دانلود رایگان مقاله انگلیسی ارزیابی رابطه خطر انقراض محلی و موقعیت آن در محدوده - وایلی 2017

ABSTRACT

Over half of globally threatened animal species have experienced rapid geographic range loss. Identifying the parts of species’ distributions most vulnerable to extinction would benefit conservation planning. However, previous studies give little consensus on whether ranges decline to the core or edge. Here we build on previous work by using empirical data to examine the position of recent local extinctions within species’ geographic ranges, addressing range position as a continuum and exploring the influence of environmental factors. We aggregated point locality data for 125 species of galliform birds across the Palearctic and Indo-Malaya into equal area half degree grid cells and used a multi-species dynamic Bayesian occupancy model to estimate the rates of local extinctions. Our model provides a novel approach to identify loss of populations from within species ranges. We investigated the relationship between extinction rates and distance from range edge, examining whether patterns were consistent across biogeographic realm and different categories of land-use. In the Palearctic, local extinctions occurred closer to the range edge in both unconverted and human-dominated landscapes. In Indo-Malaya, no pattern was found for unconverted landscapes but in human dominated landscapes extinctions tended to occur closer to the core than the edge. Our results suggest that local and regional factors over-ride any general spatial patterns of recent local extinction within species’ ranges and highlight the difficulty of predicting the parts of a species’ distribution most vulnerable to threat.

DISCUSSION

Our study of the relationship between spatial properties of species ranges and local extinction rates has shown that the nature of the relationship differs between biogeographic realms and, in IndoMalaya, between unconverted and human-dominated landscapes. Relative extinction rates do not appear to be affected by geographic range size although species with particularly high relative extinction rates tended to have relatively large geographic ranges.

Our findings raise several important issues for conservation. Firstly, local extinctions in humandominated landscapes occurred closer to the edge in the Palearctic and either with no pattern or further from the edge in Indo-Malaya, dependent on landscape. The two biogeographic realms have different histories of anthropogenic transformation; by 1700, Europe was already mostly transformed, and Asia was beginning to undergo transformation into the intensive cropland and village anthromes that would later predominate in the 20th century (Ellis et al. 2010). The intensity of extinction drivers differs between the realms with wildlife extraction in Southeast Asia estimated to be at six times the sustainable rate (Bennett 2002) and current deforestation continuing at exceptionally high rates (Sodhi et al. 2004). One explanation of the difference between realms thus might be that local extinctions are mainly central during the early stages of decline and switch to the edge later. Alternatively the difference might reflect spatial patterns in the drivers of range loss or the severity of threatening processes. The realms’ different biome compositions might also be a factor, a previous study finding biome to be a better predictor of vulnerability to local extinction than position in range (Yackulic et al. 2011). Additionally, Indo-Malaya has a more complex geometry with many instances of coastal edge occurring in the centre of a species geographic range; our measure of D`may have been less representative of range edge in these cases (see Supporting Information S4).