| 1. |
- Eklöf, Anna, et al.
(author)
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Can dispersal rescue metacommunities from extinction cascades?
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Other publication (other academic/artistic)abstract
- Climate change and habitat loss are increasingly affecting the structure and dynamics of ecological communities both at the local and regional scale. Changes in the spatial structure of landscapes as well as in the trophic structure of local communities can be expected to have important consequences for the long-term persistence of species in metacommunities. The aim of the present work is to investigate how the spatial structure of the landscape (patch density) and dispersal patterns of species (migration rate and dispersal distance) affect a metacommunities response to local loss of species and to increased mortality of individuals during dispersal. Using a spatially and dynamically explicit metacommunity model we find that the effect of dispersal on metacommunity persistence is two-sided: on the one hand, when dispersal involves no risk, high migration rate significantly reduces the risk of bottom-up extinction cascades following the local removal of a species. The explanation for this is that recolonization rates of the locally removed species increases with increasing migration rate. On the other hand, when dispersal imposes a risk to the dispersing individuals, high migration rate increases extinction risks, especially when dispersal is global (long dispersal distances). Largebodied species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. These results suggest that decreasing the mortality risk of dispersing individuals by improving the quality of the habitat matrix might greatly increase the robustness of metacommunities to local loss of species by enhancing recolonizations and rescue effects.
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| 2. |
- Eklöf, Anna, et al.
(author)
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Climate change in metacommunities : dispersal gives double-sided effects on persistence
- 2012
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In: Philosphical Transactions of the Royal Society B. - : The Royal Society Publishing. - 1471-2970 .- 0962-8436. ; 367:1605, s. 2945-2954
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Journal article (peer-reviewed)abstract
- Climate change is increasingly affecting the structure and dynamics of ecological communities bothat local and at regional scales, and this can be expected to have important consequences for theirrobustness and long-term persistence. The aim of the present work is to analyse how the spatialstructure of the landscape and dispersal patterns of species (dispersal rate and average dispersal distance)affects metacommunity response to two disturbances: (i) increased mortality during dispersaland (ii) local species extinction. We analyse the disturbances both in isolation and in combination.Using a spatially and dynamically explicit metacommunity model, we find that the effect of dispersalon metacommunity persistence is two-sided: on the one hand, high dispersal significantly reducesthe risk of bottom-up extinction cascades following the local removal of a species; on the otherhand, when dispersal imposes a risk to the dispersing individuals, high dispersal increases extinctionrisks, especially when dispersal is global. Large-bodied species with long generation times at thehighest trophic level are particularly vulnerable to extinction when dispersal involves a risk. Thissuggests that decreasing the mortality risk of dispersing individuals by improving the quality ofthe habitat matrix may greatly increase the robustness of metacommunities.
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| 3. |
- Kaneryd, Linda
(author)
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Dynamics of ecological communities in variable environments : local and spatial processes
- 2012
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Doctoral thesis (other academic/artistic)abstract
- The ecosystems of the world are currently facing a variety of anthropogenic perturbations, such as climate change, fragmentation and destruction of habitat, overexploitation of natural resources and invasions of alien species. How the ecosystems will be affected is not only dependent on the direct effects of the perturbations on individual species but also on the trophic structure and interaction patterns of the ecological community. Of particular current concern is the response of ecological communities to climate change. Increased global temperature is expected to cause an increased intensity and frequency of weather extremes. A more unpredictable and more variable environment will have important consequences not only for individual species but also for the dynamics of the entire community. If we are to fully understand the joint effects of a changing climate and habitat fragmentation, there is also a need to understand the spatial aspects of community dynamics. In the present work we use dynamic models to theoretically explore the importance of local (Paper I and II) and spatial processes (Paper III-V) for the response of multi-trophic communities to different kinds of perturbations.In paper I we investigate how species richness and correlation in species responses to a highly variable environment affect the risk of extinction cascades. We find that the risk of extinction cascades increases with increasing species richness especially when the correlation among species is low. Initial stochastic extinctions of primary producer species unleash bottomup extinction cascades, where specialist consumers are especially vulnerable. Although the risks of extinction cascades were higher in the species-rich systems, we found that the temporal stability of aggregate abundance of primary producers increased with increasing richness. Thus, species