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Archive for September, 2010

Fire and evolution: Cretaceous fires and the spread of angiosperms

September 9th, 2010 1 comment

Recently we have highlighted the importance of wildfires in the evolution of plants in many ecosystems worldwide [1 | previous post]. In this line, a recent paper by Bond & Scott suggest that the spread of angiosperms in the Cretaceous (145-65 Ma) was promoted by the development of novel fire regimes linked to the evolution of novel, highly productive (and flammable) plants. They suggest that Creatceous angiosperms were similar to current ruderal (weedy) species, i.e., short, with high maximum photosynthetic rates, rapid reproduction and small seeds. This fast-growing angiosperms would not only compete with regenerating gymnosperms, but would also rapidly accumulate fuel. More fuel would promote more frequent fires, which would help to maintain open habitats in which rapid growth traits of angiosperms would be most favoured, promoting rapid fuel accumulation. The authors emphasize the similitude of this "angiosperm–fire cycle" with  the grass fire-cycle that helped to spread C4 grasses in the Miocene (c. 8 Ma) [3] and with the grass fire-cycle replacing forests by invasive grasses in the modern world [4]. This would also imply that forest was slow to develop until the Eocene, when fire activity dropped to very low levels. This hypothesis could also help to explain the ancient origin of some fire traits like resprouting and the abundance and phylogenetically widespread examples of species with smoke-stimulated germination [1, 5]. In conclusion I think this is a nice and stimulating contribution to the evolution of angiosperms.

References

[1] Pausas J.G. & Keeley J.E. 2009. A Burning Story: The role of fire in the history of life. BioScience 59: 593-601. [doi | pdfpost | slides]

[2] Bond, W. J. and Scott, A. C. 2010. Fire and the spread of flowering plants in the Cretaceous. New Phytol. 188: 1137–1150 [doi]

[3] Keeley, J. E. and Rundel, P. W. 2005. Fire and the Miocene expansion of C4 grasslands. Ecol. Lett. 8: 1-8.

[4] D'Antonio, C. M. and Vitousek, P. M. 1992. Biological invasions by exotic grasses, the grass/fire cycle and global change. Annu. Rev. Ecol. Syst. 23: 63-87.

[5] Moreira B., Tormo J., Estrelles E., Pausas J.G. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Ann. Bot. 105: 627-635. [pdf | doi | blog]

Methods for community ecology

September 2nd, 2010 No comments

Why so many desert plant communities are dominated by spiny species, most of them cacti? The first observation refers to the community’s phenotypic structure and the second to its phylogenetic structure. What do these observations tell us about the mechanisms assembling these communities?

The way communities are assembled is an old ecological question currently experiencing renewed interest thanks to the recent advances in molecular biology and phylogenetics. The generality of these new methods has allowed us to understand the structure of communities of organisms from different kingdoms and at different scales. Concomitant with this growing interest, new methods, metrics, terms, and software have appeared that independently solve similar questions, but with different approaches. In this new paper we provide a unifying framework on methods for community structure based on the relationships between four key concepts: phylogeny, phenotype, environment, and co-occurrence. The different approaches are based on different community representations of traits, the phylogenetic relationships of species in the community, or species occurrence along the environmental gradients. We finally provide insights on future directions of this emerging discipline.

Pausas, J.G., Verdú, M. 2010. The jungle of methods for evaluating phenotypic and phylogenetic structure of communities. BioScience, 60: 614-625. [doi | pdf | slides]

Pausas-Verdu-BioScience

Figure 1. Methods for analyzing community structure can be represented in a simple framework in which the relationships (arrows) between the four key concepts (phylogeny, phenotype, environment, and co-occurrence) are integrated. The numbers in brackets refer to:

(1) Co-occurrence pattern versus the random expectation

(2) Phenotype-based approach:

(2.1) Relationship between the species' phenotypes and their co-occurrence (phenotypic community structure).

(2.2) Relationship between species response to the environment and the species phenotypes, controlling by the species' phylogenetic relatedness (phenotypic community structure).

(3) Phylogeny-based approach:

(3.1) Relationship between the species' phylogenetic relationships and their co-occurrence (phylogenetic community structure).

(3.2) Relationship between the species' phenotypes and their phylogenetic relationships (trait evolution).

(4) Environment-based approach: relationship between species response to the environment and the co-occurrence, considering the phylogenetic relatedness (phylogenetic community structure).

See previous post [link] on the effect of fire in phenotypic and phylogenetic structure of communities.

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