AmkeJapTjoenSan_BScProject_Repository

Data for the Bachelors thesis of Amke Jap Tjoen San, titled: Possible causes of the decline of the butterfly species Pyronia tithonus in the Netherlands 

Abstract:

Butterflies play a major role in the implementation of fundamental ecological roles. However, unfortunately the majority of the butterfly species in the Netherlands have been declining since 1992 (van Swaay, 2020). Many studies that investigate the explanation for these declines cover specialist butterfly species. These type of species have always showed to be more sensitive to changes and showed heavier declines (Ghazanfar et al., 2016). However, in the last two decades, fifty-five percent of all widespread species have shown significant declines in the Netherlands (van Swaay, 2020; Ghazanfar et al., 2016). The explanation for these declines is unknown for the majority of these species, often because these species are more difficult to model than specialist species (Fernández et al., 2015). Consequently, it is important to start researching the declines of these types of butterfly species.

This research analyses the changing population dynamics of the widespread butterfly species Pyronia tithonus. P. tithonus is among the fifty-five percent of the widespread Dutch butterfly species that have been declining without a known explanation. The species only occurs in northern Netherlands, mainly in the province Drenthe, and in the southern provinces Zeeland, Noord-Brabant and Limburg. The individuals in the northern provinces show steeper declines than the individuals in the southern provinces. This phenomenon does not have a known explanation either. The objective of this research was, therefore, to identify unbeneficial parameters for the population abundance of P. tithonus and to test whether these parameters could explain the heavier decline in the north. Rtrim was used to calculate trends and to test the significance of the parameters.

The results show that the following parameters are unbeneficial to the overall population abundance of P. tithonus: acoustic noise, productivity, nitrate concentration in the groundwater, mean annual precipitation, number of dry days in the year, and ammonia emissions. The following parameters positively affect the total population abundance of P. tithonus: Low values of soil nitrogen from fertilizer, buffered soils, high percentages of low vegetation, and the presence of shrubs.

Moreover, the results suggest that the higher NOx emissions in the northern provinces can be the explanation for the heavier decline in the north. However, further research into the differences between the individuals living in the northern and southern provinces is recommended, given that NOx emissions did not show to be significant for the total population abundance. Consequently, this research suggests that the individuals in the north could differ from the individuals in the south in the way they react to their environment. This could be caused by genetic differences between the individuals in the north and in the south. However the results of this analysis alone are not sufficient to draw this conclusion.

Therefore, the results of this research motivates further research into the genetic differences between the northern and southern individuals of P. tithonus. Moreover, it motivates the need for further research into the changing population dynamics of widespread species, because a lot of knowledge on these types of species is still lacking.