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Mass extinctions do not explain skew in interspecific body size distributions
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Department of Biology, Oulu University, 90014, Oulu, Finland.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2013 (English)In: Journal of Zoological Systematics and Evolutionary Research, ISSN 0947-5745, E-ISSN 1439-0469, Vol. 51, no 1, 13-18 p.Article in journal (Other academic) Published
Abstract [en]

In several higher animal taxa, such as mammals and birds, the distribution of species’ body sizes is heavily skewed towards small size. Previous studies have suggested that small-bodied organisms are less prone to extinction than large-bodied species. If small body size is favorable during mass extinction events, a post mass extinction excess of small-bodied species may proliferate and maintain skewed body size distributions afterwards. Here, we modeled mass extinctions, and found that even unrealistically strong body mass selection has little effect on the skew of interspecific body size distributions. Counter intuitively, selection against large body size may skew size distributions towards large body size. Subsequent evolutionary diversification rapidly erases the rather small effects mass extinctions may have on size distributions. Next, we tested whether skewed body size distributions in mammals and birds can be due to mass extinctions at the transition from Cretaceous to Paleogene, approximately 65 million years ago. Body size distributions of clades that originated during the Cretaceous are on average more skewed than their subclades that originated during the Paleogene, but the difference is only minor in mammals, and in birds it can be explained by a positive relationship between species richness and skewness that is also present in clades that originated after the transition. Hence, we cannot infer from extant species whether the K-Pg mass extinctions were size-selective, but they are not the reason why most extant bird and mammal species are small-bodied.

Place, publisher, year, edition, pages
2013. Vol. 51, no 1, 13-18 p.
Keyword [en]
body-size skew, Cretaceous-Paleogene, extant species, macroevolution, phylogeny
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:umu:diva-49755DOI: 10.1111/jzs.12002ISI: 000313753400002OAI: oai:DiVA.org:umu-49755DiVA: diva2:457129
Available from: 2011-11-17 Created: 2011-11-16 Last updated: 2017-12-08Bibliographically approved
In thesis
1. The tempo and mode of evolution: a neontological reappraisal
Open this publication in new window or tab >>The tempo and mode of evolution: a neontological reappraisal
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The theory of “punctuated equilibrium” suggests that species evolve rapidly during or immediately upon speciation, “punctuating” long periods of little or no morphological evolution. Here I confirm that body size differences within clades of birds and mammals are best explained using a model of punctuated evolution. This allows me to suggest that rates of speciation and extinction are responsible for why there are more small mammals than large, as large mammals likely speciate and go extinct at a higher rate than small mammals, and hence undergo cladogenetic change more often. Likewise, mammals appear to evolve at a higher rate than birds, because mammals, as a whole, speciate and go extinct at a higher rate than birds. Furthermore I show that mass extinctions and competition, i.e. forms of natural selection, do not seem to explain differences in body size between species on a macroevolutionary scale. Taken together, these findings not only contradict the idea that apparently different rates of evolution are due to differential selection intensities, and emphasize the importance of the speciation process in evolution, but raise the intriguing question as to what limits evolution in established species. Here I suggest that phenotypic traits, dependent on one another for development and/or function may constrain evolution by exerting stabilizing selection from within the organism, as opposed to external environmental selection, which has been the main focus of evolutionary studies thus far.

Abstract [sv]

Teorin om "punkterad jämvikt" säger att arter utvecklas snabbt under och omedelbart efter artbildning, vilket "punkterar" långa perioder med lite eller ingen morfologisk föränding. I den här avhandlingen visar jag att skillnader i kroppsstorlek inom klader (grupp med gemensam förfader) hos fåglar och däggdjur förklaras bäst när man använder en modell med punkterad evolution. Detta gör i sin tur att jag kan föreslå att hastigheten var med artbildning och utdöende sker, förklarar varför det finns fler små däggdjur än stora, eftersom stora däggdjur sannolikt bildar nya arter och dör ut med en högre hastighet än små däggdjur. Likaså förefaller däggdjur i sin helhet att evolvera med en högre hastighet än fåglar, detta eftersom däggdjur bildar nya arter och dör ut med en högre hastighet än fåglar. Dessutom visar jag att massutdöenden och konkurrens (naturlig selektion) inte verkar förklara skillnader mellan arter över makroevolutionära skalor (över geologisk tid). Sammantaget motsäger dessa resultat inte bara idén om att skenbart olika hastighet på evolution främst beror på skillnader i selektionstryck utan understryker också vikten av artbildningsprocessen som en viktig faktor som styr evolutionens hastighet. Dessutom leder dessa resultat till frågan om vad som begränsar evolutionen hos redan etablerade arter. Här föreslår jag att fenotypiska karaktärsdrag som är beroende av varandra för sin funktion och utveckling kan begränsa evolutionen genom att utöva stabiliserande selektion inifrån organismen, i motsats till selektion från den omgivande miljön vilket har varit fokus för de flesta evolutionära studier hittills.

Place, publisher, year, edition, pages
Umeå: Institutionen för ekologi, miljö och geovetenskap, Umeå Universitet, 2011. 38 p.
Keyword
birds, extinction, macroevolution, mammals, microevolution, punctuated equilibrium, speciation
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:umu:diva-49761 (URN)978-91-7459-306-8 (ISBN)
Public defence
2011-12-09, KBC-huset, KB3A9, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-11-18 Created: 2011-11-17 Last updated: 2011-11-17Bibliographically approved

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Monroe, Melanie J.Bokma, Folmer

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