Researching the Decline of Shorebirds and Their Risk of Extinction

Policy- and decision-makers claim information about the causes of population declines which drive species on the brink of extinction. However, it is pointed out that the causes of vulnerability remain unclear to explain the variation to the risk of extinction. According to Reynolds (2003), vulnerability is determinate by both the decline of species population and the reduction of their geographical range. These two forms of vulnerability are affected by species intrinsic biological traits, extrinsic human induced effects and adverse factors. These drivers of vulnerability have been the main targets of recently studies to explain the causes and processes of extinction.

It is suggested that extinction risk is not distributed by chance between taxa, because closely related species could share intrinsic biological traits which make them more vulnerable to extinction (Bennett & Owen 1997, Gaston & Blackburn 1997, Freckleton et al. 2002). This scenario is used to understand how intrinsic factors could make some species vulnerable to extinction. For instance, species with low rates of fecundity and large body sizes are more susceptible to extinction than the opposite due to their insufficient ability to adapt their life histories in a fluctuating environment. Strong sexual selection is also considerate important, because species with exaggerated traits or sexually dimorphic have higher selection which reduce their genetic variability (Morrow & Pitcher 2003). Finally, migratory species are more susceptible because they should face more risks in breeding and stopover areas than resident species.

On the other hand, it is clear that intrinsic factors by themselves are not explaining the entire extinction phenomenon, because species vu...

... middle of paper ...

... and threat ranking (Purvis et al. 2005). Criterion A include populations or range decline, but it is concentrate only with change over time and no with the current range size, therefore there is no included circularity. Another assumption is that using IUCN Red List categories as the response variable is that the extinction risk of species in a given category is independent of the criteria under which it qualified for listing.

We look at the influence of human-induced drivers (extrinsic factors hypothesis), species’ biology drivers (intrinsic factors hypothesis), and their interaction in: 1) measures of vulnerability between the three main groups of shorebirds (gulls, sandpipers, and plovers); 2) measures of vulnerability per region where shorebirds live; and 3) and differences between IUCN threat status and population trends which are measures of vulnerability.