Abstract
Interspecific interactions can affect population dynamics and the evolution of species traits by altering demographic rates such as reproduction and survival. The influence of mutualism on population processes is thought to depend on both the benefits and costs of the interaction. However, few studies have explicitly quantified both benefits and costs in terms of demographic rates; furthermore there has been little consideration as to how benefits and costs depend on the demographic effects of factors extrinsic to the interaction. I studied how benefits (pollination) and costs (larval fruit consumption) of pollinating seed-consumers (senita moths) affect the reproduction of senita cacti and how these effects may rely on extrinsic water limitation for reproduction. Fruit initiation was not limited by moth pollination, but survival of initiated fruit increased when moth eggs were removed from flowers. Watered cacti produced more flowers and initiated more fruit from hand-pollinated flowers than did unwatered cacti, but fruit initiation remained low despite excess pollen. Even though water, pollination and larvae each affected a component of cactus reproduction, when all of these factors were included in a factorial experiment, pollination and water determined rates of reproduction. Counter-intuitively, larval fruit consumption had a negligible effect on cactus reproduction. By quantifying both benefits and costs of mutualism in terms of demographic rates, this study demonstrates that benefits and costs can be differentially influential to population processes and that interpretation of their influences can depend on demographic effects of factors extrinsic to the interaction.
Full Text
The Full Text of this article is available as a PDF (304.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Frank S. A. Host-symbiont conflict over the mixing of symbiotic lineages. Proc Biol Sci. 1996 Mar 22;263(1368):339–344. doi: 10.1098/rspb.1996.0052. [DOI] [PubMed] [Google Scholar]
- Herre EA, Knowlton N, Mueller UG, Rehner SA. The evolution of mutualisms: exploring the paths between conflict and cooperation. Trends Ecol Evol. 1999 Feb;14(2):49–53. doi: 10.1016/s0169-5347(98)01529-8. [DOI] [PubMed] [Google Scholar]
- Holt R. D. Predation, apparent competition, and the structure of prey communities. Theor Popul Biol. 1977 Oct;12(2):197–129. doi: 10.1016/0040-5809(77)90042-9. [DOI] [PubMed] [Google Scholar]
- doi: 10.1098/rspb.1997.0208. [DOI] [PMC free article] [Google Scholar]
- doi: 10.1098/rspb.1998.0305. [DOI] [PMC free article] [Google Scholar]
- de Ruiter P. C., Neutel A. M., Moore J. C. Energetics, patterns of interaction strengths, and stability in real ecosystems. Science. 1995 Sep 1;269(5228):1257–1260. doi: 10.1126/science.269.5228.1257. [DOI] [PubMed] [Google Scholar]