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Competition, Coexistence and Character Displacement: In a Young Avian Hybrid Zone
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal Ecology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the ecological and evolutionary implications of a recent secondary contact between two closely related bird species: collared (Ficedula albicollis) and pied (F. hypoleuca) flycatchers. Collared flycatchers started to colonize the Swedish island of Öland, where pied flycatchers were already present, in the late 1950s-early1960s. My major aims were to investigate which factors are acting against versus for long-term coexistence between the two species. Specifically, I investigated the relative importance of allopatric divergence, interspecific competition, hybridization and learning in promoting or inhibiting coexistence. The combined effects of interspecific competition and hybridization drives pied flycatchers towards local extinction in their preferred deciduous habitat. However, my results also show that pied flycatchers are better able to tolerate harsh environmental conditions. This trade-off between competitive ability and resilience in the face of harsh conditions facilitates a regional coexistence between the species. Coexistence is furthermore favoured by competition-mediated divergence in breeding habitat choice, timing of breeding and male breeding plumage colouration. Due to interspecific competition, male pied flycatchers are forced to breed in a more mixed forest type with a later peak in food abundance, which is accompanied by a divergence in breeding time between the two species. In areas shared with collared flycatchers, male pied flycatchers with brown plumage coloration, most divergent from that of collared flycatchers, are favoured by selection. In addition to facilitating coexistence, the observed shift in habitat occupancy increases reproductive isolation between the two species. By using cross-fostering experiments I demonstrate that natal habitat imprinting has the potential to additionally speed up habitat segregation. Finally I show that hybrid nestlings express an intermediate response to harsh environments, indicating that another aspect of ecological-based selection may be important in reproductive isolation between the species. In summary, my results show that adaptations during historic allopatry are important both in facilitating coexistence as well as in providing a foundation for further ecological divergence at secondary contact. This is of relevance today as many species are shifting their distributions in response to habitat disturbance and global warming.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 37 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 842
Keyword [en]
Competition, coexistence, hybridization, ecological speciation, character displacement, pied flycatcher, collared flycatcher
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:uu:diva-157146ISBN: 978-91-554-8129-2 (print)OAI: oai:DiVA.org:uu-157146DiVA: diva2:435140
Public defence
2011-09-30, Lindahlsalen, Evolutionary Biology Centre (EBC), Norbyvägen 18, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2011-09-08 Created: 2011-08-17 Last updated: 2011-11-03Bibliographically approved
List of papers
1. Combined effects of interspecific competition and hybridization impede local coexistence of Ficedula flycatchers
Open this publication in new window or tab >>Combined effects of interspecific competition and hybridization impede local coexistence of Ficedula flycatchers
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2012 (English)In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 26, no 4, 927-942 p.Article in journal (Refereed) Published
Abstract [en]

At secondary contact closely related species may both compete over similar resources and/or hybridize. Simulation models suggest that hybridization increases the risk of extinction beyond the risk resulting from interspecific competition alone, but such combined effects are rarely studied empirically. Here, we use detailed records on pairing patterns, breeding success, local recruitment and immigration collected during 8 years (2002-2009) to investigate the underlying mechanism of the rapid displacement of pied flycatchers by collared flycatchers on the Swedish island of A-land. We found no differences in average reproductive success or reproductive lifespan between the two species. However, we show that young male pied flycatchers failed to establish new territories as the density of male collared flycatchers increased. In addition, as the relative frequency of collared flycatchers increased, the risk of hybridization dramatically increased for female pied flycatchers, which speeds up the exclusion process since there is a high fitness cost associated with hybridization between the two species. In a nearby control area, within the same island, where pied flycatchers breed in the absence of collared flycatchers, no decline in the number of breeding pairs was observed during the same period of time. Our results demonstrate the crucial importance of studying the combined effects of various types of heterospecific interactions to understand and predict the ecological and evolutionary implications of secondary contact between congeneric species. These findings are particularly interesting in the light of recent climate change since the expected range shifts of many taxa will increase competitive and sexual interactions between previously separated species.

Keyword
Competition, Coexistence, Extinction, Hybridization, Reproductive interference
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-157138 (URN)10.1007/s10682-011-9536-0 (DOI)000305218900011 ()
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
2. Life-history divergence facilitates regional coexistence of competing Ficedula flycatchers
Open this publication in new window or tab >>Life-history divergence facilitates regional coexistence of competing Ficedula flycatchers
2009 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 7, 1948-1957 p.Article in journal (Refereed) Published
Abstract [en]

