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Population dynamics in variable environments – impacts of noise colour and synchrony
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Environmental variation is an essential part of population dynamics, and two characteristics of such variation—variance and the temporal autocorrelation termed ‘noise colour’—are essential for determining the persistence of a population. In addition, the spatial correlation of local environmental variation between habitat patches (i.e., synchrony) is equally important in subdivided populations connected via dispersal. The research underlying this thesis explored the effects of noise colour and synchrony on population dynamics. The dynamics were studied primarily in single-species models with fast or slow population responses to environmental changes, and several-species systems (i.e., food webs) with different stability properties were also considered. Populations were spatially subdivided with local dynamics in discrete patches, and patch positions were modelled either implicitly or explicitly, with different landscape configurations in the latter case.

It has previously been shown that the effect of increased environmental redness on extinction risk in nonspatial models depends on population responsiveness, seen as increased and decreased risks for fast and slow responding populations, respectively. Here, increased redness of noise decreased the extinction risk for fast-responding populations (in accordance with non-spatial studies) in a simple implicit landscape model (Papers I and II). Slow-responding populations in some cases showed a raised extinction risk for intermediate noise colour values (Paper I), which does not agree with earlier results. However, increasing the spatial complexity evened out the differences that were caused by responsiveness (Papers III and IV). Thus, in general, the explicit landscape models displayed a decrease in extinction risk with increasing environmental redness regardless of whether the populations were fast or slow in responding to environmental variation.

Still, fast and slow responsiveness of populations differed in relation to the following: overall levels of extinction risk (Papers I, III, and IV), synchrony of population variations (Paper II), colour of population variations (Paper II), and response to landscape structure (Papers III and IV). For fast-responding populations, the degree of synchrony of population variations was similar to the synchrony of environmental noise (Paper II). Local populations of a model organism that responded slowly to environmental variation were more synchronized than the environmental variation itself, and the largest shift between the environment and the populations was seen for intermediate red noise colours (Paper II). This indicated that dispersal-induced population synchrony could be enhanced by reddened noise.

Landscape configuration proved to be important for the general levels of extinction risk. This effect was most pronounced for fast-responding populations (Papers III and IV) and became even more distinct when distance-dependent synchrony was added between the environmental variations (Paper IV). Adding explicit landscapes led to an decrease in the differences between fast- and slow-responding populations, when considering the influence of noise colour on extinction risk. Also, landscape configuration affected the importance of degree of synchrony through its impact on distances between patches, which resulted in configurations where extinction risk depended solely on noise colour. The effects on stability exerted by populations embedded in food webs were investigated in an implicit landscape model (Paper V). Three types of food webs with different properties of inherent stability all showed a decrease in stability at increased environmental variance and increased redness of environmental variation.

In conclusion, the single-species models showed that the survival conditions of populations that were near extinction were improved by all of the following: decreased synchrony, reddening of noise, and aggregation of patches. The results of the web simulations indicate that we need better understanding of how findings obtained using single-species models can be used to reveal the effects of noise colour on species communities. From a management perspective, altering landscape structure may compensate for increased extinction risks caused by changed noise colour of environmental variation, which is a predicted outcome of climate change.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2012. , 31 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1416
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-72951ISBN: 9789173930017 (print)OAI: oai:DiVA.org:liu-72951DiVA: diva2:464041
Public defence
2012-01-13, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2017-12-15Bibliographically approved
List of papers
1. Spectral Color, Synchrony and Extinction Risk
Open this publication in new window or tab >>Spectral Color, Synchrony and Extinction Risk
2012 (English)In: THEORETICAL ECOLOGY, ISSN 1874-1738, Vol. 5, no 4, 545-554 p.Article in journal (Refereed) Published
Abstract [en]

The autocorrelation of environmental variation, also called noise color, influences the population dynamics and the probability of extinction risk. Increasing the distance, the variations over time for two sites will become more unsynchronized. Thus, both degree of synchrony and noise color are parts of the same environmental variation affecting population dynamics in a spatial setting. We present a novel method of generating environmental noise controlling for its noise color and synchrony. We apply these time series to carrying capacity (K) or (indirectly) to growth rate (r), and altered the population regulation response between over- and under-compensatory. A novel finding is that the qualitative effects of noise color on extinction risk do not differ with degree of synchrony. Our results for highly responsive dynamics (large growth rates and overcompensatory dynamics) agree with previous non-spatial studies by showing that the redder the noise, the lower the extinction risk. The results for less responsive dynamics are more complex, indicating that intermediate noise color causes a larger extinction risk compared to whiter or redder color. To explain this hump-shaped response, we use classical descriptions of how means and variances of population density depend on noise color. These results allow a new straightforward interpretation of how extinction risk depends on population dynamics, noise color, and synchrony.

