This is the finding of a new model developed by researchers from the University of Leeds and Imperial College London. The model could apply both to actual islands and isolated areas of habitat on the mainland that are home to unique species, such as the table top mountains of South America.
The natural history of islands is littered with examples of unusual species found only in one place, such as the Hawaiian Goose, Galapagos Tortoises and Dodo that may once have been common on their islands, but since human contact have become rare or even extinct. Now this new modelling approach shows that in general, most unique island species should be common on their island. If they are not, then the researchers believe human activity is most likely to be the cause.
"Models of island ecology have tended to focus on the total number of different species that you might expect to find on an island, rather than on how common or rare those species are and whether or not they are unique to the island," says Dr James Rosindell, of Leeds' Faculty of Biological Sciences. "Our model is able to predict the way that new species develop in isolation from the mainland as well as how many individuals of each species we could expect to see in their natural habitat. However, there is little data on population sizes and this highlights a real gap in knowledge that we need to fill."
To develop the model, the researchers collated data on bird species found across 35 islands and archipelagos. Modern genetics makes it possible to identify which species have diverged to create new species - so the team were able to test their model against actual data.
The model and data both show that whilst islands close to the mainland have no unique species, more distant islands tend to have unique species that are closely related to mainland species. Only the islands and archipelagos furthest from the mainland are expected to contain large numbers of unique species closely related to each other, such as Darwin's finches on the Galapagos and the Hawaiian honeycreepers.
"This model is still in its early stages of development, but we hope it will help to prompt more study of population sizes on islands," says Dr Albert Phillimore, from Imperial's Department of Life Sciences. "Comparing the predictions of different models to actual data can help us to identify where other factors are coming into play - such as additional ecological processes and human intervention. In the future, we plan to look at how the model could also help make predictions relevant to conservation strategy."
The work has been funded through an EPSRC research fellowship and an Imperial Junior Research Fellowship.
Sarah Calaghan, Ed White, John Colyer, Isuru Jayasinghe, BHF (Jan 2018), £128,308
Christine Foyer, HEFCE GCRF Grant (Jan 2018), £71,158
Alison Baker, HEFCE GCRF Grant (Jan 2018), £2,000
Graham Askew, Simon Walker, BBSRC (Jan 2018), £699,781
Jennifer Tomlinson, Royal Society (Jan 2018), £512,801
Alison Dunn, NERC (Dec 2017), £18,000
Jennifer Tomlinson, Royal Society-Research Fellows Enhancement Award (Dec 2017), £94,681
Helen Miller, AB AGri Grant (Dec 2017), £73,600
Simon Walker, Royal Society Enhancement Award (Dec 2017), £10,000
Carrie Ferguson, Bryan Taylor, Harry Rossiter, The Physiological Society (Dec 2017), £7,392
Ralf Richter, Royal Society (Dec 2017), £6,000
Christine Foyer, British Council Newton Fund (Dec 2017), £49,840
Adrian Whitehouse and colleagues in School of Chemistry and University of Liverpool, MRC (Nov 2017), £622,319
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Dave Lewis, British Council India (Nov 2017), £22,540
Elton Zeqiraj, Royal Society (Nov 2017), £15,000
Hannah Dugdale, Royal Society (Nov 2017), £15,000
Shaunna Burke, Cancer Research UK Innovation Grant (Nov 2017), £20,000
Alex O'Neill and colleagues in Chemistry, BBSRC (Nov 2017), £431,865
Jessica Kwok, Wings for Life (Nov 2017), £87,365
Tom Bennett, BBSRC (Oct 2017), £523,679
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Amanda Bretman and colleagues from UEA, NERC (Oct 2017), £430,886
Juan Fontana, Rosetrees Trust consumables grant (Oct 2017), £22,500
Helen Miller, DSM Nutritional Products AG (Sep 2017), £69,988
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Jamie Johnston, Physiological Society (Sep 2017), £10,000
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Vas Ponnambalam, Darren Tomlinson, Stephen Wheatcroft, BHF (May 2017), £107,878
Graham Askew in collaboration with Bangor University, BBSRC (Mar 2017), £477,383
Stephen Muench, BBSRC (Mar 2017), £132,945
Nic Stonehouse, MRC (Mar 2017), £906,341
Bill Kunin, Steve Sait, BBSRC (Mar 2017), £602,831
Adrian Goldman, EU (Mar 2017), £546,576
Sheena Radford, Wellcome Trust (Mar 2017), £1,836,482
Tom Bennett, Royal Society (Mar 2017), £15,000
Beatrice Filippi, Royal Society (Mar 2017), £15,000
Jamie Johnston, Royal Society (Mar 2017), £15,000
Ryan Seipke, BBSRC (Feb 2017), £52,116
Mary O'Connell, BBSRC (Feb 2017), £46,986
Hannah Dugdale, NERC (Feb 2017), £504,138
Anastasia Zhuravleva, EPSRC (Jan 2017), £100,792