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Driezen et al (2007) hedgehog least-cost model predictions with dispersal data.pdf

Title: Evaluating least-cost model predictions with empirical dispersal data: A case-study using radiotracking data of hedgehogs (Erinaceus europaeus), Ecological Modelling 209; 314-322. 2007

Authors: K. Driezen, F. Adriaensen, C. Rondinini, C. P. Doncaster & E. Matthysen

Country: UK

Background to study

Least-cost path analysis has the capabilities of predicting movements of focal species by allocating costs to traversing different land use types and is thus important for quantifying the value of landscape structures for dispersal.  This study investigates the performance of least-cost path analysis against empirical data on the movement of hedgehogs within favourable and unfavourable rural landscapes.

Method

  • 12 least-cost path analysis model sets were generated in ArcGIS using 10 x 10 m grid cells where each cell represents a habitat type or feature (e.g. hedgerow or river) and is assigned a resistance value which increases with decreasing suitability for hedgehogs. Values for each habitat/feature were based on prior knowledge and across the 12 model sets, resistance values varied by habitat/feature.
  • Hedgehogs were fitted with radio transmitters and were translocated into one of four unfavourable study areas where hedgehogs were absent or into a favourable area known to support a substantial hedgehog population. After release, hedgehogs were radio tracked until they occupied the same area for 5 days and each location point was inputted into GIS to obtain a path which represented a dispersal movement.
  • 21 paths resulting from the movements of released hedgehogs were selected where individuals had been located more than 3 times, had moved through more than two different land use types for >800 m and that the paths taken did not leave the boundary of available habitat maps used in the analyses.
  • The paths taken by released individuals were assessed against the least-cost path analysis and to determine whether hedgehogs chose more favourable paths than what would be expected from random movement, a calculation based on alternative habitat types within the same distance from the previous location point was produced. Negative values that differed significantly from zero represented a path taken that was better in terms of cost than a random route.

Key results

  • Hedgehogs moved through parts of the landscape with relatively low cost values relative to the release points suggesting that hedgehogs selected their paths based on perceived risk and/or foraging opportunities and that the least-cost path analyses models suitable for predicting movement based on a-prior expectation of habitat use and movement.
  • Simpler models with fewer resistance classes and models which include higher levels of habitat heterogeneity (where a greater range of resistance values is included to represent a contrasting landscape) perform better for predicting movement of hedgehogs.
  • The best performing models included a low resistance value for urban regions and a high resistance value for arable land and both high and low values for small roads and rivers.
  • Although hedgehogs in this study took a better than random dispersal route, they still did not choose the best one based on the least-cost path analysis which suggests that their movement choices may be at a finer scale than modelled or that other factors such as disturbance, foraging and inter and intra specific interactions have a role in determining movement paths.
  • Calculating the cost of movement between each location point may prove more accurate for predicting dispersal routes for hedgehogs that are unlikely to know their entire trajectory. However, this involves a large amount of computational effort and route choices will not necessarily by reflected by the point at which a location fix was obtained. 
  • Model fits were less than ideal and thus model predictions were weak.

Key messages to landowners and managers derived from these results

  • Large areas of arable land are potentially barriers for hedgehog movement and efforts to increase permeability such as creating and/or enhancing linear features such as hedgerows surrounding arable fields is recommended.
  • Least-cost path analysis has potential to provide prediction on animal movement but more research to validate model predictions against actual dispersal routes is needed.

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