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Place of publication :
Publication year : 2009
Thematic : Conservation
Language : English
Note
It is often assumed that conservation actions targeting a threatened community (e.g. habitat protection)
will result in similar benefits for all species. However, complex interactions between species, such as interference
competition, may result in displacement of subordinate, vulnerable species. We analysed here the
spatio-temporal population dynamics of a threatened seabird community since the protection in the 1980s
of several breeding sites at the Ebro Delta, western Mediterranean, Spain during 1980–2007. Competition
for the most suitable patches was governed by body size, with smaller species avoiding associations with
larger, dominant species. We tested whether the density increase of the larger species (yellow-legged gull
Larus michahellis and Audouin’s gullLarus audouinii) at La Banya (the highest quality patch within the Delta)
affected species diversity at the local level. As expected, such diversity decreased, resulting also from the
colonisation of other sites by smaller species, some abandoning the former area. The conservation paradox
appeared because the interference competition was dominated not only by the largest species of the community,
the yellow-legged gull, which is sometimes considered a pest species, but also by the vulnerable
Audouin’s gull, a flagship species which has ca. 65% of the total world population at La Banya. Nevertheless,
the availability of alternative patches within the Ebro Delta ensured a high biodiversity at regional scale.
Results highlight the role of turnover of competing species within a community in ecosystem function
and stability, and the importance of alternative sites and dispersal abilities for the conservation of vulnerable
communities.
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Keywords : food web
Encoded by : Pauline Carmel Joy Eje
