# overlap

##### Niche overlap (Warren's-I)

Similarity Statistic for Quantifying Niche Overlap using Warren's-I

The overlap function computes the I similarity statistic (Warren et al. 2008) of two overlaping niche estimates. Similarity is based on the Hellenger distance. It is assumed that the input data share the same extent and cellsize and all values are positive.

The I similarity statistic sums the pair-wise differences between two predictions to create a single value representing the similarity of the two distributions. The I similarity statistic ranges from a value of 0, where two distributions have no overlap, to 1 where two distributions are identical (Warren et al., 2008). The function is based on code from Jeremy VanDerWal

##### Usage

`overlap(x, y)`

##### Arguments

- x
A matrix, rasterLayer or sp raster class object

- y
A matrix, rasterLayer or sp raster class object with the same dimensions of x

##### Value

A value representing the I similarity statistic

##### References

Warren, D. L., R. E. Glor, M. Turelli, and D. Funk. (2008). Environmental Niche Equivalency versus Conservatism: Quantitative Approaches to Niche Evolution. Evolution 62:2868-2883.

##### Examples

```
# NOT RUN {
# add degree of separation in two matrices
p1 <- abs(matrix(1:50,nr=50,nc=50) +
runif(n = 2500, min = -1, max = 1))
p2 <- abs(matrix(1:50,nr=50,nc=50) +
rnorm(n = 2500, mean = 1, sd = 1))
# High overlap/similarity
( I <- overlap(p1,p2) )
# }
```

*Documentation reproduced from package spatialEco, version 1.3-2, License: GPL-3*