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Population-level consequences of variation
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (EEMiS/Evolutionary Ecology group)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Consequences of within population variation have recently attracted an increased interest in evolutionary ecology research. Theoretical models suggest important population-level consequences, but many of these predictions still remain to be tested. These issues are important for a deepened understanding of population performances and persistence, especially in a world characterized by rapid fragmentation of natural habitats and other environmental changes.

I review theoretical models of consequences from intra population genetic and phenotypic variation. I find that more variable populations are predicted to be characterized by broader resource use, reduced intraspecific competition, reduced vulnerability to environmental changes, more stable population dynamics, higher invasive potential, enhanced colonization and establishment success, larger distribution ranges, higher evolvability, higher productivity, faster population growth rate, decreased extinction risk, and higher speciation rate, compared with less variable populations.

To test some of these predictions I performed experiments and compared how different degree of colour polymorphism influences predation risk and establishment success in small groups. My comparisons of predation risk in mono- and polymorphic artificial prey populations showed that the risk of being eaten by birds does not only depend on the coloration of the individual prey item itself, but also on the coloration of the other members of the group. Two experiments on establishment success in small founder groups of

Tetrix subulata pygmy grasshoppers with different degree of colour morph diversity show that establishment success increases with higher degree of diversity, both under controlled conditions in outdoor enclosures and in the wild. These findings may be important for re-stocking of declining populations or re-introductions of locally extinct populations in conservation biology projects.

I report on remarkably rapid evolutionary shifts in colour morph frequencies in response to the changed environmental conditions in replicated natural populations of pygmy grasshoppers in fire ravaged areas. This finding

1

illustrates the high adaptive potential in a polymorphic species, and indicates the importance of preserved within-species diversity for evolutionary rescue.

Finally, I review if theoretical predictions are supported by other published empirical tests and find strong support for the predictions that more variable groups benefit from reduced vulnerability to environmental changes, reduced population fluctuations and extinction risk, larger distribution ranges, and higher colonization or establishment success.

In conclusion, my thesis illustrates how within-population variation influences ecological and evolutionary performances of populations both in the short and long term. As such, it emphasizes the need for conservation of biodiversity also within populations.

Place, publisher, year, edition, pages
Kalmar: Linnaeus University Press, 2012. , 53 p.
Series
Linnaeus University Dissertations, 105
Keyword [en]
colour polymorphism, diversity, establishment success, evolutionary changes, population-level consequences, predation risk, Tetrix subulata, variation
National Category
Evolutionary Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
URN: urn:nbn:se:lnu:diva-32522ISBN: 978-91-86983-90-1 (print)OAI: oai:DiVA.org:lnu-32522DiVA: diva2:699294
Public defence
2012-12-14, Fullriggaren, Linnéuniversitetet, Landgången 4, Kalmar, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2014-03-27 Created: 2014-02-27 Last updated: 2014-12-19Bibliographically approved
List of papers
1. Population-level consequences of polymorphism, plasticity and randomized phenotype switching: a review of predictions
Open this publication in new window or tab >>Population-level consequences of polymorphism, plasticity and randomized phenotype switching: a review of predictions
2012 (English)In: Biological Reviews, ISSN 1464-7931, E-ISSN 1469-185X, Vol. 87, no 3, 756-767 p.Article, review/survey (Refereed) Published
Abstract [en]

The consequences of among-individual phenotypic variation for the performance and ecological success of populations and species has attracted growing interest in recent years. Earlier reviews of this field typically address the consequences for population processes of one specific source of variation (plasticity or polymorphism), or consider one specific aspect of population performance, such as rate of speciation. Here we take a broader approach and study earlier reviews in order to summarize and compare predictions regarding several population-level consequences of phenotypic variation stemming from genetic polymorphism, developmental plasticity or randomized phenotype switching. Unravelling cause-dependent consequences of variation may increase our ability to understand the ecological dynamics of natural populations and communities, develop more informed management plans for protection of biodiversity, suggest possible routes to increased productivity and yield in natural and managed biological systems, and resolve inconsistencies in patterns and results seen in studies of different model systems. We find an overall agreement regarding the effects of higher levels of phenotypic variation generated by different sources, but also some differences between fine-grained and coarse-grained environments, modular and unitary organisms, mobile and sessile organisms, and between flexible and fixed traits. We propose ways to test the predictions and identify issues where current knowledge is limited and future lines of investigation promise to provide important novel insights.

National Category
Ecology Evolutionary Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-18042 (URN)10.1111/j.1469-185X.2012.00231.x (DOI)2-s2.0-84863551441 (Scopus ID)
Available from: 2012-03-16 Created: 2012-03-16 Last updated: 2017-12-07Bibliographically approved
2. Does colour polymorphism enhance survival of prey populations?
Open this publication in new window or tab >>Does colour polymorphism enhance survival of prey populations?
2009 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 276, no 1665, 2187-2194 p.Article in journal (Refereed) Published
Abstract [en]

That colour polymorphism may protect prey populations from predation is an old but rarely tested hypothesis. We examine whether colour polymorphic populations of prey exposed to avian predators in an ecologically valid visual context were exposed to increased extinction risk compared with monomorphic populations. We made 2976 artificial pastry prey, resembling Lepidoptera larvae, in four different colours and presented them in 124 monomorphic and 124 tetramorphic populations on tree trunks and branches such that they would be exposed to predation by free-living birds, and monitored their 'survival'. Among monomorphic populations, there was a significant effect of prey coloration on survival, confirming that coloration influenced susceptibility to visually oriented predators. Survival of polymorphic populations was inferior to that of monomorphic green populations, but did not differ significantly from monomorphic brown, yellow or red populations. Differences in survival within polymorphic populations paralleled those seen among monomorphic populations; the red morph most frequently went extinct first and the green morph most frequently survived the longest. Our findings do not support the traditional protective polymorphism hypothesis and are in conflict with those of earlier studies. As a possible explanation to our findings, we offer a competing 'giveaway cue' hypothesis: that polymorphic populations may include one morph that attracts the attention of predators and that polymorphic populations therefore may suffer increased predation compared with some monomorphic populations.

