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Ask, Per
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Publications (8 of 8) Show all publications
Byström, P., Ask, P., Andersson, J. & Persson, L. (2013). Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators. PLoS ONE, 8(7), e70404
Open this publication in new window or tab >>Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators
2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 7, p. e70404-Article in journal (Refereed) Published
Abstract [en]

We experimentally show that the piscivorous top predator Arctic char (Salvelinus alpinus) have higher attack rates on cannibal prey compared to the interspecific prey species ninespine stickleback (Pungitius pungitius), and that sticklebacks are more efficient competitiors for zooplankton resources compared to juvenile char. We also conducted a literature survey that together with our experiments showed that piscivorous top consumers selected cannibal prey over interspecific prey in 9 out of 10 cases. Our literature survey also showed that specialist prey species are competitively superior compared to juvenile piscivorous species within the zooplankton niche. We discuss our results in relation to omnivory in fish communities and we suggest that the observed general preference for cannibal prey over interspecific prey in piscivores and the competitive advantage of prey species over juvenile piscivores may be major mechanisms for coexistence in fish communities.

Keywords
Cannibalism, piscivory, competition, Arctic char, ninespine stickleback
National Category
Ecology
Research subject
biology
Identifiers
urn:nbn:se:umu:diva-37993 (URN)10.1371/journal.pone.0070404 (DOI)000322391400088 ()23894650 (PubMedID)
Available from: 2010-11-22 Created: 2010-11-22 Last updated: 2018-06-08Bibliographically approved
Ask, P. (2010). Invasion of top and intermediate consumers in a size structured fish community. (Doctoral dissertation). Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap
Open this publication in new window or tab >>Invasion of top and intermediate consumers in a size structured fish community
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Invasion av toppredatorer och intermediära konsumenter i ett storleksstrukturerat fisksamhälle
Abstract [en]

In this thesis I have investigated the effects of invading top and intermediate consumers in a size-structured fish community, using a combination of field studies, a lake invasion experiment and smaller scale pond and aquaria experiments.

The lake invasion experiment was based on introductions of an intermediate consumer, ninespine stickleback (Pungitius pungitius L.), in to allopatric populations of an omnivorous top predator, Arctic char (Salvelinus alpinus L.). The invasion experiment was performed in two tundra lakes and in two birch forest lakes to investigate the effect of climate on the invasion success. I found that the effect of sticklebacks on char was size dependent. Small char suffered reduced growth from resource competition with sticklebacks whereas the maximum size of adult char increased from the addition of a larger prey resource, stickleback. The negative effect of sticklebacks on the growth of small char suggests that sticklebacks may be a better resource competitor than char, which was also supported by the pond and aquaria experiments. The pond experiments also suggested that char were more efficient cannibals than interspecific predators on sticklebacks. Cannibalism in char may limit the recruitment of char and decrease both their predatory and competitive effect on coexisting species and thereby also promote the coexistence of char and sticklebacks. The successful invasion by sticklebacks and their subsequent increases in density suggest that the absence of sticklebacks in char lakes in this region is not caused by biotic interactions with char. Instead, it may be suggested that co-occurrence of sticklebacks and char in the region is limited by dispersal.

The char – stickleback system resembles an intraguild predation system with char as the top consumer and stickleback as the intermediate consumer. The effects of the stickleback invasion is also contrasted with a field study of a northern pike (Esox lucius L.) invasion into a system with coexisting char and stickleback, where pike can be viewed as the top consumer and char as the intermediate consumer both feeding on sticklebacks. In this case pike excluded char. The identity of the invading species and the relative strength of the predatory and competitive interactions in the two contrasting systems are discussed in relation to coexistence in intraguild predation systems. I found that the identity of the invading species is of crucial importance for the response at the ecosystem level, and that the inherent size dependency of competitive and predatory interactions in fish communities is important for attaining a mechanistical understanding of the effects of invasive species in lake ecosystems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. p. 27
Keywords
Invasion, intraguild predation, size-structure, cannibalism, climate, temperature, Arctic char, ninespine stickleback
National Category
Ecology
Research subject
biology
Identifiers
urn:nbn:se:umu:diva-37995 (URN)978-91-7459-119-4 (ISBN)
Public defence
2010-12-17, KBC-huset, KB3B1, Umeå Universitet, Umeå, 11:03 (English)
Opponent
Supervisors
Available from: 2010-11-26 Created: 2010-11-22 Last updated: 2018-06-08Bibliographically approved
Karlsson, J., Byström, P., Ask, J., Ask, P., Persson, L. & Jansson, M. (2009). Light limitation of nutrient-poor lake ecosystems. Nature, 460, 506-509
Open this publication in new window or tab >>Light limitation of nutrient-poor lake ecosystems
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2009 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 460, p. 506-509Article in journal (Refereed) Published
Abstract [en]