Regional coexistence of ecologically similar species is facilitated when fluctuations in environmental conditions favor different species at different times or places. However, why species with similar ecology should vary in their response to environmental change is unclear. In this study, we explore the role of a life-history divergence in causing changes in relative fitness across environmental conditions experienced by populations of two closely related Ficedula flycatchers on the Baltic island of Oland, Sweden. We compared patterns of nestling survival between Pied (Ficedula hypoleuca) and Collared (F. albicollis) Flycatchers in relation to two factors known to influence the environment experienced by nestlings: natural variation in their parents' onset of breeding and artificial manipulation of the brood size. Possible differences in the location of the nests (i.e., microhabitat differences) or in habitat use (i.e., feeding patterns) by the adult birds were controlled for by partial cross-fostering of young between the two species. We found that nestling mortality was relatively higher among Collared Flycatchers and that this difference increased with later breeding. Mass gain, which predicted survival probability, of nestling Collared Flycatchers did not respond to the seasonal decline in environmental conditions when they were raised in nests with reduced brood size (i.e., where sibling competition was experimentally reduced). This latter result suggests that the smaller clutch size of Collared Flycatchers reflects an adaptive adjustment to their offspring's higher sensitivity to environmental change. We discuss the possibility that the divergence in life-history traits between the two species represents adaptation to different environments experienced during their recent evolutionary history. We conclude that the survival of nestling Collared Flycatchers is more sensitive to harsh environment and that this is likely to limit where and when the more aggressive Collared Flycatchers are able to displace Pied Flycatchers. Our results provide support for models of species coexistence that emphasize the importance of spatial or temporal heterogeneity in relative fitness or life-history divergence. More precisely, our results demonstrate that variation in life-history adaptations may result in changes in relative fitness of species across environments despite their use of similar resources.

Keyword
coexistence, competitive exclusion, Ficedula, flycatcher, life history, Oland, Sweden, relative fitness, reproductive interference, species distributions
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-128398 (URN)000267745800023 ()
Available from: 2010-07-23 Created: 2010-07-20 Last updated: 2017-12-12Bibliographically approved
3. Life-history divergence and environmentally dependent relative fitness of hybrid nestlings in Ficedula flycatchers.
Open this publication in new window or tab >>Life-history divergence and environmentally dependent relative fitness of hybrid nestlings in Ficedula flycatchers.
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:uu:diva-157143 (URN)
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2011-11-03
4. Positive feedback between ecological and reproductive character displacement in a young avian hybrid zone
Open this publication in new window or tab >>Positive feedback between ecological and reproductive character displacement in a young avian hybrid zone
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2012 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 66, no 4, 1167-1179 p.Article in journal (Refereed) Published
Abstract [en]

Character displacement can reduce costly interspecific interactions between young species. We investigated the mechanisms behind divergence in three key traits—breeding habitat choice, timing of breeding, and plumage coloration—in Ficedula flycatchers. We found that male pied flycatchers became expelled from the preferred deciduous habitat into mixed forest as the superior competitor, collared flycatchers, increased in numbers. The peak in food abundance differs between habitats, and the spatial segregation was paralleled by an increased divergence in timing of breeding between the two species. Male pied flycatchers vary from brown to black with brown coloration being more frequent in sympatry with collared flycatchers, a pattern often proposed to result from selection against hybridization, that is, reinforcement. In contrast to this view, we show that brown male pied flycatchers more often hybridize than black males. Male pied flycatcher plumage coloration influenced the territory obtained in areas of co-occurrence with collared flycatchers, and brown male pied flycatchers experienced higher relative fitness than black males when faced with heterospecific competition. We suggest that allopatric divergence in resource defense ability causes a feedback loop at secondary contact where male pied flycatchers with the most divergent strategy compared to collared flycatchers are favored by selection.

Keyword
Collared flycatcher, ecological character displacement, pied flycatcher, reinforcement, reproductive character displacement, sexual isolation, speciation
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-157144 (URN)10.1111/j.1558-5646.2011.01518.x (DOI)000302546700016 ()
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
5. Learning the hard way: imprinting can enhance enforced shifts in habitat choice
Open this publication in new window or tab >>Learning the hard way: imprinting can enhance enforced shifts in habitat choice
2011 (English)In: International Journal of Ecology, ISSN 1687-9708, E-ISSN 1687-9716, 287532Article in journal (Refereed) Published
Abstract [en]

We investigated the potential importance of learning in habitat choice within a young hybrid zone of two closely related speciesof birds. Pied flycatchers (Ficedula hypoleuca) are being excluded from deciduous habitats into a mixed forest type by collaredflycatchers (F. albicollis). We investigated whether this enforced habitat shift influenced reproductive isolation between the twospecies, and, by cross-fostering nestlings, we tested whether learning may lead to a corresponding shift in habitat choice inconsecutive generations. Our results show that the majority of the recruits, even if translocated across different habitat types,return to breed in the area where they were fostered. As male pied flycatchers were more likely to hybridize in the originallypreferred habitat, we argue that early imprinting on an alternate habitat can play an important role in increasing reproductiveisolation and facilitate regional coexistence between species experiencing secondary contact.

National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-157145 (URN)10.1155/2011/287532 (DOI)
Funder
Swedish Research CouncilEU, European Research Council
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved

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