National Category
Evolutionary Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-1963 (URN)10.1098/rspb.2009.0252 (DOI)
Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2015-09-04Bibliographically approved
3. Higher establishment success in more diverse groups of pygmy grasshoppers under seminatural conditions
Open this publication in new window or tab >>Higher establishment success in more diverse groups of pygmy grasshoppers under seminatural conditions
2012 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 12, 2519-2525 p.Article in journal (Refereed) Published
Abstract [en]

Large founder groups and habitat match have been shown to increase the establishment success of reintroduced populations. Theory posits that the diversity of founder groups should also be important, but this has rarely been investigated. Here, experimental introductions of color-polymorphic Tetrix subulata pygmy grasshoppers into outdoor enclosures were used to test whether higher phenotypic diversity promotes establishment success. We show that the number of individuals present one year after introduction increases with color morph diversity in founder groups. Variance in establishment success did not decrease with increasing founder diversity, arguing against an important contribution of sampling effects or evolutionary rescue. Color morphs in T. subulata covary with a suite of other functionally important traits and utilize different resources. The higher establishment success in more diverse founder groups may therefore result, in part, from niche complementarity. Variation in establishment among groups was not associated with differences among source populations in reproductive capacities.

Keyword
colonization, color morphs, conservation biology, establishment, phenotypic diversity, polymorphism, pygmy grasshopper, Tetrix subulata, translocation, variable founder groups
National Category
Developmental Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-24498 (URN)000312892500003 ()
Available from: 2013-02-22 Created: 2013-02-22 Last updated: 2017-12-06Bibliographically approved
4. Variation in founder groups promotes establishment success in the wild
Open this publication in new window or tab >>Variation in founder groups promotes establishment success in the wild
2012 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 279, no 1739, 2800-2806 p.Article in journal (Refereed) Published
Abstract [en]

Environmental changes currently pose severe threats to biodiversity, and reintroductions and translocations are increasingly used to protect declining populations and species from extinction. Theory predicts that establishment success should be higher for more variable groups of dissimilar individuals. To test this ‘diversity promotes establishment’ hypothesis, we introduced colour polymorphic pygmy grasshoppers (Tetrix subulata) to different sites in the wild. The number of descendants found at the release sites the subsequent year increased with increasing number of colour morphs in the founder group, and variation in founder groups also positively affected colour morph diversity in the established populations. Since colour morphs differ in morphology, physiology, behaviour, reproductive life history and types of niche used, these findings demonstrate that variation among individuals in functionally important traits promotes establishment success under natural conditions, and further indicate that founder diversity may contribute to evolutionary rescue and increased population persistence.

National Category
Ecology Evolutionary Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-18040 (URN)10.1098/rspb.2012.0174 (DOI)2-s2.0-84862152496 (Scopus ID)
Available from: 2012-03-16 Created: 2012-03-16 Last updated: 2017-12-07Bibliographically approved
5. Rapid evolution of fire melanism in replicated populations of pygmy grasshoppers
Open this publication in new window or tab >>Rapid evolution of fire melanism in replicated populations of pygmy grasshoppers
Show others...
2011 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 65, no 9, 2530-2540 p.Article in journal (Refereed) Published
Abstract [en]

Evolutionary theory predicts an interactive process whereby spatiotemporal environmental heterogeneity will maintain genetic variation, while genetic and phenotypic diversity will buffer populations against stress and allow for fast adaptive evolution in rapidly changing environments. Here, we study color polymorphism patterns in pygmy grasshoppers (Tetrix subulata) and show that the frequency of the melanistic (black) color variant was higher in areas that had been ravaged by fires the previous year than in nonburned habitats, that, in burned areas, the frequency of melanistic grasshoppers dropped from ca. 50% one year after a fire to 30% after four years, and that the variation in frequencies of melanistic individuals among and within populations was genetically based on and represented evolutionary modifications. Dark coloration may confer a selective benefit mediated by enhanced camouflage in recently fire-ravaged areas characterized by blackened visual backgrounds before vegetation has recovered. These findings provide rare evidence for unusually large, extremely rapid adaptive contemporary evolution in replicated natural populations in response to divergent and fluctuating selection associated with spatiotemporal environmental changes.

Keyword
Adaptation; biodiversity; coloration; environmental change; evolution; pigmentation pattern; polymorphism; Tetrix subulata
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-14033 (URN)10.1111/j.1558-5646.2011.01324.x (DOI)2-s2.0-80052269423 (Scopus ID)
Note

Article first published online: 9 MAY 2011

Available from: 2011-09-06 Created: 2011-09-06 Last updated: 2017-12-08Bibliographically approved
6. Strong support for predicted population-level consequences of diversity: a review of exeperimental and comparative studies
Open this publication in new window or tab >>Strong support for predicted population-level consequences of diversity: a review of exeperimental and comparative studies
(English)Manuscript (preprint) (Other academic)
Keyword
colonization, distribution range, diversity, establishment, extinction risk, genetic polymorphism, population dynamics, population-level consequences
National Category
Evolutionary Biology
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-32520 (URN)
Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2015-09-04Bibliographically approved

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