Environmental change and the extinction of ecological interactions

Summary:

  • Interactions between species allow ecosystems to function, and channel energy, nutrients, water and other resources. 
  • A new mathematical model was devised to test whether the loss of species and the loss of ecological interactions were connected.
  • Where ‘keystone’ interactions are removed, a cascade of other ecological interactions are lost, even before other species become extinct
  • Climate change and habitat loss sever ecological links between species, disrupting the function of ecosystems and reducing the benefits they provide.

“When we try to pick out anything by itself, we find it hitched to everything else in the Universe”. These were the words of John Muir, the famous twentieth century naturalist and one of the first proponents of the conservation movement. It implies that when one element of a natural system is changed there will be a cascade of effects upon all of its constituents; this is an astute observation as ‘ecological cascades’ – changes to one small part of an ecosystem having a disproportionately large effect- are well demonstrated in environmental science. If these interactions are so complex and far- reaching, then how will they change life on Earth in the face of species extinction and climatic change?

spider-s-web-1197641
Interactions between species are complex and interlinked, like the threads of a spiders web

A recent study by Alfonso Valiente-Banuet et al. may have the answer. Using a new type of mathematical model that takes into account the diversity of species, the diversity of their interactions and the degree of environmental degradation, the group investigated whether there is a link between species extinction and loss of ecological interactions.

The importance of species interactions may at first be unclear, but they are essential for the functioning of living systems. A healthy ecosystem is a web of interconnected organisms, all performing different roles and chaperoning the cycling of energy and nutrients- the unintentional product of this cycling is the provision of ecosystem services which directly benefit us. For example, think of how trees take groundwater and through transpiration turn it into rain clouds, or of the constant recycling performed by earthworms in your allotment, returning nutrients to the soil so that you can grow those prize-winning pumpkins. On a large scale and under major environmental devastation the loss of some interactions may have far more dire consequences- droughts, famine and increased susceptibility to natural disasters to name a few (Diaz et al., 2006).

In the face of environmental change, these links become more and more threatened as the species that orchestrate them go extinct, eliminating key elements of the web. The study, published in Functional Ecology, shows that with increasing environmental degradation the rate of the loss of ecological links depends on the species in question. Generalist species, species that are ecological ‘jack-of all trades’, have interactions that are easily replaced by other species in the ecosystem until most species are extinct. However, many of the most important ecological jobs are conducted by ‘keystone’ species, which demonstrate ‘keystone’ interactions- i.e. those that have a disproportionately large effect on the ecosystem, and whose loss would mean the loss of many critically important interactions. It is these species that have the strongest effect on the extinction of ecological interactions, even before many other species go extinct. These are the interactions which should be conservation priorities, as ‘…to ensure the long-term provision of ecosystem services that depend upon biodiversity, the greatest attention should be focused on those components of biodiversity, such as species interactions, that can be affected by the new scenarios emerging in a changing world. ‘

 

References:

Díaz S, Fargione J, Chapin FS III, Tilman D (2006) Biodiversity Loss Threatens Human Well-Being. PLoS Biol 4(8): e277. doi:10.1371/journal.pbio.0040277

Valiente-Banuet, A., Aizen, M.A., Alcántara, J.M., Arroyo, J., Cocucci, A., Galetti, M., García, M.B., García, D., Gómez, J.M., Jordano, P., Medel, R., Navarro, L., Obeso, J.R., Ovideo, R., Ramírez, N., Rey, P.J., Traveset, A., Verdú, M., Zamora, R. (2015) ‘Beyond species loss: the extinction of ecological interactions in a changing world’. Functional Ecology 29: 299-307.

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