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Local convex hull

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LoCoH (Local Convex Hull) is a method for estimating the size of an animal or a group of animals (e.g. a pack of wolves, a pride of lions, or herd of buffalos) homerange, as well as for constructing a utilization distribution [1],[2]. The latter is a probability distribution that represents the probabilities of finding an animal within a given area of its homerange at any point in time; or, more generally, at points in time for which the utilization distribution has been constructed. In particular, different utilization distributions can be constructed from data pertaining to particular periods of a diurnal or seasonal cycle. Utilization distributions are constructed from data providing the location of an individual or several individuals in space at different points in time by associating a local distribution function with each point and then summing and normalizing these local distribution functions to obtain a distribution function that pertains to the data as a whole[3],[4],[5],[6].

  1. Locate the k-1 nearest neighbors for each point in the dataset.
  2. Construct a convex hull for each set of nearest neighbors and the original data point.
  3. Merge these hulls together from smallest to largest.
  4. Divide the merged hulls into isopleths where the 10% isopleth contains 10% of the original data points, the 100% isopleth contains all the points, etc.

The LoCoH method has a number of strong points:

  • It generates a density distribution denoting.
  • As more data is added, the homerange becomes more accurate.
  • It is handles 'sharp' features such as lakes and fences well.
  • The generated homerange has a finite region.

LoCoH has a number of implementations including a LoCoH Web Application.

LoCoH was formerly known as k-NNCH, for k-Nearest Neighbor Convex Hulls.


See also

References

  1. ^ Getz, W. M. and C. C. Wilmers, 2004. A local nearest-neighbor convex-hull construction of home ranges and utilization distributions. Ecography 27: 489-505.View PDF
  2. ^ Getz, W.M, S. Fortmann-Roe, P. C. Cross, A. J. Lyonsa, S. J. Ryan, C.C. Wilmers, in review. LoCoH: nonparametric kernel methods for constructing home ranges and utilization distributions. View PDF
  3. ^ Silverman BW. (1986) Density estimation for statistics and data analysis. London: Chapman and Hall. 176 p.
  4. ^ Worton BJ. (1987). A review of models of home range for animal movement. Ecological Modelling, 38: 277–298.
  5. ^ Worton BJ. (1989) Kernel methods for estimating the utilization distribution in home-range studies. Ecology 70: 164–168.
  6. ^ Seaman DE, Powell RA. (1996) An evaluation of the accuracy of kernel density estimators for home range analysis. Ecology 77: 2075–2085.
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