Understanding coexistence is a central concern for community ecologists. The limited combination of parameter values over which coexistence can occur in most models of competing species suggests that coexistence may not be a general phenomenon, yet observations of communities demonstrate that coexistence of competitors is common. In this paper, I use a well-studied host-parasitoid system, California red scale and its parasitoids, to explore whether intraguild predation (IGP) is a likely coexistence mechanism for these species and to motivate an exploration of how the level of biological detail in theoretical models influences conclusions about the likelihood of coexistence via IGP. Although prior work has shown that parasitoid and host densities in the field follow the patterns predicted by simple IGP theory, in this detailed model parameterized with empirically derived values, coexistence is not predicted. Thus, in spite of the concordance between field observations and simple model predictions, the current model demonstrates that IGP is unlikely to be the sole coexistence mechanism for the parasitoids of California red scale. Furthermore, IGP is an equalizing coexistence mechanism, and these results demonstrate that adding biological detail to this type of mechanism does not substantially increase the predicted coexistence region. This important result adds to the growing literature showing that simple models often can capture the fundamental processes operating in more complex models and may be sufficient to capture underlying ecological patterns. Because models lacking system-specific details are better able to produce general conclusions, the current result suggests that general theory may be used to gain insights into a diversity of ecological systems.
Bibliographical noteFunding Information:
C. Briggs provided hours of valuable discussions about this model. S. Richards and R. Nisbet were extremely helpful with the technical details of this project. E. Seabloom gave patient instruction in LaTeX, and P. Hosseini provided help with Solver and Pascal coding. M. Bonsall, C. Briggs, P. de Valpin, S. Diehl, A. Ives, W. Murdoch, R. Nisbet, E. Seabloom, A. Stewart-Oaten, S. Swarbrick, and an anonymous reviewer provided useful feedback on earlier versions of this manuscript. ETB received support from NSF Research and Training Grants BIR94-13141 and GER93-54870, NRI Competitive Grants Program/USDA Grants #2001-35316-10989 (to W.W. Murdoch and ETB) and #2003-35316-13767 (to C. Briggs and ETB), and the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (Grant #DEB-0072909), the University of California, and UC Santa Barbara. Part of this work was done while in residence at the NERC Centre for Population Biology, Silwood Park, Imperial College London.
- Alternate stable states
- Aphytis melinus
- California red scale
- Encarsia perniciosi
- Host feeding