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Anthropogenic impact on predator guilds and ecosystem processes: Apex predator extinctions, land use and climate change
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0002-8749-6111
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Humans affect ecosystems by changing species compositions, landscape and climate. This thesis aims to increase our understanding of anthropogenic effects on mesopredator abundance due to changes in apex predator status, landscape and climate. I show that in Eurasia the abundance of a mesopredator, the red fox (Vulpes vulpes), is limited top-down by the Eurasian lynx (Lynx lynx) and bottom-up by winter severity. However, where lynx has been eradicated, fox abundance is instead related to bottom-factors such as cropland (paper I, II). Fox abundance was highest when croplands constituted 25% of the landscape (paper II). I also project red fox abundance in Sweden over the past 200 years and in future scenarios in relation to lynx density, land use and climate change. The projected fox abundance was highest in 1920, when lynx was eradicated and the proportion of cropland was 22%. In 2010, when lynx had recolonised, the projected fox abundance was lower than in 1920, but higher than in 1830. Future scenarios indicated that lynx abundance must increase in respond to climate change to keep fox at the same density as today. The results suggest a mesopredator release when lynx was eradicated, boosted by land use and climate change, and that changes in bottom-up factors can modify the relative strength of top-down factors (paper IV). From 1846-1922, lynx, wolverine (Gulo gulo) and grey wolf (Canis lupus) declined in Scandinavia due to persecution; however I show that the change in wolverine abundance was positively related to the changes in lynx and wolf abundance. This indicates that wolverine is subsidized by carrions from lynx and wolf kills rather than limited top-down by them (paper III). This thesis illustrates how mesopredator abundance is determined by a combination of top-down and bottom-up processes, and how anthropogenic impacts not only can change the structures of predator guilds, but also may modify top-down processes through changes in bottom-up factors.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2014. , 18 p.
Keyword [en]
Mesopredators, apex predators, top-down, bottom-up, interspecific killing, red fox, Eurasian lynx, grey wolf, wolverine, productivity, winter severity, cropland
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-100720ISBN: 978-91-7447-860-0 (print)OAI: oai:DiVA.org:su-100720DiVA: diva2:695755
Public defence
2014-03-21, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Manuscript.

 

Available from: 2014-02-27 Created: 2014-02-12 Last updated: 2017-06-29Bibliographically approved
List of papers
1. Where lynx prevail, foxes will fail - limitation of a mesopredator in Eurasia
Open this publication in new window or tab >>Where lynx prevail, foxes will fail - limitation of a mesopredator in Eurasia
2013 (English)In: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 22, no 7, 868-877 p.Article in journal (Refereed) Published
Abstract [en]

Aim Climate change and loss of apex predators can affect ecosystem structure and function through modified limitation processes. We investigated, on a continental scale, whether mesopredator abundance is limited from the top down by large predators, as predicted by the mesopredator release hypothesis, or by bottom-up factors. The mesopredator in focus is the red fox Vulpes vulpes, a key predator in many ecosystems due to its strong effects on prey abundance. Location Europe and northern Asia. Methods Data on red fox density were compiled from published papers and reports. For each site, we collated presence-absence data on large carnivores (Lynx lynx, Canis lupus, Canisaureus) and remote sensing data for factors potentially related to bottom-up limitation (winter severity, summer temperature, human density, primary productivity, tree cover). The data were analysed through structural equation modelling. Results The presence of lynx had a direct negative effect on red foxes, suppressing fox abundance. Also winter severity had a negative effect on red fox abundance, and in Eurasia as a whole this effect was partially mediated through lynx. Within the lynx distribution range, winter severity was the only bottom-up factor significantly affecting red fox abundance. Outside the lynx distribution range, primary productivity, summer temperature and human density had a positive effect on red fox abundance. Main conclusions Our results show that apex predators can limit mesopredator abundance on a continental scale, thus supporting the mesopredator release hypothesis. Winter severity also affected red fox abundance, partially due to an interaction between lynx and winter conditions. On the continental scale a complex network of processes operates with varying effects depending on mediation processes. Our results imply that apex predators can have an important effect on ecosystem structure by limiting mesopredator abundance, and we suggest that apex predators may dampen increases in mesopredator abundance driven by global warming.

Keyword
Apex predators, Canis aureus, Canis lupus, interference competition, intraguild killing, Lynx lynx, piecewise SEM, productivity, Vulpes vulpes
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-92118 (URN)10.1111/geb.12051 (DOI)000320326600009 ()
Funder
Formas, 2008-702
Note

AuthorCount:3;

Available from: 2013-07-22 Created: 2013-07-19 Last updated: 2017-12-06Bibliographically approved
2. Land cover effects on mesopredator abundance in the presence and absence of apex predators
Open this publication in new window or tab >>Land cover effects on mesopredator abundance in the presence and absence of apex predators
2015 (English)In: Acta Oecologica, ISSN 1146-609X, E-ISSN 1873-6238, Vol. 67, 40-48 p.Article in journal (Refereed) Published
Abstract [en]

