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Gibson, C. W. D., & Phillipson, J. (1983). The primary production of aldabra atoll, with reference to habitats used by giant tortoises. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 302(1109), 167–199. 
Added by: Admin (25 Aug 2010 21:58:47 UTC)
Resource type: Journal Article
DOI: 10.1098/rstb.1983.0050
BibTeX citation key: Gibson1983a
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 Categories: General
Keywords: Ernährung = nutrition, Habitat = habitat, Pazifik = Pacific, Schildkröten = turtles + tortoises
Creators: Gibson, Phillipson
Collection: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences		 Views: 6/488
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Abstract     
Testudinidae Cylindraspis Aldabrachelys This paper reports on the seasonal changes of standing crop and production in habitats used by a high-density population of giant tortoises on Aldabra atoll. The study had two main aims: first to investigate the primary production of a raised coral atoll (to our knowledge the first such study) and secondly to provide base data for a study of the interactions of a large reptilian herbivore (the giant tortoise) with its food supply and environment. Environmental heterogeneity made it necessary to measure separately the standing crop and the above-ground net production of different components of the vegetation; these components were usually single species or small groups of species of plants. Measurements of these components were then combined with cover data for the same components in selected places to illustrate the seasonal and spatial variability of primary production on Aldabra. Standing crop biomasses were estimated from harvest samples. Methods for production estimates varied with the component studied, but included harvest difference methods, repeated clipping of the same plots and direct measurement of leaf turnover rates on marked shoots. These methods are compared where appropriate. Net annual above-ground production varied between plant types from 3165 kJ per square metre of plant for `tortoise turf' to 47700 kJ m$^{-2}$ for Cyperus ligularis, a robust perennial sedge. Total above-ground annual net production of different habitat types (bare ground and rocks between plants being taken into account) varied from 9100 kJ m$^{-2}$ in a thinly wooded area with high tortoise turf cover (`open mixed scrub') to 28 200 kJ m$^{-2}$ in an area of thick scrub forest (`groves'). The seasonality of production and standing crop also varied considerably between habitats, owing to the role of different components of the ground layer and shrub cover. These results are discussed in terms of the roles of environmental and structural heterogeneity in setting primary production and of the tortoises themselves in their interactions with the vegetation via trampling and grazing. The effect of this heterogeneity on sampling strategies and results is also assessed.
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