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Sökning: WFRF:(Rall Björn C.)

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  • Brose, Ulrich, et al. (författare)
  • Predicting the consequences of species lossusing size-structured biodiversity approaches
  • 2017
  • Ingår i: Biological Reviews. - : Wiley-Blackwell. - 1464-7931 .- 1469-185X. ; 92:2, s. 684-697
  • 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.
  • Binzer, Amrei, et al. (författare)
  • The susceptibility of species to extinctions in model communities
  • 2011
  • Ingår i: Basic and Applied Ecology. - : Elsevier. - 1439-1791 .- 1618-0089. ; 12:7, s. 590-599
  • 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.
  • Brose, Ulrich, et al. (författare)
  • Body sizes of consumers and their resources
  • 2005
  • Ingår i: Ecology. - : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 86:9, s. 2545-2545
  • Tidskriftsartikel (refereegranskat)abstract
    • Trophic information—who eats whom—and species’ body sizes are two of the most basic descriptions necessary to understand community structure as well as ecological and evolutionary dynamics. Consumer–resource body size ratios between predators and their prey, and parasitoids and their hosts, have recently gained increasing attention due to their important implications for species’ interaction strengths and dynamical population stability. This data set documents body sizes of consumers and their resources. We gathered body size data for the food webs of Skipwith Pond, a parasitoid community of grass-feeding chalcid wasps in British grasslands; the pelagic community of the Benguela system, a source web based on broom in the United Kingdom; Broadstone Stream, UK; the Grand Caric¸aie marsh at Lake Neuchaˆtel, Switzerland; Tuesday Lake, USA; alpine lakes in the Sierra Nevada of California; Mill Stream, UK; and the eastern Weddell Sea Shelf, Antarctica. Further consumer–resource body size data are included for planktonic predators, predatory nematodes, parasitoids, marine fish predators, freshwater invertebrates, Australian terrestrial consumers, and aphid parasitoids. Containing 16 807 records, this is the largest data set ever compiled for body sizes of consumers and their resources. In addition to body sizes, the data set includes information on consumer and resource taxonomy, the geographic location of the study, the habitat studied, the type of the feeding interaction (e.g., predacious, parasitic) and the metabolic categories of the species (e.g., invertebrate, ectotherm vertebrate). The present data set was gathered with the intent to stimulate research on effects of consumer–resource body size patterns on food-web structure, interaction-strength distributions, population dynamics, and community stability. The use of a common data set may facilitate cross-study comparisons and understanding of the relationships between different scientific approaches and models.
  • Curtsdotter, Alva, et al. (författare)
  • Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs
  • 2011
  • Ingår i: Basic and Applied Ecology. - : Elsevier. - 1439-1791 .- 1618-0089. ; 12:7, s. 571-580
  • Tidskriftsartikel (refereegranskat)abstract
    • The loss of species from ecological communities can unleash a cascade of secondary extinctions, the risk and extent of which are likely to depend on the traits of the species that are lost from the community. To identify species traits that have the greatest impact on food web robustness to species loss we here subject allometrically scaled, dynamical food web models to several deletion sequences based on species’ connectivity, generality, vulnerability or body mass. Further, to evaluate the relative importance of dynamical to topological effects we compare robustness between dynamical and purely topological models. This comparison reveals that the topological approach overestimates robustness in general and for certain sequences in particular. Top-down directed sequences have no or very low impact on robustness in topological analyses, while the dynamical analysis reveals that they may be as important as high-impact bottom-up directed sequences. Moreover, there are no deletion sequences that result, on average, in no or very few secondary extinctions in the dynamical approach. Instead, the least detrimental sequence in the dynamical approach yields an average robustness similar to the most detrimental (non-basal) deletion sequence in the topological approach. Hence, a topological analysis may lead to erroneous conclusions concerning both the relative and the absolute importance of different species traits for robustness. The dynamical sequential deletion analysis shows that food webs are least robust to the loss of species that have many trophic links or that occupy low trophic levels. In contrast to previous studies we can infer, albeit indirectly, that secondary extinctions were triggered by both bottom-up and top-down cascades.
  • Riede, Jens O, et al. (författare)
  • Size-based food web characteristics govern the response to species extinctions
  • 2011
  • Ingår i: Basic and Applied Ecology. - : Elsevier. - 1439-1791 .- 1618-0089. ; 12:7, s. 581-589
  • Tidskriftsartikel (refereegranskat)abstract
    • How ecological communities react to species extinctions is a long-standing yet current question in ecology. The species constituting the basic units of ecosystems interact with each other forming complex networks of trophic relationships and the characteristics of these networks are highly important for the consequences of species extinction. Here we take a more general approach and analyze a broad range of network characteristics and their role in determining food web susceptibility to secondary extinctions. We extend previous studies, that have focused on the consequences of topological and dynamical foodweb parameters for food web robustness, by also defining network-wide characteristics depending on the relationships between the distribution of species body masses and other species characteristics. We use a bioenergetic dynamical model to simulate realistically structured model food webs that differ in their structural and dynamical properties as well as their size structure. In order to measure food web robustness we calculated the proportion of species going secondarily extinct. A multiple regression analysis was then used to fit a general model relating the proportion of species going secondarily extinct to the measured foodweb properties. Our results show that there are multiple factors from all three groups of food web characteristics that affect foodweb robustness. However, we find the most striking effect was related to the body mass–abundance relationship which points to the importance of body mass relationships for food web stability.
  • Vucic-Pestic, Oliver, et al. (författare)
  • Habitat structure and prey aggregation determine the functional response in a soil predator-prey interaction
  • 2010
  • Ingår i: Pedobiologia. - : Elsevier. - 1873-1511. ; 53:5, s. 307-312
  • Tidskriftsartikel (refereegranskat)abstract
    • Functionalresponses describe the per capita consumption rates of predators depending on prey density, which quantifies the energy transfer between trophic levels. We studied a typical interaction of the litter–soil systems between hunting spiders (Pardosa lugubris; Araneae: Lycosidae) and springtails (Heteromurus nitidus; Collembola: Entomobryidae) at varying habitatstructure, i.e. with moss vs. without moss. We found a hyperbolic increase in consumption (functionalresponse type II) in the treatment without habitatstructure that was converted into a roller-coaster (or dome-shaped in a broad sense) functionalresponse in treatments with habitatstructure. Additional experiments suggest that the reduced per capita consumption rates at high prey densities may be explained by aggregative defence behaviour of the springtails. Experimentally, this behaviour was induced by the presence of habitatstructure. We analyzed the net-energy gain of this predator–preyinteraction by comparing the predator’s metabolic energy loss to its energy gain by consumption. In treatments with habitatstructure, the net-energy gain of the predator was limited at intermediate prey densities where preyaggregation reduced the consumption rates. Our results stress the importance of habitatstructure and prey behaviour in shaping the functionalresponse in a typical soil–litter predator–preyinteraction.
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  • Resultat 1-6 av 6

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