Food Web Complexity Increases Along Gradient

Biological Strategy

Sand dune ecosystems

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Maintain Biodiversity

The greater the amount of genetic and species variation in an ecosystem, the more resilient that ecosystem is to disturbances. Variation in ecosystems across the Earth also contributes to the Earth’s resilience to unpredictable changes. This variation is called biodiversity. Because living systems compete with each other for scarce resources, maintaining biodiversity involves creating conditions for a large variety of species to successfully co-occur and reproduce. For example, within a wetland, there are different vegetation types. This diversity results in a complex mosaic of microenvironments as the vegetation types alter air flows, light regimes, and water temperatures and chemistry. Because organisms vary in their ideal environmental conditions, these micro-environments increase the diversity of plants in the wetland. In turn, having a wetland in an otherwise dry area increases biodiversity at an even larger scale.

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a mountain with snow is in the background of a landscape with trees and shrubbery

Ecosystems

Eco- ("household"), system ("organized whole")

An ecosystem consists of all the biological and nonbiological elements that make up a defined area. That definition might seem vague, but that means it’s flexible: We can apply the word across different scales and times. Ecosystems can be small, like a single tide pool, or large, like coastal wetlands. Ecosystems can include plants, animals, bacteria, fungi, rocks, temperature, light, soil, and climate—all linked through the flow of energy and cycle of nutrients. Each part of an ecosystem interacts with, and is influenced by, other members of the system. These interactions are dynamic, leading to changes to any ecosystem over time.

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The complexity of food webs in sandy dune ecosystems increases along productivity gradients, with feedback loops governing the stability of the system.

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Namibie Sossusvlei

Image: Winfried Bruenken / Wikimedia commons /

Sossusvlei dunes, Namibia.

“Understanding how complex food webs assemble through time is fundamental both for ecological theory and for the development of sustainable strategies of ecosystem conservation and restoration. The build-up of complexity in communities is theoretically difficult, because in random-pattern models complexity leads to instability¹. There is growing evidence, however, that nonrandom patterns in the strengths of the interactions between predators and prey strongly enhance system stability^{2, 3, 4}. Here we show how such patterns explain stability in naturally assembling communities. We present two series of below-ground food webs along natural productivity gradients in vegetation successions^{5, 6}. The complexity of the food webs increased along the gradients. The stability of the food webs was captured by measuring the weight of feedback loops⁷ of three interacting ‘species’ locked in omnivory. Low predator–prey biomass ratios in these omnivorous loops were shown to have a crucial role in preserving stability as productivity and complexity increased during succession. Our results show the build-up of food-web complexity in natural productivity gradients and pin down the feedback loops that govern the stability of whole webs. They show that it is the heaviest three-link feedback loop in a network of predator–prey effects that limits its stability. Because the weight of these feedback loops is kept relatively low by the biomass build-up in the successional process, complexity does not lead to instability.” (Neutel et al. 2007:599)

Last Updated July 20, 2017

References

Journal article

Reconciling complexity with stability in naturally assembling food webs

Nature | 04/10/2007 | Neutel A-M; Heesterbeek JAP; van de Koppel J; Hoenderboom G; Vos A; Kaldeway C; Berendse F; de Ruiter PC

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