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Examining the possible effect of forest area, abundance of snakes and snake species richness on the abundance of short-toed eagle, in Spain.

Romero, Ciro Patricio (2010) Examining the possible effect of forest area, abundance of snakes and snake species richness on the abundance of short-toed eagle, in Spain.

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Abstract:It is a well known fact that short-toed eagle preys on snakes and nests on trees. However, it is unknown how forest area, abundances of different snake species and snake species richness affect the abundance of short-toed eagle. Therefore, path analysis, a method that estimates direct and indirect effects using multiple regression equations, was used to identify and measure the presumed causal relationships that have support on the observed data. The presumed causal relationships were established based on knowledge about natural history, functional hypothesis, professional experience and expert’s intuition. Data about abundance of snakes and short-toed eagles are un-existent. Therefore, relative abundances of snakes and short-toed eagles, estimated based on occurrence data, were used as indirect estimations of abundance. The results revealed that the relative abundances of Malpolon monspesulanus, Rhinechis scalaris, Hemorrhois hippocrepis and Natrix natrix may not have a significant direct effect on the relative abundance of short-toed eagle. Besides, snake species richness does not seem to influence directly the relative abundance of the eagle. Apparently, snake species richness may affect directly only the relative total abundance of snakes, which it seems to affect, directly, the relative abundance of the eagle. Moreover, forest area also seems to affect, directly, the relative abundance of short-toed eagle. Path analysis does not prove or disprove causality. Thereby, a replication of the present research, using data from other countries, could increase the level of certainty that the direct and indirect effects identified and measure in the present thesis may represent causal relationships. Besides, new theories should be tested. Key words: Short-toed eagle, Circaetus gallicus, snake species richness, snakes, forests, kernel density, path analysis.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
Link to this item:https://purl.utwente.nl/essays/92495
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