Do Parasites Reduce the Chances of Triangulation in a Real Food Web

At least ten different static patterns have been suggested by the analysis of food webs. However, the existence of many of these patterns has been questioned in recent years. One pattern that has remained immune from such criticism is intervality. In this paper, we develop a continuous measure of niche overlap, by calculating the number of non-triangulated quads (the simplest structure that confounds intervality) in a web. In contrast to intervality, this measure is applicable to webs of any size. We then explore the implications for niche overlap of including parasite - host links in a real food web, that of the Ythan estuary, Aberdeenshire. Increasing the number of parasite-host links increases the number of non-triangulated quads in a web. This increase is greater than that predicted by the cascade model. One explanation for the high incidence of intervality in real food webs is that species are ordered into a hierarchy dependent on body size. Parasites should obviate this ordering, since they are smaller than their hosts. Splitting the parasite species into 'trophospecies' according to their separate life history stages reduces the number of non-triangulated quads. This indicates that parasites do not reduce the chances of intervality (or increase the number of non-triangulated quads) merely because of their smaller body sizes, but because of their complex life cycles.

[1]  C. Kennedy.  Ecological animal parasitology , 1977 .

[2]  J. E. Cohen,et al.  Food webs and niche space. , 1979, Monographs in population biology.

[3]  D. Brooks,et al.  Evolutionary biology of parasites. , 1981, Monographs in population biology.

[4]  F. Briand,et al.  Environmental Control of Food Web Structure , 1983 .

[5]  Joel E. Cohen,et al.  A stochastic theory of community food webs II. Individual webs , 1985, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[6]  Stuart L. Pimm,et al.  The Dynamics of Multispecies, Multi-Life-Stage Models of Aquatic Food Webs , 1987 .

[7]  J H Lawton,et al.  Static and dynamic explanations for patterns in food webs. , 1988, Trends in ecology & evolution.

[8]  Philip H. Warren,et al.  Spatial and temporal variation in the structure of a freshwater food web , 1989 .

[9]  Joel E. Cohen,et al.  A Stochastic Theory of Community Food Webs. V. Intervality and Triangulation in the Trophic-Niche Overlap Graph , 1990, The American Naturalist.

[10]  Joel E. Cohen,et al.  A Stochastic Theory of Community Food Webs , 1990 .

[11]  J. Holmes.  Helminth communities in marine fishes , 1990 .

[12]  K. Winemiller.  Spatial and Temporal Variation in Tropical Fish Trophic Networks , 1990 .

[13]  Joel E. Cohen,et al.  Community Food Webs: Data and Theory , 1990 .

[14]  Charles M. Newman,et al.  Community Food Webs , 1990 .

[15]  Neo D. Martinez.  Artifacts or Attributes? Effects of Resolution on the Little Rock Lake Food Web , 1991 .

[16]  Joel E. Cohen,et al.  Food web patterns and their consequences , 1991, Nature.

[17]  G. Polis,et al.  Complex Trophic Interactions in Deserts: An Empirical Critique of Food-Web Theory , 1991, The American Naturalist.

[18]  W. Sousa.  Can Models of Soft-Sediment Community Structure Be Complete Without Parasites? , 1991 .

[19]  M. Scott,et al.  Parasitism: A cryptic determinant of animal community structure. , 1991, Trends in ecology & evolution.

[20]  S. Hall,et al.  Food-web patterns : lessons from a species-rich web , 1991 .

[21]  S. Pimm.  The Balance of Nature?: Ecological Issues in the Conservation of Species and Communities , 1992 .

[22]  K. Havens,et al.  Scale and Structure in Natural Food Webs , 1992, Science.

[23]  Dolph Schluter,et al.  Species diversity in ecological communities: historical and geographical perspectives. , 1993 .

[24]  Manuel do Carmo Gomes,et al.  Predictions under uncertainty: Fish assemblages and food webs on the Grand Banks of Newfoundland , 1993 .

[25]  S. Hall,et al.  Food webs: theory and reality , 1993 .

[26]  Neo D. Martinez,et al.  Improving Food Webs , 1993 .

[27]  G. Esch,et al.  A Functional Biology of Parasitism , 1993, Functional Biology Series.

[28]  Joan Saldaña,et al.  Body sizes of animal predators and animal prey in food webs , 1993 .

[29]  G. Esch,et al.  A functional biology of parasitism: ecological and evolutionary implications. , 1994 .

[30]  P. Warren.  Making connections in food webs. , 1994, Trends in ecology & evolution.

[31]  Mark Huxham,et al.  Parasites and food web patterns , 1995 .

[32]  J. Lawton,et al.  Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure? , 1987, Oecologia.