| Butterfly population sizes and geographic distributions have been reported as declining during the past few years despite the considerable efforts performed such as natural reserves and protective legislations. This may be because several butterfly species are organized according to metapopulations models. Additionally, species that act as metapopulations live with a threshold requirement for habitat, below which they face inevitable extinction. This extinction threshold can have different causes that can be categorized in two model types: colonization-extinction in which the landscape-scale population persistence is determined by the rates of colonization and extinction and the births, immigration, deaths and emigration models where population persistence is determined by birth and death rates. It is therefore logical to assume that the details on the spatial arrangement of the habitats and species dispersal rates between them can be of major relevance for successful environmental management. On the other hand, species may respond differently to changes in their habitat depending on the scale at which the landscape is perceived and they may relate to different environmental variables at different scales. Therefore, fragmentation effects can vary between different species. In order to make use of the adequate management measures, the appropriate scale of response for different species should be studied.
Aims
General:
-Assess the effect of the amount of suitable habitat, and its configuration, in the landscape on the occurrence of different species of butterflies at different spatial scales
-The effect of the matrix that surrounds the suitable habitat
Specific:
-Assess butterfly species scale of response
-Relate species attributes to identified characteristic scales
-Determine the landscape features that affect butterflies’ biodiversity
-Predictive maps of (parts of Sweden) describing the probability of occurrence of selected species as a function of amount of suitable habitat
Methods
Data
The data used for this project will consist on three different databases. The first one is the TUVA database, which consists of two previous inventories on grassland species richness and land use of southern Sweden, thus creating a map layer of species-rich grasslands. The second database comes from the European Union’s Corine Land Cover mapping project. This database contains information about vegetation and land use which makes it suitable to perform landscape analysis. Finally, a third dataset on butterfly densities will also be used. These data have been collected by butterfly researcher of several years, and are dispersed over southern Sweden.
Data Analysis
Spatial analyses will be performed using ArcGIS 9.3 in order to determine the total area of grasslands surrounding the study sites where butterfly surveys have taken place. This will be performed for different spatial scales or radii surrounding the sites. The amount of grasslands, along with other factors such as nectar availability, will be related with the butterfly’s richness and abundance using Generalized Linear Models. Model outcomes will be used to determine to what extent a landscape factor can explain butterfly biodiversity at different spatial scales. |