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Weighted species richness outperforms species richness as predictor of biotic resistance
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. (Arcum)
Swedish University of Agriculture Sciences, Department of Forest Vegetation Ecology.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2016 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 1, 262-271 p.Article in journal (Refereed) Published
Abstract [en]

The species richness hypothesis, which predicts that species-rich communities should be better at resisting invasions than species-poor communities, has been empirically tested many times and often poorly supported. In this paper we contrast the species richness hypothesis with four alternative hypotheses with the aim of finding better descriptors of invasion resistance. These alternative hypotheses state that resistance to invasions is determined by abiotic conditions, community saturation (i.e., the number of resident species relative to the maximum number of species that can be supported), presence/absence of key species, or weighted species richness. Weighted species richness is a weighted sum of the number of species, where each species' weight describes its contribution to resistance. We tested these hypotheses using data on the success of 571 introductions of four freshwater fish species into lakes throughout Sweden (i.e., Arctic char (Salvelinus alpinus), tench (Tinca tinca), zander (Sander lucioperca), and whitefish (Coregonus lavaretus)). We found that the weighted species richness best predicted invasion success. The weights describing the contribution of each resident species to community resistance varied considerably in both strength and sign. Positive resistance weights, which indicate that species repel invaders, were as common as negative resistance weights, which indicate facilitative interactions. This result can be contrasted with the implicit assumption of the original species richness hypothesis, that all resident species have negative effects on invader success. We argue that this assumption is unlikely to be true in natural communities, and thus that we expect that weighted species richness is a better predictor of invader success than the actual number of resident species.

Place, publisher, year, edition, pages
2016. Vol. 97, no 1, 262-271 p.
Keyword [en]
biotic resistance, freshwater fish, species identity, species richness, saturation, weighted species richness
National Category
URN: urn:nbn:se:umu:diva-110249DOI: 10.1890/15-0463.1ISI: 000369852600027OAI: diva2:861759
Available from: 2015-10-19 Created: 2015-10-19 Last updated: 2016-06-20Bibliographically approved
In thesis
1. Biotic resistance in freshwater fish communities
Open this publication in new window or tab >>Biotic resistance in freshwater fish communities
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Invasions of non-native species cause problems in ecosystems worldwide, and despite the extensive effort that has been put into research about invasions, we still lack a good understanding for why some, but not other, communities resist these invasions. In this doctoral thesis I test hypotheses on biotic resistance using a large dataset of more than 1000 both failed and successful introductions of freshwater fish into Swedish lakes. We have found that the classic species richness hypothesis is a poor descriptor of introduction success because it fails to acknowledge that resident species contribute to the resistance in different ways. We developed a new measure of biotic resistance, the weighted species richness, which takes into account that the resident species contributes to the resistance with different strength and sign. Further, we correlated performance traits of species in their role as an invader and as a resident species to predict how the biotic resistance of these communities would develop over time. We found a positive correlation between performance traits: Some species have high introduction success, they make a large contribution to the resistance, and they cause extinctions when introduced but do not go extinct themselves when other species establishes, whereas other species are weak performers in these respects. Thus, the biotic resistance of these communities should grow stronger as non-native species accumulates. These results give us clues about what type of communities that should be most sensitive to further invasions, i.e., communities harboring species weak performers. 

My results show that the biotic resistance of communities is an important factor in determining invasibility of a community. They also show that methods for quantifying resistance must take into account how interactions are structured in nature. What determine the biotic resistance of a community is the type of interactions that the resident species have with the invader and not the species richness of the community.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 26 p.
biotic resistance, freshwater fish, introductions, invasions, invasion success, invasibility, invasiveness, species richness, saturation, species identity, weighted species richness
National Category
urn:nbn:se:umu:diva-110251 (URN)978-91-7601-326-7 (ISBN)
Public defence
2015-11-12, Naturvetarhuset, N320, Umeå, 10:00 (English)
Available from: 2015-10-22 Created: 2015-10-19 Last updated: 2015-11-13Bibliographically approved

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Henriksson, AnnaYu, JunTrygg, JohanEnglund, Göran
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