richness had a two-sided effect on community stability. Also during the extinction cascades it is possible that more robust species and interaction patterns will be selected which would further act to stabilize the post-extinction communities. In paper II we explore how the process of disassembly affects the structure of the interaction network and the robustness of the community to additional disturbances. We find that the disassembled communities are structurally different and more resistant to disturbances than equally sized communities that have not gone through a phase of disassembly. The disassembled communities are topologically as well as dynamically more stable than non-disassembled communities.In paper III, IV and V we expand the analysis to incorporate the spatial dimension. In paper III we analyze how metacommunities (a set of local communities coupled by species dispersal) in spatially explicit landscapes respond to environmental variation. We examine how this response is affected by varying 1) species richness in the local communities, 2) the degree of correlation in species response to the environmental variation, between species within patches (species correlation) and among patches (spatial correlation) and 3) dispersal pattern of species. First we can confirm that our previous findings from paper I regarding local species richness and correlation among species within a patch are robust to the inclusion of a spatial dimension. However our results also show that the spatial dynamics are of great importance: first we find that the risk of global extinctions increases with increasing spatial correlation. Second we find that the pattern and rate of dispersal are important; a high migration rate in combination with localized dispersal decrease the risk of global extinctions whereas a global dispersal pattern increases the risk of global extinctions. When dispersal is global the subpopulations of a species become more synchronized which reduces the potential for a patch to become recolonized following extinctions. We also demonstrate the importance of both local and spatial processes when examining the temporal stability of primary production at the scale of metapopulations, local communities and metacommunities.In paper IV we investigate how the spatial structure of the landscape (number of patches) and dispersal pattern of species affect a metacommunities response to increased mortality during dispersal and local loss of species. We find a two-sided effect of dispersal on metacommunity persistence; on the one hand, high migration rate significantly reduces the risk of bottom-up extinction cascades following the removal of a species when dispersal involves no risk. On the other hand, high migration rate increases extinction risks when dispersal imposes a risk to the dispersing individuals, especially when dispersal is global. Species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. These results suggest that decreasing the mortality risk of dispersing individuals by constructing habitat corridors or by improving the quality of the habitat matrix might greatly increase the robustness of metacommunities to local loss of species by enhancing recolonisations and rescue effects.In paper V we use network theory to identify keystone patches in the landscape, patches that are of critical importance for the local and global persistence of species in the metacommunity. By deleting patches one at a time and investigating the risk of local and global extinctions we quantified the importance of a patch’s position in the landscape for the persistence of species within the metacommunity. A selection of indices were used including some local indices that measure the connectedness of a patch in the intact network and some indices which measure the decrease in a global index after the deletion of the patch from the network. Global indices are those that give an impression of the connectivity of the entire patch network. We find that deletion of patches contributing strongly to the connectivity of the entire patch network had the most negative effect on species persistence.
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| 4. |
- Kaneryd, Linda, et al.
(author)
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Risk of global extinctions in metacommunities exposed to a highly variable environment: local and spatial processes
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Other publication (other academic/artistic)abstract
- Here we analyze how metacommunities (a set of local communities coupled by species dispersal) in spatially explicit landscapes respond to environmental variation. We examine how this response is affected by 1) species richness in the local communities, 2) the degree of correlation in species response to the environmental variation both between species within patches (species correlation) and among patches (spatial correlation) and 3) dispersal pattern of species. We find that the risk of global extinction increases with increasing species richness in the local communities and with decreasing correlation among species in their response to environmental fluctuations. We also show that the pattern of spatial correlation is of great importance; the risk of global extinctions increases with increasing spatial correlation. Moreover, we find that the pattern and rate of dispersal are important; a high migration rate in combination with localized dispersal decrease the risk of global extinctions whereas a global dispersal pattern increases the risk of global extinctions. When dispersal is global the subpopulations of a species become more synchronized which reduces the potential for a patch to become recolonized following extinctions. We also demonstrate the importance of both local and spatial processes when examining the temporal stability of primary production at the scale of metapopulations, local communities and metacommunities.
