Posts Tagged ‘Land-use change’

Overestimating biodiversity loss?

Thursday, June 2nd, 2011

Earlier this May, Fangliang He and Stephen Hubbell made headline news by publishing, in Nature, a study that demonstrates that usual estimates of species extinction rates are actually overestimates. Their argument is basically as follows:

Estimates of biodiversity loss from habitat loss are generally based on a relationship between the number of species in an area and that area’s surface. This relationship is known as the species-area curve. It is based on surveys that count species inside a survey area. The bigger the area, the more species there are. Of course, it makes sense to say that the bigger the area lost, the more species are lost.

What He and Hubbell explain is that in establishing the species – area curves, species are added to the count as they are encountered. The survey area necessary for a first encounter with a species is necessarily smaller than the area that encompasses 100% of that species (except in the trivial case of there being only one single individual of the species).

This larger area, which harbours 100% of the species, is the one which should be used for calculating species extinction from habitat loss. As a result, the species – area relationship gives less species going extinct for a given area of habitat loss… Makes sense doesn’t it?

The authors insist that their point does not mean that biodiversity is not being lost at an alarming rate. That also makes sense of course.

Vulnerability, resilience and sustainability

Sunday, January 2nd, 2011

In an interesting review paper published in Global Environmental Change, Billie L. Turner outlines the separate trajectories of vulnerability and resilience research and argues that both could “join forces” and contribute to the wider goals of sustainability science. One of his main claims is that this can be done if both fields of enquiry explicitly address trade-offs in ecosystem services.

According to Billie Turner, vulnerability has mainly focused on the effects of abrupt, external changes, on human societies and communities. In doing so, it has generated a strong literature on human adaptation and adaptive capacity (one of the three pillars of vulnerability with exposure and sensitivity). Multiple ecosystem services, and their inherent trade-offs, are however rarely addressed.

On the contrary, while they also investigate the capacity of socio-ecological systems to self-organize and to learn and adapt, most studies of resilience have focused more strongly on the response of ecosystem-level properties to external shocks. In doing so, trade-offs between multiple ecosystem processes and functions are investigated but rarely linked to human well-fare (security, health, material well-being, social relations etc.).

Billie Turner tells us that because decision making actually compares alternatives in terms of human well-fare (in a broad sense), the multiple pathways between it and ecosystem properties – which operate at multiple spatial scales and with multiple underlying values – must be investigated. Trade-off analysis enables us to track such pathways.

Within sustainability science and assisted by researchers working at the interface of research-application and open to multiple explanatory perspectives, efforts have begun that point to improved integration of vulnerability and resilience research.

He concludes that both vulnerability and resilience research would usefully contribute to furthering our understanding of trade-offs between multiple ecosystem services in a manner conductive to decision-making and sustainability.