a more general concept of spatio-temporal scales of ecological research.
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| 9. |
- 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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| 10. |
- 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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