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| 2. |
- De Roos, André M, et al.
(författare)
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Simplifying a physiologically structured population model to a stage-structured biomass model.
- 2008
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Ingår i: Theoretical Population Biology. - : Elsevier Inc.. - 0040-5809 .- 1096-0325. ; 73:1, s. 47-62
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Tidskriftsartikel (refereegranskat)abstract
- We formulate and analyze an archetypal consumer-resource model in terms of ordinary differential equations that consistently translates individual life history processes, in particular food-dependent growth in body size and stage-specific differences between juveniles and adults in resource use and mortality, to the population level. This stage-structured model is derived as an approximation to a physiologically structured population model, which accounts for a complete size-distribution of the consumer population and which is based on assumptions about the energy budget and size-dependent life history of individual consumers. The approximation ensures that under equilibrium conditions predictions of both models are completely identical. In addition we find that under non-equilibrium conditions the stage-structured model gives rise to dynamics that closely approximate the dynamics exhibited by the size-structured model, as long as adult consumers are superior foragers than juveniles with a higher mass-specific ingestion rate. When the mass-specific intake rate of juvenile consumers is higher, the size-structured model exhibits single-generation cycles, in which a single cohort of consumers dominates population dynamics throughout its life time and the population composition varies over time between a dominance by juveniles and adults, respectively. The stage-structured model does not capture these dynamics because it incorporates a distributed time delay between the birth and maturation of an individual organism in contrast to the size-structured model, in which maturation is a discrete event in individual life history. We investigate model dynamics with both semi-chemostat and logistic resource growth.
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| 3. |
- Byström, Pär, et al.
(författare)
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Substitution of top predators : effects of pike invasion in a subarctic lake
- 2007
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Ingår i: Freshwater Biology. - : John Wiley & Sons, Inc. - 0046-5070 .- 1365-2427. ; 52:7, s. 1271–1280-
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Tidskriftsartikel (refereegranskat)abstract
- 1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback. 2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char. 3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator-sensitive macroinvertebrates increased in abundance. 4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels.
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| 4. |
- de Roos, André M., et al.
(författare)
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Stage-specific predator species help each other to persist while competing for a single prey
- 2008
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Ingår i: Proceedings from the National Academy of Science of the United States of America. - Washington, USA : The National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 105:37, s. 13930-13935
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Tidskriftsartikel (refereegranskat)abstract
- Prey in natural communities are usually shared by many predator species. How predators coexist while competing for the same prey is one of the fundamental questions in ecology. Here we show that competing predator species may not only coexist on a single prey but even help each other to persist, if they specialize on different life history stages of the prey. By changing the prey size distribution a predator species may in fact increase the amount of prey available for its competitor. Surprisingly, a predator may even not be able to persist at all unless its competitor is also present. The competitor thus increases significantly the range of conditions for which a particular predator can persist. This “emergent facilitation” is a long-term, population-level effect that results from asymmetric increases in the rate of prey maturation and reproduction when predation relaxes competition among prey. Emergent facilitation explains observations of correlated increases of predators on small and large conspecific prey as well as concordance in their distribution patterns. Our results suggest that emergent facilitation may promote the occurrence of complex, stable community food webs and that persistence of these communities could critically depend on diversity within predator guilds.
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| 5. |
- Huss, Magnus, 1979-, et al.
(författare)
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Intra-cohort cannibalism and size bimodality : a balance between hatching synchrony and resource feedbacks
- 2010
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 119:12, s. 2000-2011
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Tidskriftsartikel (refereegranskat)abstract
- Cannibalistic interactions generally depend on the size relationship between cannibals and victims. In many populations, alarge enough size variation to allow for cannibalism may not only develop among age-cohorts but also within cohorts. Westudied the implications of variation in hatching period length and initial cohort size for the emergence of cannibalism andbimodal size distributions within animal cohorts using a physiologically structured population model. We found that thedevelopment of size bimodality was critically dependent on hatching period length, victim density and the presence of afeedback via shared resources. Cannibals only gained enough energy from cannibalism to accelerate in growth when victimdensity was high relative to cannibal density at the onset of cannibalism. Furthermore, we found that the opportunity forearly hatchers to initially feed on an unexploited resource increases the likelihood both for cannibalism to occur and sizebimodality to develop. Once cannibals accelerated in growth relative to victims size bimodality, reduced victim numbersand relaxed resource competition resulted. Th us, in addition to that cannibals profi ted from cannibalism through energyextraction, their potential victims also benefi ted as the resource recovered due to cannibal thinning. To ensure recruitmentsuccess, it can be critical that a few individuals can accelerate in growth and reach a size large enough to escape sizedependentpredation and winter starvation. Hence, within-cohort cannibalism may be a potentially important mechanismto explain recruitment variation especially for cannibalistic species in temperate climates with strong seasonality. However,the scope for size bimodality to develop as a result of cannibalism may be limited by low victim densities and size andfood-dependent growth rates.