Productivity denotes the rate of biomass synthesis in ecosystems and is a fundamental characteristic that frames ecosystem function and management. Limitation of productivity by nutrient availability is an established paradigm for lake ecosystems1, 2, 3. Here, we assess the relevance of this paradigm for a majority of the world's small, nutrient-poor lakes, with different concentrations of coloured organic matter4, 5. By comparing small unproductive lakes along a water colour gradient, we show that coloured terrestrial organic matter controls the key process for new biomass synthesis (the benthic primary production) through its effects on light attenuation. We also show that this translates into effects on production and biomass of higher trophic levels (benthic invertebrates and fish). These results are inconsistent with the idea that nutrient supply primarily controls lake productivity, and we propose that a large share of the world's unproductive lakes, within natural variations of organic carbon and nutrient input, are limited by light and not by nutrients. We anticipate that our result will have implications for understanding lake ecosystem function and responses to environmental change. Catchment export of coloured organic matter is sensitive to short-term natural variability and long-term, large-scale changes, driven by climate and different anthropogenic influences6, 7. Consequently, changes in terrestrial carbon cycling will have pronounced effects on most lake ecosystems by mediating changes in light climate and productivity of lakes.

Identifiers
urn:nbn:se:umu:diva-25549 (URN)10.1038/nature08179 (DOI)
Available from: 2009-08-19 Created: 2009-08-19 Last updated: 2018-06-08
Ask, J., Karlsson, J., Persson, L., Ask, P., Byström, P. & Jansson, M. (2009). Terrestrial organic matter and light penetration: Effects on bacterial and primary production in lakes. Limnology and Oceanography, 54(6), 2034-2040
Open this publication in new window or tab >>Terrestrial organic matter and light penetration: Effects on bacterial and primary production in lakes
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2009 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 6, p. 2034-2040Article in journal (Refereed) Published
Abstract [en]

We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.

Place, publisher, year, edition, pages
American Society of Limnology and Oceanography, Inc., 2009
Identifiers
urn:nbn:se:umu:diva-26800 (URN)
Available from: 2009-10-27 Created: 2009-10-27 Last updated: 2018-06-08Bibliographically approved
Ask, J., Karlsson, J., Persson, L., Ask, P., Byström, P. & Jansson, M. (2009). Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes. Ecology, 90(7), 1923-1932
Open this publication in new window or tab >>Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes
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2009 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 7, p. 1923-1932Article in journal (Refereed) Published
Abstract [en]

This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.

