Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

Experimental Ecology of Food Webs: Complex Systems in Temporary Ponds

Henry M. Wilbur
Ecology
Vol. 78, No. 8 (Dec., 1997), pp. 2279-2302
Published by: Wiley
DOI: 10.2307/2265892
Stable URL: http://www.jstor.org/stable/2265892
Page Count: 24
  • Download ($42.00)
  • Subscribe ($19.50)
  • Cite this Item
Preview not available
Preview not available

Abstract

A food web graphically represents the paths of nutrients and energy through the living components of an ecosystem and the context in which individuals exploit their prey and avoid their enemies. Temporary ponds are excellent arenas for the study of food webs because they are discrete communities that can be mimicked in containers that approach the realism of natural habitats. Artificial ponds permit repeatable initial conditions and sufficient replication of independent experimental units in complex experiments to test hypotheses about the control of structure and function in natural communities. I used a combination of observations of natural ponds, "experimental natural history" of artificial ponds in my study area, and controlled experiments in an array of 144 replicate ponds to develop, then test, hypotheses about how the structures of food webs are regulated. Understanding food webs begins with population biology. Amphibians use the aquatic larval stage of their biphasic life cycle to exploit ephemeral opportunities for growth and development in temporary ponds. The regulation of population density and the fitness of individuals are determined by complex interactions among competition, predation, and uncertainty in the length of the time ponds retain water. Exponential models of density-dependent recruitment relate the number of metamorphs to the input of eggs into ponds without predators. Extensions of these models include interspecific competition and predation. The addition of predation to these systems has three effects. (1) Predators can reduce, even eliminate, prey. There are species-specific differences among co-occurring prey in their risks of predation, and these risks change with relative body sizes of predator and prey. (2) Individuals may evoke an inducible defense that reduces their risk by either decreasing active foraging or developing morphological adaptations, such as changes in the coloration and shape of tails. These defenses may entail costs in body size and timing of metamorphosis. (3) Finally, mortality due to predators may reduce competition, thereby benefiting the population of the prey by permitting individuals that escape predation to grow rapidly enough to escape drying ponds. The order of arrival of species at breeding ponds has an impact on their own success as well as having a lasting impact on the success of species that arrive later. Such priority effects may result from size-specific changes in trophic connections or indirect effects between species mediated through the food web. Anurans can have strong effects on the partitioning of the flow of nutrients through the phytoplankton vs. the periphyton. This effect on partitioning of production can then have strong effects on zooplankton and insects. Salamanders can play the role of keystone, or critical, predators by affecting the structure of the assemblages of zooplankton and anurans that determine much of the dynamics of nutrient flows within food webs in temporary ponds.

Page Thumbnails

  • Thumbnail: Page 
2279
    2279
  • Thumbnail: Page 
2280
    2280
  • Thumbnail: Page 
2281
    2281
  • Thumbnail: Page 
2282
    2282
  • Thumbnail: Page 
2283
    2283
  • Thumbnail: Page 
2284
    2284
  • Thumbnail: Page 
2285
    2285
  • Thumbnail: Page 
2286
    2286
  • Thumbnail: Page 
2287
    2287
  • Thumbnail: Page 
2288
    2288
  • Thumbnail: Page 
2289
    2289
  • Thumbnail: Page 
2290
    2290
  • Thumbnail: Page 
2291
    2291
  • Thumbnail: Page 
2292
    2292
  • Thumbnail: Page 
2293
    2293
  • Thumbnail: Page 
2294
    2294
  • Thumbnail: Page 
2295
    2295
  • Thumbnail: Page 
2296
    2296
  • Thumbnail: Page 
2297
    2297
  • Thumbnail: Page 
2298
    2298
  • Thumbnail: Page 
2299
    2299
  • Thumbnail: Page 
2300
    2300
  • Thumbnail: Page 
2301
    2301
  • Thumbnail: Page 
2302
    2302