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| 6. |
- Nilsson, Karin A., 1977-, et al.
(författare)
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Complete compensation in Daphnia fecundity and stage-specific biomass in response to size-independent mortality
- 2010
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Ingår i: Journal of Animal Ecology. - : John Wiley & Sons, Inc. - 0021-8790 .- 1365-2656. ; 79:4, s. 871-878
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Tidskriftsartikel (refereegranskat)abstract
- 1. Recent theory suggests that compensation or even overcompensation in stage-specific biomass can arise in response to increased mortality. Which stage that will show compensation depends on whether maturation or reproduction is the more limiting process in the population. Size-structured theory also provides a strong link between the type of regulation and the expected population dynamics as both depend on size/stage specific competitive ability. 2. We imposed a size-independent mortality on a consumer-resource system with Daphnia pulex feeding on Scenedesmus obtusiusculus to asses the compensatory responses in Daphnia populations. We also extended an existing stage-structured biomass model by including several juvenile stages to test whether this extension affected the qualitative results of the existing model. 3. We found complete compensation in juvenile biomass and total population fecundity in response to harvesting. The compensation in fecundity was caused by both a higher proportion of fecund females and a larger clutch size under increased mortality. We did not detect any difference in resource levels between treatments. 4. The model results showed that both stages of juveniles have to be superior to adults in terms of resource competition for the compensatory response to take place in juvenile biomass. 5. The results are all in correspondence with that the regulating process within the population was reproduction. From this we also conclude that juveniles were superior competitors to adults, which has implications for population dynamics and the kind of cohort cycles seen in Daphnia populations. 6. The compensatory responses demonstrated in this experiment have major implications for community dynamics and are potentially present in any organisms with food-dependent growth or development.
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| 7. |
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| 8. |
- Post, J. R., et al.
(författare)
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Angler numerical response across landscapes and the collapse of freshwater fisheries
- 2008
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Ingår i: Ecological Applications. - : Ecological Society of America (ESA). - 1051-0761 .- 1939-5582. ; 18:4, s. 1038-1049
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Tidskriftsartikel (refereegranskat)abstract
- Recreational angling opportunities in lakes are distributed across landscapes and attract anglers based on the combination of angling quality, travel distance, and availability of facilities. The relationship between angler density and fishing quality, as measured by catch rate, represents a numerical response that is analogous to a predator numerical response to variability in prey abundance. We quantified this numerical response of anglers to rainbow trout, Oncorhynchus mykiss, populations distributed over a large lake district in south-central British Columbia, Canada. We developed a harvest dynamics model by linking this empirical description of the spatial numerical response of anglers to a logistic population growth rate model. The model was parameterized for rainbow trout and simulated spatial patterns of angler density and catch rates over a landscape. At locations distant from urban centers, angler density is low and catch rate high, suggesting near pristine conditions; at intermediate distances angler density is higher while catch rates are lower and approximate maximum sustainable levels; and at short distances angler density is sufficiently high to harvest to local extirpation. We extrapolated the model to other lake districts varying in human population size using an empirically derived angling participation rate relationship. Extrapolation to lake districts with one-tenth the human population maintained viable fisheries close to the urban area, and districts with 10 times the human populations could not maintain viable fisheries across much of their lake district. Landscape-scale spatial patterns differed quantitatively for species varying in rates of intrinsic population growth and carrying capacity, but the qualitative spatial patterns were consistent among species, demonstrating the pervasive impacts of the angler numerical response. To achieve a management goal of sustaining fisheries across landscapes, a change in management perspective is necessary, from that of individual lakes to one of dynamic harvest processes across landscapes. This new approach makes it clear that a one-size-fits-all management approach must be replaced with a mosaic of approaches cognizant of landscape-scale processes.
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| 9. |
- Schröder, Arne, 1974-, et al.
(författare)
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Invasion success depends on invader body size in a size-structured mixed predation-competition system
- 2009
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Ingår i: Journal of Animal Ecology. - : John Wiley & Sons, Inc. - 0021-8790 .- 1365-2656. ; 78:6, s. 1152-1162
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Tidskriftsartikel (refereegranskat)abstract
- 1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation. 2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment. 3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated. 4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity. 5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck. 6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.
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