Place, publisher, year, edition, pages
Springer, 2012
Keyword
Noise color; synchrony; extinction risk; subdivided population; temporal correlation; spatial model
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72942 (URN)10.1007/s12080-011-0145-x (DOI)000309879100006 ()
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2012-11-19Bibliographically approved
2. Biological Filtering of Noise Colour and Synchrony
Open this publication in new window or tab >>Biological Filtering of Noise Colour and Synchrony
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Environmental variation is a major force driving fluctuations in population densities. Here, we investigated the impact of such variation on population dynamics by studying noise color and synchrony of environmental variation compared to noise color and synchrony of variation of local population densities. We used Ricker models with over- or undercompensatory density-dependent regulation, and local populations were connected by dispersal. For both noise color and synchrony, we measured the shift between environmental variation and fluctuations in population densities. We also analyzed how the shifts were affected by dispersal rate and type of density regulation. Populations with undercompensatory dynamics showed the classical picture of increasing positive shifts in synchrony with increasing dispersal rates. The color of the environmental variation also affected the positive shift in synchrony, which was increased by reddened noise in populations with undercompensatory dynamics. Populations with overcompensatory dynamics showed no shifts in synchrony regardless of dispersal rates. Shifts in noise color exhibited the same pattern: populations with overcompensatory dynamics displayed only minor shifts in noise color, whereas those with undercompensatory dynamics had distinct positive shifts that increased with dispersal rates and also depended on the degree of synchrony. These findings demonstrate that noise color and synchrony are determined by and equal to synchrony and close to the color of environmental variation in populations with overcompensatory dynamics, but differ from the corresponding aspects of environmental variation in populations with undercompensatory dynamics. The shifts in populations with undercompensatory dynamics are determined by several factors: degree of population responsiveness, dispersal rates, and both the color and synchrony of environmental variation.

Keyword
Noise color; synchrony; correlated fluctuations; biological filtering; spatially subdivided
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72944 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2011-12-12Bibliographically approved
3. Effects of Noise Color and Synchrony on Extinction Risk in Patchy Environments
Open this publication in new window or tab >>Effects of Noise Color and Synchrony on Extinction Risk in Patchy Environments
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We studied interplay between landscape configuration and two characteristics known to affect population extinction risks: environmental fluctuations and population dynamics. Specifically, we tested effects of noise colour (i.e. the temporal autocorrelation) and the synchrony (i.e. spatial correlation) of environmental fluctuations by simulations using models of populations with overor undercompensatory dynamics. The results demonstrated that landscape configuration has a profound effect on extinction risks. Interaction between landscape configuration and environmental fluctuations was seen as stronger effects of noise colour (decreased extinction risk with increased redness) in random landscapes and more evident effects of synchrony in aggregated landscapes. The impact of landscape structure was more striking for over- than undercompensatory dynamics; showing strongly reduced extinction risk in aggregated landscapes compared to random configurations. Results on extinction risks using data on geographical positions of old oaks (Quercus robur) concurred with those of generated landscapes. Our findings indicate that a population on the limits of its existence is extremely sensitive to both spatial configuration and temporal variation of resources. The results underline that there are no shortcuts in ecology. Correct characterization of landscape configuration, environmental fluctuations, and population dynamics is necessary when estimatin  and analysing the causes of extinction risks.

Keyword
Noise colour; environmental noise; synchrony; landscape configuration; patch aggregation; oak landscape; metapopulation; extinction risk
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72945 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2016-08-31Bibliographically approved
4. The Importance of Distance-Dependent Synchrony of Coloured Noise
Open this publication in new window or tab >>The Importance of Distance-Dependent Synchrony of Coloured Noise
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Local populations in patches close to each other would probably be influenced by similar environmental conditions. When increasing the distance between the patches the local population will experience less synchronized environments. Since, the degree of synchrony is important for the overall extinction risk it is probably likewise important to include distance dependence in environmental variation when studying environmental forcing on spatially subdivided populations. Thus, we will investigate the importance of including such distance dependent synchrony when studying coloured environmental variation applied to populations in explicit landscapes. We will introduce a method based on controlling the phases when generating 1/fnoise. The results showed large differences between fast or slow density regulation responses in populations. Extinction risk was several magnitudes larger when including distance dependent synchrony compared to randomly distributing environmental time series for overcompensatory dynamics. There was one exception; it is not necessary to include distance dependent synchrony for landscape with random patch distribution. For undercompensatory dynamics the effect from distant dependent synchrony was only apparent in the most aggregated patch  configurations.

Keyword
Synchrony; distance dependence; landscape; patch configuration; noise colour; extinction risk; environmental noise; metapopulation
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72946 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2016-08-31Bibliographically approved
5. Stability patterns of spatial food webs in coloured environments
Open this publication in new window or tab >>Stability patterns of spatial food webs in coloured environments
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In times when climate change is expected to cause an increased environmental variability it is important to understand how species respond to disturbances. We explore how the stability of species respond to changes in environmental noise by introducing noise colour to different spatial and multi-trophic model systems: (1) a diamond shaped food web with stable oscillations, (2) a stabilized diamond shaped food web, and (3) a food web with stable dynamics. We conclude that adding space and additional trophic levels makes species response to environmental noise colour consistent. All three food webs and species decreased in stability with increased redness, positive temporal autocorrelation, of the environmental noise. Hence, interactions between noise colour and species responsiveness previously found in single- and multi-species models were not found when comparing more natural food webs differing in stability properties. When adding a spatial dimension, all food webs and species increased in stability. Both the diamond shaped and the stabilized diamond shaped food web were significantly more stable than the food web with more typical stable dynamics when existing in a variable and spatial setting. The major route to explain stability and the existence of a diverse world may then be the variable and spatial complexity of nature.

Keyword
Coloured environmental noise, dispersal, food web, stability, subpopulation, synchrony
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72947 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2011-12-12Bibliographically approved

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