Introduction

Convex Hull is a geographical model that uses the location of known occurrences and predicts that a species can be present within a spatial convex hull around these occurrence points. A convex hull is the smallest polygon that you can draw around the occurrence points enclosing all occurrence points. For any two points, the line between these two points has to fall completely within the convex.

This model does not use the input of environmental variables to predict the distribution of a species.

The International Union for Conservation of Nature (IUCN) uses the convex hull method to estimate the extent of occurrence for species, with the adaptation that large areas with obvious unsuitable habitat (such as ocean for terrestrial species) are excluded. Species are considered to be critically endangered if the extent of occurrence is <100 km², endangered when the extent of occurrence is <5,000 km², and vulnerable when the extent of occurrence is <20,000 km². 

Advantages

• Simple and easy to interpret
• Presence only model, no absence data needed

Limitations

• Does not use environmental variables to predict species occurrence
• Likely to overestimate species range; increased bias with an increased number of occurrences
  

Assumptions

N/A

Requires absence data

No

Configuration options

BCCVL uses the ‘dismo’ package. There are no configuration options for this algorithm.

References

• Burgman MA, Fox JC (2003) Bias in species range estimates from minimum convex polygons: implications for conservation and options for improved planning. Animal Conservation, 6(01), 19-28.
  
• Hijmans RJ, Elith J (2015) Species distribution modeling with R.
  
• IUCN (2012) Red list categories and criteria. Version 3.1, 2nd edition.