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| 5. |
- Kaneryd, Linda, et al.
(author)
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Robustness of food webs whose structures have been shaped by extinctions in the past
- 2011
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Other publication (other academic/artistic)abstract
- Extinctions of species might lead to changes in the trophic structure of food webs with consequences for the robustness of the webs. Using a theoretical approach we here investigate 1) how ‘natural’ extinctions of species in a variable environment affect the trophic structure of food webs and 2) which consequences these structural changes will have for the topological and dynamical robustness of the webs to further, future disturbances. We show that food webs whose structure have been shaped by extinctions in the past (disassembled webs) are structurally different and more robust to disturbances (species deletion and exposure to high levels of environmental variability) than food webs of equal size (number of species) that have not gone through a phase of disassembly. The increased robustness of the disassembled webs is due to the preservation of certain link structures, structures that have been found to promote topological and dynamical stability. Thus, our results suggest that ‘natural’ extinctions lead to changes in the trophic structure of food webs which make them more resistant to future perturbations.
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| 6. |
- Kaneryd, Linda, et al.
(author)
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Species-rich ecosystems are vulnerable to cascading extinctions in an increasingly variable world
- 2012
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In: Ecology and Evolution. - : Wiley-Blackwell. - 2045-7758. ; 2:4, s. 858-874
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Journal article (peer-reviewed)abstract
- Global warming leads to increased intensity and frequency of weather extremes. Such increased environmental variability might in turn result in increased variation in the demographic rates of interacting species with potentially important consequences for the dynamics of food webs. Using a theoretical approach, we here explore the response of food webs to a highly variable environment.We investigate how species richness and correlation in the responses of species to environmental fluctuations affect the risk of extinction cascades. We find that the risk of extinction cascades increases with increasing species richness, especially when correlation among species is low. Initial extinctions of primary producer species unleash bottom-up extinction cascades, especially in webs with specialist consumers. In this sense, species-rich ecosystems are less robust to increasing levels of environmental variability than species-poor ones. Our study thus suggests that highly speciesrich ecosystems such as coral reefs and tropical rainforests might be particularly vulnerable to increased climate variability.
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| 7. |
- Westwood, Luke, et al.
(author)
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Keystone patches: upholding diversity in multi-trophic metacommunities
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Other publication (other academic/artistic)abstract
- Due to the destruction of their habitat some organisms have an uneven distribution across the landscape. In affected areas a community of interacting organisms may be fragmented into a network of smaller patches connected through dispersal of individuals of the different species. These metacommunities can be modelled with explicit dynamics and spatial structure, with dependence on both local processes (interactions between species within a patch) and global processes (dispersal of individuals between patches). Dispersal between patches is important for the operation of processes like recolonizations and ‘rescue effects’, processes which can counteract local extinctions and hence reduce the risk of global extinctions. Recent studies have applied network theory to real ecological communities, with a wide selection of indices available to characterise either an individual patch or the whole patch network. Certain keystone patches may be the most important in upholding the local or global diversity of a metacommunity and may then be identified by such a network index. A range of network indices were calculated for the patches in a large set of simulated metacommunities and all of the indices identified the keystone patch quality to a certain degree. Some of the indices were consistently better than the others and the dependence of the keystone quality on these indices was at least two times larger than for the others. The quality identified by the indices was of being more important for upholding local rather than global diversity. Many parameters were varied between the different metacommunities and as a result of this the models for identifying keystone patches yielded small R2 values and therefore were not proven to be dependable predictors if applied to particular metacommunities.
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