Trophic downgrading due to loss of apex consumers has been detected in many ecosystems. Loss of larger predators implies that medium-sized mesopredators rise to the status of apex predators which are limited bottom-up rather than top-down. Hence the density of medium-sized predators should be more strongly related to land cover in absence of larger predators. We investigate this hypothesis at a continental scale (Eurasia) for a medium-sized predator, the red fox Vulpes vulpes, in presence and absence of an apex predator, the Eurasian lynx Lynx lynx. We predicted that in absence of lynx, fox density should be positively associated with open land covers, as these could favour foxes due to high prey availability. Our results showed that fox abundance was independent of land cover in presence of lynx. However, in absence of lynx, fox density was positively but asymptotically related to cropland, while negatively related to grassland. Fox density was highest when cropland constituted approximately 30% of the landscape, likely reflecting an optimal composition of foraging and breeding habitat. Grassland was associated with low productivity, likely reflecting low prey availability. Thus, cropland is favourable for red fox, but only in absence of top-down limitation by lynx. We suggest that there are two ecosystem states in Eurasia, one northern where lynx is present as an apex predator, and one south-eastern where red fox assumes the apex predator position and its abundance is subsidised by anthropogenic land cover.

Keyword
Vulpes vulpes, Lynx lynx, Landscape composition, Ecosystem state, Top-down, Bottom-up
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-119534 (URN)10.1016/j.actao.2015.04.002 (DOI)000358092700006 ()
Available from: 2015-08-21 Created: 2015-08-17 Last updated: 2017-12-04Bibliographically approved
3. The relationship between wolverine and larger predators, lynx and wolf, in a historical ecosystem context
Open this publication in new window or tab >>The relationship between wolverine and larger predators, lynx and wolf, in a historical ecosystem context
2014 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 2, 625-637 p.Article in journal (Refereed) Published
Abstract [en]

Apex predators play an important role in shaping ecosystem structure. They may suppress smaller predators (mesopredators) but also subsidize scavengers via carrion provisioning. However, the importance of these interactions can change with ecosystem context. The wolverine (Gulo gulo) is a cold-adapted carnivore and facultative scavenger. It has a circumboreal distribution, where it could be either suppressed or subsidized by larger predators. In Scandinavia, the wolverine might interact with two larger predators, wolf (Canis lupus) and lynx (Lynx lynx), but human persecution decimated the populations in the nineteenth and early twentieth century. We investigated potential relationships between wolverine and the larger predators using hunting bag statistics from 15 Norwegian and Swedish counties in 1846-1922. Our best models showed a positive association between wolverine and lynx trends, taking ecological and human factors into account. There was also a positive association between year-to-year fluctuations in wolverine and wolf in the latter part of the study period. We suggest these associations could result from positive lynx-wolverine interactions through carrion provisioning, while wolves might both suppress wolverine and provide carrion with the net effect becoming positive when wolf density drops below a threshold. Wolverines could thus benefit from lynx presence and low-to-intermediate wolf densities.

National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-100766 (URN)10.1007/s00442-014-2918-6 (DOI)000336378800017 ()
Funder
Formas, 2009-563
Available from: 2014-02-12 Created: 2014-02-12 Last updated: 2017-12-06Bibliographically approved
4. The changing contribution of top-down and bottom-up limitation of mesopredators during 220 years of land use and climate change
Open this publication in new window or tab >>The changing contribution of top-down and bottom-up limitation of mesopredators during 220 years of land use and climate change
Show others...
2017 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 86, no 3, 566-576 p.Article in journal (Refereed) Published
Abstract [en]

Apex predators may buffer bottom-up driven ecosystem change, as top-down suppression may dampen herbivore and mesopredator responses to increased resource availability. However, theory suggests that for this buffering capacity to be realized, the equilibrium abundance of apex predators must increase. This raises the question: will apex predators maintain herbivore/mesopredator limitation, if bottom-up change relaxes resource constraints? Here, we explore changes in mesopredator (red fox Vulpes vulpes) abundance over 220years in response to eradication and recovery of an apex predator (Eurasian lynx Lynx lynx), and changes in land use and climate which are linked to resource availability. A three-step approach was used. First, recent data from Finland and Sweden were modelled to estimate linear effects of lynx density, land use and winter temperature on fox density. Second, lynx density, land use and winter temperature was estimated in a 22650km(2) focal area in boreal and boreo-nemoral Sweden in the years 1830, 1920, 2010 and 2050. Third, the models and estimates were used to project historic and future fox densities in the focal area. Projected fox density was lowest in 1830 when lynx density was high, winters cold and the proportion of cropland low. Fox density peaked in 1920 due to lynx eradication, a mesopredator release boosted by favourable bottom-up changes - milder winters and cropland expansion. By 2010, lynx recolonization had reduced fox density, but it remained higher than in 1830, partly due to the bottom-up changes. Comparing 1830 to 2010, the contribution of top-down limitation decreased, while environment enrichment relaxed bottom-up limitation. Future scenarios indicated that by 2050, lynx density would have to increase by 79% to compensate for a projected climate-driven increase in fox density. We highlight that although top-down limitation in theory can buffer bottom-up change, this requires compensatory changes in apex predator abundance. Hence apex predator recolonization/recovery to historical levels would not be sufficient to compensate for widespread changes in climate and land use, which have relaxed the resource constraints for many herbivores and mesopredators. Variation in bottom-up conditions may also contribute to context dependence in apex predator effects.

Keyword
ecosystem processes, historical ecology, historical maps, intraguild killing, trophic interactions, wildlife monitoring, wildlife restoration
National Category
Environmental Sciences Zoology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-143409 (URN)10.1111/1365-2656.12633 (DOI)000398826400016 ()28075011 (PubMedID)
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2017-06-29Bibliographically approved

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