Anthropogenic footprints on biodiversity

One of the most concerning issues to modern ecology and society is the ongoing loss of biodiversity. Ecosystems are now losing species at rates only seen in previous mass extinction events (Hails, 2008; Barnosky et al., 2011) with rates of extinction between 100 and 1000 times higher than pre-human levels (Pimm et al., 1995). This loss, in turn, is impairing the functioning of ecosystems (Worm et al., 2006; Mora et al., 2011a) and their capacity to deliver goods and services to mankind (Díaz et al., 2006). The sharp contrast between the declining “supply” of the Earth’s services and the rising “demand” from a growing human population indicates that such services will increasingly fall short, leading to the exacerbation of hunger, poverty, and human suffering (Campbell et al., 2007; Mora & Sale, 2011). There is relatively good consensus that biodiversity loss is being driven directly or indirectly by human stressors such as overexploitation, habitat loss, invasive species, and climate change (Myers, 1995; Sala et al., 2000; Novacek & Cleland, 2001; Gaston et al., 2003; Jackson, 2008; Weidenhamer & Callaway, 2010). The relative role of such stressors, however, has been a focus of controversy as all threats do provide rational mechanisms to explain biodiversity loss and unfortunately most threats co-occur in natural conditions, making it difficult to isolate their individual effects (Myers, 1995; Sala et al., 2000; Novacek & Cleland, 2001; Mora et al., 2007). Since the cost of mitigating specific stressors could be considerable but disproportionate among different sectors of the economy (e.g., industries vs. fishers, fishermen vs. tourism developers, etc.), this uncertainty over the relative effect of anthropogenic stressors is often used as an argument to prevent the implementation of mitigation policies (e.g., Schiermeier, 2004; Worm &Myers, 2004; Grigg & Dollar, 2005). A counter-argument, however, is that any stressor at play, if proven to have a considerable effect on biodiversity, should be mitigated regardless of its effect relative to other stressors. This would, of course, require demonstrating the significance of the stressor(s) at play. In this review, we provide an overview of the current biodiversity crisis and the role of anthropogenic stressors. The evidence is considerable and although some uncertainties remain and will probably never be answered, there is considerable knowledge to suggest that a lack of policy action