Propongo due tesi compilative, una di carattere biologico (a cui chiedo di essere coadiuvato da un biologo) e una di carattere botanico (a cui chiedo di essere coadiuvato da un botanico). Entrambe le tesi riguardano l’impatto della rapida diminuzione del ghiaccio marino artico sul biota della regione. Le due tesi compilative sono basate sue due articoli apparsi su Biology Letters nel 2016 e nel 2017. Gli studenti dovranno leggere l’articolo, capirlo, esaminare parte dei lavori citati, analizzarlo e, infine redigerne una sintesi scritta, integrandola necessariamente e obbligatoriamente con una propria valutazione critica autonoma. Di seguito le due tesi, insieme al rispettivo abstract dell’articolo.
1) Effetti della diminuzione del ghiaccio marino sulla flora della tundra artica
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Forchhammer M. 2017 Sea-ice induced growth decline in Arctic shrubs. Biol. Lett. 13: 20170122. http://dx.doi.org/10.1098/rsbl.2017.0122 Abstract Measures of increased tundra plant productivity have been associated with the accelerating retreat of the Arctic sea-ice. Emerging studies document opposite effects, advocating for a more complex relationship between the shrinking sea-ice and terrestrial plant productivity. I introduce an autoregressive plant growth model integrating effects of biological and climatic conditions for analysing individual ring-width growth time series. Using 128 specimens of Salix arctica, S. glauca and Betula nana sampled across Greenland to Svalbard, an overall negative effect of the retreating June sea-ice extent was found on the annual growth. The negative effect of the retreating June sea-ice was observed for younger individuals with large annual growth allocations and with little or no trade-off between previous and current year’s growth. |
2) La diminuzione del ghiaccio marino artico sta provocando la diminuzione degli orsi polari?
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Regehr EV et al. 2016 Conservation status of polar bears (Ursus maritimus) in relation to projected sea ice declines. Biol. Lett. 12: 20160556. http://dx.doi.org/10.1098/rsbl.2016.0556 Abstract Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range. We evaluated the potential response of polar bears to sea-ice declines by (i) calculating generation length (GL) for the species, which determines the timeframe for conservation assessments; (ii) developing a standardized sea-ice metric representing important habitat; and (iii) using statistical models and computer simulation to project changes in the global population under three approaches relating polar bear abundance to sea ice. Mean GL was 11.5 years. Ice-covered days declined in all subpopulation areas during 1979–2014 (median 21.26 days year21). The estimated probabilities that reductions in the mean global population size of polar bears will be greater than 30%, 50% and 80% over three generations (35–41 years) were 0.71 (range 0.20–0.95), 0.07 (range 0–0.35) and less than 0.01 (range 0–0.02), respectively. According to IUCN Red List reduction thresholds, which provide a common measure of extinction risk across taxa, these results are consistent with listing the species as vulnerable. Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of projections to different plausible assumptions. |