Tag Archives: area

Investigating the Small Island Effect

Image Credit: Dmitry Teslya, CC BY 2.0, Image Cropped

Species-area relationships on small islands differ among plant growth forms (2020) Schrader et al., Global Ecology and Biogeography, https://doi.org/10.1111/geb.13056

The Crux

We’ve talked a lot about Island Biogeography Theory (IBT) in the last couple of weeks. One of the key tenets, established way back in the 60s, is that as an island’s area decreases, its species richness tends to as well. Yet since IBT was conceptualised, there have been a number of amendments made to it. The Small Island Effect (SIE) is one of them.

SIE essentially means that below a certain threshold (called a ‘breakpoint’), species stop obeying that species richness to area relationship. This week’s researchers wanted to test whether that breakpoint was different between species groups, and whether the species area relationship changed below that breakpoint, or simply disappeared.

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Going Beyond Range Size in Analysing Extinction Risk

Animals of wildly different sizes may have different likelihoods of extinction, but it could all depend on their range sizes (Image Credit: Harvey Barrison, CC BY-SA 2.0, Image Cropped)

Constraints on vertebrate range size predict extinction risk (2019) Newsome et al., Global Ecology and Biogeography, http://doi/epdf/10.1111/geb.1309

The Crux

To act to prevent a species going extinct, we have to know that it’s at risk of extinction. Ecologists and conservationists simply don’t have the time or resources to make sure that all species remain safe. So having reliable methods of predicting species extinction risk is crucial.

On a global scale, the relationship between a species size and the area that it is found in (geographical range) has been studied intensively since ecology’s inception, both in existing and prehistoric species. Initial research showed that in general, the larger a species is, the larger its range size needed to be, with large species that had relatively smaller range sizes more prone to extinction. However more recent work has shown (naturally) that there are exceptions to this, with mammals viable range size actually decreasing up to a certain ‘breakpoint’, after which the size grows again.

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