hillN2: Calculates Hill's Species Dominance (N2)
In dempseydanielle/marindicators: Marine Ecosystem and Fishing Pressure Indicators

Description Usage Arguments Details Value Author(s) References See Also Examples

This function calculates Hill's Species Dominance (N2) for j areas and i years.

1	hillN2(X, groups, species.table = NULL, metric = "ABUNDANCE", years)

`X`	A dataframe of fishery independent data derived from research vessel survey data or model output, with columns `YEAR`, `ID`, `SPECIES`, and `ABUNDANCE`. `YEAR` indicates the year the observation was recorded, `ID` is an area code indicating where the observation was recorded, `SPECIES` is a numeric code indicating the species sampled, and `ABUNDANCE` is the corresponding abundance (stratified and corrected for catchability as required).
`groups`	A vector indicating the species group(s) for which to calculate the indicator. If `groups = "ALL"`, all species will be included; otherwise, each entry must be a character string matching the name of a column in `species.table`.
`species.table`	A table where the column names match the entries in `groups`. Column entries are species codes indicating the species from `X` included in each group. `species.table` may also include columns for other species groups; these will be ignored. If `groups = "ALL"`, this table is not required. Default is `species.table = NULL`.
`metric`	A character string indicating which column in `X` to use to calculate the indicator. Default is `metric = "ABUNDANCE"`.
`years`	A vector of years for which to calculate indicator.

Hill's Species Dominance (HillN2):

HillN2 = 1/Σ p_i^2

p_i is the proportion of the total sample contributed by the i(th) species. HillN2 is the inverse of the Simpson's index. This index is sensitive to the evenness of the distribution of individuals between species (Hill, 1973).

Returns a dataframe with columns ID and YEAR, and a column HillDominance_group for each entry in groups.

If there is no data for spatial scale j in year i, indicator values is assigned NA.

Danielle Dempsey, Adam Cook Adam.Cook@dfo-mpo.gc.ca, Catalina Gomez, Alida Bundy

Bundy A, Gomez C, Cook AM. 2017. Guidance framework for the selection and evaluation of ecological indicators. Can. Tech. Rep. Fish. Aquat. Sci. 3232: xii + 212 p.

Greenstreet SP, Rogers SI. 2006. Indicators of the health of the North Sea fish community: identifying reference levels for an ecosystem approach to management. ICES J Mar Sci J du Cons 63:573-593

Hill MO. 1973. Diversity and evenness: a unifying notation and its consequences. Ecology 54: 427-431.

Other biodiversity indicators: allBiodiversity(), heips(), hillN1(), kemptonQ(), margalef(), pielouEvenness(), shannon(), speciesRichness()