Place, publisher, year, edition, pages
Washington, DC, USA: Ecological Society of America, 2009
Identifiers
urn:nbn:se:umu:diva-25554 (URN)10.1890/07-1855.1 (DOI)
Available from: 2009-08-19 Created: 2009-08-19 Last updated: 2018-06-08Bibliographically approved
Byström, P., Karlsson, J., Nilsson, P., Van Kooten, T., Ask, J. & Olofsson, F. (2007). Substitution of top predators: effects of pike invasion in a subarctic lake. Freshwater Biology, 52(7), 1271–1280
Open this publication in new window or tab >>Substitution of top predators: effects of pike invasion in a subarctic lake
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2007 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 7, p. 1271–1280-Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
John Wiley & Sons, Inc, 2007
Keywords
Arctic char, cascading effects, climate change, lake ecosystems, ninespined stickleback, northern pike, top predator invasions
Identifiers
urn:nbn:se:umu:diva-6187 (URN)10.1111/j.1365-2427.2007.01763.x (DOI)
Available from: 2007-12-07 Created: 2007-12-07 Last updated: 2018-06-09Bibliographically approved
Ask, P., Ask, J., Byström, P., Jansson, M., Karlsson, J. & Persson, L.Competition mediated coexistence of invading intermediate consumer, ninespine stickleback, and a resident omnivorous top predator, Arctic char.
Open this publication in new window or tab >>Competition mediated coexistence of invading intermediate consumer, ninespine stickleback, and a resident omnivorous top predator, Arctic char
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate change results in changes in the geographical distribution of species. Species invasion success into a new area is dependent both on the dispersal ability of species as well as the strength and identity of biotic interactions between resident and invading species. Coexistence in intraguild predation (IGP) systems depends on the relative strength of predation and competition interactions which in turn are temperature dependent. We investigated the effects of introducing an intermediate consumer, ninespine stickleback (Pungitius pungitius), into allopatric populations of the omnivorous top predator Arctic char (Salvelinus alpinus). Introductions were performed in lakes with different climate regimes, two tundra lakes and two forest lakes that differed in average summer temperatures with 1.4 ± 0.5 ºC (average ± 1SD). We found that sticklebacks were able to invade and increase in density in both tundra and forest lakes. Sticklebacks had strong negative effects on resource densities which also was reflected in a decreased growth of small char. Increasing stickleback density had a positive effect on growth of large adults and on the maximum size of char. We conclude that stickleback presence is not limited by biological interactions in these systems but rather by dispersion ability. We suggest that the size dependency in the response of char to the invasion of sticklebacks is fundamental for the successful invasion of sticklebacks, and that size dependent interactions including cannibalism play important roles for coexistence in natural IGP-systems.

Keywords
Intraguild predation, omnivory, competition, cannibalism, temperature, climate change, invasion
National Category
Ecology
Research subject
biology
Identifiers
urn:nbn:se:umu:diva-37992 (URN)
Available from: 2010-11-22 Created: 2010-11-22 Last updated: 2018-06-08Bibliographically approved
Ask, P., Ask, J., Byström, P., Jansson, M., Karlsson, J. & Persson, L.Temperature mediated effects on top consumer populations in subarctic lakes.
Open this publication in new window or tab >>Temperature mediated effects on top consumer populations in subarctic lakes
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of temperature on top consumer populations in subarctic lake communities were studied by contrasting two lake pairs in different climate regimes: one pair on the low alpine tundra and one pair in the subalpine birch forest. We measured zooplankton and macroinvertebrate biomasses over the season and estimated population density and size structure of the top consumer Arctic char (Salvelinus alpinus). Furthermore, we modelled char growth using literature data on temperature dependent search rate, handling time and metabolic demands. The forest lakes were warmer than the tundra lakes. Char in the forest lakes were larger and had a higher individual growth compared to char in the tundra lakes, while population density and biomasses of char were not different between the forest and the tundra lakes. There were no differences in macroinvertebrate and zooplankton resource levels available for char between lake pairs. Our modeling of char growth revealed that higher temperature increased growth of char at the observed resource densities, suggesting that the higher temperature in the forest lakes was primarily the cause of the higher growth of char in these lakes. We suggest that cannibalism in char may regulate char recruitment and thereby population density and biomass of char leading to effects of increasing temperature on consumer biomass and consumer individual growth different from what is expected in pure consumer-resource systems. Our results emphasize the importance of feedbacks within ecosystems when addressing effects of climate change and increasing temperature on lake communities.

Keywords
Arctic char, temperature, cannibalism, ecological feedbacks, climate
National Category
Ecology
Research subject
biology
Identifiers
urn:nbn:se:umu:diva-37989 (URN)
Available from: 2010-11-22 Created: 2010-11-22 Last updated: 2018-06-08Bibliographically approved
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