Reducing per capita food supply alters urchin condition and habitat
When food supply declines or population density increases, the per capita food availability is reduced causing a decline in condition of consumers. Many consumers alter their feeding behaviour and ultimately the surrounding community (e.g. overgrazing and formation of urchin barrens). This study tested the hypothesis that sea urchin populations are of greater density and poorer condition in barrens (little food) than forest habitat (lots of food). We then tested the hypothesis that a decrease in per capita food supply to urchins has a negative effect not only on their condition but also on their surrounding habitat. We experimentally assessed the effect of limited food supply and increased density of a subtidal Australian sea urchin (Heliocidaris erythrogramma) on their condition (i.e. gonad index) and surrounding benthic habitat (i.e. turf-forming algae). Our results show that a reduction in food supply led to poorer consumer condition and greater herbivory on surrounding local habitat. We provide evidence that per capita food reduction is one of the necessary conditions for the over-consumption by urchins (i.e. urchin barrens), a proposed but previously untested mechanism.
KeywordsWestern Australia Kelp Forest Gonad Index Capita Food Conspecific Density
We would like to thank John Naumann and Maria Eugenia Segade for assistance in the field and two anonymous thesis examiners for comments on earlier versions. This study was funded by an Australian Research Council grant to Sean Connell.
- Anderson WB, Polis GA (2004) Allochthonous nutrient and food inputs: consequences for temporal stability. In: Polis GA, Power ME, Huxel GR (eds) Food webs at a landscape level. The University of Chicago Press, Chicago, p 577Google Scholar
- Connell SD (2007) Subtidal temperate rocky habitats: habitat heterogeneity at local to continental scales. In: Connell SD, Gillanders BM (eds) Mar ecol. Oxford University Press, South Melbourne, pp 378–401Google Scholar
- Constable AJ (1990) An investigation of resource allocation in he sea urchin Heliocidaris erythrogramma (Valenciennes). Department of Zoology, MelbourneGoogle Scholar
- Livore JP, Connell SD (2012) Effects of food origin and availability on sea urchin condition and feeding behaviour. J Sea Res 68:1–5Google Scholar
- Polis GA, Hurd SD (1996) Allochthonous input across habitats, subsidized consumers, and apparent trophic cascades: examples from ocean-land interface. In: Polis GA, Winemiller KO (eds) Food webs: integration of patterns and dynamics. Chapman & Hall, New York, pp 275–285Google Scholar
- Polis GA, Holt RD, Menge BA, Winemiller KO (1996) Time, space and life history: influences on food webs In: Polis GA, Winemiller KO (eds) Food webs: integration of patterns and dynamics. Chapman & Hall, New York, pp xiv, 472Google Scholar
- Quinn GP, Keough MJ (2002) Experimental design and data analysis for biologists. Cambridge University Press, CambridgeGoogle Scholar
- Sanchez-Pinero F, Polis GA (2000) Bottom-up dynamics of Allochthonous Input: direct and indirect effects of seabirds on Islands. Ecology 81:3117–3132Google Scholar