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Open Access item Seagull influence on soil properties, chenopod shrub distribution, and leaf nutrient status in semi-arid Mediterranean islands.
|Authors:||García, Luis V.|
Ojeda Copete, Fernando
Clemente Salas, Luis
|Citation:||OIKOS 98: 75-86 (2002)|
|Abstract:||Concentration of seagulls in the Chafarinas Islands (three semi-arid North African
islets) induces profound changes in soil properties including eutrophication, salinization,
acidification and nutrient imbalances. Soils of heavily seabird-affected sites have
significantly higher soluble K and NO3 levels ( 20-fold), Zn and Fe availability
( 5-fold), water-retention capacity ( 40% increase) and 15N enrichment, compared
with control sites. These seabird-induced soil changes are paralleled by (i) different
patterns of abundance of the two main chenopod shrubs: Suaeda era abundance is
higher ( 30-fold) in seabird-affected sites while Salsola oppositifolia largely dominates
in low-affected areas. No differences were found for Atriplex halimus. The
abundance of the first two species may be largely explained by changes in soil soluble
K-to-available Ca ratio whose value depends of the interaction between seabird
products and soil constituents; (ii) significant increases in leaf N, P and Zn levels, and
in all K ratios, paralelled by a decrease in Ca, in Salsola; but only by increased K/Na
and P/Ca ratios in Suaeda leaves. These changes were significantly correlated to
changes in species abundances; (iii) an increase of 15N, paralleled by a decrease in
13C values, in Salsola leaves but not in Suaeda.
Conjoint analysis of the seabird-related changes in soil properties, species abundance,
leaf composition and differential response to the seabird-induced fertilization/severity
gradient of the two main chenopod shrub species, has led us to propose an
explanatory hypothesis of seagull-soil-shrub relationships. According to this, the
seagull-induced soil changes, mediated by processes of (in)tolerance-facilitation, play
a main role in determining the abundance and the leaf nutrient status of the studied
chenopod shrubs, which have contrasting physiological adaptations.|
|Description:||12 pages, 10 tables, 2 figures. We thank Georgina Álvarez for the
organizational support in our fieldtrips to Chafarinas. T.
Gómez, M. Igual, J. Charco, and P. Robles gave field assistance.
R. López, J.M. Alegre, J. Cara and E. Gutiérrez carried
out plant and soil chemical analyses. D. G. Sobey kindly
provided some key references. J.M. Murillo and L. Sack made
valuable comments on an earlier version of the manuscript.|
|Appears in Collections:||(IRNAS) Artículos|
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