Intercontinental Biotic Connectivity and Tipping Points

It is perhaps fairly clear that agricultural expansion and/or intensification is very likely to have an impact (and more so a detrimental one) on the surrounding habitats and environment. The conversion of terrestrial biomes into agricultural landscapes has reduced habitat areas available to species and can have many negative impacts for globally important ecological processes (Foley et al., 2005). As Sanderson and colleagues (2002) quantify, 'Human Footprints' can be identified across 83% of Earth's land surface, influenced by high population density, agriculture, or infrastructure. Therefore, a considerable proportion of Earth's natural environment has experienced change as a direct result of local agricultural changes.

Deforestation for conversion to agricultural land in South America (Source: plant-talk.org)

However, whilst reading a thought-provoking paper by Barry Brook and colleagues exploring the concept of tipping points within the terrestrial biosphere, I unearthed an interesting concept of 'direct intercontinental biotic connectivity' and the coupled regime shifts. Essentially, the interconnectivity of ecosystem responses translates on a global scale to biotic connections between both biomes and continents, which facilitate the diffusion of localised changes across the terrestrial biosphere. Moreover, if these teleconnections permit changes to be felt fast enough, a global tipping-point response could be created. (In case you're not 100% sure about tipping points, they are where systems shift radically to a different state, potentially irreversibly.)

So, how could agriculture play a role?

Well, I'll start with an example. Intensive agriculture in the western USA resulted in habitat change, which in turn appears to have caused abrupt losses of Arctic ecosystem structure and biogeochemical cycling, essentially meaning biodiversity and functional loss. It is suggested by Robert Jefferies and colleagues that this stems from the increased populations of migrating snow geese through their subsidisation by agricultural food supplies. Here we see that agriculture has the capability to play a role in environmental change through teleconnections.

Snow geese in Missouri, USA (Source: dailymail.co.uk)

Not all changes have a teleconnection to another part of the globe. Limiting these direct biotic linkages could be physical barriers to species movement (oceans and mountain ranges spring to mind) as well as species niches (so the range of climatic conditions specific species are adapted). Thus, not all changes caused by agriculture will contribute to a change elsewhere. But certainly, agriculture has the ability to be a direct cause of change felt in separate regions due to 'intercontinental biotic connectivity'.

Irrigation circles in Colorado (Source: ecolibrary.org)

The number and magnitude of these connections will determine the chances of a tipping-point pattern. So, if environmental changes continue globally, we could see a tipping point within the terrestrial biosphere in the future. Naturally, as it is practiced worldwide and is identified as a significant infringer on habitats and environments, agriculture (through its expansion and intensification) could play a very real role.